Search

Anaerobic co-digestion (AcoD) may be an interesting option to improve the operating conditions of anaerobic reactors used in vinasse treatment and provide an alternative for dairy cattle wastewater (DCW) management in regions near to ethanol industries. This work aimed to evaluate the effect of AcoD of sugarcane vinasse with DCW (84.8% and 15.2% of COD, respectively) in two up-flow anaerobic sludge blanket reactors (UASB—R1 and R2) in series. The improvements in the nutritional conditions of the vinasse because of the co-digestion with the DCW, combined with effluent recirculation, provided average removals of total COD of 77% for the overall system (R1 + R2) and volumetric methane production of 0.451 m3 CH4 (m3 d)−1 for R1. From the theoretical potential of electrical power production, we verified the possibility of producing 10.65 kWh d−1 per m3 of vinasse in the UASB reactors. That is 39% of the electrical energy needed to process one ton of sugarcane. Therefore, anaerobic co-digestion is an attractive alternative for energy use and reducing environmental problems of vinasse and DCW. [ABSTRACT FROM AUTHOR]

This paper aims to study dark fermentation (DF) in an upflow anaerobic sludge blanket (UASB) reactor during 20 cycles operating at different hydraulic retention times (HRTs) of 3, 9, and 12 h using substrate wastewater from the food industry and granular inoculum sludge from a treatment plant as codigestion to explore the relationship between substrates, metabolites, and microorganisms to increase the biohydrogen (BioH2) yield. Operation conditions were constant pH 5.50 ± 0.50, T = 35 °C and a carbon-to-nitrogen (C/N) ratio of 30. It is noteworthy that DF with HRT = 9 h obtained the highest yields of organic matter degradation, and BioH2 in biogas (~60%) was attributed to the adjustment of pH and the codigestion buffer capacity. During DF with HRT = 9, the reactor was 11 times more productive with regards to HRT = 3 h, resulting in its performance with a better yield mean (6.22 mmol H2 g COD−1) and productivity (0.35 LH2 L−1 d) than other HRTs with lower records of 0.42 mmol H2 g COD−1 and 0.05 LH2 L−1 d, respectively. The high abundance of native populations (Lactobacillus and Lactococcus) and intrinsic inoculum (Citrobacter) led to the highest BioH2 production. Most of the production of acetic acid ~590 mg L−1 and butyric acid ~450 mg L−1 confirmed that BioH2 is mainly produced by acetic and butyric metabolic routes, and a direct relation with the percentage of retention of total suspended solids was also found, supporting the biodegradation capacity of the process. [ABSTRACT FROM AUTHOR]

This research investigates the efficacy of a high-performance pilot-scale Internal Circulation Anaerobic Reactor inoculated with Granular Sludge (ICAGSR) for treating cattle slaughterhouse wastewater while concurrently generating biogas. The primary objective is to assess the efficiency and performance of ICAGSR in terms of organic pollutant removal and biogas production using granular anaerobic sludge. The research methodology entails operating the ICAGSR system under ambient conditions and systematically varying key parameters, including different Hydraulic Retention Times (HRTs) (24, 12, and 8 h) and Organic Loading Rates (OLRs) (3.3, 6.14, and 12.83 kg COD/m³. d). The study focuses on evaluating pollutants' removal and biogas production rates. Results reveal that the ICAGSR system achieves exceptional removal efficiency for organic pollutants, with Chemical Oxygen Demand (COD) removal exceeding 74%, 67%, and 68% at HRTs of 24, 12, and 8 h, respectively. Furthermore, the system demonstrates stable and sustainable biogas production, maintaining average methane contents of 80%, 76%, and 72% throughout the experimental period. The successful operation of the ICAGSR system underscores its potential as a viable technology for treating cattle slaughterhouse wastewater and generating renewable biogas. In conclusion, this study contributes to wastewater treatment and renewable energy production by providing a comprehensive analysis of the ICAGSR system's hydrodynamic properties. The research enhances our understanding of the system's performance optimization under varying conditions, emphasizing the benefits of utilizing ICAGSR reactors with granular sludge as an effective and sustainable approach. Identifying current gaps, future research directions aim to further refine and broaden the application of ICAGSR technology in wastewater treatment and renewable energy initiatives. [ABSTRACT FROM AUTHOR]

Biowaste fermentation is a promising technology for low‐carbon print bioenergy and biochemical production. Although it is believed that the microbiome determines both the fermentation efficiency and the product profiles of biowastes, the explicit mechanisms of how microbial activity controls fermentation processes remained to be unexplored. The current study investigated the microbiome dynamics and fermentation product profiles of biowaste fermentation under different organic loads (5, 20, and 40 g‐VS/L) and with additives that potentially modulate the fermentation process via methanogenesis inhibition (2‐bromoethanesulfonate) or electron transfer promotion (i.e., reduced iron, magnetite iron, and activated carbon). The overall fermentation products yields were 440, 373 and 208 CH4‐eq/g‐VS for low‐, medium‐ and high‐load fermentation. For low‐ and medium‐load fermentation, volatile fatty acids (VFAs) were first accumulated and were gradually converted to methane. For high‐load fermentation, VFAs were the main fermentation products during the entire fermentation period, accounting for 62% of all products. 16S rRNA‐based analyses showed that both 2‐bromoethanesulfonate addition and increase of organic loads inhibited the activity of methanogens and promoted the activity of distinct VFA‐producing bacterial microbiomes. Moreover, the addition of activated carbon promoted the activity of H2‐producing Bacteroides, homoacetogenic Eubacteriaceae and methanogenic Methanosarcinaceae, whose activity dynamics during the fermentation led to changes in acetate and methane production. The current results unveiled mechanisms of microbiome activity dynamics shaping the biowaste fermentation product profiles and provided the fundamental basis for the development of microbiome‐guided engineering approaches to modulate biowaste fermentation toward high‐value product recovery. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel combination of X-ray tomography with elemental and crystalline composition. • 3D view of microstructure and phosphate distribution based on the X-ray attenuation. • Phosphates comprised 7–17 vol% of slag particle volume. • Porosity of 15–35 vol% for slag particles from combustion of sewage sludge mixtures. The purpose of this study was to provide detailed knowledge of the morphological properties of ash particles, including the volumetric fractions and 3D distributions of phosphates that lay within them. The ash particles came from digested sewage sludge co-combusted with K- and Si-rich wheat straw or K-rich sunflower husks. X-ray micro-tomography were combined with elemental composition and crystalline phase information to analyse the ash particles in 3D. Analyses of differences in the X-ray attenuation enabled calculation of 3D phosphate distributions that showed high heterogeneity in the slag particles. This is underscored by a distinct absence of phosphates in iron-rich and silicon-rich parts. The slag from silicate-based wheat straw mixtures had lower average attenuation than that from sunflower husks mixtures, which contained more calcium. Calculated shares of phosphates between 7 and 17 vol% were obtained, where the highest value for a single assigned phosphate was observed in hard slag from wheat straw with 10 % sewage sludge. The porosity was notably higher for particles from pure wheat straw combustion (62 vol%), compared to the other samples (15–35 vol%). A high open pore volume fraction (60–97 vol%) indicates that a large part of the pores can be accessed by the surroundings. For all samples, more than 60 % of the discrete (closed) pores had an equivalent diameter < 30 μm, while the largest volume fraction consisted of pores with an equivalent diameter > 75 μm. Slag from sunflower husk mixtures had larger pore volumes and a greater relative number of discrete pores >75 µm compared to wheat straw mixtures. [ABSTRACT FROM AUTHOR]

