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Low cost digester monitoring under realistic conditions: Rural use of biogas and digestate quality
Abstract
The purpose of this work was to assess the behaviour of anaerobic digestion of cattle manure in a rural digester under realistic conditions, and estimate the quality and properties of the digestate. The data obtained during monitoring indicated that the digester operation was stable without risk of inhibition. It produced an average of 0.85 Nm³ biogas/d at 65.6% methane, providing an energy savings of 76%. In addition, the digestate contained high nutrient concentrations, which is an important feature of fertilizers. However, this method requires post-treatment due to the presence of pathogens.
... The low-cost tubular digester (LCTD) is popular because of its simple construction from readily accessible materials and humble design (polyethylene and polyvinyl chloride) [28] and low-cost materials [29]. LCTD is basically fed with the cattle manure (CM) at an organic loading ratio (OLR) between 0.3 and 2 kg VS/m 3 d [30]. ...
... Martí-Herrero et al. [41] expressed BPR and SBP as digester and AD process efficiencies, respectively. Castro et al. [29] revealed that in actual conditions with a 35 d HRT and 0.7 kg VS/m 3 d OLR, the BPR was 0.13 m 3 /m 3 d and the SBP was 0.15 m 3 /kg VS. Because of the differences in operating state, their outcomes were lower than those of the current study. ...
... Moreover, Martí-Herrero et al. [41] cited that the 47.8% CH4 content of cow dung. On the other hand, [44] and [29] established that cow dung had a methane concentration of 67% and cattle manure had a CH4 content of 65.6%, respectively. These values were more than the results of the current investigation due to the various operating parameters (such as OLR, HRT, ST, type of study). ...
Household biogas-digesters are a prospective technique that can help minimal-income rural families to meet their basic energy requirements and enhance their living standards. Nevertheless, due to the cold temperature of the digesters, the biogas generation is decreased and the digestion efficiency is generally low. The current work proposes a solar-greenhouse (SGH) heating technique united with a north wall to heat a semi-buried tubular digester, as a solution. Two similar semi-buried digesters were used in this experiment; one (DA) was heated by a SGH attached to a north wall, while the other (DB) was heated by direct sunlight (without a greenhouse), which used as a control, and both digesters were fed with cattle manure. The average slurry temperature for DA and DB was 24.9 °C and 23.45 °C, respectively, and both digesters were warmer than the outside air temperature of 22 °C. Moreover, there were no appreciable differences in the methane concentration (62.2–62.76%) between the mean specific biogas production of DA and DB, which were 173 and 155.3 L/kg VS, individually. The study showed that using combined SGH technique is enhanced the process of biogas output more than control.
Graphical Abstract
... Additionally, other Colombian researchers have focused on full-scale household digesters to determine the parameters and performance of the process under real conditions [43][44][45][46][47][48]. Monitoring comprised taking frequent samples (influent, effluent, digestate, and biogas). ...
... Psychrophilic tubular digesters represent a simplified and successful technology in the country. Two examples of studies where this technology has been deeply analyzed in real conditions in Colombia are Castro et al. (2017) [44] and Jaime-Jaimes et al. (2021) [46]. In the first case, a 9.5 m 3 total volume digester without stirring or heating devices, fed daily with cow manure and working at 23.5 • C, produced biogas after 35 days from the start-up. ...
... Psychrophilic tubular digesters represent a simplified and successful technology in the country. Two examples of studies where this technology has been deeply analyzed in real conditions in Colombia are Castro et al. (2017) [44] and Jaime-Jaimes et al. (2021) [46]. In the first case, a 9.5 m 3 total volume digester without stirring or heating devices, fed daily with cow manure and working at 23.5 • C, produced biogas after 35 days from the start-up. ...
Anaerobic digestion (AD) technology has become increasingly important due to its contribution to sustainability and a circular bioeconomy. While AD technologies are widespread in developing countries, developed countries have mainly driven research. The aim of this research is to analyze the biogas sector development from the point of view of a developing country like Colombia. AD research ranges from laboratory mesophilic AD to psy-chrophilic full-scale digesters, which are intergrated with household farms as a thermal energy source for cooking, nutrient recycling for agriculture, and waste management. Research on agricultural waste substrates, inocula, and co-digestion has dominated the Colombian publications, while full-scale digesters performance research is incipient. A survey of installed digesters collected information about 996 systems and found that 79% were psychrophilic low-cost tubular digesters. Regulations for biogas were reviewed, and it was found that they are not adequate for low-cost digesters and are inherited from developed countries, ignoring the national context. Five case studies are presented on the characterization of AD technology experiences, analyzing barriers and opportunities for the technology. National networks that include farmers, NGOs, and academia are driven slowly by Colombia's widespread AD technology, mainly on small-to medium-scale farms.
... In Colombia, livestock activity is a fundamental pillar for the economy and the sustainability of the inhabitants of rural areas, who represent about 19% of the population. 1 Currently, biogas production through anaerobic digestion (AD) is a renewable energy alternative, contributing to mitigating energetic limitations. 2 The AD process consists of the degradation of organic matter without oxygen. This process is carried out by a microbial consortium responsible for the hydrolysis, acidogenesis, acetogenesis, and methanogenesis of macromolecules such as carbohydrates, lipids, and proteins present in substrates. ...
... In many AD systems, the bovine and swine manure are peculiar. 2,7,8 The use of manures in the monodigestion process allows the obtainment of yields around 0.1-0.4 m 3 biogas /m 3 digester *d. ...
... In that sense, CM provides alkalinity (1,850 -175 mg/L) and additional nutrients (as trace elements) that improve microorganism development. 2,9 These advantages are reflected in the low content of VFA at the end of BMP assays. For all ACoD cases, the VFA content remained under 600 mg/L, allowing suitable values of buffer capacity (between 0.18 to 0.35 mg Ac. ...
... In the context of small and medium dairy farmers of developing countries, the HhD installed in rural areas are fed mainly with manures from livestock activities such as cattle, swine, and sheep breeding, providing a residues treatment and an energetic supplement to users (Garfí et al., 2016;Kinyua et al., 2016;Castro et al., 2017;Jaimes-Estévez et al., 2021). Nevertheless, in farm or household scale, the studies are applied to the mono-digestion process, and there are few successful reports about ACoD of CW and CM at this scale. ...
... The HhD start-up consisted of a three-month discontinuous phase (batch) with a single feed of 1.3 m 3 of fresh manure and 3.9 m 3 of water. The preceding was done to stimulate the growth of microbial communities' content in CM and adapt them to the system conditions (Castro et al., 2017). After batch period, the AD semi-continuous process was carried out in two feedings stages: stage A) mono-digestion of the mixture CM: water (1: 3 v/v) and stage B) ACoD of the mixture CW:CM: water. ...
... These removal values indicate the possibility of increasing the treated CW volume under psychrophilic conditions. The removal reached in this study is comparable with a mesophilic CM mono-digestion system (fed with CM and rainwater in a 1:3 volumetric ratio; average temperature upper than 25 • C) that reached an organic matter removal near 76 % with an OLR around 1 kg COD/m 3 digester d (Castro et al., 2017). Studies treating CW, as presented by Kavacik and Topaloglu (2010) and Comino et al. (2012), reported removals of around 49.4 % and 82 % at 34 • C and 35 • C, respectively. ...
This paper aims to prove the feasibility of cheese whey (CW) and cattle manure (CM) anaerobic co-digestion, from biomethane potential (BMP) laboratory assays to monitoring a farm-scale digester under psychrophilic conditions, and the impact on surrounding communities. The results show that while CW mono-digestion at 15 °C suffers inhibition, the CW:CM blend (70:30 volatile solids -VS- basis) is favorable at a similar temperature generating 0.24 m³ CH4/kg VS (35 °C yield: 0.60 m³ CH4/kg VS). A farm-scale digester (8 m³) installed in a rural school operated at 17.7 °C reached 0.42 m³CH4/kg VS, 0.31 m³ CH4/m³digester d with an organic loading rate of 0.61 kg VS/m³digester d (CW:DM 54:46). Even with CW's high volatile fatty acids (VFA) load, the digester did not show metabolic activities inhibition: VFA consumption was around 96.45 ± 2.25 %. In the rural school, biogas generation replaced the wood utilization and reduced propane consumption by 33 %. Despite these results, there are issues around psychrophilic BMP test to be reviewed, and user's misperceptions of biogas technology to overcome.
... It is interesting to note that when the cow diet is richer than simply grass (e.g., corn, soybeans), the digestate produced results in a more nutritious fertilizer (Mendonça Costa et al., 2016). However, the presence of pathogens requires a post-treatment of the effluent (Castro et al., 2017), because the total number of coliforms in the digestate would allow only a restricted irrigation use, according to the World Health Organization (WHO) guidelines for the safe use of wastewater, excreta, and greywater . Also, storage of the digestate for a longer period reduces the pathogen content to acceptable levels to avoid attendant health problems . ...
... Therefore, an important parameter to control is the concentration of Na in the digestate. When applied to fields, the high concentration Na digestate can inhibit the hydraulic conductivity of the soil, inducing soil hardening and a reduction in aeration (Castro et al., 2017). The effect on the soil's physical properties is measured through the sodium adsorption ratio (SAR), which refers to the concentration of monovalent cations (mainly Na) to divalent cations (Ca, Mg) in the water-soluble extract of the soil. ...
... According to (Summer et al., 1998), soil with a SAR > 13, and an electrical conductivity > 4 dS m − 1 is considered saline-sodic, which restricts plant growth that is not resistant to these conditions. By contrast, the presence of macromolecules (proteins, carbohydrates, lipids) and volatile fatty acids (VFA)s in the digestate indicates (Gunnarsson et al., 2011) that AD occurred successfully (Castro et al., 2017). Also, these organic substances are the immediately decomposed fraction by microbial mineralization for plants and food sources for soil microorganisms. ...
Digestate is a nutrient-rich by-product from organic waste anaerobic digestion but can contribute to nutrient pollution without comprehensive management strategies. Some nutrient pollution impacts include harmful algal blooms, hypoxia, and eutrophication. This contribution explores current productive uses of digestate by analyzing its feedstocks, processing technologies, economics, product quality, impurities, incentive policies, and regulations. The analyzed studies found that feedstock, processing technology, and process operating conditions highly influence the digestate product characteristics. Also, incentive policies and regulations for managing organic waste by anaerobic digestion and producing digestate as a valuable product promote economic benefits. However, there are not many governmental and industry-led quality assurance certification systems for supporting commercializing digestate products. The sustainable and safe use of digestate in different applications needs further development of technologies and processes. Also, incentives for digestate use, quality regulation, and social awareness are essential to promote digestate product commercialization as part of the organic waste circular economy paradigm. Therefore, future studies about circular business models and standardized international regulations for digestate products are needed.
... The biodigester was designed with the most important criteria: (a) temperature, which was measured with a sensor that recorded its value every 12 hours for 30 days; (b) hydraulic retention time (HRT), which was determined using the table reported by Martí-Herrero [2]; (c) flow rate (Q), which is the mixture fed to the biodigester and is composed of manure and water, in a 1:3 dilution as reported by Castro, et al. [10] for working with equine manure; (d) volume, Martí-Herrero [2] indicates that the total volume (VT) of the digester should house a liquid part (75%) and a gaseous part corresponding to the gas hood (25%), the volume of liquid (V ! ) is the product of two known variables as shown in the Equation (1), and from the total volume, the dimensions of the biodigester can be found, considering that it is cylindrical, using Equation (2). The length (L) depends on the perimeter of the coil, which is generally 4 m, and lastly r corresponds to the radius of the digester. ...
... In this study, an SBP of 0.19 m 3 biogas/Kg VS and a BPR of 0.10 m 3 biogas/m 3 digester were obtained by feeding the digester an organic loading rate (OLR) of 0.5 Kg VS/m 3 digester day. Castro, et al. [10] reported efficiencies of 0.13 m 3 biogas/m 3 digester day for the digester and 0.15 m 3 biogas/Kg VS for the anaerobic digestion process obtained from bovine manure with 35 days of HRT and an OLR of 0.7 Kg VS/m 3 digester day. In comparison, the current study presented a higher efficiency in the anaerobic digestion process, indicating that the equine manure presented an adequate response for biogas production. ...
... The biogas obtained in a low-cost biodigester operated at mesophilic conditions generally reaches a methane content between 55% and 65% [10,12,13]. According to Hernández [19], biogas with a methane content higher than 55% upon combustion can have a lower heating value (LHV) of approximately 26,000 kJ/m 3 . ...
The present research aims to evaluate the physicochemical variables involved in the anaerobic digestion process to produce methane from manure on an agricultural farm; the farm has 2 equines that generate 12 Kg of manure per day. A manure sample was collected, and the following physicochemical parameters were determined: total solids, volatile solids, chemical oxygen demand, and pH. A tubular household biodigester was then implemented, consisting mainly of a polyethylene geomembrane that stores the organic matter and in which anaerobic digestion takes place. The performance of the biodigester was determined by the removal of organic matter quantified by volatile solids and chemical oxygen demand in the biodigester influent and digestate, of which removal of 82% of volatile solids and 74% of chemical oxygen demand was achieved. The average biogas production was 0.5 m ³ /day, and its lower heating value was 26,000 kJ/m ³ . The pH level of the biodigester was within the range of 6-7, in order to keep the methanogenic bacteria active, in charge of carrying out physicochemical process that guarantees anaerobic digestion and thus, the production of biogas.
... One of the alternatives to chemical or inorganic fertilization is using biofertilizers, such as struvite, which naturally precipitate as crystals whenever the Mg:NH 4 :PO 4 concentration ratios exceed 1:1:1 (Castro et al. 2017). Unlike other fertilizers, struvite is characterized by low water solubility, which increases its performance by reducing uncontrolled nutrient insertion in the soil and contributes significantly to the protection of the environment (Lorick et al. 2020). ...
... To estimate the potential struvite precipitation (PSP), Mg, NH 4 þ , and PO 4 À3 contents present both in the substrate and in the digestate were considered. The maximum amount of struvite was determined according to the stoichiometry from its formation reaction (Equations 13 and 14) (Castro et al. 2017). Finally, an economic approximation of the PSP was conducted as suggested by Castro et al. (2017). ...
... The maximum amount of struvite was determined according to the stoichiometry from its formation reaction (Equations 13 and 14) (Castro et al. 2017). Finally, an economic approximation of the PSP was conducted as suggested by Castro et al. (2017). ...
