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Effect of extracellular polymeric substances disintegration by ultrasonic pretreatment on waste activated sludge acidification
Abstract
In this study, batch tests were conducted to investigate the effect of extracellular polymeric substances (EPS) disintegration on anaerobic fermentation of waste activated sludge (WAS). Ultrasonic pretreatment was used to disintegrate EPS and accelerate WAS hydrolysis. The experimental results showed that more organic substances were released from sludge with increase of ultrasonic density, and the EPS were completely disintegrated at ultrasonic parameters beyond 2.0 W/mL and 15 min. The optimal ultrasonic density for short chain fatty acids (SCFAs) accumulation was 2.0 W/mL, and the SCFAs concentration reached 3166 mg/L after 5 days of anaerobic fermentation. The SCFAs mainly consisted of acetic and propionic acids, accounting for 88% of total SCFAs. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that ultrasonic density significantly altered the bacterial communities by affecting the EPS disintegration degree. Firmicutes, Proteobacteria and Bacteroidetes were main species, contributing to proteins (PN) and polysaccharides (PS) degradation and SCFAs production.
... Considering the technological aspect, there is a list of advantages resulting from the use of ultrasounds in excess sludge management, e.g. the breakage of extracellular polymeric substances and destruction of waste activated sludge cells (Liu et al. 2015), decomposition of organic compounds and formation of soluble substances (Zhuo et al. 2012, Parkitna et al. 2013) as well as the enhancement of the formation of short chain fatty acids (SCFA) with the dominance of acetic and propionic acids , Liu et al. 2015 and VFA (Zawieja et al. 2009). All these phenomena reduce the time of anaerobic digestion. ...
... Considering the technological aspect, there is a list of advantages resulting from the use of ultrasounds in excess sludge management, e.g. the breakage of extracellular polymeric substances and destruction of waste activated sludge cells (Liu et al. 2015), decomposition of organic compounds and formation of soluble substances (Zhuo et al. 2012, Parkitna et al. 2013) as well as the enhancement of the formation of short chain fatty acids (SCFA) with the dominance of acetic and propionic acids , Liu et al. 2015 and VFA (Zawieja et al. 2009). All these phenomena reduce the time of anaerobic digestion. ...
... Some authors shorten the range of frequency from 20 to 25 kHz for the processing of excess sludge (Zielewicz 2007). Hence, in the discussed study sonication applied to waste activated sludge pretreatment was carried out at the frequency of 20 kHz for 10-15 minutes (Yan et al. 2010, Liu et al. 2015. In the case of sunfl ower oil cake fermentation carried out at the same frequency, the processes were run from 16.6 to 331.2 minutes (Fernández-Cegrí V et al. 2012). ...
The aim of the study was to determine the impact of various methods of oil mixing with wastewater on properties of synthetic municipal wastewater containing edible oil (SMW+0.02% m/v rapeseed oil). The study was carried out in 3L glass, cylindrical reactors to which SMW+0.02% were introduced. Various methods of its mixing with water were applied: mechanical mixing (SMW+0.02%+mixing) and sonication (SMW+0.02%+ultrasounds). The wastewater was sonicated at 35 kHz for 30 min. The constant temperature conditions were maintained during the experiment for each mixing method (15°C, 20°C and 30°C). The analysis of parameters (pH, COD, BOD5 and long chain free fatty acids concentration) of raw wastewater and after 2, 4, 6, 24, 48 and 72 hours of inoculation was performed to determine the effect of mixing method. The most significant changes in wastewater chemical parameters after the introduction of the oil were observed in the case of COD. For SMW+0.02%+ mixing a slow increase in COD within 24 hours of the process was observed. In the case of SMW+0.02%+ultrasounds the increase and the decrease of COD value were observed in reference to the initial value. The changes in acids concentrations observed in reactors with SMW+0.02%+ultrasounds were referred to the ones observed in reactors with SMW+0.02%+mixing but changes were more intense in the first reactor. The use of ultrasounds in pre-treatment of wastewater resulted in the intense appearance of palmitic acid for 6 hours. Regardless of the emulsion formation method (mixing or ultrasounds), the concentration of oleic acid and linoleic acid was reduced. The biggest changes in free fatty acids concentration were observed for palmitic, oleic and linoleic acids after 24 hours. © Copyright by Polish Academy of Sciences and Institute of Environmental Engineering of the Polish Academy of Sciences, Zabrze, Poland 2018.
... These increases in sCOD are probably due to the lysis of extracellular polymeric substances (EPS) and bacterial cell walls and the release of intracellular material (Tyagi et al., 2014;Liu et al., 2015;Kavitha et al., 2016a). Wastewater sludge consists of flocs made of bacteria adhered to one another by the secretion of EPS, which increases the complexity of the sludge. ...
... This synergic effect increases sludge solubilization, facilitating the metabolism of bacterial and archaeal communities in subsequent phases of AD. The organic components can be exploited by fermentative bacteria, such as Proteobacteria, Bacteroidetes, and Firmicutes, which have been reported as the dominant phyla in the AD of sludge (Zhang et al., 2015;Liu et al., 2015). ...
In this work, the effect of coupling ultrasonic pretreatment with dosing of zero-valent iron nanoparticles (nanoferrosonication, “NFS”) to improve the anaerobic digestion of sewage sludge was studied. Biochemical methane potential tests were conducted at 15,000 and 25,000 kJ/kgTS and their combinations with 2 and 7 mgFe⁰/gVS. The biogas yield increased from 106 (control) to 143 (25,000 kJ/kgTS) and 308 mL/gVS with NFS (7 mgFe⁰/gVS + 15,000 kJ/kgTS). The methane content increased from 55.6 to 66%, and the maximum VS removal was 11.5% at 7 mgFe⁰/gVS + 15,000 kJ/kgTS. The results demonstrated that NFS was effective in intensifying the process.
... 18 Pyrosequencing is a widely-used molecular biological technology, used in environmental science elds to study functional microbial communities. 19 In this study, bacterial community structures and the relative abundance of species were analyzed using cloning sequencing analysis. Bacteria abundance was quantied using real-time polymerase chain reaction (PCR). ...
... The sludge hydrolysis limited the rate and extent of organic degradation in the AD process. 1 The SCOD, protein and carbohydrate concentration rapidly increased upon UT application at the extent of the VSS concentration, indicating that UT effectively released the organic components from the sludge solid phase to the liquid phase. 19 The SCOD, protein and carbohydrate concentration gradually increased with AD time (i.e., cumulative UT time increases), while the VSS concentration decreased gradually. This might be produced by the gradually lower levels of organic matter in the solid sludge that led to lower dissolution rates of the sludge. ...
This study proposed a sludge degradation system comprised of: (i) an ultrasound treatment (UT) system to disintegrate sludge; (ii) an up flow anaerobic sludge blanket (UASB) reactor to degrade the disintegrated sludge; and (iii) a microbial electrolysis cell (MEC) in replacement of a three-phase UASB separator to deeply degrade the disintegrated sludge. The influence of the ultrasound power, the temperature, and the voltage on the sludge degradation process was discussed. The experimental results showed that the UT unit effectively promoted sludge disintegration, thereby leading to deterioration of the quality of the reactor effluent. The temperature and the voltage parameters were found to be key for the anaerobic degradation (AD) process within this system. The volatile suspended solid concentration in the effluent was maintained at 320–380 mg L⁻¹ (ca. 0.08 times the raw sludge concentration), thereby validating the utilization of MEC as a three-phase separation unit. The total chemical oxygen demand removal was maintained at 61.3% during 5 days of AD upon intermittent exposure of the sludge to the UT unit, thereby showing that the system can effectively degrade solid organic matter. The bacterial community structure of the raw sludge significantly changed, with the high biodiversity of this system increasing the ecological stability. This system can degrade sludge with high efficiency and could be used in further engineering applications.
... Group 2 (FNA) was designed to evaluate the FNA effect, where the pH was maintained at 5.5 by 1 M hydrogen chloride or 1 M sodium hydroxide and 2 mL sodium nitrite stock solution (30 g/L) was added. It has been demonstrated that ultrasonic treatment could totally disintegrate EPS at ultrasonic intensity 2.0 W/mL and ultrasonic time 15 min [21]. In this study, we used ultrasonic treatment as a pretreatment method to elute EPS attaching to cells so as to determine that whether FNA and/or its derivatives could directly affect cytomembrane. ...
... Comparing FNA treatment alone, protein and polysaccharide in S-EPS increased 43% and 18% after with ultrasonic/FNA treatment, respectively, but a slightly decrease was found in LB-EPS and TB-EPS. EPS attaching to cells was eluted by the combined cavitation by ultrasonic and FNA treatment [21]. ...
Free nitrous acid (FNA) has positive effect on the solubilization of waste activated sludge (WAS), but the mechanism is uncertain. In this study, five different pretreatments were compared to elucidate the enhanced mechanism through the variation of sludge physicochemical properties, including capillary suction time (CST), extracellular polymeric substances (EPS) and bound water. The CST values showed a significant positive correlation with soluble protein (PN) and polysaccharide (PS) under different FNA concentration and contact time. After being pretreated, the CST values increased from 156.5 (raw sludge) to 335.4 (ultrasonic), 237.5 (FNA), 258.7 (ultrasonic/FNA) and 214.4 (ultrasonic (washed)/FNA), respectively. The soluble extracellular polymeric substances (S-EPS) and loosely bound EPS (LB-EPS) increased for all pretreatment, but the tightly bound EPS (TB-EPS) decreased. The sludge filterability was in connection with the existence of humic acid in LB-EPS. Contrary to other pretreatments, bound water decreased from 82% to 79% after FNA treatment. This study showed that FNA was very effective in disintegrating cell membrane, which was indicated by increasing percentage of DNA in solution, however, its role in disintegration of EPS fractions was limited.
... The SD of carbohydrates and proteins was 18.2% and 22.9%, respectively, at the highest USp tested. These increases are due to the lysis of extracellular polymeric substances and to the release of intracellular material caused by the ultrasonic cavitation ( Liu et al., 2015). Typically, more proteins than carbohydrates were solubi- lized during USp. ...
... The greater solubilization of proteins than car- bohydrates was probably due to the lysis of the cell walls, as they have a high protein content (Houtmeyers et al., 2014). The increase in the soluble concentration of organic matter facilitates the metabolism of bacterial and archaeal communities in the subse- quent phases of the AD ( Liu et al., 2015;Zhang et al., 2015;Liao et al., 2016). Consequently, the rate of biogas production is accel- erated, and biogas and methane yields could be increased. ...
