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Nanoparticle-assisted biohydrogen production from pretreated food industry wastewater sludge: Microbial community shifts in batch and continuous processes
Abstract
Biohydrogen production from industrial waste has gained a significant attention as a sustainable energy source. In this study, the enrichment of biohydrogen production from pretreated dissolved air flotation (DAF) sludge, generated from food industry wastewater treatment plants, was investigated using SiO 2 @Cu-Ag dendrites core shell nanostructure (NS). The effect of NS on the changes of the microbial community and biohydrogen yield was evaluated through batch and continuous tests. In batch mode, various nanomaterial doses were investigated with several concentrations ranging from 20 to 50 mg/L for hydrogen production using glucose as a substrate. The optimum core-shell NS amount was 40 mg/L, achieving a maximum H 2 yield of 163 mL/g volatile solids (VS) compared to the control's 79 mL/g VS. However, 50 mg/L NS inhibited most bacteria in the sludge. The continuous experiment used a continuous stirring tank reactor (CSTR) with 40 mg/L SiO 2 @Cu-Ag core-shell NS and pretreated industrial sludge as substrate. The H 2 yield increased to 115 L/kg VS compared to the control reactor's 89 L/kg VS. The gas analysis showed compositional proportions of 83 % H 2 , 7 % CO 2 , and 4.5 % methane, while the microbial community analysis indicated the development of hydrogen-producing species such as Clostridium. In conclusion, SiO 2 @Cu-Ag core-shell NS addition enhanced anaerobic degradation of organic matter and its conversion to biohydrogen. The selected nanomaterial can be used for an effective continuous treatment system for industrial sludge while promoting dark fermentation.
... In this regard, anaerobic digestion appears as a robust and widely acknowledged approach for treating organic-rich wastewater [7,8]. This biological process involves the microbial breakdown of organic materials in an oxygen free environment, ultimately yielding biogas that comprising methane (CH 4 ) and carbon dioxide (CO 2 ) [9,10]. Several types of anaerobic reactors such as up-flow anaerobic sludge blanket (UASB) [11], sequencing batch reactor (SBR) [12], and expanded granular sludge bed (EGSB) reactors [13] have been extensively investigated for the treatment of slaughterhouse wastewater. ...
This research investigates the efficacy of a high-performance pilot-scale Internal Circulation Anaerobic Reactor inoculated with Granular Sludge (ICAGSR) for treating cattle slaughterhouse wastewater while concurrently generating biogas. The primary objective is to assess the efficiency and performance of ICAGSR in terms of organic pollutant removal and biogas production using granular anaerobic sludge. The research methodology entails operating the ICAGSR system under ambient conditions and systematically varying key parameters, including different Hydraulic Retention Times (HRTs) (24, 12, and 8 h) and Organic Loading Rates (OLRs) (3.3, 6.14, and 12.83 kg COD/m³. d). The study focuses on evaluating pollutants’ removal and biogas production rates. Results reveal that the ICAGSR system achieves exceptional removal efficiency for organic pollutants, with Chemical Oxygen Demand (COD) removal exceeding 74%, 67%, and 68% at HRTs of 24, 12, and 8 h, respectively. Furthermore, the system demonstrates stable and sustainable biogas production, maintaining average methane contents of 80%, 76%, and 72% throughout the experimental period. The successful operation of the ICAGSR system underscores its potential as a viable technology for treating cattle slaughterhouse wastewater and generating renewable biogas. In conclusion, this study contributes to wastewater treatment and renewable energy production by providing a comprehensive analysis of the ICAGSR system’s hydrodynamic properties. The research enhances our understanding of the system’s performance optimization under varying conditions, emphasizing the benefits of utilizing ICAGSR reactors with granular sludge as an effective and sustainable approach. Identifying current gaps, future research directions aim to further refine and broaden the application of ICAGSR technology in wastewater treatment and renewable energy initiatives.
... After cooling down to room temperature, PNSB, and PNSB growth media were mixed in 1:1 (v/v) and placed inside the incubator with an incandescent lamp of intensity 3000 Lux whereas temperature was maintained at 25-30 • C for 2-3 days until it reached initial cell concentration of 0.875 g/L [18]. In all three PFHP cycles, this cultivated PNSB was used with the same initial cell concentration of 0.875 g/L [11,33]. ...
The present study aims to investigate the potential of recycled corn stover (CS) residues from photo fermentative biohydrogen production (PFHP) reactors for further cycles to evaluate its PFHP potential. Results showed hydrogen generation yields of 70.32, 63.95, and 16.73 mL/g in the 1st, 2nd, and 3rd cycles respectively which confirms that PFHP in cyclic systems produces approximately twice as much hydrogen as in a single cycle. Total intermediate by-products of 2.59 g/L (19 % and 197 % higher) at 24 h indicate that hydrogen production follows the acetic acid and butyric acid pathway in the first cycle. Thermogravimetric analysis (TGA) showed that solid residues of 1st FR, 2nd FR, 3rd FR, and CS were 12.03 %, 13.02 %, 27.93 %, and 34.55 % respectively. The energy, and light conversion efficiency (ECE, LCE) of cyclic PFHP was 1.16, and 1.15-fold higher than the first cycle, consequently, the present research offers a novel way to maximize CS's potential for PFHP with minimal waste. The experimental findings of the present study revealed that recovered residues from the fermentative bioreactors can be further utilized to enhance the overall biohydrogen production yield which not only minimizes the waste generation but also helps to reduce the cost of pre-treatment in subsequent cycles of biohydrogen production.
The negative effects of the accelerating climate change due partly to fossil fuel consumption is calling for the rapid development of sustainable energies such as biohydrogen, which is produced using microorganisms. Here we review biohydrogen production from biomass, with focus on biomass pretreatment, fermentative production, factors affecting production, bioreactors, kinetics and modeling, and improved production with nanoparticles. Pretreatments include chemical, physical and biological methods. Hydrogen production is done by photo-fermentation or dark fermentation. Influencing factors comprise pH, temperature, hydraulic retention time, and the presence of fermentation inhibitors. Continuous stirred tank-, anaerobic fluidized bed-, anaerobic sequencing batch-, up-flow anaerobic sludge blanket- and dynamic membrane reactors are used. Additives include cobalt, nickel and iron nanoparticles. Compared to thermochemical, photochemical and electrochemical processes, biohydrogen production needs more time but is easy to operate, cost-effective and environmentally friendly.