Anaerobic digestion (AD) of food waste (FW) has been gaining more interest as it has potential for the production of organic amendments with high struvite (NH4MgPO4·6H2O) content, which is a nutrient of great interest in sustainable agriculture. In this study, the influence of AD of FW in one- and two-phase configurations on methane production and the potential for struvite formation using digestate was evaluated. It was found that the two-phase is more efficient as its organic loading rate is 18% higher than that of one-phase configuration. In addition, the two-phase yielded a higher methane content in biogas (>60%) and a higher organic matter transformation in each of the AD stages (>20%); further, the digestate complied with the regulatory requirements for the use of organic amendments, thereby being deemed as a Type-B material with a struvite precipitation potential, exceeding 80%, as opposed to the digestate from one-phase configuration, which may represent a revenue of up to US$ 26,505 per year. HIGHLIGHTS
Two-phase anaerobic digestion of food waste (AD-FW) is an alternative for the generation of struvite.;
The presence of struvite helps the sanitization of the digestate obtained in the AD-FW.;
Two-phase AD has potential for the treatment as well as energy and agricultural use of FW in small communities.;
... On average, the tVFA decrease was around 2.6 ± 1.4 g COD VFA /L, which represents a bioconversion of 83.6 ± 15.5%. A rural biodigester with one year of continuous operation at 34 • C showed 63% of tVFA bioconversion [5]. Thus, with a longer operational period, it is possible to achieved higher conversion rates of soluble organic matter, even under psychrophilic conditions. ...
... On average, the tVFA decrease was around 2.6 ± 1.4 g COD VFA/L, which represents a bioconversion of 83.6 ± 15.5 %. A rural biodigester with one year of continuous operation at 34 °C showed 63% of tVFA bioconversion [5]. Thus, with a longer operational period, it is possible to achieved higher conversion rates of soluble organic matter, even under psychrophilic conditions. ...
... This demonstrates the high buffer capacity of pig manure. FOS/TAC values below 0.8 mg acetic acid/mg CaCO 3 are adequate for process stability [5]. This confirmed that the pig farm digester was operating properly without inhibition risk. ...
Most biogas plants in the world run under psychrophilic conditions and are operated by small and medium farmers. There is a gap of knowledge on the performance of these systems after several years of operation. The aim of this research is to provide a complete evaluation of a psychrophilic, low-cost, tubular digester operated for eight years. The thermal performance was monitored for 50 days, and parameters such as pH, total volatile fatty acid (tVFA), chemical oxygen demand (COD) and volatile solids (VS) were measured every week for the influent and effluent. The digester operated at a stabilized slurry temperature of around 17.7 °C, with a mean organic load rate (OLR) equal to 0.52 kg VS/m3digester *d and an estimated hydraulic retention time (HRT) of 25 days. The VS reduction in the digester was around 77.58% and the COD reduction was 67 ± 3%, with a mean value for the effluent of 3.31 ± 1.20 g COD/Lt, while the tVFA decreased by 83.6 ± 15.5% and the presence of coliforms decreased 10.5%. A BioMethane potential test (BMP) for the influent and effluent showed that the digester reached a specific methane production of 0.40 Nm3CH4/kg VS and a 0.21 Nm3CH4/m3digester d with 63.1% CH4 in the biogas. These results, together with a microbiological analysis, show stabilized anaerobic digestion and a biogas production that was higher than expected for the psychrophilic range and the short HRT; this may have been due to the presence of an anaerobic digestion microorganism consortium which was extremely well-adapted to psychrophilic conditions over the eight-year study period.
... This co-substrate has been studied in different mixing proportions (between 15 and 45%) and has generated positive effects in the process [13,15]. An example of characterisation of CM is carbohydrates (47%), lignin (25%), holocellulose and hemicellulose (15%), cellulose (8%) and a low lipid content (2%; [16]). Fresh CM is a good co-substrate for CW because of its (a) high alkalinity (1.85 ± 0.17 kg m −3 ; [4]); (b) ability to provide microorganisms (can act as inoculum), nutrients and trace elements that are important for the growth of microorganisms [17]; (c) local availability and low cost; and (d) ability to replace the use of chemicals in pH regulation [18]. ...
... These types of digester are characterised by the absence of both active mixing and heating devices. Consequently, they are easy to install and operate and can be used to supply fuel for cooking and heating or to generate electricity for on-site use [16,21,22]. In the AD, the flora can be classified into two different consortia-the producers of VFAs (acidogenic bacteria) and the consumers of VFAs (acetogenic and methanogenic bacteria)-to produce methane. ...
... The SMA reached much higher values compared with those obtained by the stabilised cattle manure sludge (0.04 kg COD kg −1 VS day −1 ) from a rural digester used by Castro et al. [16]. These improvements in methanogenic activity could be explained by the extra nutrients provided by the CW used as the main substrate and the synergism achieved during the process. ...
This study carried out an anaerobic co-digestion treatment of cheese whey using cattle manure as a co-substrate. A co-digestion process was implemented in three tubular reactors, each one with a different organic load rate (0.5, 1.0 and 1.5 kg CODfed m−3digester day−1). A biochemical and microbiological analysis along the axial axis of each reactor showed that it was possible to obtain a phase separation with an organic load rate of 1.0 kg CODfed m−3digester day−1. The volatile fatty acid production phase takes place in the first reactor section and the consumption phase in the second section. Results from high-throughput sequencing analysis showed differences in the microbial communities between the samples of the three reactors for both eubacterial and archaeal compositions. In the reactor with intermediate organic loading rate, acetoclastic communities predominate, while at lower load, both acetoclastic and hydrogenotrophic communities are detected. Additionally, a microbial consortium stratification was observed.
... Tubular digesters are widely used for the AD of homogeneous waste. Previous studies have reported specific biogas production (SBP) values between 0.11 and 0.15 m 3 kg −1 VS with a methane content of 45.6% and 65.6%, using llama + sheep and cattle manure as substrates, respectively (Martí-Herrero et al., 2015;Castro et al., 2017). Regarding the heterogeneous substrates managed in the aforementioned bio-digester, essential strategies have been used to carry out the AD process. ...
... The reactor was inoculated with anaerobic sludge from a farm-scale rural tubular bio-digester fed with cow manure. It contained 46.2 ± 0.85 g TS L −1 and 35.4 ± 0.77 g VS L −1 with a buffer capacity (VFA/TA) of 0.25 ± 0.02 mg CH 3 COOH mg −1 CaCO 3 and a specific methanogenic activity of 0.035 ± 0.002 g COD g −1 VS day −1 , which were suitable to seed the ATD and begin the process (Mendieta et al., 2020a;Castro et al., 2017). O. Mendieta, et al. ...
... ATD productivity (expressed as BPR) increased by 25%, showing that digester volume is best used with ACR + SCS co-digestion than with ACR mono-digestion. Household low-cost tubular digesters that use llama + sheep manure (Martí-Herrero et al., 2015) and cow manure (Castro et al., 2017) as substrates, have shown BPR values of 0.05 and 0.13 m 3 m −3 digester d −1 , operating with an OLR of 0.44 and 0.7 kg VS m −3 d −1 , HRT of 80 and 35 days, and at temperatures of 16.6°C and 23.0°C, respectively. This indicates that the productivity of a tubular bio-digester must be linked to multiple variables, such as HRT, OLR, and temperature. ...
... Tubular digesters are widely used for the AD of homogeneous waste. Previous studies have reported specific biogas production (SBP) values between 0.11 and 0.15 m 3 kg −1 VS with a methane content of 45.6% and 65.6%, using llama + sheep and cattle manure as substrates, respectively (Martí-Herrero et al., 2015;Castro et al., 2017). Regarding the heterogeneous substrates managed in the aforementioned bio-digester, essential strategies have been used to carry out the AD process. ...
... The reactor was inoculated with anaerobic sludge from a farm-scale rural tubular bio-digester fed with cow manure. It contained 46.2 ± 0.85 g TS L −1 and 35.4 ± 0.77 g VS L −1 with a buffer capacity (VFA/TA) of 0.25 ± 0.02 mg CH 3 COOH mg −1 CaCO 3 and a specific methanogenic activity of 0.035 ± 0.002 g COD g −1 VS day −1 , which were suitable to seed the ATD and begin the process (Mendieta et al., 2020a;Castro et al., 2017). O. Mendieta, et al. ...
... ATD productivity (expressed as BPR) increased by 25%, showing that digester volume is best used with ACR + SCS co-digestion than with ACR mono-digestion. Household low-cost tubular digesters that use llama + sheep manure (Martí-Herrero et al., 2015) and cow manure (Castro et al., 2017) as substrates, have shown BPR values of 0.05 and 0.13 m 3 m −3 digester d −1 , operating with an OLR of 0.44 and 0.7 kg VS m −3 d −1 , HRT of 80 and 35 days, and at temperatures of 16.6°C and 23.0°C, respectively. This indicates that the productivity of a tubular bio-digester must be linked to multiple variables, such as HRT, OLR, and temperature. ...
The main sugarcane wastes from the non-centrifugal cane sugar (NCS) agro-industry, agricultural crop residue (ACR) and sugarcane scum (SCS), were used to produce biogas in a bench-scale semi-continuous anaerobic tubular digester. A two-stage strategy was proposed to achieve the appropriate operability and stability of the digester. In the first stage, the operability of the digester was achieved with ACR mono-digestion. In the second stage, the digester feed was changed until it reached an ACR:SCS ratio (co-digestion) of 75:25, based on volatile solids, and until stability was achieved. The strategy was successful, and specific biogas production of 0.132 m³ kg⁻¹VS with a methane content of 50.4% was achieved, confirming the technical feasibility of the process. Economic viability was established through a case study at a typical NCS mill. Therefore, anaerobic co-digestion can be consolidated as a technological alternative for the treatment of ACR+SCS and the sustainable benefit of the NCS agro-industry.
... In Ecuador, the biogas potential from livestock manure in rural areas, can potentially replace the demand for LPG and support 90% of the rural electrification target, while mitigating GHG emissions (Cornejo and Wilkie, 2010). Moreover, in Colombia, a small-scale digester implemented in rural areas with daily input of 50 kg of cow manure (i.e. the manure produced from 3 cows corralled 60% of the time), provided enough biogas to support the cooking needs of five people (Castro et al., 2017). In Cajamarca (Peru), nearly 100 digesters were installed for cooking and lighting in different biogas programs since 1988, although different barriers led to abandoning the program and most digesters after a few years (Garfí et al., 2014). ...
... Fig. 8 shows manure available in the municipalities for the livestock considered. In the case of bovine livestock, it is considered that the livestock is corralled 60% of the time (Castro et al., 2017). ...
... Moreover, the use of UASB in developing countries is limited mainly to the treatment of municipal wastewater (Tavera-Ruiz et al., 2023). Based on the above, tubular digesters are a suitable low-cost technology in the treatment of agro-industrial waste in Latin America (Garfí et al., 2016), since they are cheap to build, easy to operate, their maintenance and operation costs are low (it does not require mechanical or electrical equipment) (Kinyua et al., 2016), their start-up times are short (30-100 days) (Castro et al., 2017;Martí-Herrero et al., 2015) and can be inoculated with cattle manure (Castro et al., 2017). Every year a large number of tubular digesters are installed in the region for the treatment of agro-industrial waste, for which it has the know-how and specialized local suppliers. ...
... Moreover, the use of UASB in developing countries is limited mainly to the treatment of municipal wastewater (Tavera-Ruiz et al., 2023). Based on the above, tubular digesters are a suitable low-cost technology in the treatment of agro-industrial waste in Latin America (Garfí et al., 2016), since they are cheap to build, easy to operate, their maintenance and operation costs are low (it does not require mechanical or electrical equipment) (Kinyua et al., 2016), their start-up times are short (30-100 days) (Castro et al., 2017;Martí-Herrero et al., 2015) and can be inoculated with cattle manure (Castro et al., 2017). Every year a large number of tubular digesters are installed in the region for the treatment of agro-industrial waste, for which it has the know-how and specialized local suppliers. ...
Anaerobic digestion (AD) has been a widely tested alternative for the management and valorization of wastewater from the animal slaughter process. However, the integration of AD in slaughterhouses depends on technical and economic aspects. In Colombian slaughterhouses AD integration is limited by the availability of land. In the present study, a techno-economic evaluation of the AD of offal wastewater (OWW) stream in a laboratory scale mesophilic tubular digester was carried out. The digester was operated at organic loading rates (OLR) of 0.28, 0.50, 1.0, 1.5 and 2.0 kg VS/m3 d. Boilers and a CHP (combined heat and power) system were considered for energy integration of biogas. For the economic study, the cost structure of a Colombian slaughterhouse was considered. The AD of OWW at 2.0 kg VS/m3 d OLR was unstable with risk of inhibition. Increasing the OLR from 0.28 to 1.5 kg VS/m3 d caused a reduction in the specific biogas production (SBP) from 0.474 to 0.069 m3/kg VS However, the biogas production rate (BPR) remained constant at around 0.105 m3/m3dig d for OLRs > 0.28 kg VSm3 d. Therefore, OWW anaerobic digestion in low-cost mesophilic biogas plants is technically feasible with OLRs between 0.28 and 1.5 kg VS/m3 d. The implementation of boilers is economically favorable for OLR ≥ 1.0 kg VS/m3 d. Nevertheless, feasibility is very sensitive to variations in the cost structure. The implementation of CHP was feasible in the range of OLRs evaluated and its viability is not affected by changes in assumed costs.
... The biogas production of B1 continued to increase (>50%), eventually being enough to supply cooking requirements for a family of 5 people, especially during the three weeks of propane gas shortages that occurred in the region, at the end of the study. It is in line with the findings of [42], who found that the biogas produced by a low-cost digester could replace 80% of the traditional fuel (propane) in rural areas of Colombia. However, the sustainability of the system depends on the commitment of the owners to the required operation and maintenance. ...
... The methane content was examined by the third month of operation of B1, and the percentage of CH 4 in the biogas generated was between 61-69%. This range coincides with the methane content in the biogas generated in domestic tubular digesters at a pilot scale in Latin America, reported by the literature between 40% and 70% [43] and, more specifically, with the percentage of methane showed by [42], who reports a 65.6% of methane content in biogas when monitoring a low cost digester in Colombia under realistic conditions and operated with CM. Besides, the values found are higher than the one reported for CM and whey mixture at a pilot ...
In this research, the methane potential of the codigestion of cattle manure (CM) with guinea pig manure (GPM) and dairy wastewater (DW) was evaluated. The effect of the addition of nutrients, inoculum (I) and co-substrates on methane production was studied. Later, two low-cost tubular biodigesters were implemented, at a rural farm in the cold climate municipality of Cumbal, fed with the mixture of CM and co-substrates that produced higher biogas production at the lab scale. The results evidenced that the addition of nutrients had no significant effect on methane potential. The mixture CM + GPM + DW + I, produced a theoretical biomethane potential (BMP) of 69.07%, significantly higher than the percentage of the theoretical BMP obtained individually, 43.81% and 34.49% for CM + I and DW+ I respectively. Further, it was observed that the addition of inoculum avoided problems of acidification. Finally, it was proved that this process can reduce environmental contamination and, at the same time, be a sustainable source of renewable energy for rural families in Cumbal (Nariño-Colombia).
