Anaerobic Sequencing Batch Reactor Research Articles

High-rate volatile fatty acid (VFA) production by a granular sludge process at low pH.

Volatile fatty acids (VFA) are proposed platform molecules for the production of basic chemicals and polymers from organic waste streams. In this study we developed a granular sludge process to produce VFA at high rate, yield and purity while minimizing potential operational costs. A lab-scale anaerobic sequencing batch reactor (ASBR) was fed with 10 g l(-1) glucose as model substrate. Inclusion of a short (2 min) settling phase before effluent discharge enabled effective granulation and very high volumetric conversion rates of 150-300 gCOD l(-1) d(-1) were observed during glucose conversion. The product spectrum remained similar at the tested pH range with acetate and butyrate as the main products, and a total VFA yield of 60-70% on chemical oxygen demand (COD) basis. The requirement for base addition for pH regulation could be reduced from 1.1 to 0.6 mol OH(-) (mol glucose)(-1) by lowering the pH from 5.5 to 4.5. Solids concentrations in the effluent were 0.6 ± 0.3 g l(-1) but could be reduced to 0.02 ± 0.01 g l(-1) by introduction of an additional settling period of 5 min. The efficient production of VFA at low pH with a virtually solid-free effluent increases the economic feasibility of waste-based chemicals and polymer production. Biotechnol.

Anaerobic granular reactors for the treatment of dairy wastewater: A review

Considerable research has been conducted on the treatment of dairy wastewater by anaerobic granular reactors. Upflow anaerobic sludge blanket (UASB) reactors, anaerobic sequencing batch reactors (ASBR) and static granular bed reactors (SGBR) are the conventional granular reactor types most commonly applied in dairy wastewater treatment. Hybrid systems have also been developed to increase treatment efficiency and overcome the operational problems associated with the treatment of this substrate. Effects of parameters including temperature, organic loading and operating protocols on the performance of granular reactors are summarised. Individual and hybrid granular reactors are evaluated based on organic matter removal and methane production capacity.

Biodegradation and reversible inhibitory impact of sulfamethoxazole on the utilization of volatile fatty acids during anaerobic treatment of pharmaceutical industry wastewater

This study evaluated the chronic impact and biodegradability of sulfamethoxazole under anaerobic conditions. For this purpose, a lab-scale anaerobic sequencing batch reactor was operated in a sequence of different phases with gradually increasing sulfamethoxazole doses of 1 to 45mg/L. Conventional parameters, such as COD, VFA, and methane generation, were monitored with corresponding antimicrobial concentrations in the reactor and the methanogenic activity of the sludge. The results revealed that anaerobic treatment was suitable for pharmaceutical industry wastewater with concentrations of up to 40mg/L of sulfamethoxazole. Higher levels exerted toxic effects on the microbial community under anaerobic conditions, causing the inhibition of substrate/COD utilization and biogas generation and leading to a total collapse of the reactor. The adverse long-term impact was quite variable for fermentative bacteria and methanogenic achaea fractions of the microbial community based on changes inflicted on the composition of the residual organic substrate and mRNA expression of the key enzymes.

Ecological significance of Synergistetes in the biological treatment of tuna cooking wastewater by an anaerobic sequencing batch reactor.

Lab-scale 2L-anaerobic sequencing batch reactor was operated under mesothermic conditions. The degradation of protein-rich organic matter was determined by chemical oxygen demand, biogas production, and protein-removal activity over the operation. The structure of the microbial community was determined by qPCR and next-generation sequencing on 16S rRNA genes. At the steady state, a very efficient removal of protein (92%) was observed. Our results demonstrate a decrease of archaeal and bacterial abundance over time. Members of the phylum Synergistetes, with a peculiar emphasis for those pertaining to families Dethiosulfovibrionaceae and Aminiphilaceae, are of major ecological significance regarding the treatment of this industrial wastewater. The prominent role to be played by members of the phylum Synergistetes regarding protein and/or amino acid degradation is discussed.

Harnessing dark fermentative hydrogen from pretreated mixture of food waste and sewage sludge under sequencing batch mode.