Microorganisms in anaerobic digestion (AD) are easily affected by ammonia, especially acetoclastic methanogens. Thus, in ammonia-suppressed AD systems, acetate degradation is reported to be carried out mainly by the cooperation of syntrophic acetate oxidizers and hydrogenotrophic methanogens. Previous studies have revealed ammonia inhibition on microbial flora by AD performance, but the effect mechanism of ammonia on microbial metabolism remains poorly understood. In this study, we constructed a mesophilic chemostat fed with acetate as the sole carbon source, gradually increased the total ammonia nitrogen (TAN) concentration from 1 g L−1 to 6 g L−1, and employed the 16S rRNA gene, metagenomics, and metatranscriptomics analysis to characterize the microbial community structure and metabolic behavior. The results showed that even at the TAN of 6 g L−1 (pH 7.5), the methanogenesis kept normal, the biogas production was approximately 92% of that at TAN of 1 g L−1 and the acetate degradation ratio reached 99%, suggesting the strong TAN tolerance of the microbial community enriched. 16S rRNA gene analysis suggested that the microbial community structure changed along with the TAN concentration. Methanothrix predominated in methanogens all the time, in which the dominant species was gradually replaced from M. soehngenii to M. harundinacea with the increased TAN. Dominant bacterial species also changed and Proteiniphilum showed a significant positive correlation with increased TAN. Meta-omics analysis showed that the absolute dominant microorganisms at TAN of 6 g L−1 were M. harundinacea and Proteiniphilum, both of which highly expressed genes for anti-oxidative stress. M. harundinacea and the second dominant methanogen Methanosarcina highly expressed both acetate cleavage and CO2 reduction pathways, suggesting the possibility that these two pathways contributed to methanogenesis together. Proteiniphilum and some other species in Firmicutes and Synergistetes were likely acetate oxidizers in the community as they highly expressed genes for syntrophic acetate oxidization, H2 generation, and electron transfer. These results suggested that Proteiniphilum as well as M. harundinacea have strong ammonia tolerance and played critical roles in acetate degradation under ammonia-suppressed conditions. The achievements of the study would contribute to the regulation and management of the AD process.
Anaerobic digestion (AD) is a microbially-driven process enabling energy production. Microorganisms are the core of anaerobic digesters and play an important role in the succession of hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes. The diversity of participating microbial communities can provide new information on digester performance for biomass valorization and biofuel production. In this study anaerobic systems were used, operating under mesophilic conditions that realized biodegradation processes of waste wheat straw pretreated with NaOH—a renewable source for hydrogen and methane production. These processes could be managed and optimized for hydrogen and methane separately but combining them in a two-stage system can lead to higher yields and a positive energy balance. The aim of the study was to depict a process of biohydrogen production from lignocellulosic waste followed by a second one leading to the production of biomethane. Archaeal and bacterial consortia in a two-stage system operating with wheat straw were identified for the first time and the role of the most important representatives was elucidated. The mixed cultures were identified by the molecular-biological methods of metagenomics. The results showed that biohydrogen generation is most probably due to the presence of Proteiniphilum saccharofermentans, which was 28.2% to 45.4% of the microbial community in the first and the second bioreactor, respectively. Archaeal representatives belonging to Methanobacterium formicicum (0.71% of the community), Methanosarcina spelaei (0.03%), Methanothrix soehngenii (0.012%), and Methanobacterium beijingense (0.01%) were proven in the methane-generating reactor. The correlation between substrate degradation and biogas accumulation was calculated, together with the profile of fatty acids as intermediates produced during the processes. The hydrogen concentration in the biogas reached 14.43%, and the Methane concentration was 69%. Calculations of the energy yield during the two-stage process showed 1195.89 kWh·t−1 compared to a 361.62 kWh·t−1 cumulative yield of energy carrier for a one-stage process.
In the context of hydrogen production from biomass or organic waste with dark fermentation, this study analysed 55 studies (339 experiments) in the literature looking for the effect of operating parameters on the process performance of dark fermentation. The effect of substrate concentration, pH, temperature, and residence time on hydrogen yield, productivity, and content in the biogas was analysed. In addition, a linear regression model was developed to also account for the effect of nature and pretreatment of the substrate, inhibition of methanogenesis, and continuous or batch operating mode. The analysis showed that the hydrogen yield was mainly affected by pH and residence time, with the highest yields obtained for low pH and short residence time. High hydrogen productivity was favoured by high feed concentration, short residence time, and low pH. More modest was the effect on the hydrogen content. The mean values of hydrogen yield, productivity, and content were, respectively, 6.49% COD COD−1, 135 mg L−1 d−1, 51% v/v, while 10% of the considered experiments obtained yield, productivity, and content of or higher than 15.55% COD COD−1, 305.16 mg L−1 d−1, 64% v/v. Overall, this study provides insight into how to select the optimum operating conditions to obtain the desired hydrogen production.
Hydrogen is a clean, renewable secondary energy source. The development of hydrogen energy is a common goal pursued by many countries to combat the current global warming trend. This paper provides an overview of various technologies for hydrogen production from renewable and non-renewable resources, including fossil fuel or biomass-based hydrogen production, microbial hydrogen production, electrolysis and thermolysis of water and thermochemical cycles. The current status of development, recent advances and challenges of different hydrogen production technologies are also reviewed. Finally, we compared different hydrogen production methods in terms of cost and life cycle environmental impact assessment. The current mainstream approach is to obtain hydrogen from natural gas and coal, although their environmental impact is significant. Electrolysis and thermochemical cycle methods coupled with new energy sources show considerable potential for development in terms of economics and environmental friendliness.
Low-level alkalinity (pH 9–10) coupled with ultrasonic or mechanical cutting with different energy input for obtaining carbon sources were tested for sludge pretreatment process before anaerobic sludge digestion. The differences between the primary sludge (PS) and waste activated sludge (WAS)-derived dissolved organic matter (DOM) species were evaluated for their bioavailability and affinity (in the form of amino acids) to the bio-nutrient removal (BNR) biomass. Soluble microbial by-product-like substances as the predominant DOM components in the raw PS and WAS increased by 23 and 22%, respectively, after low-level alkaline treatment (pH 9–10) and ultrasonication. In addition, the protein components were degraded further as free amino acids (FAAs). The sludge-derived aspartate, glutamate, followed by arginine were the most commonly used FAAs by the BNR biomass. The pattern of recovering this special sludge-derived carbon source to enhance P removal and recovery in the BNR process is depicted. HIGHLIGHTS
Ultrasonic treatment of sludge has the advantage of efficiently producing non-fermentative carbon sources rich in amino acids.;
Soluble microbial by-product-like substances were the main DOM components released by ultrasonication treatment of sludge.;
The BNR communities showed high affinity to the ionized amino acids contained in the sonication-induced sludge carbon source.;
Microbes, including bacteria and fungi, easily form stable biofilms on many surfaces. Such biofilms have high resistance to antibiotics, and cause nosocomial and postoperative infections. The antimicrobial and antiviral behaviors of Ag and Cu nanoparticles (NPs) are well known, and possible mechanisms for their actions, such as released ions, reactive oxygen species (ROS), contact killing, the immunostimulatory effect, and others have been proposed. Ag and Cu NPs, and their derivative NPs, have different antimicrobial capacities and cytotoxicities. Factors, such as size, shape and surface treatment, influence their antimicrobial activities. The biomedical application of antimicrobial Ag and Cu NPs involves coating onto substrates, including textiles, polymers, ceramics, and metals. Because Ag and Cu are immiscible, synthetic AgCu nanoalloys have different microstructures, which impact their antimicrobial effects. When mixed, the combination of Ag and Cu NPs act synergistically, offering substantially enhanced antimicrobial behavior. However, when alloyed in Ag–Cu NPs, the antimicrobial behavior is even more enhanced. The reason for this enhancement is unclear. Here, we discuss these results and the possible behavior mechanisms that underlie them.