Brewery (BW) and dairy (DW) wastewater are two types of agro-industrial wastewater that are generated in large amounts and, therefore, should be treated effectively and in an environmentally beneficial manner. Both these wastewater types are characterized by a high COD, BOD5, and nutrient content, and conventional wastewater treatment methods such as an activated sludge process may prove to be inefficient due to the possibility of foaming, large biomass production, low activity at low temperatures, and risk of overloading the reactor with a load of organic pollutants. In the context of the described difficulties, anaerobic processes seem to be the best alternative. An interesting research area is the co-digestion of these wastewaters. However, this research direction, so far, has not been frequently reported. Given the gap in the current knowledge, this literature review aims to assess the possibility of BW and DW digestion in anaerobic reactors and provide up-to-date data on the post-treatment methods of effluent generated after the anaerobic digestion process. Despite numerous advantages, anaerobic treatment often requires post-effluent treatment to complete the treatment cycle. [ABSTRACT FROM AUTHOR]

The current investigation delved into the utilization of cattle and municipal sanitary inocula for anaerobic digestion of poultry wastes, addressing a crucial and pragmatic challenge in waste management. The emphasis on poultry waste is pertinent due to its well-documented impediments in anaerobic digestion, attributed to heightened levels of ammonia and volatile fatty acids (VFAs). The strategic selection of cattle and municipal sanitary inocula suggests an approach aimed at bolstering the anaerobic digestion process. In this study, we evaluated the use of cattle and municipal sanitary inocula for the anaerobic digestion of various poultry wastes, which is often challenged by high levels of ammonia and volatile fatty acids (VFAs). The substrates tested included belt waste (Poultry A), poultry litter plus feed residues (Poultry B), tray hatchery ©, and stillage. These substrates were processed in two continuous stirred tank reactors (CSTRs), R-1 (with antibiotic monensin) and R-2 (without monensin). Initially, both reactors operated with the same hydraulic retention time (HRT), using a substrate ratio of stillage: belt: tray hatchery (S:B:T) of 70:15:15. On the 41st day, the HRT was adjusted to 20 days, and the substrate ratio was changed to S:A:T 70:40:40. The specific methane yield for R-1 started at 10.768 L g−1 COD, but decreased to 2.65 L g−1 COD by the end of the experiment. For R-2, the specific methane yield varied between 0.45 L g−1 COD and 0.243 L g−1 COD. Microbial composition in the reactors changed over time. In R-1, bacteroides were consistently dominant, while firmicutes were less abundant compared to R-2. Proteobacteria were initially low in abundance, but spirochetes were found in both reactors throughout the experiment. The study concluded that Poultry B substrates, due to their rich nutrient and trace element composition, are suitable for biogas plants. Municipal sanitary inocula also showed promise due to their resilience in high ammonia concentrations. Further research into biofilm interactions is recommended to better understand microbial responses to high ammonia concentrations, which can lead to propionate production in anaerobic digestion (AD). [ABSTRACT FROM AUTHOR]

The anaerobic ammonium oxidation (anammox) application on mainstream wastewater treatment is limited by the ambient environment and slow growth rate of anammox bacteria. Bulk liquid in established anammox granular sludge bioreactors naturally contains active factors that could potentially boost anammox process under suboptimal conditions. In this study, effluent of a granular sludge-based anammox up-flow anaerobic sludge blanket treating ammonium-rich wastewater was harvested (the effluent is named as UAE) and continuously added into a bioreactor treating low-strength wastewater at 25 °C to study the effects and mechanisms on enhancing the anammox process. The NH 4 +-N removal efficiencies increased from 6.5% - 32.5% to 89.7% – 93.8%, and anammox genera accounted from 0.1% to 12.1% of microbial community in the receiving reactor with UAE addition. Coupled partial denitrification and dissimilatory nitrate reduction to ammonium (DNRA) processes with anammox were stimulated by UAE addition. Metagenomic analysis showed that the acyl-homoserine lactone-dependent quorum sensing molecules synthesis pathway was enhanced and an increased concentration of C8-HSL from 2.59 ng/L to 4.62 ng/L was observed in the UAE-receiving reactor. Selective amino acid transportation, amino acids biosynthesis and energy metabolic pathways of microbial community were upregulated with UAE addition. We demonstrate UAE as anammox biocatalyst and facilitate a deeper understanding for synergistic effect of active factors in UAE modified microhabitat for anammox metabolism in the UAE-receiving reactor. [Display omitted] [ABSTRACT FROM AUTHOR]