Waste activated sludge (WAS) is a polluting waste with severe management problems that must be treated to prevent pollution and human health risks. Anaerobic digestion (AD) is the most used process to stabilize sludge; however, it must be improved because the biomethanation of sludge entails low biodegradability, pathogen inactivation, and biogas production. This study investigated the effects of ultrasonic pretreatment (USp) of WAS as a strategy to improve AD. Macromolecule solubilization, heavy metal behavior, pathogen inactivation and biogas production were evaluated. USp was applied at a range of 5000–35000 kJ/kg TS (total solids). The maximum solubilization degree of soluble chemical oxygen demand was 26%, and 22.9% of proteins at 35000 kJ/kg TS. The highest USp reduced only 2 log units of pathogens; nevertheless, a high inactivation was obtained when TS were reduced to 2% and continuous stirring was applied. AD of raw and sonicated WAS were compared with biochemical methane potential tests, and a biogas overproduction of 31.43% (219.5 mL/g VS) was achieved at highest USp. A modified Gompertz model was used for kinetic study of biogas production. The kinetic parameters at highest energy were: biogas production potential, G0 = 634.2 mL; maximum biogas production rate, Rmax = 57.23 mL/day.
... Simultaneous anaerobic digestion (AD) technology is typically applied for the treatment of high-strength organic wastewater and the generation of bioenergy resources [2]. Since the membrane of the microorganism cells restricts sludge digestibility, sludge pre-treatment before AD is a promising technology for sludge degradation and energy recovery [3]. Therefore, researchers have focused on sludge pretreatment and degradation processes leading to reduced sludge production. ...
... Thus, intermittent UT achieved higher degradation efficiencies in the same ultrasound system [14]. This system effectively disintegrated flocs in the sludge while releasing organic components from the sludge solids into the liquid phase, thereby accelerating the degradation of the organic matter in the sludge [3,10]. ...
This study proposes a process with the following steps: (i) use of ultrasound treatment (UT) to disintegrate sludge; (ii) application of an up-flow anaerobic sludge blanket (UASB) reactor to degrade the disintegrated sludge; and (iii) utilization of a microbial electrolysis cell (MEC) composed of graphite fiber brush and titanium in replacement of a three-phase UASB separator. The soluble chemical oxygen demand (SCOD) and protein concentration in the MEC effluent reached 569.5 and 373.1 mg/L, respectively, after 7 days of anaerobic degradation. The concentration of volatile suspended solid (VSS) in the MEC effluent was maintained at 320–380 mg/L (ca. 0.08% of raw sludge concentration), thereby revealing successful separation by MEC during sludge degradation. The total chemical oxygen demand (TCOD) concentration, TCOD removal, and VSS/SS ratio in the UT reactor reached 1885.8 mg/L, 71.4%, and 24.7%, respectively. The proposed sludge degradation system can potentially minimize the energy consumption during ultrasound disintegration while simultaneously accelerating the anaerobic sludge degradation process. This study provides the basis for a further development of sludge mineralization processes.
... As Fig. 1(a) shows, after applying UD for 30 min, the SCOD concentration increased to 4537.5 mgL À1 . This indicated that strong physical effects (such as hydromechanical shear forces) and sonochemical reactions (such as free radicals) generated by collapsing cavitation bubbles disintegrated the sludge, releasing soluble organics from the solids into the liquid phase (Liu et al., 2015). The SCOD concentration was 1246.0 mgL À1 in the sludge after applying AD for 3 days; this level was 2.6 times the concentration in raw sludge. ...
... These were dominant microorganisms in the anaerobic digestion of sludge, playing crucial roles in hydrolysis and acetogenesis (Jaenicke et al., 2011). Other studies have also found that the bacterial community structure significantly changed after applying UD (Liu et al., 2015) and AD (Zhang et al., 2010). In this study, the relative abundance of Proteobacteria significantly decreased, likely because Proteobacteria were disintegrated by UD. ...
... The remaining sludge has a complex composition, which contains a lot of organic pollutants and toxic and harmful substances, such as heavy metal ions, viruses, pathogenic microorganisms and parasite eggs. If it is not properly handled this problem, it will cause serious secondary pollution to the environment, resulting in environmental degradation [73]. Therefore, it is particularly important that how should we deal with this problem of remaining sludge effectively. ...
In recent years, non-thermal plasma technology has gained considerable attention. It can produce highly reactive hydroxyl radicals and other strong oxidants, which is promising in environment pollutants removal. This article mainly reviews the recent advances in environment contaminants removal with several well-known non-thermal plasma technologies. We first introduce non-thermal plasma technology and its development，and then summarize their applications for air purification organic wastewater treatment and sludge organic crack，and prospect their further development in the future.
... The ultrasonication modifies the biological, chemical, and physical specifications of the sludge. Some of these variations are pathogen reduction, settling velocity improvement, and protein concentrations increase (Cella et al. 2016;Liu et al. 2015;Feng et al. 2009). ...
This review showcases a comprehensive analysis of studies that highlight the different conversion procedures attempted across the globe. The resources of biogas production along with treatment methods are presented. The effect of different governing parameters like feedstock types, pretreatment approaches, process development, and yield to enhance the biogas productivity is highlighted. Biogas applications, for example, in heating, electricity production, and transportation with their global share based on national and international statistics are emphasized. Reviewing the world research progress in the past 10 years shows an increase of ~ 90% in biogas industry (120 GW in 2019 compared to 65 GW in 2010). Europe (e.g., in 2017) contributed to over 70% of the world biogas generation representing 64 TWh. Finally, different regulations that manage the biogas market are presented. Management of biogas market includes the processes of exploration, production , treatment, and environmental impact assessment, till the marketing and safe disposal of wastes associated with biogas handling. A brief overview of some safety rules and proposed policy based on the world regulations is provided. The effect of these regulations and policies on marketing and promoting biogas is highlighted for different countries. The results from such studies show that Europe has the highest promotion rate, while nowadays in China and India the consumption rate is maximum as a result of applying up-to-date policies and procedures.
... The ultrasonication modifies the biological, chemical, and physical specifications of the sludge. Some of these variations are pathogen reduction, settling velocity improvement, and protein concentrations increase (Cella et al. 2016;Liu et al. 2015;Feng et al. 2009). ...
This review showcases a comprehensive analysis of studies that highlight the different conversion procedures attempted across the globe. The resources of biogas production along with treatment methods are presented. The effect of different governing parameters like feedstock types, pretreatment approaches, process development, and yield to enhance the biogas productivity is highlighted. Biogas applications, for example, in heating, electricity production, and transportation with their global share based on national and international statistics are emphasized. Reviewing the world research progress in the past 10 years shows an increase of ~ 90% in biogas industry (120 GW in 2019 compared to 65 GW in 2010). Europe (e.g., in 2017) contributed to over 70% of the world biogas generation representing 64 TWh. Finally, different regulations that manage the biogas market are presented. Management of biogas market includes the processes of exploration, production, treatment, and environmental impact assessment, till the marketing and safe disposal of wastes associated with biogas handling. A brief overview of some safety rules and proposed policy based on the world regulations is provided. The effect of these regulations and policies on marketing and promoting biogas is highlighted for different countries. The results from such studies show that Europe has the highest promotion rate, while nowadays in China and India the consumption rate is maximum as a result of applying up-to-date policies and procedures.
... The action of the thermal pretreatment consists in the rupture of the cell walls releasing the soluble material, which reflects an increase in the percentage of solubilization of organic matter measured by means of the COD variable [50]. This increase facilitates the metabolism of bacterial and Archaea communities in the later stages of anaerobic digestion, and therefore, the production of biogas is accelerated, producing an increase in biogas and methane yield [37,[51][52][53]. However, one of the drawbacks of the application of thermal pre-treatment is the high requirements in energy consumption. ...
The coffee pulp is the solid waste most generated during the coffee humid pulping. It contains an elevated concentration of organic matter and lignocellulosic materials. In addition, the low rate of biodegradability of the coffee pulp waste may cause severe environmental damage. Therefore, the aim of this study was to evaluate the effect of acid and thermal pre-treatments in the biodegradability rate, followed by an anaerobic digestion of the coffee pulp and collect biogas production. Thermal and acid pre-treatments (50, 70, and 90 °C, and concentration of 2.5, 5, and 10% V·V⁻¹ of acetic acid, respectively) were applied, both during 1 h, evaluating the organic matter solubilization. Posteriorly, the biodegradability and biogas production using anaerobic digestion for 35 days were evaluated. Finally, during 90 days in semicontinuous, the increase of applied organic load of 1 kg VS m⁻³ day⁻¹ with Δ 1 kg VS m⁻³ day⁻¹ every 30 days until reaching 3 kg m⁻³ day⁻¹ was evaluated. The thermal pretreatment to 90 °C and 1 h improved the solubility and hydrolysis considered limiting of the anaerobic process, reducing the hydraulic retention time from 21 to 15 days, and increasing the biogas yields (0.92 L g VSrem⁻¹ year 79.8% CH4).
... Physical pretreatments, such as ultrasonic, microwave and thermal treatments, can directly change the structure of organics or the environment of microbes. Ultrasonic pretreatment uses high-energy ultrasonic waves to create a momentary pressure difference in the aqueous phase of the sludge, which thereby destroys the cell walls of the microorganisms ( Liu et al., 2015). In addition, the high heat generated by ultrasound can cleave the organic substances, and the hydroxyl radicals can decompose organic substances into small molecules (Liu et al., Showed the synergistic impact on WAS fermentation, and improved the VFA yield 2015). ...
... It also modifies the physical characteristics of sludge such as settling velocity, floc structure and particle size which, unlike turbidity, decreases with the supplied energy. Chemical characteristics of sludge also change after the ultrasonication [129]: soluble polysaccharide and protein concentrations increase due to cell disruption and the release of organic macromolecules [130]. Ultrasonic treatment enhanced methane production by 34% at an energy supplied of 14 000 kJ kg TS −1 . ...