This article presents the results of the start-up of continuous production of biohydrogen from cheese whey (CW) in an anaerobic filter (AF) and anaerobic fluidized bed (AFB) with a polyurethane carrier. Heat and acid pretreatments were used for the inactivation of hydrogen-scavengers in the inoculum (mesophilic and thermophilic anaerobic sludge). Acid pretreatment was effective for thermophilic anaerobic sludge to suppress methanogenic activity, and heat treatment was effective for mesophilic anaerobic sludge. Maximum specific yields of hydrogen, namely 178 mL/g chemical oxygen demand (COD) and 149 mL/g COD for AFB and AF, respectively, were obtained at the hydraulic retention time (HRT) of 4.5 days and organic load rate (OLR) of 6.61 kg COD/(m3 day). At the same time, the maximum hydrogen production rates of 1.28 and 1.9 NL/(L day) for AF and AFB, respectively, were obtained at the HRT of 2.02 days and OLR of 14.88 kg COD/(m3 day). At the phylum level, the dominant taxa were Firmicutes (65% in AF and 60% in AFB), and at the genus level, Lactobacillus (40% in AF and 43% in AFB) and Bifidobacterium (24% in AF and 30% in AFB).
Herein, we report a novel supplement called TiO 2 @Ag core-shell nanostructure that revealed a high removal of hydrogen sulfide gas with boosting the bio-methane production from the anaerobic digestion process of sewage sludge. TiO 2 @Ag core-shell nanostructure was synthesized by the deposition of Ag shell NPs on TiO 2 core NPs using a reduction method. The prepared samples of the core-shell and its components were characterized using different techniques such as XRD, SEM, TEM and AFM. A concentration of TiO 2 @Ag core-shell NS (50 mg/L) was supplemented with anaerobic bioreactors to study their effect on the removal of hydrogen sulfide from the anaerobic digestion of sewage sludge compared to silver and titanium dioxide nanoparticles alone. The results showed a 3-fold increase in the produced bio-methane upon the use of TiO 2 @Ag core-shell NS with a high removal of hydrogen sulfide (91.9 %) compared to using only silver nanoparticles or titanium dioxide nano-particles. Concisely, the prepared TiO 2 @Ag core-shell NS was multifunctional and more active than its components in removing hydrogen sulfide, enhancing bio-methane production, and detoxifying hazardous materials from sewage sludge.
Improper disposal of lignocellulosic wastes may produce a large quantity of greenhouse gases and pollute the environment. Through anaerobic digestion processes, lignocellulosic wastes can be recycled to produce clean and renewable biogas. However, the lignin in lignocellulose limits its potential as such a biomass resource, and the efficacy of biogas production is not satisfactory although recent research efforts have attempted to address this issue. In this review, the physicochemical characteristics of three lignocellulosic wastes, including municipal solid waste, forestry waste, and crop straw, are summarized. Then, the mechanism and influencing factors of biogas production from these wastes through anaerobic digestion are presented. Biological pretreatment techniques have been confirmed to increase lignocellulose hydrolysis and then enhance biogas production, among them, co-culture systems, metabolic engineering and anaerobic co-digestion are worthy of focus in future research. Furthermore, natural lignocellulose degrading systems, like xylophagous insects and ruminants, also have potential for improving the anaerobic digestion system. This review also considers the future perspective of anaerobic digestion of lignocellulosic wastes, including kinetics and model studies to optimize anaerobic digestion process, and policy to facilitate biogas production from lignocellulosic wastes. This article aims to comprehensively review challenges with anaerobic digestion of lignocellulosic wastes and summarize available pretreatment methods focusing mainly on biological techniques to find efficient and low-cost strategies for improving the anaerobic digestion process and biogas production.
Antibiotics have become emerging pollutants occurring in wastewater, influencing the activity of microorganisms responsible for wastewater treatment. Moreover, the potential application of the anammox process in the treatment of antibiotic-containing wastewater has paid much attention. A common antibiotic, OTC (oxytetracycline), CIP (ciprofloxacin), and CLA (clarithromycin) are recognized to be monitored in wastewater due to their relatively high concentration and hazardous impact on the environment. However, their effect on the anammox process remains unknown. Therefore, this paper presents the study concerning the long-term effects of a successive concentration of three antibiotics (OTC, CIP, CLA) on the anammox process, with special emphasis on treatment efficiency, resistance mechanism, bacteria cell morphology, and activated sludge community structure. It is worth noting that the influence of a successive concentration of CIP and CLA has been studied for the first time. Results revealed that anammox community could adapt to CIP, OTC, and CLA at low concentrations (< 1 mg L⁻¹), while the high concentration of antibiotics (100 mg L⁻¹) reduced the nitrogen removal rate (NRR) by 27% (OTC), 30% (CIP), and 56% (CLA). Community structure analysis showed that the abundance of Planctomycetes increased with the increase of CIP and CLA concentration while decreasing under OTC stress. On contrary, other nitrogen-cycle bacteria (e.g., Nitrospira) contributed to the nitrogen removal, especially during antibiotic suppression. The abundance of corresponding ARGs (OTC resistance gens: tetX, tetC, tetW, CIP resistance gens: qnrB4, qnrS, CLA resistance gens: mphA) generally increased under antibiotic suppression. In addition, co-occurrence analysis showed that anammox bacteria might participate in the transfer of macrolide resistance genes. The findings of this study are essential in understanding the mechanisms of three antibiotics commonly occurring in wastewater during the anammox process. Moreover, the results have implications for using the anammox process for antibiotic-containing wastewater treatment and provide the operational guidance for stable conducting of the anammox process under antibiotics suppression.
Increasing accumulation of food waste (FW) exerts pressure on resource conservation and environmental protection, while conventional anaerobic digestion (AD) of raw FW for bioenergy recovery and waste minimization often encounters limitations such as fast acidification and process failure. Herein, mild hydrothermal pretreatment (HTP: 140 °C, 20 min) of raw FW was employed to advance subsequent AD performances in a long-term continuous mode. With a decreased overall hydraulic retention time (HRT) from 30 to 18 days, the two-stage system digesting HTP-treated FW maintained very stable and robust biohydrogen (38.1 mL/gVS) and biomethane (439.6 mL/gVS) co-production, whereas both the two-stage system digesting raw FW and the one-stage system digesting HTP-treated FW exhibited deteriorating trends with significantly lower energy yields by 61.1% and 28.1%, respectively. Microbial community analyses revealed the less involvement of carbohydrate-fermenting and proteolytic microbes in the second-stage biomethane reactors as a result of the enhanced hydrolysis and acidogenesis of FW through HTP and first-stage biohydrogen fermentation. A proximate energy balance assessment indicated that the energy gain of increased biogas generation offset the extra heat requirement for the HTP of FW, while a significant treatment capacity enhancement of 66.7% was achieved given the HRT reduction from 30 to 18 days through this integrated system.