Food waste and sewage sludge are the most abundant and problematic organic wastes in any society. Mixture of these two wastes may provide appropriate substrate condition for dark fermentative biohydrogen production based on synergistic mutual benefits. This work evaluates continuous hydrogen production from the cosubstrate of food waste and sewage sludge to verify mechanisms of performance improvement in anaerobic sequencing batch reactors. Volatile solid concentration and mixing ratio of food waste and sludge were adjusted to 5% and 80:20, respectively. Five different hydraulic retention times (HRT) of 36, 42, 48, 72, and 108h were tested using anaerobic sequencing batch reactors to find out optimal operating condition. Results show that the best performance was achieved at HRT 72h, where the hydrogen yield, the hydrogen production rate, and hydrogen content were 62.0mL H2/g VS, 1.0L H2/L/day, and ~50%, respectively. Sufficient solid retention time (143h) and proper loading rate (8.2g COD/L/day as carbohydrate) at HRT 72h led to the enhanced performance with better hydrogen production showing appropriate n-butyrate/acetate (B/A) ratio of 2.6. Analytical result of terminal-restriction fragment length polymorphism revealed that specific peaks associated with Clostridium sp. and Bacillus sp. were strongly related to enhanced hydrogen production from the cosubstrate of food waste and sewage sludge.

Development of antibiotic resistance genes in microbial communities during long-term operation of anaerobic reactors in the treatment of pharmaceutical wastewater

Biological treatment processes offer the ideal conditions in which a high diversity of microorganisms can grow and develop. The wastewater produced during these processes is contaminated with antibiotics and, as such, they provide the ideal setting for the acquisition and proliferation of antibiotic resistance genes (ARGs). This research investigated the occurrence and variation in the ARGs found during the one-year operation of the anaerobic sequencing batch reactors (SBRs) used to treat pharmaceutical wastewater that contained combinations of sulfamethoxazole-tetracycline-erythromycin (STE) and sulfamethoxazole-tetracycline (ST). The existence of eighteen ARGs encoding resistance to sulfamethoxazole (sul1, sul2, sul3), erythromycin (ermA, ermF, ermB, msrA, ereA), tetracycline (tetA, tetB, tetC, tetD, tetE, tetM, tetS, tetQ, tetW, tetX) and class Ι integron gene (intΙ 1) in the STE and ST reactors was investigated by quantitative real-time PCR. Due to the limited availability of primers to detect ARGs, Illumina sequencing was also performed on the sludge and effluent of the STE and ST reactors. Although there was good reactor performance in the SBRs, which corresponds to min 80% COD removal efficiency, tetA, tetB, sul1, sul2 and ermB genes were among those ARGs detected in the effluent from STE and ST reactors. A comparison of the ARGs acquired from the STE and ST reactors revealed that the effluent from the STE reactor had a higher number of ARGs than that from the ST reactor; this could be due to the synergistic effects of erythromycin. According to the expression of genes results, microorganisms achieve tetracycline and erythromycin resistance through a combination of three mechanisms: efflux pumping protein, modification of the antibiotic target and modifying enzymes. There was also a significant association between the presence of the class 1 integron and sulfamethoxazole resistance genes.

Use of PCR-DGGE based molecular methods to assessment of microbial diversity during anaerobic treatment of antibiotic combinations

As it is currently often not know how anaerobic bioreactors, e.g. for biogas production, react if the substrate is contaminated by toxic compounds like antibiotics. This study evaluated how anaerobic sequencing batch reactors were affected by amendments of different antibiotics and stepwise increasing concentrations. The compositions of microbial community were determined in the seed sludge using 16S rRNA gene clone libraries and PCR-DGGE analyses were used for the detection of microbial community changes upon antibiotics additions. According to PCR-DGGE results, the syntrophic interaction of acetogens and methanogens is critical to the performance of the reactors. Failure to maintain the stability of these microorganisms resulted in a decrease in the performance and stability of the anaerobic reactors. Assessment of DGGE data is also useful for suggesting the potential to control ultimate microbial community structure, especially derived from Gram-negative bacteria, through bioaugmentation to successful for antibiotic biodegradation.

BIOHYDROGEN FROM CHEESE WHEY TREATMENT IN AN AnSBBR: ACHIEVING PROCESS STABILITY

An AnSBBR (anaerobic sequencing batch reactor containing biomass immobilized on an inert support) with liquid phase recirculation, containing a 3.5 L working volume, treated 1.5 L of cheese whey wastewater in 3 and 4 h cycles at 30 oC to produce biohydrogen. From startup the bioreactor presented process instability. To overcome this problem the following measures were taken, however without success: adaptation of the biomass with uncontaminated easily degradable substrates, pH control at very low levels, and a different form of inoculation (natural fermentation of the feed medium). The problem was solved by cooling the feed medium to 4 oC to prevent acidification in the storage container, by eliminating nutrient supplementation to prevent possible formation of H2S by sulfate-reducing bacteria and by periodic washing of the support material to improve the food/microorganism ratio. Hence, stable hydrogen production could be achieved with minimal presence of methane (36% H2; 62% CO2; 2% CH4) and the AnSBBR fed with cheese whey (influent concentration of 4070 mgCOD.L-1 and 3240 mgCarbohydrate.L-1 and applied volumetric organic loading of 14.6 gCOD.L-1.d-1) presented improved productivity and yield indicators compared to pure lactose and other reactor configurations, reaching values of 420 NmLH2.L-1.d-1 and 0.60 molH2.molCarbohydrate-1 in the steady-state phase (conversions of carbohydrates and COD were 98% and 30%, respectively).