Dark fermentation is attracting great attention due to some capabilities such as wastewater treatment and biofuel production. In this study, the performance of different machine learning algorithms, including Bagging-Extreme Gradient Boosting (BagXGBoost), Categorical Boosting (CatBoost), K Nearest Neighborhood (KNN), Light Gradient Boosting Machine (LightGBM), and Decision Trees (DT) in the prediction of biohydrogen production from wastewater during dark fermentation is investigated. Effect of parameters Ni, Fe, biomass, pH, chemical oxygen demand (COD), HRT, acetate, ethanol, butyrate, and acetate/butyrate ratio as inputs were considered for the model development. A databank with 208 data points was culled from the literature. For the validation of the proposed models, various statistical criteria were determined. CatBoost and BagXGBoost exhibited superior performance in predicting fermentative hydrogen (H 2) production. Shapley additive explanations were used for relative analysis, revealing the highest absolute SHAP values of 1.1, 1, and 0.07 for COD, nickel, and butyrate, respectively, highlighting their significance in H 2 production. The insights gained from this study can contribute to further optimization of the dark biohydrogen fermentation process. [Display omitted] • H 2 generation from wastewater through the dark fermentation process was modeled. • CatBoost, LightGBM, BagXGBoost, KNN and DT models were used for modeling. • Ni, Fe, biomass, pH, COD, HRT, acetate, ethanol, butyrate were used as model inputs. • The CatBoost algorithm showed the best performance to estimate fermentative hydrogen. • Ni, COD and butyrate are highlighted through relevancy analysis employing SHAP values. [ABSTRACT FROM AUTHOR]

The immobilized cells technology was used for enhancing the two stages batch bioreactors in series from high-strength food waste hydrolysate. Carrageenan and gelatin were used as support materials to create immobilized cells to improve microorganisms' stability, activity, and productivity. It was found a promising advantages of a higher hydrogen and methane production rates, better stability, and resistance to shock loads to reduce the cost of producing biogaseous fuels from food waste. It was found that optimal biohydrogen production based on the working volume was 1.00 L H 2 /L which using 80 g COD/L of food waste hydrolysate and 20% of immobilized cells, and peak of methane production of 11.72 L CH 4 /L which using 120 g COD/L and 30% of immobilized cells. The yield of hydrogen and methane were 21.33 mL H 2 /g VS and 373.83 mL CH 4 /g VS respectively. TS, VS, and COD removal efficiency were 91.24, 90.64, and 86.35%, respectively. This study can support an efficient bioenergy production system development from a sustainable valuable feedstock such as a high-strength organic food waste. [Display omitted] • Enhancing H 2 and CH 4 productions from food waste by immobilized cells technology. • Improving microorganisms' stability and productivity by immobilized cell technology. • Producing peaks of hydrogen and methane yields of 21.33 and 373.83 mL/g VS. • Exploring the impacts of industrial-level food waste hydrolysate on H 2 production. [ABSTRACT FROM AUTHOR]

Underground hydrogen storage can lead to the activation of methanogenic Archaea , demanding to quantify microbial activities within the pore space to evaluate potential hydrogen conversion rates. This study presents a method to determine microbial activities within various water-saturated reservoir rocks, inoculated media containing sand particles and rock fragments as well as bulk solution, by monitoring pressure and gas composition. Measured activities in water-saturated rock specimens with identical bulk volumes varied between 0.15 and 1.28 mM H 2 /h correlating with pore volume. Additionally, the results reveal that activities within intact rocks are 8–10 times higher than in corresponding bulk solutions. This observation demonstrates that the surface area available for microorganism colonization is another potential factor controlling microbial activity when the substance amount is held constant. This notion is supported by activities measured in inoculated media containing sand particles and rock fragments, as well as in rocks with similar pore volumes. • Methanogenic activities in rocks and bulk solutions correlate with substance amounts. • Methanogenic activity is higher in the presence of grains than in bulk solution. • Methanogens-accessible surface area has a stimulating impact on microbial activity. • Microbial activity is formation specific and needs to be evaluated individually. [ABSTRACT FROM AUTHOR]

The Leach Bed Reactor (LBR) application is a promising alternative for the anaerobic digestion of solid waste and wastewater. In this study, the LBR was continuously operated for 160 days in four different phases, for co-fermentation of solid and liquid waste from the citrus agroindustry, at 37 °C, evaluating the effect of hydraulic retention time (HRT) and organic loading rate (OLR). The maximum volumetric hydrogen production (VHPR) was observed at an HRT of 12h (958.3 mLH 2.L-1.d-1); however, the highest hydrogen yield (HY) was identified at an HRT of 24h (104.9 mLH 2.g-1CHO). Based on the metabolic characteristics of microorganisms identified in higher relative abundance, by 16S rRNA sequencing, such as Lactobacillus, Caproicoproducens, Bifidobacterium, Olsenella, and Solobacterium, an occurrence of chain elongation pathways in the production of butyric and caproic acids was inferred, with hydrogen production resulting from the lactic acid oxidation. The maximum electricity production potential of 16.3 kWh.m-3 liquor was estimated. [Display omitted] • The leach bed reactor was applied to the dark fermentation of citrus waste. • The highest H 2 yield was obtained in a hydraulic retention time (HRT) of 24h. • The highest volumetric H 2 production rate was verified in HRT of 12h. • Lactobacillus was predominant in the fixed bed and leachate tank at HRT of 12h. • Caproiciproducens were identified with high relative abundance in HRT of 36h. [ABSTRACT FROM AUTHOR]

Proper treatment of dye wastewater containing significant concentrations of organic matter is imperative for the abatement of water pollution. Unfortunately, most studies on the treatment of dye wastewater employ synthetic wastewaters that hardly match the characteristics of real wastewater. In the present study, real wastewater generated from the manufacturing of Solvent Black 46 (SB46) dye was treated in an internal circulation reactor, modified with a bed of sponge cubes. The reactor was operated in different phases to investigate the impact of parameters such as feed chemical oxygen demand (COD), organic loading rate (OLR), and hydraulic retention time (HRT) on COD removal and methane generation. At a feed COD concentration of 10,000 mg/L and an OLR of up to 3 Kg COD/m3/day , 82% COD was removed with methane generation ranging from 0.28 to 0.31 L/g-COD removed. COD removal and methane generation increased with an increase in upflow velocity. The rate of substrate (COD) removal correlated well with the organic loading rate using the modified Stover–Kincannon model with a correlation factor (R2) of 0.9974. LC-MS analysis of treated wastewater revealed that one of the constituents of SB46, namely Metanil yellow, was decomposed by azo bond cleavage, producing corresponding aromatic amines. Overall, this study provides evidence of the successful anaerobic treatment of real industrial wastewater and its potential contribution to achieving UN Sustainable Development Goals 6 (Clean Water and Sanitation) and 7 (Affordable and Clean Energy). Importantly, the process parameters developed in this study have been utilized by the industry to install two full-scale anaerobic reactors to treat SB46 wastewater which has led them to double the SB46 production while conforming to the prescribed environmental discharge norms. [ABSTRACT FROM AUTHOR]