Currently, sludge is not considered as a waste any more, since it is capable of producing valuable products. Besides land disposal and thermochemical processes (i.e. pyrolysis, combustion, gasification), biological processes appear as promising valorisation routes to treat wastewater sludge efficiently. Anaerobic digestion (AD) processes are already being applied at industrial scales for the effective disposal and valorisation of sludge. However, methane yields from sludge anaerobic digestion remain low compared to other types of organic waste. Thus, pretreatment and co-digestion contribute to improve the degradability of organic matter and methane potential of sludge, respectively. This paper reviews the recent achievements in sludge pretreatment and co-digestion with other substrates such as the organic fraction of municipal solid waste, fatty waste, lignocellulosic and algal biomass. Furthermore, recent studies combining co-digestion and pretreatment are examined. The paper also provides recommendations to better manage sludge recovery by taking into account multiple aspects such as techno-economic feasibility, the effect of pretreatment on both the physico-chemical properties of sludge and the quality of digestate. The socio-environmental and legislative aspects are also essential in order to ensure the sustainability of the process.
... These fermenters were divided into two groups (Group-I and Group-II) and with seven in each group. In Group-I, WAS was not pretreated by US while WAS used in Group-II was pretreated by ultrasonicator (VC 130 PB,Sonics & Materials,Inc.,US) with operated condition at 20 kHz under US intensity was 2.0 W/mL and US time was 15 min before being transferred into the fermenters (Liu et al., 2015) (please see Table 1 for details). Among these fermenters, fermenter 1 was set to the blank without additions except for pH at 5.5. ...
This study presents a novel and effective method, i.e., adding nitrite into acidic fermentations after ultrasonic (US) pretreatment to form free nitrous acid (FNA), to further enhance hydrogen yield. Experimental results showed that when 180 mg/L nitrite was added into the US (2 W/mL, 15 min) pretreated waste activated sludge (WAS), the maximal hydrogen yield of 24.81 ± 1.24 mL/g VSS (volatile suspended solids) was obtained under acidic fermentation (1.0 mg/L FNA was initially formed under this condition), which was 2.21-folds (or 1.36-folds) of that from US pretreatment (or FNA treatment) alone. This combination approach caused a positive synergy on sludge disintegration and enhanced the transformation of the released organics from non-biodegradable to biodegradable. Further study showed that the inhibiting effect of this combination method on hydrogen consuming microorganism was severer. Considering its pollution free, this combination strategy is an attractive technology for hydrogen recovery from WAS.
... Low frequency ultrasound, such as 20 kHz, is effective in WAS disintegration (Houtmeyers et al. 2014). Liu et al. (2015) presented that ultrasonic irradiation can disintegrate EPS and accelerate WAS hydrolysis efficiently, and the amount of VFA produced increased with the increasing ultrasonic time and intensity. Another study by Yan et al. (2010) found the maximum accumulation of VFA (3109.8 ...
This paper reviews the recent achievements in the enhanced production of volatile fatty acids (VFAs) from waste activated sludge (WAS). The enhanced strategies are divided into two approaches. The first strategy focuses on the regulation of carbon-to-nitrogen (C/N) ratio by co-digestion of WAS with carbon-rich substrates, including municipal solid wastes (MSW), marine algae, agricultural residues, and animal manures. The other strategy is to enhance the solubilization and hydrolysis of WAS or inhibit the methanogenesis by applying various pretreatments, such as mechanical, chemical, enzymatic, and thermal pretreatment. Finally, the applications of WAS-derived VFAs are discussed. The future researches in enhancing VFAs production and wide application of the VFAs from both technical and economic perspectives are proposed.
... [3][4] 。因此，对污泥实施稳 定化处理，削弱污泥对环境的影响，对环境保护和 生态文明建设具有重要意义。 目前，污泥稳定化处理常采用厌氧消化的方 法 [5] 。其中的水解过程是厌氧菌将大分子有机成分 分解为小分子有机成分的过程，该过程进行缓慢， 是限制厌氧消化速率的关键步骤 [6] 。这是因为在剩 余污泥中，微生物细胞总质量占污泥(干重)总质量 的比例达 70 % [7] 。污泥中包含的大部分有机成分均 被微生物细胞膜所包裹，不能穿过细胞膜与厌氧菌 接触，限制了水解过程的速率 [8] 。如何在污泥厌氧 消化前实施有效的预处理，破解微生物细胞，释放 胞内有机成分，从而加快水解速度，是提高厌氧消 化效率的核心问题 [9] 。近 30 年来，研究者已提出臭 氧、碱、热、微波和超声波破解等多种污泥破解方 法 [10][11][12] 可表征水体中溶解性有机物的相对含量 [15] 。 当污泥中微生物细胞破解时，细胞中包含的蛋 白质、脂质和碳水化合物等有机成分将渗出，污泥 溶液的 SCOD 将升高 [2] 。本文定义污泥的 SCOD 增 长率 η 为 1 0 0 100% D D D η − = × (1) 式中：D1 为处理后的污泥 SCOD 值；D0 为处理前 的污泥 SCOD 值。 式(1) ...
The disruption of microbial cells in urban excess sludge to release the intracellular organics is an important step for improving the efficiency of anaerobic digestion. So, excess sludge was employed to investigate the disruption behavior of the microbial cells within the sludge by means of DC and AC corona discharge. The Soluble Chemical Oxygen Demand (SCOD) of the sludge sample was measured to evaluate the disruption performance of the cells, and the effects of DC voltage magnitude, polarity and AC voltage frequency on the performance were discussed. The results indicated that the microbial cells could be disrupted by either DC or AC corona, which leaded to the increase in SCOD. With the application of DC corona, the growth rate of SCOD decreased from 15.6% to 6.8% as the positive DC voltage increased from 1 kV to 5 kV, whereas the growth rate of SCOD increased from 0.1% to 21.4% as the negative DC voltage grew from -1 kV to -5 kV. With the application of AC corona, the increase rate of SCOD showed a close relationship to frequency and magnitude. AC corona exhibited a better treatment performance compared with DC corona. It is suggested that the disruption of the cells, as well as the release of intracellular organics, is due to the generation of oxidative species, such as hydroxyl radical and ozone within the corona discharge. The microphysical processes of cells disruption and extracellular organics degradation varies as a function of the parameters of corona discharge, which leads to the variation of SCOD increase rate. © 2017, High Voltage Engineering Editorial Department of CEPRI. All right reserved.
... For this reason, a group of microbes including Actinomycetes, Thermomonospora, Ralstonia and Shewanella was reported to be used for the production of VFA from the degradation of food waste [24]. Meanwhile, Alcaligenes species were reported to involve into the acidification process of pig manures [25], and among these species, A. faecalis was often found in sludge anaerobic acidification process [26]. As a result, the two isolates were eligible for acidogenic digestion. ...
For the efficient treatment of sludge accumulated on a rainbow trout farm, two novel strains were isolated that possessed the ability for acidogenic digestion. The strains were identified as Alcaligenes faecalis HCB2-A1 and Alcaligenes faecalis A2, respectively, and there was synergism between the two strains. Acidogenic digestions using the mixed culture of the two isolates were performed on various sludge mixtures under examinations of changes in major reaction parameters. Among the sludge mixtures, the most stable acidogenic digestion was observed on 1:1 mixture of primary and secondary sludge. During this acidogenesis, pH and ORP dropped to 6.5 and -274 mV within 1 day and then increased steadily. At the same time total solids, COD, and total nitrogen were reduced 58, 79.3 and 42.7%, respectively, with the COD removal rate of 13,017 mg/L/day. The C: N ratio changed from 27:1 to 10:1 as the sludge was digested, and total volatile fatty acids of 6065.3 mg/L was produced for 7 days. The results demonstrated an efficient means to treat aquaculture sludge, which is the alternative to the discharge of the sludge into the river.
... Disintegration is a common pretreatment method for sludge, which can destroy the sludge floc structure and releases the cell and EPS contents into the liquid phase (Niu et al., 2016). To the best of our knowledge, ultrasound application has been extensively used for disintegrating sludge (Luostarinen et al., 2011;Park et al., 2013;Liu et al., 2015;Ren et al., 2015) and thereby improving dewaterability (Dewil et al., 2006;Khanal et al., 2007;Shao et al., 2010). Neyens et al. (2004) addressed that the sludge disintegration was due to the disruption of the sludge EPS during the ultrasonic pretreatment. ...
The floc rupture and fractal structure during the ultrasonic pretreatment, rheological parameters as well as bound water content of activated sludge before/after extracellular polymeric substances (EPS) extraction was investigated to examine the variations of internal structure and moisture distribution in activated sludge with stratified EPS extraction. It was observed that the floc disruption was dominated by the model of large-scale fragmentation initially and by smaller-scale surface erosion subsequently for activated sludge before/after EPS extraction. Activated sludge with tightly bound EPS (TB-EPS) showed greater mass fractal dimension (Df) and rheological parameters hysteresis loop area, limiting viscosity (η∞), yield stress (τy), energy of cohesion of network structure (Ec) and shear modulus (G) than the other sludge samples, indicating that activated sludge after loosely bound EPS (LB-EPS) extraction exhibited a denser and stronger network structure. A water classification is also proposed: free water (bulk water and some portion of interstitial water) and bound water (osmotic, surface and intracellular water). The osmotic water (interstitial-bound water) in the LB-EPS fraction (4.3% of the total water content) exhibited much more than that in the TB-EPS (0.2% of the total water content). Bound water (surface and intracellular water) in the TB-EPS and Pellet comes to be the subject to be treated after mechanical dewatering.
... Excess sludge is a byproduct of activated sludge process. This byproduct restricts the development and application of activated sludge process because it generates new environmental problems and requires higher energy consumption and processing costs in the treatment and disposal of excess sludge (Kaya et al. 2013;Huang et al. 2014;Liu et al. 2015). Excess sludge contains a large amount of organic matters such as microbial cells and extracellular substrates, and these organic substances can be used as a potential carbon source . ...
A pilot-scale side-stream reactor process with single-stage sludge alkaline treatment was employed to systematically investigate characteristics of excess sludge hydrolysis and acidification with alkaline treatment and evaluate feasibility of recovering a carbon source (C-source) from excess sludge to enhance nutrient removal at ambient temperature. The resulting C-source and volatile fatty acid specific yields reached 349.19 mg chemical oxygen demand (COD)/g volatile suspended solids (VSS) d⁻¹ and 121.3 mg COD/g VSS d⁻¹, respectively, the process had excellent C-source recovery potential. The propionic-to-acetic acid ratio of the recovered C-source was 3.0 times that in the influent, which beneficially enhanced biological phosphorus removal. Large populations and varieties of hydrolytic acid producing bacteria cooperated with alkaline treatment to accelerate sludge hydrolysis and acidification. Physicochemical characteristics indicated that recovered C-source was derived primarily from extracellular polymeric substances hydrolysis rather than from cells disruption during alkaline treatment. This study showed that excess sludge as carbon source was successfully recycled by alkaline treatment in the process.