Evaluation of the microbial diversity in sequencing batch reactor treating linear alkylbenzene sulfonate under denitrifying and mesophilic conditions using swine sludge as inoculum

The objective of this study was to evaluate the degradation of Linear Alkylbenzene Sulfonate (LAS) in anaerobic sequencing batch reactor (ASBR) under denitrifying conditions using swine sludge as inoculum. The reactor was operated for 104 days with synthetic substrate containing nitrate, and LAS was added later (22 mg/L). Considering the added mass of the LAS, the adsorbed mass in the sludge and discarded along with the effluent, degradation of the surfactant at the end of operation was 87%, removal of chemical oxygen demand was 86% and nitrate was 98%. The bacterial community was evaluated by cutting the bands and sequencing of polymerase chain reaction (PCR) fragments and denaturing gradient gel electrophoresis (DGGE). The sequences obtained were related to the phylum Proteobacteria and the alpha-and beta-proteobacteria classes, these bacteria were probably involved in the degradation of LAS. The efficiently degraded LAS in the reactor was operated in batch sequences in denitrifying conditions.

INFLUENCE OF INTERFACIAL FORCES ON THE MIXTURE PREDICTION OF AN ANAEROBIC SEQUENCING BATCH REACTOR (ASBR)

In the operation of bioreactors, the fluid movement promotes mixing between sludge and substrate. The dynamics of this system are complex, and the interaction between the phases is difficult to evaluate accurately. In this work, Computational Fluid Dynamics is applied to simulate a pilot-scale anaerobic sequencing batch reactor, using a three-dimensional, transient and multiphase modeling. Several correlations were applied to estimate the interfacial forces. Results indicate that the use of different coefficients for the drag and lift forces strongly affects the predicted turbulent kinetic energy, and thus the mixture estimation in the bioreactor. The use of the drag as the only interfacial force provided an average turbulent kinetic energy close to the value found using a more complete model. However, the absence of lift and virtual mass forces had a significant impact on the resulting turbulence distribution.

Investigation of anaerobic biodegradability of real compost leachate emphasis on biogas harvesting

Anaerobic treatability of real compost leachate was assessed using laboratory-scale anaerobic sequencing batch reactor at mesophilic conditions. Interventional study was conducted at wide range of organic loading rate 0.93–25 g l−1 day−1 by varying hydraulic retention times 23 and 12 h. Initial chemical oxygen demand (COD) was 1.85–25 g l−1. pH variations; total, soluble (SCOD), readily biodegradable (rbCOD) chemical oxygen demand; volatile fatty acids degradation; biogas production; and methane fraction were considered in this study. The organic matter removal efficiencies were in the range of 76–81 % depending on loading rates applied. The maximum volumetric methane production rate of 5.7 l CH4 l−1 day−1 was achieved at the loading rate of 19.65 g l−1 day−1. About 85 % of removed organic matters during the biodegradation were converted to the methane. The results have shown that the anaerobic batch reactor could be an appealing option for changing compost leachate into the useable products such as biogas and other energy-rich compounds, which may play a serious role in meeting the world’s ever-increasing energy requirements in the future.

Biohydrogen from food waste in a discontinuous process: Effect of HRT and microbial community analysis

There are several parameters that affect the hydrogen (H2) production when using organic solid waste in a discontinuous process, such as the hydraulic retention time (HRT). To optimize the process, it is necessary to determine the HRT such that the H2 production is maximized. The objective of this study is to evaluate the effect of different HRTs on the hydrogen production in an anaerobic sequencing batch reactor (ASBR) using food waste as the substrate. The microbial community was analyzed and correlated with the reactor performance. The results showed that the highest percentage of H2 in biogas, maximum volumetric H2 production, and maximum H2 production rate was obtained with an HRT of 24 h. The percentage of H2 in biogas varied from 22 to 53%, which depended on the HRT. Acetic acid was the main volatile fatty acid obtained. The highest propionic acid production was observed with an HRT of 6 h, which was related to a decrease in H2 generation, where a low diversity and low evenness were obtained compared with those of the reactor samples obtained from different HRTs. The genus Megasphaera was found to be the dominant genus in the microbial community.