... In Ecuador, the biogas potential from livestock manure in rural areas, can potentially replace the demand for LPG and support 90% of the rural electrification target, while mitigating GHG emissions (Cornejo and Wilkie, 2010). Moreover, in Colombia, a small-scale digester implemented in rural areas with daily input of 50 kg of cow manure (i.e. the manure produced from 3 cows corralled 60% of the time), provided enough biogas to support the cooking needs of five people (Castro et al., 2017). In Cajamarca (Peru), nearly 100 digesters were installed for cooking and lighting in different biogas programs since 1988, although different barriers led to abandoning the program and most digesters after a few years (Garfí et al., 2014). ...
... Fig. 8 shows manure available in the municipalities for the livestock considered. In the case of bovine livestock, it is considered that the livestock is corralled 60% of the time (Castro et al., 2017). ...
Modern energy services are essential to replace the extensive use of traditional biomass fuels driving several environmental, health, and social issues affecting the welfare of low-income citizens. Particularly, in Colombia, 11% of the households rely on inefficient firewood cooking systems, while two million people have either intermittent access or no access to electricity. This is particularly important in the department of Cordoba, where an average of 32% of the households relies on firewood for cooking, increasing to 66% of the households in rural areas. Furthermore, 20% of the rural population lack access to electricity. Therefore, this study aims at defining the biogas-based energy potential of the available agricultural and manure wastes in the department. To this end, governmental data is used to estimate the demand for firewood for cooking, the resulting GHG emissions, and the available agricultural and manure wastes. Overall, there are around 1.2 million t of agricultural wastes and 2.2 million t of manure yearly available in the department, representing an energy potential of 6687 TJ. Using 26% of the biogas-based energy potential identified suffices to support the 1334 TJ of biogas needed to replace cooking firewood and to supply the 390 TJ needed for household electricity generation. The use of biogas can reduce GHG emissions to 11% of the emissions resulting from cooking firewood. Polyethylene tubular digesters appear as the most indicated household technology, contrasted to geomembrane tubular digesters that need 2.4 times the initial capital investment while fixed dome digesters need 7.9 times the initial capital investment. Implementing household digesters to support the energy demand for cooking in the department, necessitates a minimum of 18 million USD, while the implementation of 'digester + electric generator' needs between 1.7 and 5.7 million USDdepending on the monthly demand of electricity of 60 kWh or 187 kWh.
... This indicates that a large amount of organic matter was still present in the digestate. In fact, the VS/TS ratio usually ranges between 40 and 50% in digestates from anaerobic processes operating under mesophilic conditions (Castro et al., 2017;Garfí et al., 2011a;Solé-Bundó et al., 2017). The high VS/TS ratio in these digestates could be related to several factors, including slow digestion kinetics under psychrophilic conditions that can result in poor VS removal in digesters with an HRT of 25-75 days. ...
... As mentioned above, a feasible strategy to improve digestate stabilization could be to increase the HRT of the digester in order to enhance the biogas production and mineralize the highest amount of organic matter (Meegoda et al., 2018). Castro et al. (2017) have proposed the implementation of a degasification tank to recover retained biogas from digestate obtained from a plastic tubular digester fed with cattle manure. This strategy may also increase the digestate stabilization, making its agricultural reuse suitable. ...
The aim of this study is to characterize the digestates from three plastic tubular digesters implemented in Colombia fed with: i) cattle manure; ii) cattle manure mixed with cheese whey; iii) pig manure. All the digesters worked under psychrophilic conditions. Physico-chemical characteristics, heavy metals, pathogens, and agronomic quality were investigated.
All the digestates were characterized by physico-chemical characteristics and nutrients concentration suitable for their reuse as biofertilizer. However, these digestates may only partially replace a mineral fertilizer due to the high nutrients dilution. Heavy metals were under the detection limit of the analytical method (Pb, Hg, Ni, Mo, Cd, Chromium VI) or present at low concentration (Cu, Zn, As, Se) in all the digestates. Biodegradable organic matter and pathogens (coliform, helminths and Salmonella spp.) analysis proved that all the digestates should be post-treated before soil application in order to prevent environmental and health risks, and also to reduce residual phytotoxicity effects. The digestate from pig manure had a higher nutrient percentage (0.2, 0.6 and 0.05 % w/w of total N, P2O5 and K2O, respectively), but also higher residual phytotoxicity than the other digestates. Co-digestion seemed not to significantly improve the digestate fertilizing potential. Finally, further studies should address how to improve fertilizing potential of digestates from plastic tubular digesters, avoiding environmental and health risks.
... In addition, cow dung already contains a significant population of methanogens; this could explain the fast production rate despite its's fibrous nature. It also contains sufficient alkalinity for the process as shown in a study by Castro et al. (2017). Cow dung has indeed been reported by several authors to be a suitable feedstock for anaerobic digestion (Castro et al., 2017;Hasan et al., 2018;Ibn Abubakar & Ismail, 2012). ...
... It also contains sufficient alkalinity for the process as shown in a study by Castro et al. (2017). Cow dung has indeed been reported by several authors to be a suitable feedstock for anaerobic digestion (Castro et al., 2017;Hasan et al., 2018;Ibn Abubakar & Ismail, 2012). ...
The purpose of this paper is to evaluate the performance of five purposely-designed biogas systems installed at early childhood development centres (ECDCs) in Ndwedwe Local Municipality (LM), KwaZulu-Natal (KZN), South Africa, as an integrated energy, water, and sanitation solution. Analysis shows that sustainable and economically viable feedstocks are abundant throughout the study area, including faecal sludge, food waste, and cow dung, which produce quantities and qualities of gas appropriate for an ECDC context. Moreover, results suggest that anaerobic digestion can contribute to the reduction of chemical oxygen demand (COD) and pathogen indicator organisms (E.Coli, Faecal Coliforms, Faecal Streptococci, Enterococci) in faecal sludge, prior to digestate disposal, and although further evaluation of the systems outcomes remain, initial results suggest that such integrated systems can serve as cost-effective and sustainable energy and sanitation solutions within institutional settings, such as ECDCs, and particularly in rural areas, where the service provision burden on local municipalities is more acutely felt.
... The samples were analyzed for organic carbon, nitrogen (alkaline KMnO 4 method), 0.5 M NaHCO 3 (pH 8.5) extractable P, and 1 N NH 4 OAc-extractable K and other trace elements. In addition, emission, atomic absorption, volumetric, colorimetric, and photometric methods were used to determine physicochemical digestate property measurements that were adopted from Castro et al. [20]. ...
... It contains a number of main components (cellulose, hemicellulose, and lignin) that have, in their turn, also complex structures. Before undergoing anaerobic digestion, the biomass should be suitably conditioned in order to offer the microorganisms in the digester an efficient target surface area and thus to improve and accelerate the degradation process [13,20]. The most common alkalis used (sodium, ammonium, calcium, and potassium hydroxides) have been used for the pretreatment of lignocellulosic materials; the alkali pretreatment effectiveness depends on the lignin content of the biomass. ...
Anaerobic digestion (AD) processes performed biogas production of crushed water hyacinth (WH) combined with swine dung (SD) was investigated in this study. AD carried out for 45 days at mesophilic temperatures ranging from 34 to 36°C. Alkali (sodium hydroxide, NaOH) hydrolysis of WH was performed prior to batch dry AD at four different mild concentrations. Results revealed that NaOH pretreated samples produced a high yield of biogas than untreated (raw) samples. The scanning electron microscopy (SEM) was thus used to provide supporting confirmation on the main structural transformations that chanced in WH. The optimum WH concentration in the 1:1 ratio of co-digestion mixture with SD produced the highest methane yield, and the biogas composition of carbon dioxide, CO 2 (29.08%), methane, CH 4 (68.89%), and 1.09% of hydrogen sulfide, H 2 S. Upgraded biogas through chemical purification results revealed that CH 4 and CO 2 were 92.35% and 8.04%, respectively. Enhanced biogas high heating value was 36.83 MJ/m 3 and low heating value 33.18 MJ/m 3. Furthermore, the digestate has high nutrient concentrations that can potentially use as fertilizer; it contains nutrients nitrogen, phosphorus, potassium were 107.506, 18.838 and 39.552 g kg −1 , respectively. The digestate from biogas fermenter was confirmed to be an efficient alternative fertilizer with high nutrients and environmentally-friendly comparing to chemical fertilizer.
... Tabla 2 | Parámetros fisicoquímicos del inóculo, desechos de alimentos y heces de perro utilizados para alimentar el biodigestor. Los DA contenían un 33 % de frutos ácidos (limones) (Tabla 1), lo cual provocó un pH ácido y fue la posible causa de inhibición de actividad metanogénica, para esta etapa un rango de pH de 6,88-8,20 es óptimo para la metanogénesis (Castro et al., 2017), no obstante, el pH, tanto a la entrada como a la salida del biodigestor en este estudio, se encontraba en ese rango. Por otro lado, la presencia de HP y el inóculo en el arranque mostraron un pH ligeramente alcalino; así como por el inóculo previamente cargado en el arranque, favoreciendo la capacidad buffer para amortiguar los cambios de pH en co-digestión. ...
El manejo inadecuado de desechos orgánicos domésticos genera diversas problemáticas ambientales y de salud humana como la generación de gases efecto invernadero, contaminación de agua, propagación de vectores y enfermedades. Se evaluó la producción de biogás de un biodigestor a escala real para la valorización de una mezcla de desechos alimenticios y heces de perro. Se fabricó un sistema de dos fases de tipo tubular utilizando geomembrana de 1,00 mm de espesor con volúmenes de trabajo de 0,75 m3 y 0,25 m3 para las fases líquida y gaseosa, respectivamente. Una vez concluida la etapa de estabilización, durante el proceso de monitoreo de producción de biogás con duración de 31 días en condiciones psicrofílicas, se obtuvo una producción promedio diaria de biogás de 101,66 L,
con una composición promedio de 59,36 % de metano y alcanzó una eficiencia térmica de 39,95 %. El rendimiento promedio del sistema fue de 188,41 L kg-1 de desechos.
... After obtaining the best carbon emissions reduction ratio of 94% and the maximum primary energy savings of 32%, this system showed an average performance level of 151%. Under actual circumstances, the performance of the biogas plant using cattle manure as a feed was evaluated by (Castro et al., 2017). The volume of the biogas digester was 9.5 m 3 . ...
... The growth in agricultural biogas production has stimulated more intensive research into the rational management of digestate, including its use for fertilization purposes. The importance of digestate application to soil is being determined across the world (Nakamya et al., 2020;Castro et al., 2017;Roubík et al., 2018;Ogwang et al., 2021). The wide array of substrates that are processed in agricultural biogas plants produces a qualitative diversity of digestate. ...
... AD process comprises hydrolysis, acetogenesis, and methanogenesis to produce the methane CH 4 as the leading natural gas [3,4]. It is a promising and sustainable technology convenient for the management of organic waste [5], considered the most environmentally friendly process in terms of energy consumption, low biomass production, and its high pathogen removal rate during the waste transformation into gas and digestate [6,7]. Effective biogas recovery from fecal sludge depends on the treatment process used. ...
Plant seed–based bio-coagulant development and application are promising for fecal sludge treatment and biogas production improvement. However, improving methane yield in anaerobic digestion processes is an important research direction. This work addresses the development and application of Cucumeropsis mannii and Luffa acutangula seed proteins as novel bio-coagulants for fecal sludge concentration to increase the biogas yield. Their seeds’ protein content was determined and extracted using 1 M (NaCl), then isolated and precipitated by ammonium sulfate [(NH4)2 SO4], and purified using a dialysis process. Their coagulation/flocculation was compared to Moringa oleifera and Cucurbita pepo seeds as the primary treatment for the fecal sludge concentration. Optimal coagulant dosages of 20 mg/L at pH 7.25 increased the total solids from 0.4 to 2.8% and obtained 180 to 340 mL/L of fecal sludge volume per liter. Their bio-coagulant effect on the supernatant water reduced 76.48 to 96.88% of turbidity, 71.20 to 88.76% of COD, and 81.33 to 95.30% of ammonia–nitrogen. The biomethane potential result has shown that plant seed–based bio-coagulants are effective and produce substrates potentially favorable to increased methane yield in anaerobic digestion with 350.5 to 465.3 NmL CH4/gVS, by a ratio 2:1 on VS, compared to the FS without bio-coagulant treatment with a specific methane yield of 192.8 NmL CH4/gVS.
Graphical Abstract
... O autor explica que o processo natural da decomposição desses materiais emite gases poluentes, e o espaço destinado para os aterros demanda o desmatamento de grandes áreas verdes, além do perigo iminente de substâncias nocivas que percolam pelas camadas do solo. Outra vantagem considerável é o reaproveitamento do digestato subproduto proveniente do substrato aplicado em práticas de digestão anaeróbia para a produção do biogás, e que se mostrou eficiente na adequação de parâmetros químicos e físicos do solo, como apresentado por Castro et al. (2017) para a fertilização e recuperação de frações de solo. ...
One of the main challenges for the present and future of citiesare new energy sources that allow good efficiency and low environmental impact. In this sense, this study analyzed biogas, an energy source from the decomposition of organic matter. A theoretical essay was carried out from bibliographical research, with the aim of presenting the current scenario of the different perspectives of production and application of biogas in Brazil, in urban and rural areas of the country. The observed results showed that, in rural areas, the input for the production of biogas comes mainly from animal husbandry, and that the form of use is mainly directed towards obtaining thermal energy. In urban areas, practically all biogas production is carried out in sanitary landfills and sewage treatment plants, given the large amount of excess organic matter from the waste treatment activity. However, even though the country has relatively important indices of biogas production and use, it was clear from the theoretical framework analyzed that not only is the amount generated very low for generation potentials in Brazil, but there is also an evident lack of technologies in relation to biodigesters, in addition to a weak legislation to promote Brazilian biogas, which led to the conclusion that biogas production in the country is proceeding at a very slow pace. The study is limited in terms of detailing the barriers observed, and, therefore, it is suggested that future studies seek an in-depth analysis of these barriers.
... 33 VFAs represent the readily biodegradable organic matter available during the anaerobic process. 34 The VFAs concentration is a characteristic parameter of the early stages of biogas, and monitoring their evolution allows estimating the degradation status of the substrate. The variation of their concentrations in the environment directly affects the alkalinity and pH of the medium. ...