... Neis found that the biogas production was enhanced by 30% after ultrasonic pretreatment 32 . In another research of treated at ultrasonic parameters beyond 2.0 W/mL and 15 min for WAS, more organic substances were released 33 . Alkaline pretreatment by NaOH can increase the methane production from 251.2 mL/L·d to 362.2 mL/L·d 34 . ...
Three individual seed sludges, which domesticated by filter paper (SS1), food waste (SS2) and grease (SS3), respectively, were used for enhancing the methane production of waste activated sludge (WAS). Also CaO-ultrasonic pretreatment was performed on WAS to evaluate the effectiveness on improving efficient anaerobic digestion (AD). The results showed that WAS being acidated for 24h after CaO-ultrasonic pretreatment was an effective method for increasing initial methane production rate. The daily concentration of volatile fatty acids (VFAs) during the AD course showed that the propionic was easier to be reduced after adding seed sludge. The optimum seed sludge for improving methane production and biodegradability of WAS was SS3, which led to an increase in the methane production of 68.92% and VS reduction of 69.20% higher than the control. This pretreatment combined with adding optimum seed sludge can greatly improve clean energy generation from WAS.
... Excess sludge treatment and disposal usually accounts for more than 50e60% of the total operational expenses of wastewater treatment plants (Yang et al., 2011). Thus, treatment and disposal of excess sludge has been considered as one of the most serious problems to wastewater treatment due to the higher energy consumption and higher treatment cost (Huang et al., 2014;Liu et al., 2015). Recently, side-stream reactor (SSR) technologies involving alkaline treatment, ultrasonication, thermal treatment, chemical oxidation, microwave irradiation, and other physico-chemical treatments have been developed to reduce biomass production within activated sludge process based on lysis-cryptic growth mechanism (Wei et al., 2003). ...
Background
Epidemiological studies on the association between levels of plasma vitamin E and first stroke risk are inconclusive.
Methods
A nested, case–control study was conducted utilizing data on 115,337 hypertensive patients from the H-type Hypertension and Stroke Prevention and Control Project. The current analysis comprised 2193 cases of first stroke and 2193 controls matched for age, sex, and study site.
Results
The mean plasma concentration of vitamin E was 12.37 (3.61) μg/mL. The smoothing curve showed a linear correlation between plasma vitamin E levels and the risk of the first stroke. Hypertensive patients with plasma vitamin E levels ≥14.1 μg/mL (Q4) had an increased risk of first stroke (adjusted odds ratios [OR]: 1.18; 95% confidence interval [CI]: 1.01, 1.37) compared with those with plasma vitamin E < 14.1 μg/mL (Q1–Q3). Sub-group analysis revealed that the relationship between plasma vitamin E (≥14.1.1 vs. P interaction = 0.035).
Conclusions
This study suggests that higher levels of plasma vitamin E are associated with an elevated risk of first stroke among Chinese hypertensive patients.
Anaerobic fermentation of secondary sludge is a crucial bio-energy tactic for achieving stabilization, reduction, and resource utilization of secondary sludge in wastewater treatment plants. Short-chain fatty acids (SCFAs), the end product of anaerobic fermentation, have received substantial attention owing to shorter fermentation time, higher economic value, and broader application range. This review summarizes the composition and structure of secondary sludge, the main tactics for SCFAs accumulation, the metabolic pathway of anaerobes’ participation in SCFAs production, and the impact of SCFAs composition from the fermented liquid on its subsequent application. It was found that the composition and structure of secondary sludge may limit its decomposition and impede SCFAs production. Diverse technologies adopted can promote SCFAs accumulation to some extent. It was concluded that the application of SCFAs derived from anaerobic fermentation of secondary sludge depends on its individual SCFAs composition. This review would help advance the SCFAs production and specific applications from anaerobic fermentation of secondary sludge.
In this study, palm oil mill effluent (POME) treated by ultrasonication at optimum conditions (sonication power: 0.88 W/mL, sonication duration: 16.2 min and total solids: 6% w/v) obtained from a previous study was anaerobically digested at different hydraulic retention times (HRTs). The reactor biomass was subjected to metagenomic study to investigate the impact on the anaerobic community dynamics. Experiments were conducted in two 5 L continuously stirred fill-and-draw reactors R1 and R2 operated at 30 ± 2 °C. Reactor R1 serving as control reactor was fed with unsonicated POME with HRT of 15 and 20 days (R1-15 and R1-20), whereas reactor R2 was fed with sonicated POME with the same HRTs (R2-15 and R2-20). The most distinct archaea community shift was observed among Methanosaeta (R1-15: 26.6%, R2-15: 34.4%) and Methanobacterium (R1-15: 7.4%, R2-15: 3.2%). The genus Methanosaeta was identified from all reactors with the highest abundance from the reactors R2. Mean daily biogas production was 6.79 L from R2-15 and 4.5 L from R1-15, with relative methane gas abundance of 85% and 73%, respectively. Knowledge of anaerobic community dynamics allows process optimization for maximum biogas production.
Anaerobic digestion technology has drawn immense interest in the recent past as it addresses both increasing energy requirements as well as environmental pollution, the two major challenges faced by the rapidly developing world. However, to be able to meet the fast-growing energy needs and to substitute the conventional energy options, the anaerobic digestion process needs significant improvement in its yield and efficiency. Low methane yield, long hydraulic retention time (HRT), production of inhibitory compounds, reactor instability are major obstacles that prevent the wide application of this technology. Besides, anaerobic co-digestion that uses the combination of different feedstocks has proved to have many advantages like improved microbial stability, methane yield, and low HRT. The co-digestion technique helps to maintain the optimum carbon to nitrogen ratio as well as increase the conversion rate from acidification to methanogenesis phase by reducing the intermediate inhibitory compounds like volatile fatty acids and free ammonia. Another important technique that enhances the anaerobic digestion process is the pretreatment of feedstock by accelerating the hydrolysis phase and can induce a tremendous reduction in HRT. Therefore, in this chapter, we include various pretreatment processes and their effect on biogas enhancement. The chapter also provides a comprehensive overview of methods that aid anaerobic digestion and concludes with proposals to future studies.
Anaerobic digestion (AD) is an effective approach for waste activated sludge (WAS) disposal with substantial recovery of valuable substrates. Previous studies have extensively explored the correlations of common operational parameters with AD efficiency, but the impacts of intrinsic characteristics of WAS on the AD processes are generally underestimated. This study focused on disclosing the association of intrinsic drawbacks in WAS with AD performance, and found that the cemented WAS structure, low fraction of biomass and various high levels of inhibitory pollutants (e.g., organic pollutants and heavy metals), as the integral parts of WAS all greatly restricted the AD performance. The main potential strategies and underlying mechanisms to mitigate the restrictions for efficient WAS digestion, including the practical pretreatment methods, bioaugmentation and aided substances addition, were critically analyzed. Also, future directions for the improvement of WAS digestion were proposed from the perspectives of technical, management and economic aspects.
Long treatment times, large quantity of sludge generation, inhibition by micro-organisms and inability to degrade refractory pollutants are common disadvantages of biological treatment processes. Cavitation-based pre-treatment processes can enhance the treatment efficiency of biological treatment including aerobic oxidation and anaerobic digestion. This work presents a critical review on cavitation-based pre-treatment for subsequent biological oxidation process as well as for the treatment and modification of waste sludge for subsequent anaerobic digestion. For wastewater pre-treatment, important metrics to be assessed are COD reduction, and biodegradability index enhancement. In several studies, a BI improvement up to 50-60% has been observed with cavitation. For sludge pre-treatment, particle size reduction, soluble COD and degree of disintegration (DDCOD) increase, and enhancement of biomethane production potential have been reviewed. The effect of several process parameters like ultrasound power, hydrodynamic cavitation pressure and geometry, time, and pH are critically reviewed and compared for various studies. Improvements in treatment times, higher enzymatic digestibility, removal of refractory pollutants, and lower inhibition in the biological processes were observed as the key advantages. Optimum cavitation numbers for efficient pre-treatment lie between 0.05 and 0.15. It is observed that low hydrodynamic pressures are the most advantageous for sludge disintegration and also the process is highly time dependent. Cavitation, especially the hydrodynamic mode, is demonstrated as an economically feasible advanced oxidation-pretreatment for sludge modification and biological oxidation processes leading ultimately to an ‘energy-positive system’. Future studies in this context should mainly focus on continuous flow-pilot scale systems applicable commercially.
Persulfates, an advanced oxidation process, has been recently used as an alternative pretreatment method to enhance short-chain fatty acids (SCFAs) yield from waste activated sludge (WAS) anaerobic fermentation (AF). But so far, the effects of peroxydisulfate dosages on mesophilic anaerobic fermentation are still not studied fully. Herein, we explored the influences of potassium peroxydisulfate (PDS) addition on mesophilic AF of WAS. Notably, the addition of PDS could drastically accelerate WAS solubilization and hydrolysis, which was proportional to the amount of PDS. The maximal total SCFAs yield of 249.14 mg COD/L was obtained with 120 mg PDS/g SS addition at 6 days of AF, which was 2.2-fold that of the control one. Tightly bound extracellular polymeric substances (EPSs) were transformed into loosely bound EPS and dissolved organic matters, and aromatic proteins and humic-like substances of EPSs were disintegrated, which were caused by the devastating effects of PDS treatments on EPSs disruption. The intracellular constituents of microbial cells in the sludge was released accordingly. As a result, the release of soluble substrates derived from the disintegration of both EPSs and cells, the amounts of which was proportional to the dose of PDS. Moreover, microbial diversity and richness were both decreased in the presence of PDS, and the relative abundance of phyla Actinobacteria increased with the increase of PDS dosage. In addition, the stability of sludge flocs was destroyed in the presence of PDS, the distribution of particle size tended to small and dispersive, and dewaterability of the sludge was deteriorated.
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.