In this study, the immobilization of anaerobic sludge in sodium alginate (SA) with polyaniline (PANI) nano-particles (NPs) was performed for producing biohydrogen from dairy wastewater (DWW). The effect of PANI on immobilization in SA was investigated at different PANI concentrations (5, 10, 20, 40, and 80 mg L − 1). DWW, PANI NPs, and immobilized beads were characterized through physicochemical analysis, surface area, X-ray diffractometry, and scanning electron microscopy (SEM). The results revealed that the immobilization of anaerobic sludge in SA with PANI NPs enhanced the degradation of organic matter in DWW into volatile fatty acids and biohydrogen yield. There is a direct relationship between PANI NPs concentration in SA, degradation in DWW, and bio-hydrogen production. The degradation of organic matter in terms of chemical oxygen demand reached 75.5% at the optimum dose of PANI NPs (40 mg L − 1), which confirmed the high reactivity of PANI NPs with SA compared with the control sample. In addition, at 40 mg L − 1 PANI NPs concentration, the maximum hydrogen yield were 54.5 mL g − 1 VS from anaerobic fermentation was obtained with a 285% increase compared with the fermentation without using any PANI. The SEM image of beads before and after treatment indicated that the addition of PANI NPs up to 40 mg L − 1 enhanced the production of bio-hydrogen yield through SA in a regular pattern, whereas increasing the concentration to 80 mg L − 1 resulted in shrinking of SA surface and consequently decreased the biohydrogen yield.
Energy demand currently is mostly satisfied by the use of fossil fuels that present not only problems for the environment, but also are not renewable. Dark fermentation (DF) is a biological process that can provide an alternative to meet energy needs. The use of industrial effluents from carbon-rich waters in the production of hydrogen and volatile fatty acids (VFAs) through the DF is a promising strategy. However, determining the optimal operating conditions to increase the production of the sub-products has been not being thoroughly studied. This study aims at determining the optimal condition of hydraulic retention time (HRT) and pH to improve hydrogen production in an internal recirculation (IC) reactor treating beverage wastewater using Response Surface Methodology and interaction between factors. The study also assessed VFAs concentrations when operating at optimal conditions. The results showed that the combination of an 8.0 h HRT and 5.5 produced 30% of hydrogen and the interaction between factors established that the pH was the main factor influencing the results. Also, it was observed that the concentration of lactic acid did not inhibit the production of H2 for the optimal value of pH. However, it is evident that more studies using HRT of less than 8 h and of VFAs distribution are needed. Future optimization technique considerations are necessary to reduce uncertainties for biological hydrogen production purposes.
Corn starch processing wastewater (CSPW) is a high-strength organic wastewater and biological treatment is considered as the dominant process. The present work investigated the effects of pH on the bioenergy production and spatial succession of microbial community in an anaerobic baffled reactor (ABR) treating CSPW. The results showed that above 90.5% of COD removal and above 16.6 L d⁻¹ of methane were achieved at the influent pHs of 8.0 and 7.0 under organic loading rate of 4.0 kg COD·m⁻³·L⁻¹ condition. Further decreasing the influent pH to 6.0 resulted in the COD removal decreased to 89.7%. Besides, 9.2 L d⁻¹ of hydrogen and 13.0 L d⁻¹ of methane were obtained. There was significant difference in the volatile fatty acids profiles during the variation of pH. Illumina Miseq sequencing showed that Clostridium, Ethanoligenens, Megasphaera, Prevotella and Trichococcus with relative abundance of 2.1%∼28.1% were the dominant hydrogen-producing bacteria in C1. Methanogens (Methanothrix and Methanobacterium) dominated in the last three compartments. Function predicted analysis revealed that the abundance of metabolic-related gene families containing carbohydrate, amino acids and energy in the last three compartments were higher than that in C1. A deduced biodegradation model of CSPW in ABR revealed that the anaerobic sludge in C1 mainly produced hydrogen. Microbial population in C3 was responsible for COD removal and methane production. The redundancy analysis revealed that hydrogen production was highly correlated with some hydrogen-producing bacteria in C1, whereas methane production was positively correlated with microbial group in C2∼ C4.
Herein, we report a novel supplement called Cu@Fe3O4 core shell nanostructure (NS) that revealed a tremendous increment in the biogas production from anaerobic digestion of sewage sludge. Cu@Fe3O4 core-shell NS is synthesized using feasible co-precipitation method and characterized using different techniques before and after anaerobic digestion of sewage sludge. Five different concentrations (5, 10, 20, 40, and 80 mg/L) of Cu@Fe3O4 core-shell NS was supplemented to separate bioreactors to study their effect on biogas production from anaerobic digestion of sewage sludge compared to Fe3O4 nanoparticles alone. Microbial community assessed by next generation sequencing techniques has been used. The results showed a 3-fold increase in the biogas upon the use of moderate concentration (i.e., 20 43 mg/L) Cu@Fe3O4 core-shell NS compared to using 40 mg/L of Fe3O4 nanoparticles alone. There was a change in the microbial population after adding Cu@Fe3O4 core-shell NS. The increase in the order of Clostridiales stands out, parallel to the decrease in Bacteroidetes. Regarding archaea, hydrogenotrophic pathway was the predominant, with partial replacement of Methanobrevibacter by Methanobacterium, while acetoclastic methanogen, especially Methanosaeta increased. Concisely, the deploying of the prepared Cu@Fe3O4 core-shell NS not only resulted in enhancing the biogas production but also detoxified sewage sludge from hazardous materials.
Two various materials, copper and aluminum doped cobalt ferrite nanoparticles (NPs) were fabricated for investigating their effects of addition amounts on hydrogen (H2) synthesis and process stability. CoCu0.2Fe1.8O4NPs enhanced H2 production more than CoAl0.2Fe1.8O4 NPs under same condition. The highest H2 yield of 212.25 mL/g glucose was found at optimal dosage of 300 mg/L CoCu0.2Fe1.8O4 NPs, revealing the increases of 43.17% and 6.67% compared with the control without NPs and 300 mg/L CoAl0.2Fe1.8O4 NPs groups, respectively. NPs level of more than 400 mg/L inhibited H2 generation. Further investigations illustrated that CoCu0.2Fe1.8O4 NPs were mainly distributed on extracellular polymer substance while CoAl0.2Fe1.8O4 NPs were mostly enriched on cell membrane, which facilitated electron transfer behavior. Community structure composition demonstrated that CoCu0.2Fe1.8O4 and CoAl0.2Fe1.8O4 separately caused a 9.67% and 9.03% increase in Clostridium sensu stricto 1 compared with the control reactor without NPs exposure.