An up-flow anaerobic sludge blanket (UASB) reactor targeting sulfate reduction was operated under a constant TOC/S-SO 4 2− ratio of 1.5 ± 0.3 g C/g S for 639 days using crude glycerol as carbon source. A filamentous and fluffy flocculant material, namely slime-like substances (SLS), was gradually accumulated in the bioreactor after the cease of methanogenic activity. The accumulation of SLS was followed by a decrease in the removal efficiencies and a deterioration in the performance. Selected characteristics of SLS were investigated to explore the causes of its formation and the effect of SLS on the UASB performance. Results showed that glycerol fermentation and sulfate reduction processes taking place in the reactor were mainly accomplished in the bottom part of the UASB reactor, as the sludge concentration in the bottom was higher. The accumulation of SLS in the UASB reactor caused sludge flotation that further led to biomass washout, which decreased the sulfate and glycerol removal efficiencies. Batch activity tests performed with granular sludge (GS), slime-covered granular sludge (SCGS) and SLS showed that there was no difference between GS and SLS in the mechanism of glycerol fermentation and sulfate reduction. However, the specific sulfate reduction rate of GS was higher than that of SLS, while SLS showed a higher glycerol fermentation rate than that of GS. The different rates in GS and SLS were attributed to the higher relative abundances of fermentative microorganisms found in SLS and higher relative abundances of sulfate reducing bacteria (SRB) found in GS. [Display omitted] [ABSTRACT FROM AUTHOR]

This critical review for anaerobic degradation of complex organic compounds like butyrate using reactors has been enormously applied for biogas production. Biogas production rate has a great impact on: reactor granulation methanogenesis, nutrient content, shear velocity, organic loading and loss of nutrients taking place in the reactor continuously. Various technologies have been applied to closed anaerobic reactors to improve biogas production and treatment efficiency. Recent reviews showed that the application of closed anaerobic reactors can accelerate the degradation of organics like volatile fatty acid-butyrate and affect microbial biofilm formation by increasing the number of methanogens and increase methane production 16.5 L−1 CH4 L−1 POME−1. The closed anaerobic reactors with stable microbial biofilm and established organic load were responsible for the improvement of the reactor and methane production. The technology mentioned in this review can be used to monitor biogas concentration, which directly correlates to organic concentrations. This review attempts to evaluate interactions among the: degradation of organics, closed anaerobic reactors system, and microbial granules. This article provides a useful picture for the improvement of the degradation of organic butyrate for COD removal, biogas and methane production in an anaerobic closed reactor. Recent reviews showed that the application of closed anaerobic reactors can accelerate the degradation of organic compounds, such as volatile fatty acid-butyrate, and affect microbial biofilm formation by increasing the number of methanogens, thus enhancing biogas production. The closed anaerobic reactors with stable microbial biofilm established the organic load and improved the performance of the reactor for methane production. The technology used involves monitoring biogas concentrations which correlates with organic concentrations. This review attempts to evaluate interactions among: the degradation of organics, closed anaerobic reactors system, and microbial granules. This review, therefore, provides a useful picture for the improvement of butyrate degradation for COD removal and methane production with the help of various anaerobic closed reactors. The performance of UASBR depends on granulation. The granulation process in UASB reactors can be divided into four steps: (1) Transport of cells to the surface of other cells; (2) Initial reversible adsorption by physicochemical forces; (3) Irreversible adhesion of the cells by microbial appendages and/or polymers; and (4) Multiplication of the cells and development of the granules. Any factor which can complement any one of the four steps will be able to accelerate the granulation process and shorten the startup time of UASB reactors. [ABSTRACT FROM AUTHOR]

The potential for biogas provision through household-scale anaerobic digestion in rural sub-Saharan Africa is limited due to perceived water shortages. The most common substrate is animal dung diluted 1:1 with water. Two experimental methods tested the potential of reducing water demand. The first experiment compared the chemical oxygen demand (COD) and volatile solid removal of four cow dung dilutions ranging from 3.5-10.6% total solids. In the second experiment, bioslurry filtrate was recirculated back into the fresh substrate at different concentrations. The highest COD removal rate of 28.3% was obtained from mixing equal volumes of dung with filtrate (mean total solids 7.4%) while the highest methane production rate of 0.40 g/L/day, calculated from COD balance, was obtained from undiluted cow dung (total solids 10.6%). Results suggest the potential for a 75-100% reduction in water demand. [ABSTRACT FROM AUTHOR]

Livestock wastes can serve as the feedstock for biogas production (mainly methane) that could be used as an alternative energy source. The green energy derived from animal wastes is considered to be carbon neutral and offsetting the emissions generated from fossil fuels. In this study, an evaluation of methane production from anaerobic digesters utilizing different livestock residues (e.g., poultry rendering wastewater and dairy manure) was carried out. An anaerobic continuous flow system (15 million gallons, polyethylene-covered) subjected to natural conditions (i.e., high flow rate, seasonal temperatures, etc.) containing poultry rendering wastewater was set up to evaluate methane potential and energy production. A parallel pilot-scale plug-flow anaerobic digestion system (9 m3) was also set up to test different feedstocks and operating parameters. Biogas production was sampled and monitored by gas chromatography over several months of operation. The results showed that methane production increased as the temperature increased as well as depending on the type of feedstock utilized. The covered rendering wastewater lagoon achieved an upward of 80% (v/v) methane production. The rates of methane production were 0.0478 g per g of COD for the poultry rendering wastewater and 0.0141 g per g of COD for dairy manure as feedstock. Hence, a poultry processing plant with a rendering wastewater flow rate of about 4.5 million liters per day has the potential to capture about two million kilograms of methane for energy production per year from a waste retention pond, potentially reducing global warming potential by about 50,000 tons of CO2 equivalent annually. [ABSTRACT FROM AUTHOR]