To understand the denitrification efficiency and microbial community shift with increasing salinity in salinity adaptation and shock loading process, nitrate (NO3--N), nitrite (NO2--N) and chemical oxygen demand (COD) removal efficiencies were monitored feeding acetate and primary sludge fermentation liquid. During adaptation process, salinity had little effect on NO3--N removal efficiency (>99.0%) with acetate-fed, while for fermentation liquid-fed, it decreased to around 97% at high salinity (>2.5%). Effluent NO2--N was lower than 0.1 mg/L, though obvious fluctuation of NO2--N was observed with fermentation liquid-fed when salinity change. During shock loading process, denitrification process all had slight decrease when the salinity abruptly increased to 5.0%. Traditional denitrifier of Thauera was the dominant genus, and a specialized microbial community of Azoarcus in salinity adaptation and Paracoccus in shock loading for denitrification showed high salinity tolerant. Meanwhile, microbial diversity was enriched with fermentation liquid-fed at high salinity condition.
The aim of this study was to investigate membrane fouling performance of anaerobic side-stream reactor (ASSR) coupled membrane reactors (MBR), and effects of representative enhancement strategy, namely packing carriers and low-strength ultrasonication, on sludge properties and membrane fouling by four pilot-scale MBRs. Compared to anoxic/oxic MBR (AO-MBR) for control, ASSR coupled AO-MBR (ASSR-MBR), ASSR-MBR with ASSR packed with carriers (AP-MBR) and AP-MBR with part of sludge ultrasonicated before fed into ASSR (AUP-MBR) reduced sludge production by 8.4%, 17.5% and 32.9% with efficient pollutants removal. ASSR-MBR showed more severe membrane fouling because inserting ASSR disintegrated sludge floc structure, increased the secretion of extracellular polymeric substances (EPS) and deteriorated viscoelastic property of sludge. Packing carriers in ASSR alleviated membrane fouling of ASSR-MBR by inhibiting EPS-secreting bacteria (Flavobacteriia, γ-Proteobacteria, δ-Proteobacteria and norank_Saccharibacteria), enlarging particle size and improving dewaterability. AUP-MBR showed the most severe membrane fouling and obvious cake layer fouling because ultrasonication disintegrated sludge to small particles, increased adherence property of EPS, and deteriorated dewaterability and viscoelastic property of sludge. MiSeq sequencing revealed Proteobacteria and Bacteroidetes were responsible for membrane fouling at the phylum level, and norank_Neisseriaceae, Arcobacter, norank_Parcubacteria and Mycobacterium were dominant genera easily attached on membrane surface.
Excess sludge contains a large amount of organic matter, most of which is present in the form of bacteria and extracellular polymeric substances. In this study, a photosynthetic bioelectrochemical system (BES) combined with ultrasonic treatment (UT) was investigated to mineralize sludge. The sludge was disintegrated by the UT and the supernatant separated from the treated sludge was further degraded through a bioelectrochemical system containing photosynthetic bacteria (PSB‐BES). The UT efficiency was enhanced by supernatant separation. The PSB‐BES method effectively improved the degradation of the soluble chemical oxygen demand (SCOD) from the supernatant. The SCOD and protein removal were increased 1.4 and 1.5 times, respectively, compared to BES without PSB. In addition, the effects of several key operating factors including illumination, voltage and temperature were systematically investigated. This study provides a basis for further development of sludge mineralization processes.
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Ultrasound pretreatment was proved to be effective in accelerating waste activated sludge (WAS) disintegration and promoting anaerobic fermentative short-chain fatty acids (SCFA) production. However, due to the high activities of SCFA consumers, SCFA yield is limited. Herein we reported an efficient strategy, i.e., using free ammonia (FA) to aid ultrasound pretreatment, to enhance SCFA accumulation. Experimental results showed that the greatest SCFA yield of 316.7 ± 14.9 mg COD/g VSS was obtained at 2 w/mL ultrasound pretreatment for 15 min followed by initial 60 mg/L FA pretreatment for 2 d, which was 2.2 times (1.7 times) of that from sole ultrasound (FA) pretreatment. The mechanism study revealed that this combination method accelerated sludge solubilization, enhanced the release of biodegradable organics, and caused severe inhibitions to SCFA consumption. Moreover, this method has inhibitory effects on specific activities of hydrolytic microorganisms, SCFA-producing bacteria and methanogens, but the inhibitions to methanogens were severe.
In this study, the effects of lysozyme, protease and α-amylase pretreatments for improving the hydrolysis and biodegradability of waste activated sludge (WAS) were investigated. The results showed that lysozyme was more effective in increasing the soluble chemical oxygen demand (SCOD) concentration in the liquid phase of sludge and improving the release of protein and carbohydrate from sludge flocculation to enhance sludge hydrolysis. After 8 h hydrolysis, the net SCOD increase in a reactor with lysozyme was 2.23 times and 2.15 times that of the reactors with protease and α-amylase, respectively. Meanwhile, lysozyme and protease could improve the lysis of microorganism cells and the dissolution of extracellular polymeric substances (EPS) to a certain extent, and lysozyme was more effective. Furthermore, the compositional characteristics of dissolved organic matter (DOM) and EPS were analyzed by EEM fluorescence spectroscopy and fluorescence regional integration (FRI) analysis. Tryptophan-like protein was the main component of sludge, which accounted for 31% and 38% of DOM and EPS, respectively. Lysozyme could decrease the percentage of non-biodegradable materials in sludge, such as humic acid-like substances and fulvic acid-like substances, so it could improve the biodegradability of sludge. This study can provide valuable information for future studies about hydrolytic enzyme pretreatments for WAS disposal.
The effects of three kinds of waste activated sludge (WAS) thermo-chemical pretreatments, including thermo-NaOH, thermo-mixed alkali and thermo-CaO2 pretreatments, on volatile fatty acids (VFAs) production and sludge dewaterability were investigated in a large-scale WAS anaerobic fermentation project. Performances of VFAs production of sludge pretreated with thermo-NaOH (7.48 ± 0.64 g VFAs/L) and thermo-CaO2 (7.91 ± 0.56 g VFAs/L) were proved to be better than that with thermo-mixed alkali (6.93 ± 0.63 g VFAs/L). Sludge pretreated with thermo-CaO2 presented the best dewaterability and the moisture content of the sludge cake could be reduced to as low as 63.4 ± 4.4% after dewatering by plate-and-frame filter press. Conversely, the dewaterability of sludge pretreated with thermo-NaOH was significantly deteriorated and the VFAs were hard to be recovered. Furthermore, the economic feasibility comparison of thermo-NaOH, thermo-mixed alkali and thermo-CaO2 pretreatments for WAS anaerobic fermentation showed that the net profits were 1.55, 34.44 and 38.69 USD/ton dewatered sludge, respectively. Thermo-mixed alkali and thermo-CaO2 pretreatments are promising pretreatment methods for the wide application of WAS anaerobic fermentation.
This study investigated the effect of microwave combined with biosurfactant alkyl polyglucose (APG) on sludge anaerobic fermentation in a lab-scale sequencing batch reactor. The experimental results showed that microwave combined with APG has a synergistic effect on sludge solubilization and methanogenesis, and that the optimal dosage of APG was 0.32 g g⁻¹ TSS, the SCFA yield was 351.2 mg COD/volatile suspended solids (VSS), which was 4.7-fold of that in blank. In addition, it was found that microwave pretreatment combined with APG can promote the activity of key enzymes, which was beneficial for the accumulation of SCFA. Microbial community analysis showed that the proportion of Firmicutes greatly improved due to the combination of microwave pretreatment and APG, and the percentage of Firmicutes in the microwave pretreatment & APG reactor was 46.5%, which was 3.1- and 1.1-fold of that in microwave pretreatment and APG reactor alone, respectively.
The production and management of sludge in wastewater treatment plants is a significant environmental issue. Sludge is a complex material, treated primarily by biological stabilization methods, i.e., anaerobic and aerobic digestion. However, the presence of complex organics, microbial flocs, extracellular polymeric substances, and various inhibitory compounds, considerably hinders the efficiency of these processes. In order to overcome the effect of these rate-limiting factors, the literature proposes a number of pretreatment technologies, which can be used either as single pretreatment methods, or in combination. The present review describes both the anaerobic and aerobic digestion of sludge, and highlights the issues that limit the efficiency of the process. Emphasis is placed on the potential use of pretreatment methods, including: thermal; ultrasonic; microwave; Fenton; wet oxidation; photocatalysis and some others. These pretreatment approaches demonstrate varying potential for sludge disintegration and solubilization under different circumstances (e.g., operating conditions and sludge composition). However, the ultimate goal is to improve the subsequent biological treatment of sludge. In short durations, thermal, ultrasonic and microwave processes can efficiently solubilize the components of sludge and disrupt the cell walls of microbial flocs. However, issues related to high levels of energy requirements render these processes uneconomical for field application. The Fenton process can be used in combination with either bioleaching or ultrasound. Visible-Photocatalysis pretreatment for sludge can improve the anaerobic treatment of sludge and biogas production, with low energy demand.
Applying low frequency ultrasound could effectively pretreat waste activated sludge (WAS) undergoing anaerobic digestion (AD), because the ultrasound can break up the flocs and cell walls. In this study, we applied ultrasound to three types of biological nitrogen activated sludge in an ice bath. Power densities ranged from 0 to 1.30 W mL−1 and reaction times ranged from 0 to 30 min. The three types of sludge included: short-cut nitrification denitrification sludge (SCND-SBR), complete nitrification denitrification sludge (CND-MUCT), and anaerobic ammonium oxidation sludge (AMX-SHARON). Experiments showed that reductions in average particle size were significantly decreased, due to breakage, at an ultrasonic duration of 10 min with different energy densities. More soluble chemical oxygen demand (SCOD) was detected when the ultrasonic density was higher and the duration was shorter, compared to when the density was lower and the duration was longer. Results suggest that ultrasonic density has a greater impact on the SCOD disintegration degree (DDCOD) as compared to operation time. Soluble proteins (SP) and NH4+N were released during the ultrasound; however, this process does not inhibit the subsequent methanogenic activity during the AD process. The ultrasonic density of 1.04 W mL−1 was the most economic and effective, with the highest efficiency in reducing particle size and releasing SCOD. Therefore, applying ultrasound can accelerate the hydrolysis rate, a rate-limiting factor during AD. This may ultimately reduce treatment construction and operational costs.
Objective:
Although gender differences in smoking have received much attention, few studies have explored the importance of contextual effects on male and female smoking rates. The aim of this study is to examine the association between variations in city-level sex ratios and gender differences in smoking in China.
Methods:
Participants included 16,866 urban residents, who were identified through multi-stage sampling conducted in 21 Chinese cities.
Results:
The study found that, independent of personal characteristics, cities with more males had higher male smoking rates and lower female rates.