Digester performance and microbial community changes in thermophilic and mesophilic sequencing batch reactors fed with the fine sieved fraction of municipal sewage

This study investigates the start-up and operation of bench-scale mesophilic (35 °C) and thermophilic (55 °C) anaerobic sequencing batch reactor (SBR) digesters treating the fine sieved fraction (FSF) from raw municipal sewage. FSF was sequestered from raw municipal wastewater, in the Netherlands, using a rotating belt filter equipped with a 350 micron mesh. For the given wastewater, the major component of FSF was toilet paper, which is estimated to be 10–14 kg per year per average person in the western European countries. A seven months adaptation time was allowed for the thermophilic and mesophilic digesters in order to adapt to FSF as the sole substrate with varying dry solids content of 10–25%. Different SBR cycle durations (14, 9 and 2 days) were applied for both temperature conditions to study methane production rates, volatile fatty acids (VFAs) dynamics, lag phases, as well as changes in microbial communities. The prevailing sludge in the two digesters consisted of very different bacterial and archaeal communities, with OP9 lineage and Methanothermobacter being pre-dominant in the thermophilic digester and Bacteroides and Methanosaeta dominating the mesophilic one. Eventually, decreasing the SBR cycle period, thus increasing the FSF load, resulted in improved digester performances, particularly with regard to the thermophilic digester, i.e. shortened lag phases following the batch feedings, and reduced VFA peaks. Over time, the thermophilic digester outperformed the mesophilic one with 15% increased volatile solids (VS) destruction, irrespective to lower species diversity found at high temperature.

Investigation of intertidal wetland sediment as a novel inoculation source for anaerobic saline wastewater treatment.

Biological treatment of saline wastewater is considered unfavorable due to salinity inhibition on microbial activity. In this study, intertidal wetland sediment (IWS) collected from a high saline environment was investigated as a novel inoculation source for anaerobic treatment of saline pharmaceutical wastewater. Two parallel lab-scale anaerobic sequencing batch reactors (AnSBR) were set up to compare the organic removal potential of IWS with conventional anaerobic digested sludge (ADS). Under steady-state condition, IWS reactor (R(i)) showed organic reduction performance significantly superior to that of ADS reactor (R(a)), achieving COD removal efficiency of 71.4 ± 3.7 and 32.3 ± 6.1%, respectively. In addition, as revealed by fluorescent in situ hybridization (FISH) analysis, a higher relative abundance of methanogenic populations was detected in R(i). A further 16S rRNA gene pyrosequencing test was conducted to understand both the bacterial and archaeal community populations in the two AnSBRs. A predominance of halophilic/tolerant microorganisms (class Clostridia of bacteria, genera Methanosarcina, and Methanohalophilus of archaea) in R(i) enhanced its organic removal efficiency. Moreover, several microbial groups related with degradation of hardly biodegradable compounds (PAHs, n-alkenes, aliphatic hydrocarbons, and alkanes, etc.) were detected in the IWS. All these findings indicated that IWS is a promising inoculation source for anaerobic treatment of saline wastewater.

Effects of manipulating cyclic duration and pH on fermentative hydrogen production in an anaerobic sequencing batch reactor

The effects of cyclic duration and pH on biological hydrogen production were investigated in an anaerobic sequencing batch reactor. Experiments were conducted using cyclic duration of (4, 8, and 12 h) in combination with pH (4, 5, and 6) in a 3 × 3 factorial design, while hydraulic retention time and organic loading rate were maintained at 24 h and 10.3 g COD L−1.d−1, respectively. At pH 4, the effect of cyclic duration on hydrogen production was found to be insignificant. However, in runs with pH 5 and 6, a shorter cyclic duration of 4 h led to lower hydrogen productivity. The operational condition (pH 6, cyclic duration 12 h) induced higher hydrogen production rate of 2.3 ± 0.6 L H2/L reactor.d, whereas higher hydrogen yield of 2.2 ± 0.4 mol H2/mol sucrose was achieved at pH 5 and the same 12 h cyclic duration. The differences in hydrogen production were not statistically significant between 8 h and 12 h cyclic duration. Higher hydrogen production rates were associated with biomass (mixed liquor volatile suspended solids) concentration ranging from 8–13 g L−1, but further increase in biomass growth was not accompanied by increased hydrogen production. Furthermore, a food-to-microorganism ratio of 0.84 was found to result in higher hydrogen production rate.

Influence of Organic Load on Biohydrogen Production in an AnSBBR Treating Glucose-Based Wastewater.