In recent years, expanded granular sludge blanket (EGSB) reactor has been widely used in the treatment of high-concentration organic wastewater, but its research mainly focused on treatment efficiency and microbial community composition. There were few studies on the relationship of operation conditions and energy utilization efficiency. Therefore, the methanogenic characteristics and energy utilization efficiency of EGSB reactor were studied by using cassava alcohol wastewater (CAW) as a raw material at (36 ± 1) °C. The results show that the degradation of volatile fatty acids (VFAs) is an important step affecting methane generation compared to the hydrolysis stage. When organic load rate (OLR) was 12.73 gCOD/L·d, the chemical oxygen demand (COD) removal rate was above 95%, the methane production efficiency of raw material was 202.73 mLCH4/ gCOD·d, the four-stage conversion efficiency was the highest, and the energy utilization efficiency was 62.26%, which was the optimal stage for EGSB reactor to treat CAW. These findings support high-efficiency bioenergy recovery from CAW in practice and highlight the potential wide application of high-performance anaerobic reactors for CAW. [ABSTRACT FROM AUTHOR]

While palm oil mill effluent (POME) from different sources will have varying characteristics due to the different process flows in mills, efficient monitoring and performance evaluation of anaerobic digesters in POME treatment are crucial to ensure stable biogas production with minimal operational problems. Therefore, this study aims to evaluate and compare the performances of in‐ground lagoon anaerobic digesters under mesophilic conditions in four different biogas plants (BGPs A, B, C and D) located in Malaysia with respect to total chemical oxygen demand (COD) removal and total biogas produced. Results show that all BGPs are still functioning well with satisfactory methane yields (.135–.364 Nm3 CH4/kgCOD removed) and COD removal efficiencies (67%–85%). ANOVA analysis shows that organic loading rate (OLR), temperature (T) and recirculation ratio (RR) have significant effects on the COD removal and biogas production of all four plants. BGP B has the highest amount of biogas produced (4.12 × 105 Nm3/month) and COD removal rate amongst other BGPs due to its most stable and lowest T (<40°C), high RR, and consistent and high COD load. Conversely, BGP D has the lowest COD removal and biogas production, which are mainly contributed by a high COD inlet (92 000 mg/L) and a high T in the anaerobic digester (48.7°C). Despite having a similar design of an anaerobic digester, this comparative study reveals that different BGPs will have different optimum operating conditions and limitations, depending not only on the operating conditions of the BGP (OLR, T and RR) but also on the raw POME quality stemming from the palm oil milling process. A future study would be focused on the optimisation of four BGPs for maximum biogas removal. [ABSTRACT FROM AUTHOR]

Organics in domestic wastewater contain more chemical energy than is required for treatment; however, current wastewater treatment approaches are energy intensive. The chemical energy in wastewater can be converted to methane-rich biogas through anaerobic bioreactor technologies. While recent research has examined anaerobic bioreactor configurations for domestic wastewater treatment, such as anaerobic membrane bioreactors (AnMBRs) or anaerobic sludge blanket bioreactors, none have conducted energy balances on proposed full-scale anaerobic wastewater treatment facilities (WWTFs; i.e., those that include all processes, such as preliminary treatment, sludge pumping, odor control, etc.). Using Monte Carlo simulation, we address this gap in the literature by examining whole-facility net energy balances for three potential anaerobic wastewater treatment configurations composed of anaerobic sludge blanket bioreactors (e.g., the upflow anaerobic sludge blanket, UASB), AnMBRs, and partial nitritation/anammox (PN/A) to a conventional WWTF designed for biological nutrient removal. For comparison, all energy values were normalized to treatment of 37,850 m3 of wastewater per day to U.S. EPA secondary effluent standards and nitrogen removal to 1 mg·N/L. Results suggest that a configuration based on anaerobic sludge blankets and PN/A can achieve a net energy positive condition, generating 670 ± 3,580 kWh/day. AnMBR-based configurations currently do not achieve an energy-neutral condition; however, reduction in AnMBR energy requirements will bring AnMBR configurations closer to this goal. Our results suggest that full-scale WWTFs that leverage anaerobic technologies can become energy neutral or net energy positive even when all WWTF energy requirements are examined. [ABSTRACT FROM AUTHOR]

A massive use of nitrogen based fertilizers in agriculture is worldwide one of the main causes for nitrate contamination of groundwater. Methods for removing nitrate from aquatic environment through physical and/or chemical processes often turn out to be not applicable because of unaffordable financial resource as well as essential infrastructure lack. On the other hand, biological processes seem to have potentiality to overcome these limitations since they are less expensive and easier to be performed. Accordingly, in the present work, a moving bed biofilm reactor (MBBR) filled with Kaldnes K1 as carrier media was used to remove nitrate from a synthetic groundwater at bench scale. Acetate was used as organic source. Different operational conditions were tested: influent nitrate concentrations of 30, 40, 50 and 60 mg/L; hydraulic retention times of 24, 18, 12 and 8 h; and COD/NO3-N mass ratios of 3.00 and 2.98. Experimental results showed that NO3-N = 60 mg L−1, HRT = 8 h and COD/NO3-N ratio = 2.98 were the optimal operating conditions that allowed achieving a NO3-N removal by 99 % and a COD removal by almost 100 %. Moreover, almost no NO2−-N accumulation and null COD concentration were observed at the optimal operating conditions. An activated carbon filter was placed downstream to remove residual organic compounds prior to disinfection unit, thus avoiding the potential formation of harmful disinfection by-products (e.g. trihalomethanes (THMs)). The MBBR was able to show a rapid recovery whenever the operating conditions were defined as more severe, thus proving that the operating conditions can vary over a wider range. Furthermore, the results showed that the MBBR system can be used effectively as a biological process to remove nitrate from groundwater. [ABSTRACT FROM AUTHOR]

The performance of two tropical plants, Rhynchospora corymbosa L. (RC) and Coix lacryma-jobi, L (CL) in treatment of primary sewage effluent in lab-scale vertical-flow constructed wetlands (VFCW) along with no plant control wetland was investigated. A batch-flow VFCWs were operated under batch fill and drain hydraulic loading system with hydraulic retention times (HRT) of 0.5, 1, and 2 days and fill rate of 8 L/day. Removal of solids, organics, nutrients, and pathogens were monitored. The volumetric contaminant removal rates were best described by 1st order kinetics except for ammonia and phosphate, which was best described by Stover-Kincannon kinetics. Influent TSS, PO43−, COD, BOD5, and total coliform concentration were low but high in NH4+ concentration. CL was better in nutrient removal as HRT increases compared to RC. RC was more efficient at TSS, turbidity, and organics removal. Pathogen removal was independent of plant type but HRT. Solids and organic removal were lower in CL planted CWs due to preferential flow paths created by their bulky root. CL planted CWs removed more nutrients followed by RC planted CWs and then no-plant control CWs. The results of these tests demonstrate that both CL and RC are suitable for the treatment of municipal wastewater in VFCW system. [ABSTRACT FROM AUTHOR]