Conclusions:
Our research underscores the importance of city-level contextual effects in understanding gender differences in smoking in China.
Effects of peroxymonosulfate (PMS) oxidation on disintegration degree (DD) and extracellular polymeric substances (EPS) properties of waste activated sludge were investigated. A combined approach of fractionation procedure and parallel factor (PARAFAC) analysis was applied to characterize EPS of sludge. Results indicated that PMS oxidation effectively broke sludge particles, resulting in DD in total nitrogen of 39.8% at 10 mg PMS (g SS)-1. After PMS treatment, EPS increased significantly and mostly transferred to slime layer rather than loosely bound EPS (LB-EPS), and the ratio of slime to tightly bound EPS was correlated significantly with PMS dosage. With increasing PMS dosage, polysaccharides in EPS increased, while proteins in EPS and DNA in slime EPS increased firstly and then decreased. PARAFAC analysis of excitation-emission matrix spectra showed that tryptophan-like substances in both slime and LB-EPS were greatly influenced by PMS oxidation, and humic-like fluorophores in slime EPS were positively correlated with PMS dosage.
The effects of sulfate radical oxidation pretreatment on the disintegration of waste activated sludge were investigated at different dosages of peroxymonosulfate (PMS). Indicators for estimating sludge disintegration were selected by analyzing concentrations of released substances and statistical analysis. Results indicated that COD and total phosphorus (TP) were unsuitable for estimating sludge disintegration by oxidants. Pearson correlation analysis indicated that total nitrogen (TN), total organic carbon (TOC), UV254 and polysaccharides had strong correlation with each other, thus suitable for sludge disintegration estimation. Chemical analysis and 3D-EEM fluorescence spectra showed that at high dosage, sulfate radical oxidation was effective for sludge disintegration by inducing aromatic and tryptophan protein-like substances degradation. At PMS dosage of 12mg(g SS)-1, sludge disintegration degrees in TOC and TN were 24.8% and 29.9%, respectively.
In previous publications we reported that by controlling the pH at 10.0 the accumulation of short-chain fatty acids (SCFA) during waste activated sludge (WAS) fermentation was remarkably improved [Yuan, H., Chen, Y., Zhang, H., Jiang, S., Zhou, Q., Gu, G., 2006. Improved bioproduction of short-chain fatty acids (SCFAs) from excess sludge under alkaline conditions. Environ. Sci. Technol. 40, 2025-2029], but significant ammonium nitrogen (NH(4)-N) and soluble ortho-phosphorus (SOP) were released [Chen, Y., Jiang, S., Yuan, H., Zhou, Q., Gu, G., 2007. Hydrolysis and acidification of waste activated sludge at different pHs. Water Res. 41, 683-689]. This paper investigated the simultaneous recovery of NH(4)-N and SOP from WAS alkaline fermentation liquid and the application of the fermentation liquid as an additional carbon source for municipal wastewater biological nitrogen and phosphorus removal. The central composite design (CCD) of the response surface methodology (RSM) was employed to optimize and model the simultaneous NH(4)-N and SOP recovery from WAS alkaline fermentation liquid. Under the optimum conditions, the predicted and experimental recovery efficiency was respectively 73.4 and 75.7% with NH(4)-N, and 82.0 and 83.2% with SOP, which suggested that the developed models described the experiments well. After NH(4)-N and SOP recovery, the alkaline fermentation liquid was added to municipal wastewater, and the influence of volume ratio of fermentation liquid to municipal wastewater (FL/MW) on biological nitrogen and phosphorus removal was investigated. The addition of fermentation liquid didn't significantly affect nitrification. Both SOP and total nitrogen (TN) removal were increased with fermentation liquid, but there was no significant increase at FL/MW greater than 1/35. Compared to the blank test, the removal efficiency of SOP and TN at FL/MW=1/35 was improved from 44.0 to 92.9%, and 63.3 to 83.2%, respectively. The enhancement of phosphorus and nitrogen removal was mainly attributed to the increase of influent SCFA, or rather, the increase of intracellular polyhydroxyalkanoates (PHA) which served as the carbon and energy sources for denitrification and phosphorus uptake. The addition of alkaline fermentation liquid to municipal wastewater, however, increased the effluent COD, which was caused mainly by the increase of influent humic acid, not protein or carbohydrate.
The biosolids accumulation and biodegradation of domestic wastewater treatment plant (DWTP) sludge by filamentous fungi have been investigated in a batch fermenter. The filamentous fungi Aspergillus niger and Penicillium corylophilum isolated from wastewater and DWTP sludge was used to evaluate the treatment performance. The optimized mixed inoculum (A. niger and P. corylophilum) and developed process conditions (co-substrate and its concentration, temperature, initial pH, inoculum size, and aeration and agitation rate) were incorporated to accelerate the DWTP sludge treatment process. The results showed that microbial treatment of higher strength of DWTP sludge (4% w/w of TSS) was highly influenced by the liquid state bioconversion (LSB) process. In developed bioconversion processes, 93.8 g/kg of biosolids was enriched with fungal biomass protein of 30 g/kg. Enrichment of nutrients such as nitrogen (N), phosphorous (P), potassium (K) in biosolids was recorded in 6.2% (w/w), 3.1% (w/w) and 0.15% (w/w) from its initial values of 4.8% (w/w), 2.0% (w/w) and 0.08% (w/w) respectively after 10 days of fungal treatment. The biodegradation results revealed that 98.8% of TSS, 98.2% of TDS, 97.3% of turbidity, 80.2% of soluble protein, 98.8% of reducing sugar and 92.7% of COD in treated DWTP sludge supernatant were removed after 8 days of microbial treatment. The specific resistance to filtration (SRF) in treated sludge (1.4x10(12) m/kg) was decreased tremendously by the microbial treatment of DWTP sludge after 6 days of fermentation compared to untreated sample (85x10(12) m/kg).
The use of photosynthetic microalgae for nutrient removal and biofuel production has been widely discussed. Anaerobic digestion of waste microalgal biomass to produce biogas is a promising technology for bioenergy production. However, the methane yield from this anaerobic process was limited because of the hard cell wall of Chlorella vulgaris. The use of ultrasound has proven to be successful at improving the disintegration and anaerobic biodegradability of Chlorella vulgaris. Ultrasonic pretreatment in the range of 5-200 J ml−1 was applied to waste microalgal biomass, which was then used for batch digestion. Ultrasound techniques were successful and showed higher soluble COD at higher applied energy. During batch digestion, cell disintegration due to ultrasound increased in terms of specific biogas production and the degradation rate. Compared to the untreated sample, the specific biogas production was increased in the ultrasound-treated sample by 90% at an energy dose of 200 J ml−1. For the disintegrated samples, volatile solids reduction was also increased according to the energy input and degradation. These results indicate that the hydrolysis of microalgal cells is the rate-limiting step in the anaerobic digestion of microalgal biomass.
Short chain fatty acids (SCFAs) are value-added products from waste activated sludge (WAS) anaerobic fermentation. The effects of alkaline adjustment, in the range of pH 7–10, on SCFAs accumulation and microbial community of ultrasonic-pretreated WAS at 20 ± 2 °C were investigated in this study. Experimental results indicated that optimum conditions for SCFAs accumulation were pH 9 and fermentation time of 7 days. The changes of protease activity showed that on the initial phase, ultrasonic pretreatment and alkaline adjustment rather than biotic effect was the leading cause of SCFAs improvement at high pHs. DGGE analysis revealed that alkaline adjustment had a strong impact on microbial community. Some bacteria belonged to Firmicutes, Proteobacteria and Bacteroidetes could adapt to high alkaline environments and contribute to proteins and carbohydrates degradation and SCFAs production in the later phase of anaerobic fermentation.
Primary sewage sludge solubilization by Lactobacillus brevis was studied in a 15-L lab-scale anaerobic reactor. L. brevis was inoculated in a low-cost broth medium to optimize strain growth and activity and enhance the medium's usability and economic feasibility over commercial MRS broth. L. brevis was freeze-dried, powdered, and inoculated in the treatment groups, with un-inoculated controls maintained under similar conditions. The effect of the powdered components on primary sewage sludge solubility was examined using an unwashed powdered form (p-type) and a powdered form washed twice with distilled water (w-type). Both inoculants showed maximum solubilization rates of 36.9% and 20.7%, respectively, which were higher than that observed in controls (6.1%). Thus, L. brevis can solubilize sludge without the addition of other soluble substrates. Total volatile fatty acid concentrations (mg COD L−1) were 7990 (AVE: 6800) and 5574 (AVE: 4293) mg L−1 in p-type and w-type reactors, respectively, which were higher than that of controls, i.e., 3333 (AVE: 2393) mg L−1. Real-time polymerase chain reaction showed that L. brevis cell count in anaerobic reactors decreased gradually with time (initial: 107 cells mL−1; day 19: 105 cells mL−1). Nevertheless, a solubilization rate >35% was maintained following a single inoculation of freeze-dried L. brevis.
Anaerobic mesophilic co-digestion of mixed sewage sludge from wastewater treatment plants, WWTP, with crude glycerol, the major byproduct of the biodiesel industry, has been examined using a two-phase digestion process in a semi-continuous CSTR at laboratory scale. The objective was to determine the operational conditions that enhanced biohydrogen and methane production and to evaluate the effect of the organic loading rate (OLR) applied to the process. It was concluded that the Hydraulic Retention Time HRT of the methanogenic stage did not have an important influence on the operational process of co-digestion of sewage sludge and glycerol in terms of efficiency of organic removal and biogas yield. Hence, the results obtained were 73–77% organic matter removal (as CODr) with 0.032 LH2/gCODr and 0.16 LCH4/gCODr when the system operated at OLRs in the range of 15.33–17.90 gCODs/L d with HRTs of 3 days in the acidogenic digester and 6, 8, and 10 days in the methanogenic digester. In terms of volatile solids, the results obtained were 92–88% organic matter removal (as VSr) with 0.20 LH2/gVSr and 1.27 LCH4/gVSr when the system operated at OLRs in the range of 1.94–2.79 gVS/L d.
However, the OLR had an important influence on the H2 and CH4 yields. Hence, the best operational condition was an OLR of 7.82 gCOD/L d, with removal of 93% CODr and hydrogen and methane yields of 0.026 LH2/gCODr and 0.29 LCH4/gCODr, respectively.