The present research focuses on the experimental study of the effect of alkaline pretreatment with NaOH on biogas production. Different concentrations of NaOH, i.e. 1, 2.5 and 5% (w/w), were tested on the lagoon station's sludge (dry basis) at room temperature for 24 h. The results obtained after 60 days of digestion, through the cumulative volume of biogas recorded, clearly indicate a positive effect of the chemical alkaline pretreatment on the anaerobic digestion since the amount of biogas produced increased by 42.6% when the NaOH concentration was close to 2.5%. This concentration is considered optimal under the chosen conditions. Indeed, inhibition of the methanogenic activity and a blockage of the digestion process are observed beyond this concentration. These results suggest that the alkaline pretreatment can improve the energy efficiency of the obtained biogas (CH 4 content) and reduce the residence time.
... En general, ésta tecnología condujo a mejoras sociales, ambientales y económicas; sin embargo, la falta de asistencia calificada y mantenimiento fue un problema grave detectado. Castro et al. (2017) evaluaron el comportamiento de la digestión anaerobia del estiércol del ganado en un digestor tubular rural en condiciones realistas, en una granja en una región de difícil acceso de Colombia, con el posible uso de biogás para reemplazar otras fuentes de energía. Se construyó un digestor de polietileno de bajo costo con 1,3 m de diámetro, 7,5 m de longitud y 9,5 m 3 de volumen total. ...
Energy plays a central role in society's development, and the search for renewable and sustainable sources is increasing every day. Anaerobic digestion is a technology that allows the production of clean energy from organic waste, improving the environment and the quality of life of the population. This work's objective was to evaluate the publication of scientific articles on a small scale anaerobic digestion. The search for scientific articles uses databases such as Scielo, Scopus, Science Direct, and Google Scholar, based on the keywords: small scale anaerobic digestion, biogas, small scale digestor, small scale anaerobic co-digestion, and renewable energy. Twenty scientific articles published between 2008 and 2019 were evaluated in nine different journals, emphasizing the journal Renewable Energy. Concerning the countries where the studies, Bolivia, Costa Rica, China, and Colombia stood out. It is essential to emphasize the need to carry out more scientific work to disseminate and popularize knowledge about small-scale anaerobic digestion technology, especially in developing countries.
... En general, ésta tecnología condujo a mejoras sociales, ambientales y económicas; sin embargo, la falta de asistencia calificada y mantenimiento fue un problema grave detectado. Castro et al. (2017) evaluaron el comportamiento de la digestión anaerobia del estiércol del ganado en un digestor tubular rural en condiciones realistas, en una granja en una región de difícil acceso de Colombia, con el posible uso de biogás para reemplazar otras fuentes de energía. Se construyó un digestor de polietileno de bajo costo con 1,3 m de diámetro, 7,5 m de longitud y 9,5 m 3 de volumen total. ...
Las vinazas de mezcal son residuos líquidos recalcitrantes con alta carga orgánica y elementos disueltos, la cual puede ser utilizada en la nutrición de plantas. El objetivo del trabajo fue evaluar la toxicidad de las vinazas del mezcal en la germinación de semillas y su efecto biofertilizante en el rendimiento de hortalizas. Se realizaron dos experimentos en lechuga, tomate y pepino: 1) prueba de fitotoxicidad en la germinación en semillas con diferentes concentraciones de vinaza (2.5, 5, 10, 20, 40, 80 y 100%); y 2). Se evaluó el efecto biofertilizante de las combinaciones de 100-0, 80-20, 40-60 y 20-80% de vinaza y solución nutritiva Steiner, y como testigo el 100% de la solución nutritiva; en ambos experimentos se utilizó un diseño completamente al azar. La concentración del 2.5% de vinaza del mezcal, fue tóxica para las semillas de lechuga y más del 10% inhibió su germinación. Para semillas de tomate el 20% resultó tóxico, mientras que en semillas de pepino provocó hormesis. La concentración del 80% de vinazas inhibió la germinación en semillas de tomate. La combinación: 40 + 60% de vinaza y solución nutritiva aplicados en la nutrición de lechuga y tomate, alcanzó los máximos valores de todas las variables evaluadas. En pepino, el rendimiento disminuyó de forma lineal al aumentar el porcentaje de vinaza como complemento de la solución nutritiva.
... This is because cow dung provides alkalinity (1850±175 mg/dm 3 ), other nutrients, and trace elements that are important for the growth of microorganisms. The advantages of using cow manure as an inoculum are its local availability, low cost, and ability to replace the chemicals needed to achieve a stable pH [38,39]. ...
The purpose of the study was to evaluate the methods of processing whey. The valorization
method is suitable for the use of cheese whey and whey permeate to produce beverages with or without
microbial conversion. However, this method does not ensure microbial conversion of lactose. Therefore, the organic load will not be reduced. The main advantage of aerobic decomposition is the relatively rapid degradation of organic matter. However, the high organic load in the crude cheese whey
makes aerobic decomposition unsuitable and restrictions on oxygen transport may occur. Anaerobic
decomposition can be used in various areas for the treatment of waste with a high organic load. The
disadvantage of anaerobic processes is a higher cost compared to aerobic treatment. The combination
of individual technologies significantly reduces the hydraulic retention time of the aerobic process and
improves waste treatment. At present, there is a lack of studies in this area.
... Small-scale biodigesters produce around 2-4 m 3 /day biogas, sufficient to meet the cooking lighting needs of a family [62]. The biogas potential in Colombia showed that 80% of propane, which is used the traditional fuel, could be replaced by biogas; results showed that a low-cost tubular digester in polyethylene with a total volume of 9.5 m 3 and feed with cattle produces enough biogas to supply cooking of five hours/day for five people [81]. In India, positive achievements were obtained using different design models simultaneously; it was possible to produce approximately 40.5 m 3 biogas/day and supply the community of 48 households that had cooking needs of 0.85 m 3 /day each [82]. ...
The world’s rural population surpasses the three billion people mainly located in Africa and Asia; roughly half the global population lives in the countryside. Access to modern fuels is a challenge for rural people compared to their urban counterparts, which can easily access infrastructures and commercial energy. In developing countries rural populations commonly depend on traditional biomass for cooking and heating. A key strategy in tackling the energy needs of those rural populations is to advance their energy ladder from the inefficient, traditional domestic burn of biomass, organic waste, and animal manure. Governments and non-governmental institutions have supported small biogas digesters in rural areas, mainly in Asia, South America, and Africa, over the last 50 years. This chapter reviews the literature to offer an overview of experimental and theoretical evidence regarding the characteristics of design, construction material, feedstock, and operation parameters that made anaerobic digestion in small digesters a valuable source. Small-scale rural biogas digesters can generate environmental, health, and social benefits to rural areas with a net positive impact on energy access. Remarkable improvement in living standards was achieved with small inputs of the methane, produced via anaerobic digestion; however, challenges associated with lack of technical skills, awareness, and education remain and obstruct biogas’ full potential in rural areas, mainly in developing countries.
... Overall, respondents found LCB useful for waste management, even though the technology has yet to be implemented. Currently, LCB is a useful solution for organic waste generated in various neighboring agro-industries that have benefited economically and environmentally from the technology [53,54]. Perhaps due to these personal experiences, NCS producers are more receptive to technology acceptance, as the utility benefits of LCB outweigh the disadvantages of traditional waste management methods such as landfills or land disposal. ...
Anaerobic digestion using low-cost biodigesters (LCB) is a promising alternative for Colombian producers of non-centrifugal cane sugar (NCS). Since the integration of anaerobic digestion technology in this agro-industry is novel, it is critical to understand the factors that affect the acceptance behavior of such technology by NCS producers to develop future policies that promote the adoption of sustainable energy alternatives. This study aimed to analyze NCS producers’ behavioral intention to use LCB by utilizing an extended technology acceptance model (TAM). Data from a survey of 182 producers were used to evaluate the proposed model empirically. The extended TAM accounted for 78% of the variance in producers’ behavioral intention to use LCB. Thus, LCB acceptability could be fairly precisely predicted on the basis of producers’ intentions. This study’s findings contribute to research on the TAM and provide a better understanding of the factors influencing NCS producers’ behavioral intention to use LCB. Furthermore, this approach can assist policymakers at the local and global levels, given that NCS is produced in various developing countries worldwide.
... Recent research has explored on the optimal parameters of biogas production factors such as inoculum size (%), type of diluents and dilution ratio, to deliberate the symbiotic relationship between microbial consortia for biogas production in laboratory scale using cow manure (CM). The study was then extrapolated to field scale using low-cost tubular digester with 1:3 dilution (CM:water) for higher specific methanogenic activity produced biogas of 0.04 Nm 3 kg −1 of cow manure and reported the abundance of 19.8% archaeal and 80.2% bacterial microbial community (Castro et al., 2017). The mentioned instances are the key researches that have been carried out in respective subject category and resulted in growth of biogas research arena which could promote rural welfare. ...
The strength of rural area in pioneering technologies encountering the current challenges of biogas research has been less addressed. Scientometric analysis has been carried out to understand research trends, perspectives and promising future prospects of biogas technology in rural development. 1427 publications have been retrieved from scientific databases and analyzed for major contribution of international collaborative partners, current research hotspots and subject areas to assess the evolution of biogas technology. Scientific publications on biogas grew rapidly from last decade wherein China has the highest research publications of 324 with 23.08% significant contribution. Keywords clustering analysis showed pretreatment strategies, influence of substrate mediators and its microbial interaction for process upgradation were the promising main research hotspots. The subject categories, “Energy and Fuels” is more popularized whereas “Economics” needs more attention. This study gives and insight on scientific advances and potential research gaps of biogas technology for rural development at global level.
... Sin embargo, el gas propano tiene un alto costo mensual de compra -USD 50-y transporte -USD 25-, así como existe riesgo en su gestión y almacenamiento. Por tal motivo, la digestión anaerobia surge como una alternativa de energía renovable para las zonas ZNI (Castro-Molano et al., 2017), tal como se puede evidenciar en el Atlas del potencial energético de la biomasa residual en Colombia (SI3EA, 2010). ...
En el 2019, el Instituto de Planificación y Promoción de Soluciones Energéticas para las Zonas no Interconectadas (IPSE) reportó 1710 zonas rurales con 128 587 personas que acceden a energía eléctrica entre cuatro y doce horas por día. Este acceso limitado a electricidad genera inseguridad y altos costos en mantener en funcionamiento las plantas eléctricas, con inversiones que superan los cien dólares diarios para generar energía con diésel en municipios con ingresos bajos. Este déficit energético en Colombia es una oportunidad para la generación de electricidad a partir de energías renovables como, por ejemplo, la biomasa, las cuales podrían superar las condiciones geográficas que dificultan la infraestructura eléctrica convencional en las zonas rurales colombianas. Este artículo de revisión presenta los avances y las tendencias sobre las tecnologías de aprovechamiento energético de biomasa en las zonas rurales de Cundinamarca. El objetivo de esta revisión es presentar las principales tecnologías implementadas en Cundinamarca sobre el aprovechamiento energético de la biomasa a partir de biodigestión anaerobia. La revisión incluye proyectos productivos que se han desarrollado mediante el diseño y la implementación de biodigestores de bajo costo. Estos proyectos de ingeniería sostenible, desde el año 2000, han permitido empoderar a las comunidades rurales mediante la transferencia de tecnología y la promoción de economías circulares basadas en el emprendimiento y la mejora de la competitividad regional; por eso el texto plantea la necesidad de un futuro estudio ambiental que determine el impacto de estos proyectos productivos sobre los ecosistemas que predominan en estos ambientes rurales.
... Biogas can be used as an alternative energy source through its combustion in boilers or combined heat and power units; however, the interest in biogas conversion to highvalue products has been increasing recently (Patel et al., 2020;Wu et al., 2016). Digestate is widely considered as a potential organic fertilizer, being rich in plant macronutrients (N, P and K) and organic matter (Castro et al., 2017;Peng et al., 2020;Tambone et al., 2017). AD can be operated at psychrophilic (18-20 • C), mesophilic (35-40 • C) and thermophilic (50-60 • C) temperature regimes (Hupfauf et al., 2018), with the last two conditions being the more effective for organic matter degradation and biogas production. ...
Bioplastics are becoming more and more widespread as substitutes for petroleum-derived plastics due to their biodegradability. Bioplastics degradation under different environments has been described and reported to depend mainly on bioplastics’ compositions and the environmental conditions. Incomplete degradation during waste management processes and leakage of bioplastics into the environment are becoming major concerns that need to be further investigated. In this context, the present paper aimed to review recent literature dealing with biodegradation of bioplastics under industrial (e.g. anaerobic digestion and composting) and natural (e.g. soil and water) environments, and to link it to the potential bioplastics’ leakage into the environment. Reviewed data were used to estimate the potential role of waste management processes in decreasing the potential leakage of bioplastics. Depending on bioplastics’ type and processing conditions, waste management can effectively reduce bioplastics’ potential leakage, decreasing the concentration of these materials that can reach the natural environments.
... Throughout the operation of the anaerobic system (Fig. 2), in phase one (7 to 21 d) and phase two (28 to 56 d), the VFA/TA ratio was below 0.4 (Fig. 1B), which is considered appropriate for an anaerobic digestion process (Castro et al., 2017;López-López et al., 2015). Therefore, it was possible to increase the organic load. ...
Current global prospects of increasing ethanol production face the problem of one of the highest consumptions of fresh water and the generation of large volumes of effluents. This study evaluated the reuse of effluent from the anaerobic digestion of vinasse as a replacement of freshwater in ethanol production. This process combines the use of vinasse and anaerobic digestion effluent to produce biogas energies. The effect of reusing 0, 30, 60, and 100 % effluent to dilute sugarcane molasses to produce ethanol was evaluated. The viability and vitality of the cells of the yeast were not altered by using the effluent. The efficiency of ethanol production with effluent (0,30, 60, and 100%) was 43.3, 42.3, 39.2, 38.4 g/L, respectively. Also, we tested reusing 100% effluent without treatment for dilution of sucrose. This assay gave the highest ethanol production (80.6 g/L). The difference in ethanol production might be due to a wide range of buffering capacity of the combination of molasses and effluent, which moderately affected the performance of Saccharomyces cerevisiae. Nonetheless, additional research is required to determine a causal relationship between the buffer capacity of the molasses/effluent mixture and ethanol production.
... Due to the dry organic matter content not exceeding 8%, it can be poured onto fields, just like slurry [62]. Digestate contains phosphorus, nitrogen, and potassium and has a neutral to alkaline pH, making it a good fertilizer [63]. Moreover, the digestion of manure can significantly reduce methane emissions from storages [64]. ...