[Display omitted] Co-hydrothermal carbonization (co-HTC) is a promising strategy to improve hydrothermal carbonization (HTC) of low-quality wastes. HTC of swine manure (SM), with high N (2.9 wt%), S (0.7 wt%) and ash (22.6 wt%) contents, as well as low C (35.6 wt%) and higher heating value (HHV; 14.3 MJ kg−1), resulted in a hydrochar with unsuitable characteristics as a solid fuel. Co-HTC of SM and garden and park waste (GPW) improved hydrochar properties (C content (43 – 48 wt%) and HHV (18 – 20 MJ kg−1), and decreased N (∼2 wt%), S (<0.3 wt%) and ash (<15 wt%) content. A high GPW ratio (>50 wt%) during co-HTC resulted in a hydrochar similar to that obtained from GPW. The co-HTC increased nutrient migration to the process water, which allowed the precipitation of salt with high P (7.8 wt%) and negligible heavy metal content. Anaerobic digestion of co-HTC process water allowed high organic matter removal (up to 65%), and methane production (315 – 325 mL CH 4 g-1COD added). Gross energy recovery by HTC and anaerobic digestion was 5 – 6-fold higher than anaerobic treatment of feedstocks. Therefore, co-HTC of SM and GPW with a ratio > 50% GPW proved to be a suitable approach to valorize and manage SM and obtain value-added products (hydrochar, mineral fertilizer and methane). [ABSTRACT FROM AUTHOR]

Long-term operation of four in-series horizontal anaerobic reactors with fixed bed (HARFB) R1, R2, R3, and R4 was conducted to evaluate the co-digestion of domestic sewage (DS) with different proportions of crude glycerol (CG) from biodiesel production. The main objective was to examine the effect of the increase of CG in the influent with the proportions of 1.5%, 2%, and 3% (v/v). The anaerobic co-digestion was conducted in sequential reactors with increasing diameters to favor the fermentation in the R1 and R2 and the methanogenesis in the R3 and R4. The increase in CG proportions in the influent resulted in mean OLRs of 18.06, 26.75, and 37.85 kg COD/(m3 day) for 1.5%, 2%, and 3% of CG, respectively. The highest hydrogen production was (L H2 /(m3 day)) 277.88 (R1, at the 1.5% CG) and 84.43 (R2, at the 2% CG). The highest methane volumetric production occurred during the 1.5% CG in R3 (306.7 L CH4/(m3 day)), with a 98% COD removal. The configuration of four in-series reactors could promote total removals of CG, even at the 3% CG. Reactor R1 produced 4 g/L of 1,3-propanediol and 2.8 g/L of propionic acid. The changes in the microbiota were verified, mainly on how the Lactobacillales and Selenomonadales orders were favored, respectively, in the fermentative reactor (R1) and the methanogenic reactor (R3). The inhibition of the methanogens verified in the in-series reactors selected the Methanosarcinales order. Even though CG increased caused some instabilities in the reactor parameters, no toxic effect was reached and the HARFB in-series system showed robustness to removing CG continuously for extended times. [ABSTRACT FROM AUTHOR]

This study evaluated the mechanical properties and self-healing performance of freshly casted and 19-month-aged bioconcrete samples with integrated sulfate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB) granules that were cultivated in an upflow anaerobic sludge blanket (UASB) reactor with synthetic wastewater. The 28-day compressive strength fulfilled the design requirement of 50 MPa. The apparent volume of permeable voids (AVPV) of fresh and aged bioconcrete met the limit of 13%. The self-healing ability was determined by exposing cracked bioconcrete to water media such as glucose, calcium acetate, tap water, and wastewater, which have shown calcite deposition in fresh and aged samples. The highest amount of calcite deposition was seen on fresh samples after glucose exposure (420 μm) and on aged bioconcrete after calcium acetate exposure (320 μm). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS/XRD) results demonstrated that SRB/NRB granules survived mortar integration and deposition of calcite in both fresh and aged samples. The water permeability and acid resistance of bioconcrete samples were correlated to the amount of deposited calcite. [ABSTRACT FROM AUTHOR]

The efficiency of a hybrid upflow anaerobic sludge blanket reactor (HUASB) where coconut fiber is used as an inert media was investigated under different hydraulic residence times (started with 6 h and then decreased to 2 h) with varied organic loading rates (ranged from 0.5 to 6.0 kg chemical oxygen demand (COD)/m−3day−1). The 3.5-L lab-scale reactor was used for sewage treatment under mesophilic conditions for 8 months. The COD reduction varied from 74%±1.7% to 61%±2.4% , the total suspended solids (TSS) reduction was in the range of 72%±2.2% to 54%±2.7% , and the methane content in the biogas was 65.1%±0.3%. An attempt has been made to understand the performance of the lab-scale reactor for primary population of microorganisms using a microscopic technique. Different groups of anaerobic bacteria and granulation were visualized and quantified using unstained observations, Gram staining, ocular micrometry (granular size determination), Neubauer's chamber (counting of microorganisms), and scanning electron microscopy. Correlation analysis among the various operational parameters has also been prepared. Overall, the performance of the HUASB reactor using coconut fiber appears to be a cost-efficient sewage treatment alternative in developing nations. A HUASB is a high-rate anaerobic treatment process that consists of a suspended and attached growth treatment method. The treatment unit can sustain a high organic loading because it has a high biomass content and good sludge-settling characteristics. The study investigates the effectiveness of a HUASB reactor using coconut fiber as a novel inert media for sewage treatment. Based on the findings, this technology can be applied at a sewage treatment facility. This treatment also has the potential for reduced environmental and economical footprints. [ABSTRACT FROM AUTHOR]

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L−1), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L−1, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH4+, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system. [ABSTRACT FROM AUTHOR]