In terms of volatile solids, the best operational condition was an OLR of 1.01 gVS/L d, with removal of 89% VSr and hydrogen and methane yields of 0.50 LH2/gVSr and 1.48 LCH4/gVSr, respectively.
Short-chain fatty acids (SCFAs) have been regarded as the excellent carbon source of wastewater biological nutrient removal, and sludge alkaline (pH 10) fermentation has been reported to achieve highly efficient SCFAs production. In this study, the underlying mechanisms for the improved SCFAs production at pH 10 were investigated by using 454 pyrosequencing and fluorescent in situ hybridization (FISH) to analyze the microbial community structures in sludge fermentation reactors. It was found that sludge fermentation at pH 10 increased the abundances of Pseudomonas sp. and Alcaligenes sp., which were able to excrete extracellular proteases and depolymerases, and thus enhanced the hydrolysis of insoluble sludge protein and polyhydroxyalkanoates (PHA). Meanwhile, the abundance of acid-producing bacteria (such as Clostridium sp.) in the reactor of pH 10 was also higher than that of uncontrolled pH, which benefited the acidification of soluble organic substrates. Further study indicated that sludge fermentation at pH 10 significantly decreased the number of methanogenic archaea, resulting in lower SCFAs consumption and lower methane production. Therefore, anaerobic sludge fermentation under alkaline conditions increased the abundances of bacteria involved in sludge hydrolysis and acidification, and decreased the abundance of methanogenic archaea, which favored the competition of bacteria over methanogens and resulted in the efficient production of SCFAs.
Batch tests were carried out to analyze the effect of pH in the range of 7–12 on the hydrolysis and acidification of sludge at room temperature. Ultrasonic pretreatment was conducted to disintegrate waste activated sludge (WAS) and accelerate WAS hydrolysis. The experimental results showed that the sludge with ultrasonic pretreatment was readily degraded in the hydrolysis and acidification process, and more organic substances were released with increase of initial pH. The optimal initial pH for sludge acidification was 11, and the short chain fatty acids (SCFAs) concentration reached about 1751 mg/L after 15 days of hydrolysis and acidification. Phosphorus release was investigated during hydrolysis and acidification at any pH adjustment. The SCFAs mainly consisted of acetic and propionic, accounting for 74.6–84% of total SCFAs. Three microbial species, including Bacteroidetes, γ-proteobacteria, and β-proteobacteria, were involved in different pH environments of the hydrolysis and acidification process, and, simultaneously, the three species were identified as being responsible for SCFAs accumulation and protein degradation. This study indicated that the combination of ultrasonic pretreatment, alkaline adjustment for hydrolysis, and acidification of WAS was an appropriate method for SCFAs accumulation and contributed to the demand of carbon source for WWTPs.
Pre-treatment is used extensively to improve degradability and hydrolysis rate of material being fed into digesters. One emerging process is temperature phased anaerobic digestion (TPAD), which applies a short (2 day) 50–70 °C pre-treatment step prior to 35 °C digestion in the main stage (10–20 days). In this study, we evaluated a thermophilic–mesophilic TPAD against a mesophilic–mesophilic TPAD treating primary sludge. Thermophilic–mesophilic TPAD achieved 54% VS destruction compared to 44% in mesophilic–mesophilic TPAD, with a 25% parallel increase in methane production. Measurements of soluble COD and NH4+-N showed increased hydrolysis extent during thermophilic pre-treatment. Model based analysis indicated the improved performance was due to an increased hydrolysis coefficient rather than an increased inherent degradability, suggesting while TPAD is suitable as an intensification process, a larger main digester could achieve similar impact.
In order to enhance the efficiency of anaerobic digestion, the effects of ultrasonic pretreatment have been studied on waste-activated sludge. Solubilisation of chemical oxygen demand (COD), solid and nitrogen has been proved. Flocs were broken and compounds were made soluble. In the same time, particle size decreased with specific energy applied. In terms of biodegradability, ultrasound led to an increase in biogas production. Moreover, the relationship between biogas production and sludge fractions has been examined. For specific energy input lower than 3000 kJ/kg of total solids, biogas production linked to the particulate fraction of sludge was constant, even if the solids concentration decreased. On the other hand, biogas production linked to the soluble part of sludge increased with ultrasonic power.
Feasibility of high-solid anaerobic digestion of sewage sludge was investigated in single-stage completely stirred tank reactors at 35±1 °C. System stability and the effect of organic loading rate (OLR), sludge retention time (SRT) and total solid (TS) content on the performance of high-solid system was examined. Experimental results showed that, with the concentration of free ammonia nitrogen (FAN) lower than 600 mg l(-1), high-solid anaerobic digestion of sewage sludge could maintain satisfactory stability. Slight, moderate and significant inhibition was found with FAN concentration ranging from 250 to 400, 400 to 600 and 600 to 800 mg l(-1), respectively. The VFA/TA criteria could not foresee system instability in significant ammonia inhibition system by its traditional ratio grades. High-solid system could support higher OLR (4-6 times as high) and obtain similar methane yield and VS reduction as conventional low-solid system at the same SRT, thus reach much higher volumetric methane production rate.
Bacterial population dynamics during the start-up of three lab-scale anaerobic reactors treating different wastewaters, i.e., synthetic glucose wastewater, whey permeate, and liquefied sewage sludge, were assessed using a combination of denaturing gradient gel electrophoresis (DGGE) and real-time PCR techniques. The DGGE results showed that bacterial populations related to Aeromonas spp. and Clostridium sticklandii emerged as common and prominent acidogens in all reactors. Two real-time PCR primer/probe sets targeting Aeromonas or C. sticklandii were developed, and successfully applied to quantitatively investigate their dynamics in relation to changes in reactor performance. Quantitative analysis demonstrated that both Aeromonas- and C. sticklandii-related populations were highly abundant for acidogenic period in all reactors. Aeromonas populations accounted for up to 86.6-95.3% of total bacterial 16S rRNA genes during start-up, suggesting that, given its capability of utilizing carbohydrate, Aeromonas is likely the major acidogen group responsible for the rapid initial fermentation of carbohydrate. C. sticklandii, able to utilize specific amino acids only, occupied up to 8.5-55.2% of total bacterial 16S rRNA genes in the reactors tested. Growth of this population is inferred to be supported, at least in part, by non-substrate amino acid sources like cell debris or extracellular excretions, particularly in the reactor fed on synthetic glucose wastewater with no amino acid source. The quantitative dynamics of the two acidogen groups of interest, together with their putative functions, suggest that Aeromonas and C. sticklandii populations were numerically as well as functionally important in all reactors tested, regardless of the differences in substrate composition. Particularly, the members of Aeromonas supposedly play vital roles in anaerobic digesters treating various substrates under acidogenic, fermentative start-up conditions.
To enhance nutrient removal performance and reduce disposal amount of waste activated sludge (WAS), a pilot-scale continuous system consisting of a 2-step sludge alkaline fermentation process and an A(2)O reactor was proposed. The feasibility of WAS reducing and resourcing by alkaline fermentation was investigated. Volatile fatty acids (VFA) yield was higher under alkaline condition than that under acidic condition. Through 2-step alkaline fermentation, substantial VFA was accumulated, and then elutriated out continuously from an up-flow column by domestic wastewater. The results showed that 38.2% of sludge was hydrolyzed, 19.7% was finally acidified into VFA, and as high as 42.1% of WAS was reduced. Moreover, after introducing the fermentation liquids with higher proportion of acetic acid and propionic acid into the A(2)O reactor, the total nitrogen and phosphorus removal efficiencies reached to 80.1% and 90.0%, respectively. Sludge reduction and enhanced nutrient removal could be achieved simultaneously in the proposed system.
Most of the studies on sewage sludge treatment in literature were conducted for methane generation under acidic or near neutral pH conditions. It was reported in our previous studies that the accumulation of short-chain fatty acids (SCFAs), the preferred carbon source of biological wastewater nutrient removal, was significantly enhanced when sludge was fermented under alkaline conditions, but the optimal pH was temperature-dependent (pH 10 at ambient temperature, pH 9 at mesophilic, and pH 8 at thermophilic), and the maximal SCFAs yields were in the following order: thermophilic pH 8 > mesophilic pH 9 > ambient pH 10 > ambient uncontrolled pH. In this study the kinetic and microbiological features of waste activated sludge fermented in the range of pH 7-10 were investigated to understand the mechanism of remarkably high SCFAs accumulation under alkaline conditions. The developed sludge alkaline fermentation model could be applied to predicate the experimental data in either batch or semicontinuous sludge alkaline fermentation tests, and the relationships among alkaline pH, kinetic parameters, and SCFAs were discussed. Further analyses with fluorescence in situ hybridization (FISH) and PCR-based 16S rRNA gene clone library indicated that both the ratio of bacteria to archaea and the fraction of SCFAs producer accounting for bacteria were in the sequence of thermophilic pH 8 > mesophilic pH 9 > ambient pH 10 > ambient uncontrolled pH, which was in correspondence with the observed order of maximal SCFAs yields.
Microbial community shifts were determined by denaturing gradient gel electrophoresis (DGGE) and real-time PCR for an anaerobic batch digester treating secondary sludge. The batch process was successfully operated with an organic removal efficiency of 35% associated with a 91% decrease in the bacterial 16S rRNA gene concentration. The microbial community structures showed continuous shifts within four bacterial phyla and three archaeal orders. Several bacterial species, such as Fusibacter-related, Clostridium-like, and Syntrophus-like organisms, appeared to be responsible for acidogenesis or syntrophic acid degradation. Both hydrogenotrophic and aceticlastic methanogens appear to have been involved in the methanogenesis with the acidogenic products. The quantitative structure of the methanogenic populations varied continuously, with the growth of Methanomicrobiales and Methanosarcinales in series, to result in a Methanomicrobiales-dominant population. The ordination of microbial community structures demonstrated that the quantitative methanogenic structure converged to the seed inoculum while the bacterial and archaeal DGGE band patterns diverged. These results provide an insight into the microbial behavior in the transitional phase (e.g., a start-up period) of anaerobic sludge digestion.