Microbial fermentation of organic matter under anaerobic conditions is currently the prominent pathway for biohydrogen production. Organic matter present in waste residues is regarded as an economic feedstock for biohydrogen production by dark and photo fermentative bacteria. Agricultural residues, fruit wastes, vegetable wastes, industrial wastewaters, and other livestock residues are some of the organic wastes most commonly used for biohydrogen production due to their higher organic content and biodegradability. Appropriate pretreatments are required to enhance the performance of biohydrogen from complex organic wastes. Biohydrogen production could also be enhanced by optimizing operation conditions and the addition of essential nutrients and nanoparticles. This review describes the pathways of biohydrogen production, discusses the effect of organic waste sources used and microbes involved on biohydrogen production, along with addressing the key parameters, advantages, and difficulties in each biohydrogen production pathway.
Dark fermentation is considered as a promising method for sustainable hydrogen generation. Microorganisms play a pivotal role in hydrogen production efficiency. Strains from genus Clostridium have been the most widely detected and used microorganisms in dark fermentative hydrogen production. In this review, the characteristics of hydrogen-producing Clostridium species are introduced, including the metabolic pathways, hydrogen production performance, and substrate diversity. In addition, strategies for improving the hydrogen production by Clostridium species were extensively reviewed, and the promising applications of the fermentation system from the points of economic and environmental benefits were displayed. Finally, perspectives concerning the further application of hydrogen production by Clostridium species were proposed. Extensive studies demonstrate that Clostridium species are good candidates for fermentative hydrogen production with both high hydrogen yield and wide substrate range, but more efforts are still needed to ensure the efficient and stable operation of the system, and make the process economically applicable.
Paper-manufacturing industries utilize rice straw (RS) as raw material, generating huge quantity of black liquor (BL), which should be treated before reaching the environment. BL is mainly rich in organic pollutants that can be utilized to obtain valuable by-products and meet sustainable development goals (SDGs). In this investigation, BL from a paper-making industry was efficiently employed as a substrate for bio-H 2 generation via dark fermentation at pH value of 7.5 and temperature of 35 • C for 14 days, resulting in a hydrogen yield (HY) of 0.579 mol/mol glucose. The HY was substantially increased up to 1.654, 1.908, and 2.187 mol/mol glucose with immobilization of anaerobes on Graphene (GN), hydroxyapatite (HN), and Graphene/hydroxyapatite nano-particles (GHN). Further, the activities of protein-and carbohydrate-degrading enzymes i.e. protease, α-amylase, xylanase, and CM-cellulase was highly improved. Results were validated with respect to the operational tax-onomical unit (OUT) richness estimators (ACE and Chao), diversity indices (Shannon and Simpson), and electron-equivalent and mass balances. The H 2 productivity data were techno-economically assessed for proposing a bioenergy-based project, revealing a payback period of 5.92 y to recoup the initial investment. The findings of this study would promote interaction in the areas of industrialization, pollution prevention, and clean energy production to attain SDGs keys.
The development of the anaerobic digestion (AD) process and its mild operating conditions of complex organic carbon distinguish it from conventional energy technologies and make it highly desirable to meet a sustainable green energy technology. Although, the effectiveness of this AD method is often constructed by few issues such as surface heterogeneity, ammonia inhibition, poor methane production, slow microbe growing rates, and slow mass transfer which needs rectification. Conductive nanoparticles (CNPs) helps to increase anaerobic digestion rates as nano-sized structures with specific physicochemical properties interact with the substrate and microorganisms. CNPs as additive have resulted in high efficiency for the AD process because of their unique physicochemical characteristics, i.e. high surface area, high active sites, high reactivity levels, high specificity, self-assembly, increased mobility, and AD media transmission. This review concentrates on the recent attempts to examine the impact of CNPs, pro and cons on biogas production while using a metal oxide, zero-valent metals, and nano-carbon materials. The traditional view of binding CNPs to living organisms and the current view of mechanisms for improving aerobic digestive performance with metal CNPs. Furthermore, the effect of the physical parameter and kinetic limitations has discussed by the mathematical modelling that essential to observe, optimize simulate, and predict the behaviour of microbes at different conditions in the AD process. Later the methanogenic activity and chemical content inhibition of CNPs on the AD system was discussed. Finally, future prospects and other recommendations discussed as conclusive remarks, which help in the substantial use of CNPs to the AD process.
Proper pretreatment of waste activated sludge is commonly needed before biohydrogen fermentation due to its complex floc structure. Considering that the outer-layer extracellular polymeric substances (EPS) could restrict the disintegration of inner-layer microbial cells during the pretreatment of sludge, this study firstly applied sodium citrate pretreatment (0.3 g/g-TSS) for removing EPS from sludge flocs, followed by ultrasonic pretreatment (2 W/mL, 15 min), which aimed to enhance the disintegration efficiency. The subsequent hydrogen fermentation performance was tested in batch mode at 37 °C and initial pH 7.0. Results showed that the combined sodium citrate-ultrasonic pretreatment significantly disrupted the sludge floc structure and promoted soluble COD concentration by 157.5 times, which synergistically enhanced the biohydrogen fermentation performance. The maximum hydrogen yield of 38.8 mL/g-VSadded was achieved with the combined pretreatment, which was 604.2%, 155.1%, and 92.6% higher compared to the control, individual ultrasonic pretreatment, and individual sodium citrate pretreatment, respectively. Correspondingly, the energy conversion efficiency increased from 7.4% to 32.8% through the combined pretreatment. The combined pretreatment also enhanced the organics utilization, induced a more efficient fermentative pathway, and shortened the hydrogen-generating lag phase. More enrichment of hydrogen-producing bacteria, especially the genera Clostridium sensu stricto and Paraclostridium, was responsible for the synergistic enhancement in hydrogen yield and energy conversion efficiency. The present work puts forward an effective and eco-friendly pretreatment approach for enhancing bioenergy recovery from waste activated sludge.
Anaerobic digestion (AD) is one of the most energy-efficient waste treatment technologies for biodegradable wastes. Owing to the increasing trend of metallic nanoparticle applications in industry, they are ubiquitous to the waste streams, which may lead to remarkable impacts on the performance of the AD process. This review addresses the knowledge gaps and summarises the findings from the academic articles published from 2010 to 2019 focusing on the influences on both AD processes of biochemical hydrogen-generation and methane-production from selected metallic nano-materials. Both qualitative and quantitative analyses were conducted with selected indicators to evaluate the metallic nanoparticles' influences on the AD process. The selected metallic nanoparticles were grouped in the view of their chemical formulations aiming to point out the possible mechanisms behind their effects on AD processes. In summary, most metallic nanoparticles with trace-element-base (e.g. iron, cobalt, nickel) have positive effects on both AD hydrogen-generation and methane-production processes in terms of gas production, effluent quality, as well as process optimisation. Within an optimum concentration, they serve as key nutrients providers, aid key enzymes and co-enzymes synthesis, and thus stimulate anaerobic microorganism activities. As for the nano-additives without trace-element base, their positive influences are relied on providing active sites for the microorganism, as well as absorbing inhibitory factors. Moreover, comparisons of these nano-additives’ impacts on the two gas-production phases were conducted, while methane-production phases are found to be more sensitive to additions of these nanoparticles then hydrogen-production phase. Research perspectives and research gaps in this area are discussed.