The present study focuses on bio-hydrogen production using palm oil mill effluent (POME) at a semi-pilot scale of an "up-flow anaerobic sludge blanket fixed-film (UASFF) reactor". The reactor was operated in the palm oil mill industry for over 180 days of operation at ambient temperature through dark fermentation process with different organic loading rates (OLR) of 22–36 g-COD/l.d, depending on the COD concentration of POME. By acclimatizing the sludge, the semi-pilot scale UASFF reactor achieved hydrogen content, and hydrogen production rate (HPR) of 20%–68%, and 12 L H 2 /d to 39 L H 2 /d, respectively with a maximum COD removal of 35%. Moreover, from high through pyrosequencing analysis, hydrogen fermentation was attributed to Clostridium sensu stricto , Lactobacillus , and thermoanaerobium spp. This study offers an extensive approach to developing a semi-pilot scale bio-hydrogen production and, provides further prospects for profitable exploitation which could be a promising approach for reaching sustainability and economic feasibility (using wastewater as a low-cost feedstock) in commercial applications for future studies. [Display omitted] [ABSTRACT FROM AUTHOR]

Peach has a big share of the world fruit market, with significant annual waste production. This study reports dark fermentative hydrogen gas production from waste peach pulp using intermittent feeding. In this context, the effects of hydraulic residence time (HRT) and substrate loading rate (SLR) on hydrogen production were determined in two sets of experiments. All experiments were performed in 310 mL serum bottles. During the first set of experiments, HRT was varied between 1 and 6 days and hydrogen production was more favorable at short HRTs. In the second set of experiments, SLR was varied between 9 and 90 gTOC/L.d, and more efficient hydrogen formation was observed by increasing the SLR. The most convenient HRT and SLR resulting in maximum hydrogen formation rate (931.8 mLH 2 /L.d) was obtained at 1 day and 90 gTOC/L.d, respectively. • Effects of HRT and SLR on H 2 formation from waste peach pulp were investigated. • H 2 formation rate increased by decreasing HRT and increasing SLR. • Low HRT enabled the wash-out of H 2 consumers and maintained H 2 producers. • Most convenient H 2 formation was obtained at 1 day of HRT and 90 g TOC/L.d of SLR. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is an economic method to treat high-salinity organic wastewater (HSOW). However, due to the inhibitory effect of high salinity, the start-up of the anaerobic digestion reactor is slow and easy to fail. In this study, as a potassium source, rice-straw ash (RSA) was used to enhance the HSOW treatment performance and shorten the start-up time of anaerobic digestion reactor under 3.0% NaCl content and high loading rate. The results showed that RSA could provide adequate potassium ion (K+) for alleviating the inhibitory effect of high salinity on anaerobic microorganisms. The rapid start-up of the anaerobic digestion reactor was realized, and the TOC removal rate reached 81.65%. In the reactor with RSA addition, the activities of dehydrogenase, acetic kinase and coenzyme F 420 were 25.67%− 89.81%, 19.03%− 50.93% and 35.83%− 944% higher than that of the control reactor, respectively. The addition of RSA promoted the accumulation of acetoclastic methanogen Methanothrix , and changed the methanogenic pathway from hydrogenotrophic methanogenesis in the beginning stage of anaerobic digestion to acetoclastic methanogenesis under high salinity condition. After stopping the addition of RSA, the performance of the anaerobic digestion reactor remained stable, indicating that RSA was only needed at the start-up stage. This study could provide a feasible method for rapid start-up of anaerobic digestion reactor treating HSOW in practice. [Display omitted] [ABSTRACT FROM AUTHOR]

This study describes the performance of a two-phase tubing bioreactor operated with an extractive polymeric membrane able to selectively transfer and biologically remove the toxic fraction of an industrial/hazardous waste landfill leachate. An additional feature of this bioreactor is the separation of the biomass from the polluted stream with consequent marked reduction of the inhibitory/toxic effect exerted by leachate constituents. Process performance has been optimized for decreasing HRTs, from 5.5 to 1.9 h, and step-increased OLRs, from 300 to 900 g COD /L d with excellent removal efficiencies (88–99%). Removal rates of toxic chemicals, represented by phenolic compounds, as well as mass transfer and biomass activity, were not negatively affected by severe loading conditions. On the contrary, the trend of oxygen consumption rate suggested increased activity of the microorganisms with raised loads. Furthermore, biodegradation efficiency of 90% has been observed by evaluating the final mass balance after washing the polymer, which retained only 1.5% of totally fed phenolics. This work provided reliable results to conclude that the tested tubing bioreactor is an effective and stable treatment technology ready for commercial application, with evident operating advantages and the possibility to recover concurrently other valuable leachate constituents as VFAs and ammonia. [ABSTRACT FROM AUTHOR]

Sponge iron (s-Fe0) has a large specific surface area, is cheap and easy to obtain, and has a good reduction capacity. Therefore, its efficacy in enhanced wastewater denitrification and phosphorus removal has been extensively examined. Because of the strong magnetic properties and reactivity of s-Fe0, a passivation layer dominated by iron oxides is formed in liquid phase environments, and this layer inhibits the dissolution of Fe0. In this study, s-Fe0 was used as the carrier filler in an SBR reactor to remove the passivation layer on the surface of s-Fe0 by anaerobic means, and the performance of this reactor was investigated for the removal of chemical oxygen demand (COD), nitrogen, and phosphorus from actual domestic wastewater. The anaerobic treatment of the reactor for 4 days effectively removed the passivation layer on the s-Fe0 surface while the carbon source of the system was maintained with normal feed water. The average removal rates of COD, NH 4 +-N, and TP in the reactor were 85.67%, 99.8%, and 93.98%, respectively, and the efficient removal of phosphorus in the system was stable for 22–26 days. X-ray diffraction and microbial community analysis showed that, in addition to the formation of FePO 4 , Fe(PO 3), and Fe 2 P 4 O 12 precipitates were generated in the system to remove phosphorus, and that a synergistic effect aided biological phosphorus removal. Additionally, the presence of abundant microorganisms with corrosion functionality (such as Rhodobacter , Brevundimonas , and Thiobacillus) in the activated sludge system, on the s-Fe0 carrier surface, and inside the carrier, played an essential role in the corrosion and removal of the s-Fe0 passivation layer. These results demonstrated that s-Fe0 is a promising material for nitrogen and phosphorus removal, and anaerobic treatment can effectively alleviate the passivation of s-Fe0. Thus, the efficient removal of phosphorus from actual domestic wastewater can be sustainably achieved. [ABSTRACT FROM AUTHOR]