Microbial community structures were assessed in a two-stage anaerobic digestion system treating food waste-recycling wastewater. The reactors were operated for 390 d at 10 different hydraulic retention times (HRTs) ranging from 25 to 4 d. Stable operation was achieved with the overall chemical oxygen demand (COD) removal efficiency of 73.0-85.9% at organic loading rate of up to 35.6 g COD/L·d. Performance of the acidogenic reactors, however, changed significantly during operation. This change coincided with transition of the bacterial community from one dominated by Aeriscardovia- and Lactobacillus amylovorus-related species to one dominated by Lactobacillus acetotolerans- and Lactobacillus kefiri-like organisms. In methanogenic reactors, the microbial community structures also changed at this stage along with the shift from Methanoculleus- to Methanosarcina-like organisms. This trend was confirmed by the non-metric multidimensional scaling joint plot of microbial shifts along with performance parameters. These results indicated that the overall process performance was relatively stable compared to the dynamic changes in the microbial structures and the acidogenic performance.
Changes in organic matter degradation and microbial communities during thermophilic composting were compared using two different types of anaerobic sludge, one from mesophilic methane fermentation, containing a high concentration of proteins (S-sludge), and the other from thermophilic methane fermentation, containing high concentrations of lipids and fibers (K-sludge). The difference in the organic matter degradation rate corresponded to the difference in the organic matter constituents; the CO(2) evolution rate was greater in the composting of S-sludge than of K-sludge; moreover, the NH(3) evolution resulting from the protein degradation was especially higher in the composting of S-sludge. Then the differences in the microbial communities that contributed to each composting were determined by the PCR-DGGE method. Ureibacillus sp., which is known as a degrader with high organic matter degradation activity, was observed during the composting of S-sludge, whereas Thermobifida fusca, which is a well known thermophilic actinomycete that produces enzymes for lignocellulose degradation, were observed during the composting of K-sludge.
The enzymatic activity of activated sludge was investigated with special emphasis on the localization of the enzymes in the sludge floc matrix. Activated sludge from an advanced activated-sludge treatment plant, performing biological N and P removal, was used. An enzymatic fingerprint was established using a panel of six different enzymes. The fingerprint revealed peptidase as the most dominating specific enzyme tested. By monitoring sludge bulk enzymatic activity over a 3-month period using fluorescein diacetate as an enzyme substrate, considerable variations in activity were observed even over short periods (a few days). The variation in esterase activity was to some extent correlated to the presence of humic compounds in the sludge, but not to the sludge protein content. Comparison of full sludge enzyme activity to the activity of a batch-grown sludge culture indicated that enzymes accumulated in sludge flocs. A large proportion of the exoenzymes were immobilized in the sludge by adsorption in the extracellular polymeric substances (EPS) matrix. This was demonstrated by extraction of EPS from the activated sludge using cation exchange. Contemporary to the release of EPS a very large fraction of the exoenzymes was released into the water. This showed that the exoenzymes should be considered to be an integrated part of the EPS matrix rather than as direct indicators of the microbial activity or biomass.
The pretreatment of waste activated sludge by ultrasonic disintegration was studied in order to improve the anaerobic sludge stabilization. The ultrasound frequency was varied within a range from 41 to 3217 kHz. The impact of different ultrasound intensities and treatment times was examined. Sludge disintegration was most significant at low frequencies. Low-frequency ultrasound creates large cavitation bubbles which upon collapse initiate powerful jet streams exerting strong shear forces in the liquid. The decreasing sludge disintegration efficiency observed at higher frequencies was attributed to smaller cavitation bubbles which do not allow the initiation of such strong shear forces. Short sonication times resulted in sludge floc deagglomeration without the destruction of bacteria cells. Longer sonication brought about the break-up of cell walls, the sludge solids were distintegrated and dissolved organic compounds were released. The anaerobic digestion of waste activated sludge following ultrasonic pretreatment causing microbial cell lysis was significantly improved. There was an increase in the volatile solids degradation as well as an increase in the biogas production. The increase in digestion efficiency was proportional to the degree of sludge disintegration. To a lesser degree the deagglomeration of sludge flocs also augmented the anaerobic volatile solids degradation.
Starch industry wastewater (SWW), slaughterhouse wastewater (SHWW) and secondary sludges from three different wastewater treatment plants (Jonquière--JQS, Communauté Urbaine de Québec--CUQS and Black lake-BLS) were used as raw materials for the production of Bacillus thuringiensis (Bt) based biopesticides in a pilot scale fermentor (100 L working volume). The slaughterhouse wastewater exhibited the lowest Bt growth and entomotoxcity (Tx) potential (measured against spruce budworm) due to low availability of carbon, nitrogen and other nutrients. Performance variation (growth, sporulation, proteolytic activity and Tx potential) within the three types of sludges was directly related to the availability of nitrogen and carbohydrates, which could change with sludge origin and methods employed for its generation. The Tx potential of Bt obtained in different secondary sludges (JQS: 12 x 10(9) SBU/L; CUQS: 13 x 10(9) SBU/L and BLS: 16 x 10(9) SBU/L) and SWW (18 x 10(9) SBU/L) was higher than the soybean based synthetic medium (10 x 10(9) SBU/L). The maximum protease activity was obtained in CUQ secondary sludge (4.1 IU/mL) due to its high complex protein concentration. Nevertheless, high carbohydrate concentration in SWW repressed enzyme production. The secondary sludges and SWW were found to be suitable raw materials for high potency Bt biopesticide production.
The aim of this work was to study the effect of ultra sound treatment on the solid content of sludge and biological activity, and the increase in the soluble chemical oxygen demand (SCOD), proteins and nucleic acids concentrations during sonication. The results showed that sonication effectively degraded and inactivated the sludge. The sludge disintegration and cell lysis occurred continuously while sludge inactivation mainly occurred in the second stage (10-30 min) during sonication. The SCOD, supernatant proteins and nucleic acids concentrations, and sludge mass reduction and inactivation degrees increased with the sonication time and power density increases. Higher energy ultrasound was more efficient than lower energy ultrasound for the sludge treatment.
Laboratory experiments on the activated sludge (AS) process were carried out to investigate the influence of microbial extracellular polymeric substances (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), on biomass flocculation, sludge settlement and dewaterability. The heat EPS extraction method was modified to include a mild step and a harsh step for extracting the LB-EPS and TB-EPS, respectively, from the sludge suspension. Six lab-scale AS reactors were used to grow AS with different carbon sources of glucose and sodium acetate, and different sludge retention times (SRTs) of 5, 10 and 20 days. The variation in the bioreactor condition produced sludge with different abundances of EPS and different flocculation and separation characteristics. The sludge that was fed on glucose had more EPS than the sludge that was fed on acetate. For any of the feeding substrates, the sludge had a nearly consistent TB-EPS value regardless of the SRT, and an LB-EPS content that decreased with the SRT. The acetate-fed sludge performed better than the glucose-fed sludge in terms of bioflocculation, sludge sedimentation and compression, and sludge dewaterability. The sludge flocculation and separation improved considerably as the SRT lengthened. The results demonstrate that the LB-EPS had a negative effect on bioflocculation and sludge-water separation. The parameters for the performance of sludge-water separation were much more closely correlated with the amount of LB-EPS than with the amount of TB-EPS. It is argued that although EPS is essential to sludge floc formation, excessive EPS in the form of LB-EPS could weaken cell attachment and the floc structure, resulting in poor bioflocculation, greater cell erosion and retarded sludge-water separation.
The effect of pH from 4.0 to 11.0 on the hydrolysis and acidification of waste activated sludge (WAS) was investigated. Experimental results showed that at room temperature the sludge hydrolysis was in the following order: alkaline>acidic>(neutral and blank test), and between pH 6.0 and 11.0 the sludge hydrolysis increased with pH. The three main components, soluble protein, carbohydrate and volatile fatty acids (VFAs) in the hydrolytic product were analyzed. It was observed that both the soluble protein and carbohydrate increased with pH in the pH range 7.0-11.0, but also increased to a smaller extent with pH from 7.0 to 4.0. The VFAs concentration was also affected by pH. Under alkaline conditions, the VFAs production was significantly higher than under other conditions. The concentration of VFAs on the 8th day of fermentation at pH 4.0, 7.0 and 10.0 was, respectively, 354.49, 842.00 and 2708.02 mg/L, while VFAs in the blank test was only 633.59 mg/L. The VFAs consisted of acetic, propionic, iso-butyric, n-butyric, iso-valeric and n-valeric acids, but acetic, propionic and iso-valeric were the three main products. Also, the release of soluble phosphorus and ammonia and the production of methane was studied during WAS fermentation at different pHs.
The high sequence identity among the Mycobacterium bovis and Mycobacterium tuberculosis genomes contrasts with the physiological differences reported between these pathogens, suggesting that variations in gene expression may be involved. In this study, microarray hybridization was used to compare the total transcriptome of M. bovis and M. tuberculosis, during the exponential phase of growth. Differential expression was detected in 258 genes, representing a 6% of the total genome. Variable genes were grouped according to functional categories. The main variations were found in genes encoding proteins involved in intermediary metabolism and respiration, cell wall processes, and hypothetical proteins. It is noteworthy that, compared to M. tuberculosis, the expression of a higher number of transcriptional regulators were detected in M. bovis. Likewise, in M. tuberculosis we found a higher expression of the PE/PPE genes, some of which code for cell wall related proteins. Also, in both pathogens we detected the expression of a number of genes not annotated in the M. tuberculosis H37Rv or M. bovis 2122 genomes, but annotated in the M. tuberculosis CDC1551 genome. Our results provide new evidence concerning differences in gene expression between both pathogens, and confirm previous hypotheses inferred from genome comparisons and proteome analysis. This study may shed some new light on our understanding of the mechanisms relating to differences in gene expression and pathogenicity in mycobacteria.
The study was undertaken to evaluate the effect of pH and temperature control on the generation of soluble fermentation products from primary sludge. The effect was tested by running parallel experiments under pH and temperature controlled and uncontrolled conditions. In fermentation experiments conducted at 20 degrees C without pH control, the average soluble COD release was 14 mg per liter of wastewater treated, representing a potential increase of 5% in the biodegradable COD content of the primary sedimentation effluent. The corresponding average VFA generation was 9.2mg COD l(-1). The nutrient release was practically negligible and stayed at 0.4 mg l(-1) for nitrogen and 0.1mg l(-1) for phosphorus. Acetic acid accounted more than 45% of the generated VFA in all experimental runs. The acetic acid content of the VFA decreased with increasing initial VSS concentrations and higher pH levels. VFA generation by fermentation was significantly affected with temperature and pH control. Temperature change between 10 and 24 degrees C induced a five-fold increase in VFA generation, from 610 mg l(-1) at 10 degrees C to 2950 mg l(-1) at 24 degrees C.