Although cow manure is a valuable natural fertilizer, it is also a source of extreme greenhouse gas emissions, mainly methane. For this reason, this study aims to determine the impact of investments in a biogas plant on the energy and economic aspects of the operation of a dairy farm. A farm with a breeding size of 600 livestock units (LSU) was adopted for the analysis. In order to reach the paper’s aim, the analysis of two different scenarios of dairy farm functioning (conventional–only milk production, and modern–with biogas plant exploitation) was conducted. The analysis showed that the investment in biogas plant operations at a dairy farm and in using cow manure as one of the main substrates is a more profitable scenario compared to traditional dairy farming. Taking into account the actual Polish subsidies for electricity produced by small biogas plants, the scenario with a functioning biogas plant with a capacity of 500 kW brings €332,000/a more profit compared to the conventional scenario, even when taking into account additional costs, including the purchase of straw to ensure a continuous operation of the installation. Besides, in the traditional scenario, building a biogas plant allows for an almost complete reduction of greenhouse gas emissions during manure storage.
... Esto no solo evita los problemas mencionados, además mejora la producción de biogás. Colombia cuenta con más de 500 biodigestores de bajo costo operando con estiércol porcino (EP) y estiércol bovino (EB) [9,10], en zonas interconectadas, generando biogás para cocción de alimentos. Sin embargo, para el estiércol equino (EE) aún no ha sido reportado ningún biodigestor. ...
Los digestores domésticos han sido utilizados para la gestión y valorización energética de estiércoles, en procesos de mono-digestión anaerobia. Sin embargo, el conocimiento es limitado con respecto a los rendimientos de biogás a partir de la co digestión de estiércoles. En este sentido, el objetivo de esta investigación fue determinar, mediante un diseño experimental usando la sinergia (Φ) como un indicador, las relaciones de mezcla adecuadas para digestión anaerobia de estiércoles, contribuyendo a obtener un mejor aprovechamiento tanto del digestor como de los residuos. En esta investigación se realizó un estudio de mezclas de diluciones de estiércol bovino, equino y porcino teniendo en cuenta como variables de respuesta el potencial de biometanización (PBM) y la sinergia (Φ). Los resultados demostraron que en el proceso de mono-digestión, en orden ascendente, los potenciales de biometanización fueron 10,44 N l CH4/kgSV; 14,50 N l CH4/kgSV; y 17,09 N l CH4/kgSV para el estiércol bovino, porcino y equino respectivamente. La mezcla de estiércoles (binarias y ternarias), presentaron sinergias >1, y en consecuencia se obtuvieron mejores potenciales de biometanización. La mayor sinergia (3,63), la presentó la mezcla estiércol equino-bovino en proporción 35,5:64,5 (%p) respectivamente. A partir del potencial energético, los usuarios de los biodigestores domésticos podrán disponer de diferentes escenarios de codigestión de mezclas de estiércoles, para un mejor rendimiento en la producción de biogás
... An alternative to reduce the negative impacts of these residues is the implementation of biodigesters in the agricultural environment. The anaerobic biodigestion process occurs inside the equipment, transforming biomass into alternative means of obtaining electric and thermal energy (biogas) and biofertilizer, which can be used in the production system of the rural property or commercialized (Castro et al., 2017;Kadam & Panwar, 2017). ...
One way of making livestock farming a more sustainable practice is to raise cattle organically. However, regardless of the production system, there is a generation of residues that can be converted into energy resources using biodigesters. This study aimed to evaluate the addition of inoculum in the anaerobic biodigestion of cattle manure under organic (OPS) and conventional production systems (CPS) in an Indian model biodigester. The physicochemical (pH, EC, TS, VS, DBO, and COD) and microbiological characteristics of the affluent and effluent, as well as the production, potential, and qualitative characteristics of the biogas, were evaluated. CPS showed higher reductions in TS, VS, BOD, and COD than OPS, with the highest effect of biogas production. Regarding the effect of inoculum addition, the treatment with 20% inoculum provided in both production systems high acceleration at the starting point of biogas production and increased energy potential, as well as high reductions in VS, BOD, and COD. Thus, there is a need to use 20% inoculum for high biogas productivity, regardless of the production system.
... During this period, no microbial nutrition is fed to the anaerobic digester, forcing microbes into starvation and death. [5] As the next batch begins, there inevitably occurs a lag phase where bacteria take approx. 2 weeks before starting to produce biogas again [6][7][8][9]. This leads to insufficient electricity for farming activities during such operation and thus extra electricity from Provincial Electricity Authority (PEA) is purchased. ...
A conventional all-in/all-out batch management, applied in most small to medium scale swine farming, often provides an inconsistent feed of wastewater for the biogas system, causing imbalance between the farm’s power requirement and its generation capacity. This study proposed two developed models that could be employed to ease this problem. In Model 1, the operation was divided into two batch intervals, while in Model 2, the operation used four separate batches. The developed models helped avoid an unnecessary long lag phase, allowing more stable anaerobic digestion performance, and a more evenly distributed amount of biogas being produced. Accordingly, the developed models more stably supplied energy for domestic use, achieving 36-44% reduction of the electricity expense, or a saving of 43,782 m ³ biogas or 35,834 kWh equivalent compared with that of the conventional management. Moreover, excess biogas which occurred in the conventional management, up to 14,714 m ³ or 12,043 kWh equivalent at the peak period, could be reduced by 79-100%, evaluated as a greenhouse gas reduction of 9,441 and 11,902 m ³ CO 2 eq by Models 1 and 2, respectively. This suggests that without additional investment, more profit could be attained from the significant reduction of operating cost by proper farm management.
... During this period, no microbial nutrition is fed to the anaerobic digester, forcing microbes into starvation and death [5]. As the next batch begins, a lag phase inevitably occurs where bacteria take approximately 2 weeks before starting to produce biogas again [6][7][8][9]. This phase leads to insufficient electricity for farming activities during the lag phase, and thus extra electricity is purchased from the Provincial Electricity Authority (PEA). ...
The conventional all-in/all-out batch management that is applied in most small to medium swine farms often provides an inconsistent feed of wastewater to biogas systems, causing an imbalance between the power requirements and generation capacity of a farm. This study proposes two alternative models that can be employed to ease this problem. In Model 1, the operation was divided into two offset batch intervals, while in Model 2, the operation used four separate offset batch intervals. The models developed here help avoid an unnecessary long lag phase in the digester, allowing more stable anaerobic digestion performance and more evenly distributed biogas production. Accordingly, the models produce a more stable supply of energy for domestic use, achieving a 36–44% reduction in the electricity expense or a savings of 43,782 m³ biogas/year or 35,834 kWh equivalent compared with that of conventional management. Conventional farm management has periods of excess and deficient biogas production; excess biogas is produced at a rate of up to 14,714 m³/year or 12,043 kWh equivalent at the peak period. This excess could be reduced by 79–100% by using the proposed farming models. This reduction is equivalent to greenhouse gas reductions of 9441 and 11,902 m³ CO2 eq./year by Models 1 and 2, respectively. Finally, a sensitivity analysis is used to show how the profitability of biogas plants would vary due to changes in some key parameters, such as the electricity buyback price. The results suggest that more profit could be attained from a significant reduction in operating costs by proper farm management without requiring additional investment.
Graphic Abstract
... 1. Pure cattle manure 227 sludge shows a specific methanogenic activity of 0.0338 ± 0.002 g COD g -1 VS day -1 . This 228 value was found to be in the range of reported values for the same type of inoculum in low-229 cost tubular digesters(Castro et al., 2017). Adding SCS up to 5 kg VS m -3 increased SMA 230 by 9%(Fig. ...
Anaerobic co-digestion (AcoD) of the main residues from the non-centrifugal cane sugar (NCS) making process, agricultural crop residues (ACR) and sugarcane scum (SCS), was evaluated using biochemical methane potential tests. Substrates were pretreated: ACR through particle size reduction, and SCS with dilution. The maximum methane yield of 0.276 Nm3 CH4 kg-1 VSadded occurred at an ACR of 2 mm and at 12.5% dilution of SCS, at a ratio of 75:25 based on volatile solids, which was 30.2% and 5.9% higher compared to SCS and ACR in mono-digestion, respectively. ACR was a substrate of adequate buffer capacity for the AcoD stability, while the SCS, in addition to helping accelerate the process, also helped improve the inoculum's methanogenic and hydrolytic activity. The first-order kinetic and dual-pool two-step models were suitable to describe methane yield. AcoD of ACR with SCS is a good option for the treatment of streams in the NCS agribusiness sector.
Designing a biodigester that allows treating organic waste from cattle to obtain biogas in rural areas is a challenge in biomass management and productivity indices. The design of the biodigester was carried out considering a possible increase in the size of the cattle. The amount of manure available and the amount of biogas expected to be produced were also estimated. In addition, a metal dome was selected to facilitate access to the interior of the biodigester and to be able to carry out its maintenance in a simpler way. Graphs were added that show the minimum values of manure collection that allow its profitability. The most notable conclusion of the project is that for biodigesters in rural areas, biogas represents a minimal fraction of the profit that can be obtained through the project due to its low production, so the commercialization of biol is considered the main source of income.
This work addresses the development and application of Cucumeropsis mannii and Luffa acutangula seed proteins as novel bio-coagulants for fecal sludge concentration to increase the biogas yield. The seed protein content was determined and extracted using 1M NaCl, isolated and precipitated by ammonium sulfate [(NH₄)₂SO₄], and dialyzed to obtain the purified proteins. Their coagulation/flocculation was compared to Moringa oleiefera and pumpkin seeds as the primary treatment for the fecal sludge concentration. Optimal coagulant dosages of 20 mg/l at pH 7.25 increased the total solids from 0.4–2.8% and obtained 180 to 350 ml/l of fecal sludge volume per liter. The bio-coagulants effect on the supernatant water reduced 71.20% to 96,88% of turbidity, 76.48–88.70% of COD, and 81.33 to 95.30% of ammonia nitrogen. The BMP result has shown that plant seed-based bio-coagulant are effective and triple the methane yield result compared to the FS without bio-coagulant treatment with a specific methane yield of 192.8 NmL CH 4 /gVS, and FS with bio-coagulant pretreatment was increased up 350.5 to 465.3 NmL CH 4 /gVS, with a ratio 2:1 on VS basis.
Biogas technology has matured over the years and is gaining acceptance; however, challenges with optimum operation and maintenance of digesters are a massive hurdle for developing countries that threaten the successful adoption of the technology. The failures of biogas digesters leading to the low diffusion of the technology in developing countries have been attributed to several factors spanning from social to technical. This study employed a scoping review and bibliometric analysis to synthesize literature in the Scopus database to map and discuss scientific knowledge. The synthesized data suggest the need for real-time monitoring systems for the optimal operations and maintenance of small-scale biogas digesters. A bibliometric analysis with the VOSviewer software of the study suggested that there is limited research output from developing countries such as Ghana. It, therefore, necessitates the need for conscious commitments from stakeholders to invest resources to advance research to address the challenge.
Anaerobic digestion (AD) offers enormous potential towards a sustainable bioeconomy. AD is suitable for waste management of various sources and generates value in multiple sectors such as electricity, heating, or agriculture through biogas or fertilizer production. However, attention must be paid to cheap fertilizers such as digestates because these digested fractions contain heavy metals, (nano) microplastics, hormones, and other chemical compounds that, when accessible, can be detrimental to humans, animals, plants and the environment. Digestates originating from manure substrates should be monitored to control the spread of antimicrobial resistance genes to the environment. Digestate toxicity can be a problem for aquatic and terrestrial organisms as determined by bioassays to detect the adverse consequences of digestate applied to the soil. Anaerobic digestate must meet specified quality requirements prior to utilization in the soil or crops to prevent dangers to human health and the environment. The digestate is available in three forms: whole, liquid, and solid, and can be applied to the soil as a final disposal location if it complies with applicable regulatory standards and is classified as a ‘product’.
Wastewater such as digestate from waste biomass anaerobic digestion contains a high concentration of nutrients such as nitrogen and phosphorus. A novel process for simultaneous nitrogen removal and phosphorus recovery was recently developed based on the combination of the anammox process and hydroxyapatite (HAP) crystallization. This study firstly investigated the feasibility of operating this process under low temperature using an anammox-HAP type expanded bed reactor. By gradually increasing nitrogen loading and phosphorus loading rate, a nitrogen removal rate of 8.45±0.49 gN/L/d with a simultaneous phosphorus recovery rate of 0.63±0.06 gP/L/d was obtained at 15°C. The efficiency for both nitrogen removal and phosphorus recovery was higher than 80%. The addition of Ca²⁺ was confirmed to be an effective strategy to enhance the efficiency of phosphorus recovery by affecting the supersaturation condition of the solution. However, a high phosphorus load may result in excessively high mineral concentrations in the sludge and affect anammox performance. The granular sludge formed under low temperature conditions in this study has a typical double-layer structure of HAP-core and anammox biofilm. This study firstly demonstrated the feasibility of the anammox-HAP process even under low temperatures and give new options for future digestate treatment.
Because of the robustness and high catalytic activity of p-type CuO semiconducting nanostructures, they are applied as sensing materials for various gases. However, pristine CuO materials exhibit relatively low sensing performance to some gases, such as SO2 and H2. Here, we demonstrate an enhancement in the gas-sensing characteristics of CuO nanoplates through surface decoration with Pd nanoparticles. CuO nanoplates were synthesized by a facile hydrothermal method, and Pd nanoparticles were decorated effectively via a directed room-temperature reducing pathway without need for stabilizing agents. The Pd-CuO nanoplates exhibited superior sensitivity, fast response, and recovery times to SO2 and H2 compared with their pristine CuO counterpart. The gas-sensing mechanism is discussed from the perspective of the heterojunction between Pd and CuO, as well as the catalytic activity of Pd for the dissociation of gaseous molecules. Such Pd-CuO nanoplate-based sensors could be effectively applied for SO2 and H2 gas monitoring.
Phenolic acids represent a big group of plant secondary metabolites that can be used as food additives, nutraceuticals, and pharmaceuticals. Obtaining phenolic acids from the plant in vitro cultures provide an attractive alternative to produce high-value plant-derived products. The impact of yeast extract and jasmonic acid on the induction of defense responses and consequently the production of phenolic acids in vitro hairy root cultures of O. aristatus have been investigated. Treatment of O. aristatus cultures with jasmonic acid caused accumulation of 12.98 mg.g-1 DW of phenolic acids, elicitation with yeast extract resulted in the highest amount of phenolic acids, particularly in 17.99 mg.g-1 DW as compared to 4.03 mg.g-1 DW for the non-treated cultures. Individual phenolic acids showed a different response to elicitation. Particularly rosmarinic acid content on the control plot reached 2.89 mg.g-1 DW, while after the treatment with jasmonic acid is increased to 10.84 mg.g-1 DW and after yeast application, it was 14.31 mg.g-1 DW. Also, caffeic acid content increased until 0.75 and 2.01 mg.g-1 DW after application of jasmonic acid and yeast extract, while at the control plot its concentration was 0.58 mg.g-1 DW. Application of yeast extract influenced synthesis of phenolic acids in vitro cultures of O. aristatus stronger as jasmonic acid treatment.