Microbial bioremediation of metals in wastewater by sulfate-reducing bacteria (SRB) has received much attention due to its high efficiency, eco-friendly techniques, and low cost. We investigated upflow anaerobic fixed film reactors (UAFFR) for removal of metals from artificial mine wastewater in the presence of two different carbon sources (lactate and ethanol), a range of temperatures, and pH. The UAFFR had different remediation reactors: R1 (inoculated directly with the sludge), R2 (inoculated with SRB-enriched culture), R3 (inoculated with SRB-enriched culture in combination with a pure culture of SRB species, i.e. Desulfotomaculum ruminis, to treat all of the metals together), and R4 (inoculated with an SRB-enriched culture in combination with the Desulfotomaculum ruminis, to treat individual metals). Of the four seeded reactors, those supplemented with SRB-enriched cultures (R2, R3, R4) removed the metals more efficiently than R1. The reactors using ethanol as the carbon source and polyhedral hollow balls removed sulfate and metals more efficiently than those with lactate and small pall rings. [ABSTRACT FROM AUTHOR]

Methane recovery in up-flow anaerobic sludge blanket (UASB) reactors performing anaerobic digestion (AD) can be improved with adjustments in operational factors such as temperature, organic loading rate, and the addition of granular activated carbon (GAC). This study aims to perform a multiple operational factor analysis for their impacts on UASB microbial communities. Data collected from seven continuously operated UASB reactors and batch tests were analyzed using a range of bioinformatics and statistical tools. Temperature and reactor types were the most important factors in microbial communities in UASB reactors, although the addition of GAC also had a statically significant impact. The positive and negative correlations between classified phylotypes and performance indicators were determined. It was noted that more phylotypes were positively correlated with hydrogenotrophic specific methanogenic activity (SMA) than acetoclastic SMA. The occurrence network of the overall microbial communities from samples amended with GAC was modularized into eight main groups (occupying 92% of the nodes). Seven modules containing both methanogens and syntrophs were identified as potential functional communities for AD. These modules were mainly regulated by reactor types and driven by different combinations of operational factors using co-occurrence network analysis and generalized joint attribute modeling. Overall, the paper bridged operational configurations and reactor performance with microbial community dynamics. [ABSTRACT FROM AUTHOR]

Tetramethylammonium hydroxide (TMAH) is a known toxic chemical used in the photolithography process of semiconductor photoelectronic processes. Significant amounts of wastewater containing TMAH are discharged from electronic industries. It is therefore attractive to apply anaerobic treatment to industrial wastewater containing TMAH. In this study, a novel TMAH-degrading methanogenic archaeon was isolated from the granular sludge of a psychrophilic upflow anaerobic sludge blanket (UASB) reactor treating synthetic wastewater containing TMAH. Although the isolate (strain NY-STAYD) was phylogenetically related to Methanomethylovorans uponensis, it was the only isolated Methanomethylovorans strain capable of TMAH degradation. Strain NY-STAYD was capable of degrading methylamine compounds, similar to the previously isolated Methanomethylovorans spp. While the strain was able to grow at temperatures ranging from 15 to 37°C, the cell yield was higher at lower temperatures. The distribution of archaeal cells affiliated with the genus Methanomethylovorans in the original granular sludge was investigated by fluorescence in situ hybridization (FISH) using specific oligonucleotide probe targeting 16S rRNA. The results demonstrated that the TMAH-degrading cells associated with the genus Methanomethylovorans were not intermingled with other microorganisms but rather isolated on the granule's surface as a lone dominant archaeon. Key points: • A TMAH-degrading methanogenic Methanomethylovorans strain was isolated • This strain was the only known Methanomethylovorans isolate that can degrade TMAH • The highest cell yield of the isolate was obtained at psychrophilic conditions [ABSTRACT FROM AUTHOR]

Simultaneous pollutant removal and electricity production using microbial fuel cells is a promising environmental sustainable technology that contributes to the circular economy. Numerous studies have been conducted previously using exogenously adding easily degradable sugars for electricity generation in microbial fuel cells (MFCs). However, in real-world applications involving wastewater, the performance of the process varies according on the source, the microorganisms presented and the electrodes employed. The simultaneous treatment of baker's yeast industrial effluents and electricity generation is investigated in various MFCs using titanium and graphite electrodes. Reduced chemical oxygen demand (COD) is reported to be between 73% and 92% depending on the MFC configuration and electrodes employed. The two-chamber MFC with titanium electrodes and inoculum sludge from upflow anaerobic sludge blanket reactors (UASB) perform better, reaching 51.02 mW/m2 and 12.74 μA/cm2 power and current densities, respectively. [Display omitted] • MFC technology removed up to 92% of COD from baker's yeast wastewater. • Dual chamber MFCs were more successful at treating high strength real wastewater. • The power generations were consistent with COD reductions in all MFCs. • UASB and activated sludge reactors in yeast industries could be used to develop MFC. [ABSTRACT FROM AUTHOR]

The effect of selenate on the removal of glycerol in up-flow anaerobic sludge blanket (UASB) reactors was investigated. Two UASB reactors, R Control and R Selenium, were operated at a hydraulic retention time of 48 h and an upflow velocity of 2 m/h at 37 °C. A GAL (glucose, acetate and lactate) and glycerol mixture were used as the only feedstock throughout the experiment for R Control. After acclimation to GAL and glycerol in the start-up period, R Selenium was additionally exposed to selenate (SeO 4 2−) concentrations from 1.43 to 71.49 mg/L (10–500 μM) in a stepwise manner. An average daily methane yield of about 150 mL/g COD, which was comparable with R Control , and 90% Se removal were achieved until 400 μM SeO 4 2−. Simultaneously, SeO 4 2− was reduced to elemental Se or metal selenide, supported by X-ray diffraction, as well as scanning and transmission electron microscopy. However, the methane production rapidly deteriorated when the influent SeO 4 2− concentration was increased to 500 μM. The Se toxicity was evident from the reduction in the activity of Methanosaeta. This study showed that the SeO 4 2− concentration, but not the COD/SeO 4 2− ratio, governs the AD of selenate rich wastewaters. [Display omitted] • Selenate concentration, but not COD/selenate ratio, governs the anaerobic digestion process. • Methane yield of 150 mL/g COD·d with 90% selenium removal until 400 μM selenate. • Inhibition of Methanosaeta activity observed at 500 μM selenate. • Increase in solids content and settling velocity suggests selenium facilitated sludge granulation. • Elemental selenium and metal selenide biosynthesis observed from XRD, TEM, SEM and SEM-EDX. [ABSTRACT FROM AUTHOR]