An anaerobic sequencing batch reactor with immobilized biomass (AnSBBR) was applied to the production of biohydrogen treating a glucose-based wastewater. The influence of the applied volumetric organic load was studied by varying the concentration of influent at 3600 and 5250mg chemical oxygen demand (COD) L(-1) and cycle lengths of 4, 3, and 2h resulting in volumetric organic loads of 10.5 to 31.1g CODL(-1). The results revealed system stability in the production of biohydrogen and substrate consumption. The best performance was an organic removal (COD) of 24% and carbohydrate removal (glucose) of 99%. Volumetric and specific molar productivity were 60.9molH2 m(-3)day(-1) and 5.8molH2 kg SVT(-1)day(-1) (biogas containing 40% H2 and no CH4) at 20.0g CODL(-1)day(-1) (5250mg CODL(-1) and 3h). The yield between produced hydrogen and removed organic matter in terms of carbohydrates was 0.94molH2 Mol GLU(-1) (biogas containing 52% H2 and no CH4) at 10.5g CODL(-1)day(-1) (3600mg CODL(-1) and 4h), corresponding to 23 and 47% of the theoretical values of the acetic and butyric acid metabolic routes, respectively. Metabolites present at significant amounts were ethanol, acetic acid, and butyric acid. The conditions with higher influent concentration and intermediate cycle length, and the condition with lower influent concentration and longer cycle showed the best results in terms of productivity and yield, respectively. This indicates that the best productivity tends to occur at higher organic loads, as this parameter involves the biogas production, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter also involves substrate consumption.

Biohydrogen production from lactose: influence of substrate and nitrogen concentration

Hydrogen produced from renewable sources may be considered the energy vector of the future. However, reducing process costs is imperative in order to achieve this goal. In the present research, the effect of nitrogen (N), initial pH and substrate content for starting up the dark fermentative process was studied using the response surface methodology. Anaerobic digested dried sludge (biosolid pellets) was used as the inoculum. Synthetic wastewater was used as the substrate in batch reactors. A decrease in H2 production was observed with the increase in N and lactose concentrations. This drop was considerably greater when the concentration of lactose was at its lower level. Although the increase in lactose concentration results in a lower H2 production, the effect of N on the response is attenuated at higher levels of lactose. On the other hand, the effect of initial pH on the fermentation system was not significant. The evaluation on the process under semi-continuous conditions was performed using anaerobic sequencing batch reactors (ASBRs). The process was evaluated at different C/N ratios using synthetic wastewater. Results showed higher hydrogen yields with the gradual decrease in nitrogen content. The addition of cheese whey to the ASBR resulted in a H2 production rate of 0.18 L H2 L−1 d−1.

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Microbial community structure associated with treatment of azo dye in a start-up anaerobic sequenced batch reactor

The start-up efficiency of an anaerobic sequencing batch reactor (ASBR) fed with increasing methyl orange (MO) concentrations (from 25 mg l−1 to 500 mg l−1) were investigated in this study. The relationship between MO decolorization capacity and the microbial community structure was evaluated. More than 85% of COD and 75% of MO were removed during the whole operation period. However, little methane was generated, due to the successful competition of azo reduction over sulfate reduction and methanogenesis. The scanning electron microscopy and denaturing gradient gel electrophoresis analysis showed a significant variation of the microbial community composition with MO concentration increase. The thresholds of structural and functional disturbances were similar, suggesting a good correlation between degradation performance and community structure. Phylogenetic analysis indicated that Sulfuricurvum and Anaerolineaceae family were the most abundant microorganisms in ASBR responsible for MO decolorization. Batch experiments indicated that acclimated sludge could also use quinoide and Fe(III) as the electron acceptors, thus allowing an efficient reduction of azo dye.

Inhibitory effect of erythromycin, tetracycline and sulfamethoxazole antibiotics on anaerobic treatment of a pharmaceutical wastewater.

Pharmaceuticals enter ecosystems, which causes changes to microbial community structure and development of resistant genes. Anaerobic treatments can be an alternative application for treatment of pharmaceutical wastewaters, which has high organic content. This study aims to develop an understanding of the effects of sulfamethoxazole-erythromycin-tetracycline (ETS), sulfamethoxazole-tetracycline (ST), erythromycin-sulfamethoxazole (ES) and erythromycin-tetracycline (ET) combinations on the anaerobic treatment of pharmaceutical industry wastewater. The results of this investigation revealed that bacteria have a competitive advantage over archaea under all antibiotic combinations. The ET reactor showed a better performance compared to other reactors; this could be due to antagonistic effects of sulfamethoxazole. Acute inhibition in the microbial community was also strongly affected by antibiotics concentrations. This indicated that the composition of the microbial community changed in association with anaerobic sequencing batch reactor performances. The results of this research support the idea that an acute test could be used to control and improve the anaerobic treatment system.