Hydrolysis is the rate limiting stage in the anaerobic digestion (AD) of solid waste, such as food waste (FW), due to the presence of lignocellulosic material, which affects methane production. Mitigation strategies, such as thermal pre-treatment of the substrate, can be used to accelerate hydrolysis. In this study, the influence of temperature (72–128 °C) and exposure time (15–33 min) on the physicochemical properties of the substrate, biochemical methane potential (BMP) hydrolysis, the balance of organic matter (as measured by the chemical oxygen demand (COD)), and net energy production were determined. In terms of the substrate, positive results were obtained: a 50% reduction in lignin; up to a 34% increase in hemicellulose; up to a 99% reduction in Fe, Mn, Cu and Zn; an 83% decrease in Mg; and a 150% increase in K. In addition, methane production was higher than for the untreated substrate (120 vs 90 mLCH4 gVS−1). The modified first-order kinetic model and adjusted Gompertz model, showed that the pre-treatment reduced the lag-phase (by less than 1 d), and increased the hydrolysis constant to above 40%. The optimal pre-treatment condition was approximately 72 °C-22 min, promoted hydrolysis, increased the COD and produced a positive energy balance (7821.07 kJ).
This study was carried out with the principal aim of obtaining reliable outcomes for the future implementation of a temperature-phased anaerobic digestion (TPAD) process in a large (2 M population equivalent, p.e.) WWTP. With the aid of pilot-scale (10 L) reactors fed by pure primary sludge (PS), a TPAD process, where the first and the second reactor were operated at 50 °C and 38 °C, respectively, was compared with a conventional mesophilic (38 °C) anaerobic digestion (AD) process. The initial hydraulic retention time (HRT) of the first, acidogenic, reactor of the TPAD was reduced from 3 to 2 days in the second part of the test.
The results demonstrated that the TPAD system had been stable for all the duration of the test (approx. 100 days), as testified by the steady values of pH and tVFAs/TA ratio, notwithstanding the decrease in the HRT. The TPAD proved to be more efficient in volatile solid (VS) reduction and methane generation, compared to the conventional mesophilic AD process. In fact, the VS reduction increased from 42% to approx. 55% and the specific methane potential (SMP) from 280 to 332 NL/kg VS added. An excellent phase separation was observed between the two acidogenic and methanogenic reactors, as demonstrated by the low SMP (only 3% of the overall production) recorded from the first reactor of the TPAD system.
However, the energy analysis demonstrated that the higher SMP obtained in the TPAD was not sufficient to compensate the higher amounts of heat required for sludge heating and heat loss compensation. Only a process of heat recovery could make the TPAD system really profitable, thus increasing the aliquot of energy in the form of methane, available for users external to the WWTP, by 20%. This result represents a step in the evolution of traditional WWTPs towards more energy efficient and sustainable facilities.
Anaerobic digestion is a promising waste-to-energy alternative technology. However, the efficiency upgrading for conventional mesophilic digestion of organic solid waste is always indispensable. Employing hyperthermophilic or thermophilic microbial community is one of the viable upgrading alternatives. Given the unavailability of the superior microbial communities, mesophilic digested sludge was used as inoculum, and instantly controlled at 70 °C and 55 °C for acclimation of hyperthermophilic and thermophilic inocula, respectively. Waste activated sludge was continuously and synchronously fed into two digesters. After one round, thermophilic digester achieved stable biogas production rate at 0.22 L L⁻¹ d⁻¹, with a methane proportion over 60%, whereas fluctuation was observed in the hyperthermophilic digester, and approximately triple time was needed to reach a relatively stable biogas production rate 0.12 L L⁻¹ d⁻¹. Nevertheless, higher hydrolysis ratio 24.4% was observed in the hyperthermophilic digester despite the lower biogas production. Therefore, methanogenesis step limited the whole anaerobic process for the hyperthermophilic digestion, and digestion at 70 °C was appropriate as a pre-fermentation stage to enhanced hydrolysis. The genus Methanothrix proportion in the thermophilic digester gradually decreased, while another acetoclastic genus Methanosarcina ultimately was acclimated to the dominant methanogen. In addition to Methanothrix, hydrogenotrophic archaea became competitive in the hyperthermophilic digester, with Methanothermobacter dominant at 22.6%. The genus Psychrobacter, affiliated to the phylum Proteobacteria could survive better than the others at 70 °C, with a final proportion of 62.5%.
En los últimos años la producción de biogás en biodigestores domésticos ha tenido un
creciente desarrollo, siendo empleado en zonas rurales principalmente para iluminar y
calentar. Sin embargo, la presencia de CO2 reduce considerablemente el valor calorífico
del biogás, generando una disminución en la eficiencia térmica, lo que hace necesaria
la remoción de este componente para mejorar la calidad del gas y aumentar sus
posibilidades de aplicación como combustible.
En este trabajo se evaluó la capacidad de adsorción de CO2 de nanopartículas de sílice,
sílice pirogénica comercial Aerosil 380 y xerogeles de carbón impregnados con aminas.
Las nanopartículas de sílice se prepararon mediante el método sol-gel usando como
precursor de silicio Tetraetil ortosilicato, los xerogeles de carbón mediante
carbonización de un gel de resorcinol-formaldehido. Los materiales se funcionalizaron
mediante impregnación húmeda con 15 y 30% p/p de dietanolamina y etilendiamina.
Las pruebas de caracterización permitieron determinar el tamaño de partícula (TEM,
SEM), área superficial (BET), estabilidad térmica (TGA) y composición química (FTIR)
de las nanoestructuras y relacionar dichas propiedades con la afinidad por el adsorbato.
Los ensayos de adsorción de CO2 se realizaron a una temperatura de 30 °C bajo un
flujo de 60 ml/min de CO2. Los materiales basados en xerogeles de carbón presentaron
una mayor capacidad de adsorción comparados con los materiales de nanopartículas
de sílice, se obtuvo la mayor capacidad de adsorción (71,1 mg/g) para la muestra
impregnada al 30% p/p de dietanolamina, que además puede adsorber el CO2 en
condiciones de humedad.
This study identified and quantified microbial populations in cattle manure slurry, responsible for anaerobic degradation of kitchen waste using activity tests and Most Probable Number for key trophic groups in the process. Hydrolytic, acidogenic, acetogenic, specific methanogenic acetoclastic and hydrogenotrophic activities were evaluated using as model substrates starch, glucose, propionate-butyrate mix, acetate and formate, respectively. Anaerobic digestion from kitchen waste was developed for 35 days in batch reactors of 50mL containing an inoculums/substrate ratio of 3. Samples were taken from digesters every 7 days to evaluate microbial populations by counting metabolic groups. This study demonstrates that there is an association between biomass activity and population of trophic groups related. Additionally, CMS is an inoculum with high quality to start-up the anaerobic process with kitchen waste. On the other side, MA/FB ratio and MA/SRB ratio are important microbial parameters to evaluate performance of reactor. Finally, AD from kitchen waste reached a yield coefficient of 0.41m³CH4/kgVS using cattle manure sludge as inoculum.
There is a lack of literature reporting the methane potential of several livestock manures under the same anaerobic digestion conditions (same inoculum, temperature, time, and size of the digester). To the best of our knowledge, no previous study has reported biochemical methane potential (BMP) predicting models developed and evaluated by solely using at least five different livestock manure tests results. The goal of this study was to evaluate the BMP of five different livestock manures (dairy manure (DM), horse manure (HM), goat manure (GM), chicken manure (CM) and swine manure (SM)) and to predict the BMP using different statistical models. Nutrients of the digested different manures were also monitored. The BMP tests were conducted under mesophilic temperatures with a manure loading factor of 3.5 g volatile solids (VS)/L and a feed to inoculum ratio (F/I) of 0.5. Single variable and multiple variable regression models were developed using manure total carbohydrate (TC), crude protein (CP), total fat (TF), lignin (LIG) and acid detergent fiber (ADF), and measured BMP data. Three different kinetic models (first order kinetic model, modified Gompertz model and Chen and Hashimoto model) were evaluated for BMP predictions. The BMPs of DM, HM, GM, CM and SM were measured to be 204, 155, 159, 259, and 323 mL/g VS, respectively and the VS removals were calculated to be 58.6%, 52.9%, 46.4%, 81.4%, 81.4%, respectively. The technical digestion time (T80–90, time required to produce 80–90% of total biogas production) for DM, HM, GM, CM and SM was calculated to be in the ranges of 19–28, 27–37, 31–44, 13–18, 12–17 days, respectively. The effluents from the HM showed the lowest nitrogen, phosphorus and potassium concentrations. The effluents from the CM digesters showed highest nitrogen and phosphorus concentrations and digested SM showed highest potassium concentration. Based on the results of the regression analysis, the model using the variable of LIG showed the best (R2 = 0.851, p = 0.026) for BMP prediction among the single variable models, and the model including variables of TC and TF showed the best prediction for BMPs (R2 = 0.913, p = 0.068–0.075) comparing with other two-variable models, while the model including variables of CP, LIG and ADF performed the best in BMP prediction (R2 = 0.999, p = 0.009–0.017) if three-variable models were compared. Among the three kinetic models used, the first order kinetic model fitted the measured BMPs data best (R2 = 0.996–0.998, rRMSE = 0.171–0.381) and deviations between measured and the first order kinetic model predicted BMPs were less than 3.0%.
Despite the importance of quantifying inhibitory capacity of compounds in anaerobic digestion, there is currently no well-defined method to assess it. Experimental methods in literature are frequently time-consuming and resource intensive. As a result, detailed inhibition testing rarely forms part of anaerobic digestion studies, despite the importance and utility of this information. This study develops and validates a simple and rapid inhibition test protocol, based on relative inhibition of acetoclastic methanogens. The inhibition potential of a compound is determined from the reduction in specific methanogenic activity as inhibitor concentration is increased. The method was successfully performed on two inoculums from different source environments and with both biostatic and biocidal inhibitors. Optimisation work indicated that: (i) sodium acetate is a preferred carbon source compared to acetic acid; (ii) an inoculum to acetate ratio of 5 g VS g(-1) acetate is preferred, and (iii) that the inoculum concentration should be normalised to 10 g L(-1) VS to reduce mass transfer problems and promote consistency. A key advantage over existing methods is that the sampling strategy has been optimised to three events over 1.5 days while effectively controlling the relative analytical error.
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Intensive soil fertilization with mineral fertilizers has led to several issues such as high cost, nitrate pollution and loss of soil carbon. Fertilization with organic matter such as compost therefore represents an alternative for sustainable agriculture. Traditional organic amendments such as manures, composts and sewage sludge have been extensively studied in the past. However, applications of biogas digestates and their impacts on the environment and human health are still unexplored. Recent articles report the agricultural potential and conflicting results of digestate performances. As a consequence, the effectiveness of digestate as organic amendment and fertilizer is still under debate. Here we review the legislative, chemical, agronomic and environmental literature on anaerobic digestates. We found that digestates can be considered as organic amendments or organic fertilizers, when properly handled and managed. Indeed we further show that anaerobic digestates have a higher potential to harm the environment and human health than undigested animal manures and slurries. The main points are the following: (1) Most solid digestates comply with the European organic matter minimal requirement for an organic amendment; (2) the fertilizer values of liquid digestates lie between those of livestock manures and inorganic fertilizers; (3) anaerobic digestates have higher NH3 emission potential than undigested animal manures and slurries and, consequently, pose a greater risk to the broad environment; (4) high Cu and Zn concentrations in digestates from co-digestion of pig and cattle slurry feedstock could jeopardize the sustainability of agricultural soils and (5) high Mn concentrations in digestates can induce Mn toxicity in agricultural soils, upon repeated applications.
Fique's bagasse (Furcraea macrophylla) anaerobic digestion generate 0.3m3 CH4/kg SV and 7L of sludge per kg of treated bagasse. The sludge can be applied in agriculture. The aim of this research was to produce a biosolid from sludge stabilized by alkali treatment and evaluates its remedial effect in a sandy loam soil of Mogotes - Santander. The methodology consisted in physicochemical and microbiological characterization of effluent sludge from fique's bagasse anaerobic digestion, followed by an alkaline stabilization process to obtain biosolids as byproduct and the evaluation as soil conditioner using Phalaris canariensis seeds. The seedling emergence, the height of plants and the change in soil nutrient composition were evaluated as response variables. According to levels of fecal coliforms, Salmonella, and helminth eggs, the biosolid can be applied without biological risk with the respective application restriction. As organic soil conditioner, it is used for the recovery of sterile ground deteriorated by fique's crops. The application of stabilized sludge in agriculture contributes to amendment of acidic soils and the reduction of environmental pollution.
Field experiments were conducted to evaluate the effects of repeated annual manure applications on sodium adsorption ratios and electrical conductivity in semi-arid environments. Swine effluent, beef manure, and anhydrous ammonia were annually applied at loading rates of 0, 56, 168, and 504 kg nitrogen (N) ha to an irrigated, conventionally tilled, continuous corn (Zea mays L.) cropping study in the Oklahoma panhandle. Sodium adsorption ratios increased with swine effluent additions at the high N loading rate application; however, sodium adsorption ratio decreased with the high anhydrous ammonia loading applications and remained unchanged with beef manure applications. Linear correlations were found for swine effluent and anhydrous ammonia applications when N levels increased. Electrical conductivity levels increased 2.35 dS m with the high anhydrous ammonia loading rate to a level where relative yields for crop production may be at risk of being reduced 50%.
SUMMARY As anaerobic digestion (AD) is quickly being harnessed in Italy and in other European countries, there is a need for a more in-depth description of the main by-product of the process, the digestate. Little information on digestate characteristics and composition is available and unclear legislation causes problems in biogas plant management. In this work, the organic matter (OM) of this matrix was described through chemical, biological, spectroscopic, and statistical approaches. It was shown that AD results in a strong reduction of the easily degradable fraction of the OM and an accumulation of recalcitrant molecules (possible humus precursors). This contributes to a relatively high biological stability of the residual OM content in the digestate and may lead to good amendment properties. Besides, the observed relative accumulation and the high mineralisation of nitrogen and phosphorus may point to the digestate as a readily available liquid fertiliser for agronomic use. Moreover, xenobiotics and pathogens respected limits for both biosolids and compost in Italian and European legislation.