Hydrogen is considered the energy of the future. In order to meet the requirements of a green production, many technological advances were achieved in the last 20 years. Reviewing these advances allows the understanding the constraints of the sector and the identification of the paths for future research. In this work three routes for renewable hydrogen production from renewable sources were reviewed with focus on patented technologies: dissociation of the H2O molecule, microbial production and thermochemical processes. Three patent databases were accessed, covering documents written in English, Spanish and Portuguese. Water dissociation is the only commercial technology and most efforts were identified in new materials for electrodes, new catalysts and reagent recycling. Microbial production is thermodynamic limited but strategies to maximize the production and overcome economic barriers are mostly related to the use of wastewaters, improving microbial communities' composition and genetic manipulation. Most patents of thermochemical production patents brought contributions to the efficient use of energy especially by the combination with other energy producing technologies. The establishment of a green hydrogen society is strongly dependent of future developments on new materials, recycle of chemical catalysts and efficient use of energy in the short-term.
Hydrogen applicability in the power, chemical and petrochemical industries is constantly growing. Efficient methods of hydrogen generation from renewable sources, including waste products, are currently being developed, even though hydrogen is mainly produced through steam reforming or thermal cracking of natural gas or petroleum fractions. In paper alternative methods of hydrogen production with a particular emphasis on dark fermentation are discussed. The review compiles essential information on strains of bacteria used in the production of hydrogen from waste products in the agroindustry and from lignocellulosic biomass. The effect of such parameters as kind of raw material, method of processing, temperature, pH, substrate concentration, partial pressure of hydrogen, hydraulic retention time, method of inoculum preparation and the type and operating parameters of a reactor on the yield of dark fermentation is discussed. The review aims at presentation of current state of knowledge on the dark fermentation process utilizing waste materials as substrates. The results of investigations with emphasis on the most important issues regarding operating parameters of dark fermentation are also included.
Anaerobic digestion (AD) of sewage sludge is one of the most efficient, effective, and environmentally sustainable remediation techniques; however, the presence of complex floc structures, hard cell walls, and large amounts of molecular organic matter in the sludge hinder AD hydrolysis. Consequently, sewage sludge pretreatment is a prerequisite to accelerate hydrolysis and improve AD efficiency. This review focuses on pretreatment techniques for improving sewage sludge AD, which include mechanical, chemical, thermal, and biological processes. The various pretreatment process effects are discussed in terms of advantages and disadvantages, including their effectiveness, and recent achievements are reviewed for improved biogas production.
This paper illustrates the method to predict the production of biohydrogen and biogas from the horizontal and vertical continuous mixed tank reactor using a numerical approach. Utilization of computational fluid dynamics on the estimation of bioreactor performance is very crucial owing to the uncertainty in the numerical results. Since there has been little work on CFD to determine the influence of hydraulic retention time, impeller speeds, vortex growth, and pH on biohydrogen yield rate the effort had been made. A series of simulations are done with optimal boundary conditions to ensure maximum hydrogen and biogas production rate. Two types of reactors HCSTR and VCSTR are operated at different impeller speed from 40 rpm to 120 rpm. Further, the rate of HRT and organic loading are varied. As the rpm of the impeller increase the rate of hydrogen and biomass production increases not later than 80 rpm. Meanwhile, the optimal range of HRT and pH are 4–8 h and 6.0–8.0. Running the impeller at optimized rate with derived conditions leads to high hydrogen and biogas production of 6 LH2/Ld and 30 L/d. The obtained results are validated with the experimental findings to compare the uncertainty formed due to the numerical simulations. The optimum boundary condition obtained from the study is expected to provide the essential knowledge in establishing the full-scaled reactors.
The efficiency of microbial electron transfer is fundamental for determining the performance of fermentative hydrogen/methane production. To facilitate microbial electron transfer, conductive magnetite nanoparticles (MNPs) were added into a cascading dark fermentation and anaerobic digestion system that was inoculated with Enterobacter aerogenes ZJU1 and methanogenic activated sludge (MAS), respectively. During the hydrogen-producing stage, the ratio of NADH/NAD⁺ and the activities of hydrogenase and electron transport system (ETS) of E. aerogenes ZJU1 were all increased by dosing 200 mg/L MNPs, which was conducive to hydrogen production through the NADH-dependent pathway. In the presence of 200 mg/L MNPs, hydrogen production increased by 21.1%, while subsequent methane production improved by 22.9%. Electrochemical analysis demonstrated the improvement in extracellular electron transfer capacity of MAS after adding MNPs, which can be ascribed to the contribution of MNPs and electrochemically active extracellular polymeric substances (EPS) induced by MNPs, such as humic acid-like and fulvic acid-like substances. Bacteria Syntrophomonas and Archaea Methanosarcina were the dominating enriched syntrophic partners, and the expression of functional genes involved in CO2 reduction to methane pathway was found to increase. Therefore, a more efficient fermentative hydrogen and methane co-production system was established by improving microbial electron transfer with the addition of MNPs.
Photo-fermentation seems to be an attractive hydrogen production pathway. However, the light conversion efficiency and photo-hydrogen production of purple non-sulphur bacteria (PNSB) are very low, and hence, various biotechnological approaches are investigated to improve biohydrogen production. This article presents an overview of the advanced biotechnological approaches to enhance the photo-fermentative biohydrogen production. The advancements reviewed include optimisation of the medium, abiotic factors, the lighting regime, immobilisation techniques, application of photoluminating nanomaterials, genetic engineering, and other strategies. These approaches show positive results in the enhancement of photo-hydrogen production by PNSB. Some recommendations are suggested for further studies in the enhancement of photo-hydrogen production, such as green nanomaterials application, integrated dark- and photo-fermentation, genetic manipulation, and the application of the non-technological analysis approaches.
In this study, the effects of alkaline (pH 10) and acidic (pH 2–5) chemical pretreatment on dissolution of organic matters and biochemical methane potential (BMP) at waste activated sludge (WAS). For each pretreatment methods at different temperature (25, 40, 50 and 60 °C) and operating time (5, 15, 30, 45 min) are the two factors. In the first step, the feasibility of chemical pretreatment in anaerobic digestion was investigated. Increases in soluble chemical oxygen demand (sCOD)/total chemical oxygen demand (tCOD) were determined in all chemical pretreatments. In the second step, the sCOD/tCOD ratio was used to determine the effects on the pretreatment and BMP assay was used to examine the enhanced anaerobic digestion. The pretreatment study conditions were determined due to the highest sCOD/tCOD ratios. These highest ratios were obtained at different pH values, operational times and temperatures. The highest cumulative BMP values were taken at pH 10, 10 min, 60 °C and pH 5, 15 min, 40 °C. Under these pretreatment conditions, the cumulative BMP values were 47.7 mL CH4/g VSS and 12.3 mL CH4/g VSS at conditions pH 10, 10 min, 60 °C and pH 5, 15 min, 40 °C (the control BMP value was extracted). The methane yield values were 43.61% and 12.34% at alkaline acidic conditions (pH 10 and 5). In the pH 2 study results indicated that the cumulative BMP values were 105.1 and 90.5 mL CH4/g VSS for 50–60 °C. These values were exactly the same or lower than the control BMP value.