Methane production, electricity production, and wastewater transformations were quantified for a digestion system that combines biogas from a swine digester and dairy digester in Costa Rica. The low-cost, plug-flow digesters were not heated and were operated in the lower portion of the mesophilic range (25–27 °C).The dairy digester produced 27.5 m3/day of biogas with 62.6% methane and reduced organic matter (COD) by 86%. The swine digester produced 6.0 m3/day of biogas with 76.4% methane and reduced COD by 92%. Combining biogas from a swine and dairy digester, increased electricity production due to the higher biogas production rate of the dairy farm and the higher quality biogas obtained from the swine farm. The farm’s 2-h peak electricity demand (12.9 kW/day) was 81.8% met. The electricity was produced using manure equivalent to the quantity excreted by 5 dairy cows and 40 pigs remaining in corrals 100% of the time.The $21,000 capital cost of the digester project will be recovered in 10.1 years through electricity savings and reductions in wastewater fines. If the generator were more appropriately sized for the farm, the capital recovery time would have been 7.6 years.
In Colombia there are 20,000 ha of fique fields (Furcraea sp., family Agavaceae), that produce around 93,400 tons of fique's bagasse per year. These residuals are disposed into rivers and soil causing pollution. According to physicochemical characteristics, the lignocellulosic residues from fique crops (fique's bagasse) are appropriate carbon source to biogas production. Anaerobic digestion from fique's Bagasse (FB) requires a specialized microbial consortium capable of degrading its high lignocellulosic concentration. In this study, the capacities of seven microbial consortia for biomethane potential (BMP) from FB were evaluated. Inoculum of ruminal liquid achieved high hydrolytic activity (0.068 g COD/g VSS day), whereas pig waste sludge inoculum showed high methanogenic activity (0.146 g COD/g VSS day). Mixtures of these two inoculums (RL+PWS) showed the best yields for biomethane potential (0.3 m(3) CH4/Kg VS ad).
The application of anaerobic digestion technology is growing worldwide because of its economic and environmental benefits. As a consequence, a number of studies and research activities dealing with the determination of the biogas potential of solid organic substrates have been carrying out in the recent years. Therefore, it is of particular importance to define a protocol for the determination of the ultimate methane potential for a given solid substrates. In fact, this parameter determines, to a certain extent, both design and economic details of a biogas plant. Furthermore, the definition of common units to be used in anaerobic assays is increasingly requested from the scientific and engineering community. This paper presents some guidelines for biomethane potential assays prepared by the Task Group for the Anaerobic Biodegradation, Activity and Inhibition Assays of the Anaerobic Digestion Specialist Group of the International Water Association. This is the first step for the definition of a standard protocol.
A study on 18 full-scale centralized biogas plants was carried out in order to find significant operational factors influencing productivity and stability of the plants. It was found that the most plants were operating relatively stable with volatile fatty acids (VFA) concentration below 1.5 g/l. VFA concentration increase was observed in occasions with dramatic overloading or other disturbances such as operational temperature changes. Ammonia was found to be a significant factor for stability. A correlation between increased residual biogas production and high ammonia was found. When ammonia was higher than approx. 4g-N/l the degradation efficiency of the plant decreased and as a consequence, the residual methane potential was high. Decrease of the residual methane potential with increasing hydraulic retention time was found. Digestion temperature was very important for effective post-digestion. Post-digestion for recovering the residual methane potential at temperatures below 15 degrees C was very inefficient.
A series of batch experiments were conducted to investigate the effects of inoculum type, oxygen (O2) dosage, and incubation time on volatile fatty acids (VFAs) production during anaerobic digestion (AD) of Napier grass (Pennisetum purpureum), a high yielding energy crop. The results showed that anaerobically digested cattle manure (ADCM) as an inoculum generated significantly higher VFAs compared to that of anaerobically digested waste activated sludge (ADWAS) as an inoculum. Additionally, the incubation time of 3days and O2 dosage of 15mL/g volatile solidsadded showed the highest VFAs production when ADCM was used as an inoculum. Moreover, the VFAs production had a quadratic correlation with O2 dosage with R(2) of 0.86. The Scanning Electron Microscopy (SEM) images of the digested fiber showed rough and crumbled surface structures as opposed to that of the undigested fiber, which was further confirmed by changes in structural composition of the digested fiber.
To obtain high calorific biogas via anaerobic digestion without additional upgrading equipment, a two-phase pressurized biofilm system was built up, including a conventional continuously stirred tank reactor and a pressurized biofilm anaerobic reactor (PBAR). Four different pressure levels (0.3, 0.6, 1.0 and 1.7 MPa) were applied to the PBAR in sequence, with the organic loading rate maintained at 3.1 g-COD/L/d. Biogas production, gas composition, process stability parameters were measured. Results showed that with the pressure increasing from 0.3 MPa to 1.7 MPa, the pH value decreased from 7.22 ± 0.19 to 6.98 ± 0.05, the COD removal decreased from 93.0 ± 0.9% to 79.7 ± 1.2% and the methane content increased from 80.5 ± 1.5% to 90.8 ± 0.8%. Biogas with higher calorific value of 36.2 MJ/m³ was obtained at a pressure of 1.7 MPa. Pressure showed a significant effect on biogas production and gas quality in methanogenesis reactor.
The combined and coordinated metabolic activity of an anaerobic reactor population is required for the complete degradation of complex organic matter to CO2 and CH4. The intermediates necessary for certain microorganisms are produced as a consequence of the action of others and therefore consortia of bacteria are frequently involved in these conversions. Despite several analyses of the major non-methanogenic bacteria present in anaerobic digesters, detailed investigations into the generic and specific nature of the hydrolytic and fermentative populations have not generally been reported. The predominant organisms in some waste-treatment systems may not, moreover, participate actively in the process but may merely be components of the wastestream itself; coliforms have been implicated here [1].
Many of the existing low-tech biogas reactors in the remote rural areas of developing countries have been abandoned due to the lack of substrates. This study investigated if unutilized biomasses are able to support an efficient biomethanation process with low carbon footprint, in these rural areas where low-tech reactors have been abandoned. Thus, the aims of this study were: a) to identify and evaluate alternative biomasses as anaerobic digestion substrates at a remote rural area site in India; b) to propose an efficient continuous biomethanation scenario for low-tech reactors; c) to assess the influence of the operational parameters on the stability of the anaerobic digestion process. The highest methane yield (137-159 NmL CH4 L-1) and co-digestion synergy (>20% more CH4 than expected) were achieved by co-digestion of wastewater, cow manure, banana and rice by-products at 79.3/4.2/16.3/0.2 ww-1 VS ratio, respectively. Three fixed-dome reactors, R30, R45 and R60, fed with all substrates, operated with hydraulic retention times of 30, 45, and 60 days and organic loading rates of 2.18, 1.46, and 1.09 g VS L-1 d-1, respectively (different co-digestion scenarios). R60 was the best continuous co-digestion scenario with 45% and 13% higher energy recovery from biomasses' utilization and 69% and 25% less greenhouse gas (GHG) emissions, compared to R30 and R45, respectively. These results indicate that it is possible to operate efficiently low-tech biogas reactors with utilized biomasses as anaerobic digestion substrates.
In many developing countries where pathogenic diseases of animal waste origin, such as giardiasis and cryptosporidiosis, are often prevalent, facilities are limited to treat livestock waste. However, household-scale anaerobic digesters are currently being promoted for bioenergy production from livestock manure. Since the effluent is often used as a fertilizer for food crops, it is critical to understand the effect of environmental conditions within household-scale digesters on the viability of Cryptosporidium parvum oocysts and Giardia lamblia cysts. In this study, key environmental parameters affecting (oo)cyst inactivation were measured in four tubular anaerobic digesters, which are a type of household-scale digester promoted for treatment of swine waste in rural Costa Rica. Interviews and participant observations were used to understand digester operation and maintenance procedures. Ambient temperatures (21-24°C), near-neutral pH, total ammonia nitrogen (TAN) concentrations<250mg/L and hydraulic retention times (HRTs) between 23 and 180days were observed. Laboratory (oo)cysts inactivation studies were performed in bench-scale digesters, which were maintained under conditions similar to those observed in the field. Apparent first-order inactivation rate coefficients for Giardia lamblia and Cryptosporidium parvum were 0.155±0.041 and 0.054±0.006day(-1), respectively. Temperature and volatile fatty acids were the main factors contributing to Cryptosporidium parvum and Giardia lamblia inactivation. A mathematical model was developed that predicts the concentration of (oo)cysts in the liquid effluent of tubular digesters like those observed in Costa Rica. A mathematical model was developed that predicts the concentration of (oo)cysts in the liquid effluent of tubular digesters like those observed in Costa Rica. Two dimensionless groups can be used to predict the performance of the digesters for inactivating pathogens; both dimensionless groups depend upon the average HRT in the digester. This is the first study to combine mathematical modeling with qualitative analysis, field and laboratory studies to predict the concentrations of (oo)cysts in tubular digester effluents.
Small-scale tubular anaerobic digesters are an attractive technology for treatment of livestock waste in the developing world. These systems produce biogas (a mixture of CH4 and CO2) that is mainly used for cooking. Digester effluent is rich in nutrients (nitrogen and phosphorus) and can be used as a soil amendment. These systems also assist in mitigating deforestation by providing an alternative fuel source, reducing water pollution due to runoff of untreated livestock waste, decreasing air pollution from biomass combustion and promoting gender equality. However, for these benefits to be significant, the effects of design, substrate characteristics and operating parameters on system performance must be understood. This review provides a detailed summary of the research that has been conducted on tubular anaerobic digesters treating livestock waste in developing countries. Links between successful digester performance and energy, environmental, public health and social benefits are also provided. In addition, this review discusses governmental policies that have successfully increased adoption of livestock waste anaerobic digestion systems in Africa, Asia and Latin America.
Abstract Tubular anaerobic digesters are used in developing countries to produce biogas from livestock waste. In this research, field measurements and physical and biological process modeling studies were used to investigate transport and transformation mechanisms for particulate and soluble organic matter in household-scale tubular digesters in the Monteverde region of Costa Rica. Greater than 75% removal of volatile solids and biochemical oxygen demand (BOD5) were observed. The high effluent quality was attributed to the formation of a biologically active floccular sludge layer, which allowed for separation of hydraulic and mean cell residence times (HRT and MCRT). A reduced order transport model was developed and validated using field tracer study data. Key assumptions of the reduced order model were verified via computational fluid dynamics (CFD) analysis. The mean HRT predicted by the reduced order model was 23 days and was in good agreement with the tracer experiment. A simplified floccular sludge biological process model was developed and used to estimate an average MCRT of 115 days. The results showed that household-scale tubular anaerobic digesters can provide enough biogas to meet households’ cooking energy needs, which was consistent with field results. This is the first study to combine mathematical modeling with field studies of tubular anaerobic digester performance.
Biogas is extensively promoted as a promising renewable energy. Therefore, the search of appropriate co-substrates has come into focus. In this study, we examined the potential of using agricultural byproducts as alternative co-substrates for increased biogas production. The biochemical methane potential (BMP) of six agricultural organic byproducts were tested. Consecutively, the byproduct with the highest BMP was used as a co-digestion substrate with manure, in a continuous stirred tank reactor (CSTR). Meadow grass had the highest BMP value [388 ± 30 NmL of CH4 g-1 of volatile solids (VS)] among all mono-substrates tested. On the basis of BMP, the substrates ranked as follows: meadow grass > spring barley, winter wheat, winter barley, ryegrass > rapeseed > manure. Co-digestion of manure with byproducts resulted in only an additive and not synergistic methane production. Continuous co-digestion of 34 g L-1 raw meadow grass with manure increased the methane production rate of the CSTR reactor by 114% compared to the manure alone.
Nitrogen (N) tied up in or lost from decomposing biomass decreases the residual N effects of green manure and of other crop residues. During anaerobic degradation in a biogas digestor (biodigestion), N mineralization takes place under conditions in which losses can be kept to a minimum. Therefore, biodigestion of green manure biomass and beet foliage was tested to generate readily available N and compared with a direct green manure fertilization system. The effluent was applied as fertilizer in field experiments on a sandy soil as a tool for improving N supply for an organic farming system. Data from the field experiments were used for simulating the amount of net inorganic N equivalents (inorganic N equivalents from effluent plus inorganic N equivalents from pre-crops) in three crop sequences: A) green manure ley, red beets, winter rye; B) harvested ley, red beets, winter rye; and C) harvested ley, spring barley, red beets in which (B) and (C) represented biogas nutrient management systems and (A) a green manure system. When all available effluent from biogas production from 1 ha of grass-clover ley with two or three harvests (2H-ley or 3H-ley) and one hectare of beet foliage was used as a fertilizer for red beets (Beta vulgaris var. conditiva Alef) after barley (Hordeum vulgare L.), the yield of marketable red beets increased by 5.7 Mg_ha-1 (33%) with effluent from 2Hley and beet foliage and 9.1 Mg_ha-1 (53%) with effluent from 3H-ley and beet foliage compared with red beets grown without effluent fertilization after a green manure ley. When total dry matter production was taken into account, the advantage for the BG systems with 2H- and 3H-ley was 15% and 28%, respectively. The nitrate concentration in the red beets was not higher with effluent supplied at this level than with green manure as the only N source. The simulated amount of net inorganic N equivalents was 128 kg N for the whole of crop sequence (C) with 1 ha of each crop and where effluent supply to red beets was based on digested biomass in ley and beet tops. The corresponding amount of net inorganic N equivalents for the green manure crop sequence (A), in which no effluent was supplied, was 73 kg N. Unused soil mineral N (0- to 90-cm depth) at red beet harvest indicated that the risk of leaching in BG systems was lower than in GrM systems (88, 76, and 61 kg Nmin/ha left after unmanured beets after Gr-M-ley, low manured beets after 3H-ley and high manured beets after barley, respectively). Effluent fertilization of red beets directly after 2H- and 3H-ley gave unexpectedly low yield responses compared with red beets after barley. The reasons may be the result of nutritional imbalance of other nutrients than N or may be plant pathological in nature. The conclusion is that a nutrient management system with biodigestion can increase net inorganic N equivalents and reduce risk for N leaching, but inappropriate use of the effluent, i.e., at an unsuitable point in the crop rotation, may negate the benefits.
Titration methodologies have been used for the many years for low cost routine monitoring of full scale anaerobic digestion plants. These methodologies have been correlated to indicate the carbonate alkalinity and the volatile fatty acids (VFA) content within digesters. Two commonly used two end-point titration methods were compared using a dataset of 154 samples from energy crop and animal slurry digestates and were shown to be inaccurate in the estimation of tVFA. Using this dataset correlated with HPLC VFA analysis, two empirical bivariate linear regression equations were derived, where the validation dataset showed an absolute tVFA mean error improvement from ±3386 and ±3324 mg kg(-1) tVFA to ±410 and ±286 mg kg(-1) tVFA, respectively. The same equation was then applied to a food waste dataset where an absolute tVFA mean error was improved from ±3828 to ±576 mg kg(-1) tVFA. The newly derived titration equations can provide greater confidence in digester performance monitoring and are tools that can improve digester management.
The objective of the present study was to evaluate the effect of dairy cow diets on feces composition and methane (CH4) potential from manure with emphasis on fat level and roughage type and compare these results with the corresponding enteric CH4 emission. In experiment 1 six different diets, divided into two fat levels (low and high) and three different roughage types (early cut grass silage, late cut grass silage and maize silage), were used. The high fat level was achieved by adding crushed rapeseed. In experiment 2, the influence of increasing the fat level by using three different types of rapeseed: rapeseed cake, whole seed and rapeseed oil against a low fat ration with no rapeseed fat supplementation was studied. The diet and fat level had a significant influence on feces composition and CH4 yield. In general, ultimate CH4 yields (B0) were 8–9% higher than the present international default values for diets without extra fat and in feces from diets with extra fat supply the yield was 25–31% higher. It was possible to predict the B0 value from feed and feces characteristics; in fact, the best correlation was obtained by including both feed and feces characteristics. Addition of crude fat to diets to dairy cows reduced enteric CH4 emission but at the same time increased CH4 potential from feces both in terms of organic matter in feces and dry matter intake which might lead to increasing emissions unless proper manure handling such as anaerobic digestion is included. Without subsequent anaerobic digestion to produce energy the positive effect achieved at cow level could be counteracted by increasing manure emissions.
The on-farm production of renewable energy from animal manures has rapidly expanded in central and northern Europe, with thousands of anaerobic reactors. This process has increased the land spreading of biogas digestates, replacing the use of fresh manure as a fertiliser. The environmental benefits and risks of such a change still need to be defined. We hypothesised that applying to the soil anaerobically digested instead of fresh manure might control the release of pathogens but increase that of inorganic N. Pots including γ- or non-irradiated soils, either control or amended with digestate or manure (80kgNha−1), were incubated for 0, 1 and 3 months. Escherichia coli, Salmonella and Listeria were cultivated and pathogenicity genes invA and hlyA PCR-amplified. Soil ammonium and nitrate concentrations, and their leaching through the upper soil layer was quantified in 20cm-depth lysimeters for 100d. Anaerobic digestion significantly sanitised the manure by completely eliminating cultivable E. coli and Salmonella but not Listeria (1.7×104CFUsg−1). Thus, manure increased all microbes and invA gene numbers when applied to soils, while the digestate supplied only hlyA-negative Listeria. Potential pathogens were significantly more abundant in γ- than in non-irradiated treatments indicating suppression by indigenous soil microbiota. Control levels of all potential pathogens were recovered after 3 months, which could be thus considered a safe delay between land spreading amendments and harvesting. Concentration of nitrates in soil and their movement through the upper layer in soils amended with digestate were doubled compared to the other treatments. Hence, care should be taken that in the field nitrate liberation does not exceed plant demand.
Anaerobic digestion (AD) for biogas production leads to several changes in the composition of the resulting digestates compared to the original feedstock (ammonia content, pH, carbon to nitrogen ratio, etc.), which are relevant for the plant availability of macro- and micronutrients after field application. Increased NH 4 +-N content in digested slurries compared to undigested slurries does not guarantee improved uptake efficiency of slurry nitrogen and increased savings in fertilizer nitrogen. AD of crop residues and cover crops leads to an increase in the total amounts of mobile organic manures within the farming system, resulting in a higher nitrogen use efficiency and an increased scope for target-oriented nitrogen application in time and space, when needed by the crop, as an alternative to the site-bound soil incorporation as green manures. AD of dairy manure appears to reduce the fraction of immediate plant available phosphorus and micronutrients. This does, however, not affect short-term crop availability under field conditions. More studies are needed to improve current knowledge on sulfur losses during AD and fertilizer value of digestates. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
High activity levels and balanced anaerobic microbial communities are necessary to attain proper anaerobic digestion performance. Therefore, this work was focused on the kinetic performance and the microbial community structure of six full-scale anaerobic digesters and one lab-scale co-digester. Hydrolytic (0.6-3.5gCODg(-1)VSSd(-1)) and methanogenic (0.01-0.84gCODg(-1)VSSd(-1)) activities depended on the type of biomass, whereas no significant differences were observed among the acidogenic activities (1.5-2.2gCODg(-1)VSSd(-1)). In most cases, the higher the hydrolytic and the methanogenic activity, the higher the Bacteroidetes and Archaea percentages, respectively, in the biomasses. Hydrogenotrophic methanogenic activity was always higher than acetoclastic methanogenic activity, and the highest values were achieved in those biomasses with lower percentages of Methanosaeta. In sum, the combination of molecular tools with activity tests seems to be essential for a better characterization of anaerobic biomasses.
Agro-residues account for a large proportion of the wastes generated around the world. There is thus a need for a model to simulate the anaerobic digestion processes used in their treatment. We have developed model based on ADM1, to be applied to agro-wastes. We examined and tested the biodegradability of apple, pear, orange, rape, sunflower, pig manure and glycerol wastes to be used as the basis for feeding the model. Moreover, the fractions of particulate COD (Xc) were calculated, and the disintegration constant was obtained from biodegradability profiles, considering disintegration to be the limiting process. The other kinetic and stoichiometric parameters were taken from the ADM1 model.The model operating under mono-substrate and co-substrate conditions was then validated with batch tests. At the same time the model was validated on a continuous anaerobic reactor operating with pig manure at lab scale. In both cases the correlation between the model and the experimental results was satisfactory. We conclude that the anaerobic digestion model is a reliable tool for the design and operation of plants in which agro-wastes are treated.
Struvite precipitation causes important operational problems during the sludge treatment process, especially when EBPR sludge is treated. Predicting struvite formation is critical to be able to design process alternative that best minimises struvite precipitation. With this aim, phosphorus precipitation in an anaerobic digestion pilot plant was studied using experimental data and mass balance analysis. The results obtained showed significant phosphorus precipitation as struvite (58% of the fixed phosphorus) and a low precipitation of calcium phosphates (15%), forming mainly hydroxyapatite (HAP). The rest of the phosphorus fixed in the digester (27%) was attributed to adsorption processes on solid surfaces. The effect of pH and available phosphorus concentration on phosphorus fixation in the digester was also studied, indicating that a decrease of available PO4-P concentration in the digester can minimise phosphorus precipitation, reducing the maintenance problems associated with struvite deposits.
It is generally accepted that the low quality of soil carbon limits the amount of energy available for soil microorganisms, and in turn the rate of soil carbon mineralization. The priming effect, i.e. the increase in soil organic matter (SOM) decomposition rate after fresh organic matter input to soil, is often supposed to result from a global increase in microbial activity due to the higher availability of energy released from the decomposition of fresh organic matter. Work to date, however, suggests that supply of available energy induces no effect on SOM mineralization. The mechanisms of the priming effect are much more complex than commonly believed. The objective of this review was to build a conceptual model of the priming effect based on the contradictory results available in the literature adopting the concept of nutritional competition. After fresh organic matter input to soils, many specialized microorganisms grow quickly and only decompose the fresh organic matter. We postulated that the priming effect results from the competition for energy and nutrient acquisition between the microorganisms specialized in the decomposition of fresh organic matter and those feeding on polymerised SOM.
The trend towards specialization in conventional farming led to large agricultural areas in Germany and in Europe lacking livestock. Also stockless organic farming has increased during recent years. In organic farming clover/grass-ley (CG) provides nitrogen (N) to the whole cropping system via symbiotic N2 fixation and also controls certain weeds. A common practice in organic farming, when ruminants are not present, is to leave the biomass from CG in the field for their residual fertility effect. CG biomass, crop residues (CR) and cover crops (CC) represent a large unexploited energy potential. It could be used by anaerobic digestion to produce biogas. A field experiment was carried out by implementing a whole cropping system with a typical crop rotation for such farming systems on the research station Gladbacherhof from 2002 to 2005. The crop rotation consisted of six crops (two legumes and four non-legume crops). The aim was to evaluate whether the use of N could be improved by processing biomass from CG, CR and CC in a biogas digester and using the effluents as a fertilizer, compared to common practice. In the control treatment, represented by the usual stockless system, the CG, CR and CC biomass were left on the ground for green manure purposes. In the biogas systems these substrates were harvested for digestion in a biogas plant. The effluents of digestion were used to manure the non-legumes in the same crop rotation. Results indicate that digestion of CG, CR and CC can increase the crop dry matter and N yields and the N content of wheat grains in organic stockless systems. Harvesting and digestion of residues and their reallocation after digestion resulted in a better and more even allocation of N within the whole crop rotation, in a higher N input via N2 fixation and lower N losses due to emissions and probably in a higher N availability of digested manures in comparison to the same amounts of undigested biomass.
Recovering struvite from dairy manure has consistently posed problems for researchers. This study separated solids from anaerobically digested dairy manure using a filtration system. Filtrate was rich in free magnesium (160 to 423 mg/L), ammonium (320 to 1800 mg N/L) and orthophosphate (93 to 332 mg P/L). High concentrations of free calcium (128 to 361 mg/L) and alkalinity (3309 to 6567 mg/L as CaCO3), however, may hinder struvite precipitation. Batch precipitation tests were conducted to identify and overcome factors that interfere with struvite formation. Precipitation tests at pH 9 identified calcium and ionic strength as most probable interferences. Calcium addition did not significantly change phosphorus removal efficiency, but decreased struvite purity because of formation of calcium phosphates when Ca:P activity ratio was greater than 0.5 to 1. Batch tests demonstrated effective calcium removal from anaerobically digested dairy manure through precipitation of calcium carbonate at pH 9 to 10 while retaining magnesium and orthophosphate, lessening hindrance to struvite formation.
The performance of the only dairy manure biogas plant in Cantabria (Northern coast of Spain) was evaluated in terms of liquid-solid separation and anaerobic digestion of the liquid fraction. Screened liquid fraction was satisfactorily treated in a CSTR digester at HRTs from 20 to 10 days with organic loading rates ranging from 2.0 to 4.5 kg VS/(m(3)d). Stable biogas productions from 0.66 to 1.47 m(3)/(m(3)d) were achieved. Four anaerobic effluents collected from the digester at different HRTs were analyzed to measure their residual methane potentials, which ranged from 12.7 to 102.4 L/gVS. These methane potentials were highly influenced by the feed quality and HRT of the previous CSTR anaerobic digestion process. Biomethanization of the screened liquid fraction of dairy manure from intensive farming has the potential to provide up to 2% of total electrical power in the region of Cantabria.
Agrarian biomass as a renewable energy source can contribute to a considerable CO(2) reduction. The overriding goal of the European Union is to cut energy consumption related greenhouse gas emission in the EU by 20% until the year 2020. This publication aims at optimising the methane production from steam-exploded wheat straw and presents a theoretical estimation of the ethanol and methane potential of straw. For this purpose, wheat straw was pretreated by steam explosion using different time/temperature combinations. Specific methane yields were analyzed according to VDI 4630. Pretreatment of wheat straw by steam explosion significantly increased the methane yield from anaerobic digestion by up to 20% or a maximum of 331 l(N)kg(-1) VS compared to untreated wheat straw. Furthermore, the residual anaerobic digestion potential of methane after ethanol fermentation was determined by enzymatic hydrolysis of pretreated wheat straw using cellulase. Based on the resulting glucose concentration the ethanol yield and the residual sugar available for methane production were calculated. The theoretical maximum ethanol yield of wheat straw was estimated to be 0.249 kg kg(-1) dry matter. The achievable maximum ethanol yield per kg wheat straw dry matter pretreated by steam explosion and enzymatic hydrolysis was estimated to be 0.200 kg under pretreatment conditions of 200 degrees C and 10 min corresponding to 80% of the theoretical maximum. The residual methane yield from straw stillage was estimated to be 183 l(N)kg(-1) wheat straw dry matter. Based on the presented experimental data, a concept is proposed that processes wheat straw for ethanol and methane production. The concept of an energy supply system that provides more than two forms of energy is met by (1) upgrading obtained ethanol to fuel-grade quality and providing methane to CHP plants for the production of (2) electric energy and (3) utility steam that in turn can be used to operate distillation columns in the ethanol production process.
The effect of anaerobic digestion on phosphorus (P) forms and water P extractability was investigated using dairy manure samples from six full-scale on-farm anaerobic digesters in Wisconsin, USA. On an average, total dissolved P (TDP) constituted 12 +/- 4% of total P (TP) in the influent to the anaerobic digesters. Only 7 +/- 2% of the effluent was in a dissolved form. Dissolved unreactive P (DUP), comprising polyphosphates and organic P, dominated the dissolved P component in both the influent and effluent. In most cases, it appeared that the fraction of DUP mineralized during anaerobic digestion became subsequently associated with particulate-bound solids. Geochemical equilibrium modeling with Mineql+ indicated that dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, octacalcium phosphate, newberyite, and struvite were the probable solid phases in both the digester influent and effluent samples. The water-extractable P (WEP) fraction in undigested manure ranged from 45% to 70% of TP, which reduced substantially after anaerobic digestion to 25% to 45% of TP. Anaerobic digestion of dairy manure appears capable of reducing the fraction of P that is immediately available by increasing the stability of the solid phases controlling P solubility.
Seven low-cost digesters in Costa Rica were studied to determine the potential of these systems to treat animal wastewater and produce renewable energy. The effluent water has a significantly lower oxygen demand (COD decreased from 2,968 mg/L to 472 mg/L) and higher dissolved nutrient concentration (NH(4)-N increased by 78.3% to 82.2mg/L) than the influent water, which increases the usefulness of the effluent as an organic fertilizer and decreases its organic loading on surface waters. On average, methane constituted 66% of the produced biogas, which is consistent with industrial digesters. Through principle component analysis, COD, turbidity, NH(4)-N, TKN, and pH were determined to be the most useful parameters to characterize wastewater. The results suggest that the systems have the ability to withstand fluctuations in the influent water quality. This study revealed that small-scale agricultural digesters can produce methane at concentrations useful for cooking, while improving the quality of the livestock wastewater.
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