Dark fermentative hydrogen production from organic wastes can achieve dual benefits of clean energy generation and waste utilization, which offers the best prospects for a biohydrogen production process with high environmental benefits. Biohydrogen production system is a complex biological process, which is affected by many factors, including operational conditions (e.g. temperature, pH), substrate type, reactor design etc., and depends on the microbial type, retention time, activity, productivity and end products. Among these influencing factors the hydrogen-producing microorganisms play a vital role. Great efforts have been made to enhance the hydrogen production efficiency from the perspective of microbiology. In this review, the microbiology, biochemistry and enzymology for biological hydrogen production were briefly summarized and analyzed. The recent progress in microbiology for hydrogen production through dark fermentation was reviewed, including microorganisms, biochemistry, enzymology, microbial modification and the identification of the microbial community structure. Metabolic pathways can be modified by metabolic engineering, thus enhancing the biological hydrogen production through overcoming limiting factors for hydrogen production in various systems by increasing the flow of electrons to hydrogen-producing pathways, increasing substrate utilization, and engineering more efficient and/or oxygen-resistant hydrogen-evolving enzymes. Finally, concluding remarks and perspectives are given.
Ultrasonic treatment has become a modern method for removal of micropollutants and refractory compounds from water/wastewater and to improve biodegradation efficiency of biological activated sludge from wastewater treatment plants, in order to produce biogas. This paper is referring to the ultrasonic pretreatment of biological activated sludge, before anaerobic fermentation phase, to increase the amount of biogas generation. The pretreatment of biological sludge is based on two steps: alkaline digestion and ultrasonication. Ten minutes of alkaline condition (pH 9.5 - 10.5) followed by 10 minutes ultrasonication (20 kHz frequency) were the general operating condition of sludge pretreatment phase. Parallel tests (with and without ultrasonic pretreatment step) were performed in order to assess the effect of ultrasonic pretreatment on biogas generation. Ultrasonication in alkaline condition of biological sludge heave led to doubling the amount of biogas generated in anaerobic fermentation phase.
Pretreatment of waste activated sludge (WAS) results in an improved efficiency of the subsequent anaerobic biotransformation of the organic matter to volatile fatty acids. The pretreatment process has been carried out using alkaline treatment, ultrasonic treatment (20 KHz, 120 W) and different combination of these two methods: alkaline followed by ultrasonic, as well as the combining method in which ultrasonic treatment is applied to WAS samples dosed with alkaline. The hydrolysis efficiency was evaluated based on the quantity of soluble COD (SCOD) and organic nitrogen in the pretreated WAS as well as the production of total volatile fatty acids (TVFA) in the following biochemical acid potential (BAP) test. For WAS samples with described pretreatments, the released SCOD varied from 36% to 89% of the total COD (TCOD) and soluble organic nitrogen from 34% to 42%. The TVFA/TCOD ratio of the raw WAS used in this study was less than 10%. For the alkaline pretreated WAS, the TVFA/TCOD ratio increased to 30%, and the following ultrasonic treatment enhanced the ratio 66%. Further, WAS samples pretreated using simultaneous ultrasound and alkaline treatment in which ultrasonic was applied to WAS samples dosed with 40 meq/L NaOH for 14.4 sec/mL could achieve a maximum TVFA/TCOD ratio of 84% in 21 hours. Therefore, the combination of simultaneous alkaline and ultrasound pretreatment is efficient in enhancing the production of volatile acids in WAS in order to achieve recovery of volatile fatty acids from the WAS.
Biohydrogen production is considered as one of the most promising alternative processes to produce hydrogen due to its effectiveness, renewability, and environmental friendliness compared to the conventional way, such as thermochemical and electrochemical methods. Biohydrogen production via photofermentation produces hydrogen by photo-decomposing organic matters through the nitrogenase of photosynthetic bacteria. Despite its advantages, high energy requirement during nitrogenase-catalyzed reaction and low biohydrogen production efficiencies in the reality have become the foremost concern in a large scale application of photofermentation. Thus, an improvement of biohydrogen yield and light conversion efficiency is necessary to increase the feasibility of photofermentation. One of the simplest ways to improve photofermentation is by adding suitable chemical enhancer. Various studies have shown that an addition of some chemicals, such as iron, molybdenum, ethylenediaminetetraacetic acid (EDTA), vitamins, buffer solution, and others chemicals could increase the biohydrogen production rates and yields by a significant value. However, an addition of other chemicals, such as nickel ions, diphenylene iodonium, dimethylsulphoxide, and copper ions, might cause an adverse effect on the process. Addition of EDTA, molybdenum, ethanol or yeast may inhibit the photofermentation process, depending on the type of bacteria and substrates used during photofermentation process, as well as the concentration of the added chemicals. Hence, the importance and effects of chemicals addition on photofermentative biohydrogen production were discussed in this review paper.
ZVI was reported to enrich H2-utilizing methanogens that enhanced interspecies H2 transfer, while Fe(III) oxide served as a conductive material to promote direct interspecies electron transfer (DIET). However, the interaction of these two modes in anaerobic digestion has not been clarified yet. In this study, when adding Fe3O4 and ZVI simultaneously into an anaerobic digester, the abundance of hydrogenotrophic methanogens decreased drastically compared to ZVI-added digester and Fe-free digester. However, the methane production of ZVI + Fe3O4 added digester were 68.9% higher than Fe-free digester and 20.0% higher than ZVI-added digester, respectively. Sludge reduction rate of these three digesters also showed similar results. These indicated that hydrogenotrophic methanogenesis was not the main reason for methanogenesis in Fe3O4-added digester. Instead, Syntrophomonas and Methanosaeta were specially enriched in Fe3O4-added digesters, which implied that the potential DIET between Syntrophomonas and Methanosaeta was likely a crucial reason for accelerating anaerobic digestion of waste sludge.
Hydrogen production from organic wastes by dark fermentation is promising. Among a variety of organic wastes, sewage sludge has drawn extensive attention due to its huge amount, high organic content and stable source. This paper reviewed the characterization of sludge and the principles and potential of sludge hydrogen fermentation. Poor hydrolysis and low C/N ratio of sludge were two main limitations for sludge hydrogen fermentation. To improve hydrogen production, some pretreatment methods (heat, ultrasound, microwave, alkaline, acid, oxidation, enzyme and bacteria) and the addition of co-fermentation substrates have been applied for enhancing hydrogen production from sludge fermentation. The effect of key factors (temperature, pH, retention time and organic loading rate, agitation intensity, nutrients, inhibitors and inoculum) on hydrogen production and process stability was introduced and discussed. Furthermore, the kinetic models were briefly discussed. After sludge hydrogen fermentation, some end products, including acetate, propionate, butyrate and ethanol, could be used for deducing the fermentation type, and applied as substrates for second stage process (e.g. anaerobic digestion and photo fermentation) for further energy recovery. The development of these two-stage processes was illustrated. Concluding remarks and perspectives for this process were also evaluated.
The phenol-sulfuric acid method is a simple and rapid colorimetric method to determine total carbohydrates in a sample. While the method detects virtually all classes of carbohydrates (mono-, di-, oligo-, and polysaccharides), the absorptivity of the different carbohydrates varies. Thus, unless a sample is known to contain only one carbohydrate, the results must be expressed arbitrarily in terms of one carbohydrate. In this laboratory exercise, the total carbohydrate content of soft drinks and beers is determined with the phenol-sulfuric acid method, using a glucose standard curve. Data generated are used to calculate the caloric content of those beverages.
Sewage sludge management is now becoming a serious issue all over the world. Anaerobic digestion is a simple and well-studied process capable of biologically converting the chemical energy of sewage sludge into methane-rich biogas, as a carbon-neutral alternative to fossil fuels whilst destroying pathogens and removing odors. Hydrolysis is the rate-limiting step because of the sewage sludge complex floc structure (such as extracellular polymeric substances) and hard cell wall. To accelerate the rate-limiting hydrolysis and improve the efficiency of anaerobic digestion, various pretreatment technologies have been developed. This paper presents an up-to-date review of recent research achievements in the pretreatment technologies used for improving biogas production including mechanical (ultrasonic, microwave, electrokinetic and high-pressure homogenization), thermal, chemical (acidic, alkali, ozonation, Fenton and Fe(II)-activated persulfate oxidation), and biological options (temperature-phased anaerobic digestion and microbial electrolysis cell). The effectiveness and relative worth of each of the studied technologies are summarized and compared in terms of the resulting sludge properties, the digester performance, the environmental benefits and the current state of real-world application. The challenge and technical issues encountered during sludge cotreatment are discussed, and the future research needs in promoting full-scale implementations of those approaches are proposed.
Biohydrogen production from waste bread in a continuous stirred tank reactor (CSTR) was techno-economically assessed. The treating capacity of the H2-producing plant was assumed to be 2 ton waste bread per day with lifetime of 10 years. Aspen Plus was used to simulate the mass and energy balance of the plant. The total capital investment (TCI), total annual production cost (TAPC) and annual revenue of the plant were USD931020, USD299746/year and USD639920/year, respectively. The unit hydrogen production cost was USD1.34/m³ H2 (or USD14.89/kg H2). The payback period and net present value (NPV) of the plant were 4.8 years and USD1266654, respectively. Hydrogen price and operators cost were the most important variables on the NPV. It was concluded that biohydrogen production from waste bread in the CSTR was feasible for practical application.
Silver nanoparticles were added into anaerobic batch reactors to enhance acidogenesis and fermentative hydrogen production simultaneously. The effects of silver nanoparticles concentration (0-200nmolL(-1)) and inorganic nitrogen concentration (0-4.125gL(-1)) on cell growth and hydrogen production were investigated using glucose-fed mixed bacteria dominated by Clostridium butyricum. The tests with silver nanoparticles exhibited much higher H2 yields than the blank, and the maximum hydrogen yield (2.48mol/molglucose) was obtained at the silver concentration of 20nmolL(-1). Presence of silver nanoparticles reduced the yield of ethanol, but increased the yield of acetic acid. The high silver nanoparticles had higher cell biomass production rate. Further study using the alkaline pretreated culture as inoculum was carried out to verify the positive effect of silver nanoparticles on H2 production. Results demonstrated that silver nanoparticles could not only increase the hydrogen yield, but reduce the lag phase for hydrogen production simultaneously.
The influence of self-immobilization of enriched acidogenic mixed consortia on fermentative hydrogen (H2) production was studied on different supporting materials [SBA-15 (mesoporous) and activated carbon (granular; GAC and powder; PAC)] using chemical wastewater as substrate. Batch fermentation experiments were performed with same substrate at different organic loading rates (OLRs) under acidophilic microenvironment (pH 5.5) and room temperature (28 ± 2 °C). Experimental data evidenced the effectiveness of attached growth on both the H2 yields and substrate degradation efficiency, particularly at higher loading rates. Among the three materials evaluated, immobilization on SBA-15 material showed comparatively effective performance in enhancing both H2 yield and substrate degradation. Suspended growth (SG-control) culture showed inhibition in terms of both H2 production and substrate degradation especially at applied higher loading rates. Immobilization on SBA-15 resulted in nine times higher H2 production (7.29 mol/kg CODR-day at OLR of 0.83 kg COD/m3-day) than the lowest yield observed (suspended growth at OLR of 2.55 kg COD/m3-day). Maximum substrate degradation rate (SDR) of 0.96 kg COD/m3-day (OLR 2.55 kg COD/m3-day) was also observed with SBA-15 immobilization, which is 1.62 times higher than the lowest substrate degradation observed with SG-control experiments with the same OLR. Attached growth on GAC and PAC also showed remarkable improvement in the process performance at higher OLRs compared to SG-control.
Pretreatment of waste activated sludge (WAS) results in an improved efficiency of the subsequent anaerobic biotransformation of the organic matter to volatile fatty acids. The pretreatment process has been carried out using alkaline treatment, ultrasonic treatment (20 KHz, 120 W) and different combination of these two methods: alkaline followed by ultrasonic, as well as the combining method in which ultrasonic treatment is applied to WAS samples dosed with alkaline. The hydrolysis efficiency was evaluated based on the quantity of soluble COD (SCOD) and organic nitrogen in the pretreated WAS as well as the production of total volatile fatty acids (TVFA) in the following biochemical acid potential (BAP) test For WAS samples with described pretreatments, the released SCOD varied from 36% to 89°/a of the total COD (TCOD) and soluble organic nitrogen from 34% to 42%. The TVFA/TCOD ratio of the raw WAS used in this study was less than 10%. For the alkaline pretreated WAS, the TVFA/TCOD ratio increased to 30%, and the following ultrasonic treatment enhanced the ratio 66%. Further, WAS samples pretreated using simultaneous ultrasound and alkaline treatment in which ultrasonic was applied to WAS samples dosed with 40 meq/L NaOH for 14.4 sec/mL could achieve a maximum TVFA/TCOD ratio of 84% in 21 hours. Therefore, the combination of simultaneous alkaline and ultrasound pretreatment is efficient in enhancing the production of volatile acids in WAS in order to achieve recovery of volatile fatty acids from the WAS.