Methanogenic Reactor Research Articles

Optimization of two-stage thermophilic anaerobic digestion of dairy wastewater: Effect of carrier material on process performance and microbial community

Although two-stage anaerobic digestion (TSAD) is not a novel process, information of the process stability, microbial community and effective operating conditions is limited and often contradictory. In this work, the influence of different carrier materials (polyurethane foam, carbon felt, Raschig rings and a combination of carbon felt and Raschig rings) on the performance of the thermophilic TSAD of dairy wastewater was studied. The organic loading rate (OLR) in the acidogenic reactor (RH) was gradually increased from 13.74 to 32.56 g COD/(L d), and from 0.64 to 11.46 g COD/(L d) in the methanogenic reactors by correspondingly reducing the hydraulic retention time (HRT). The highest hydrogen production rate of 1280.3 mL/(L·d) and hydrogen yield of 93.2 mL/g COD were achieved at OLR of 13.74 g COD/(L·d), but hydrogen production stopped at higher OLR. The main soluble metabolites in RH were butyrate and lactate, and the microbial community was dominated by Streptococcus, Thermoanaerobacterium, Veillonellales-Selenomonadales and Pseudomonas. The highest methane production rate (2674 mL/(L·d) at HRT of 0.5 days) was observed in the reactor with polyurethane foam, while the highest methane yield (305.5 mL/g COD at HRT of 1.5 days) was obtained in a reactor containing carbon felt. Spirochaetaceae, Desulfomicrobium, Anaerolineaceae, Candidatus Caldatribacterium and Cloacimonadaceae W5 were linked to these materials and explained the highest methanogenic performance.

Synergizing sugarcane waste valorization: Optimization of two-stage anaerobic co-digestion for enhanced methane recovery and organic matter removal

Multiple strategies have been used in anaerobic digestion of effluents aiming to enhance the efficiency of the methane (CH4) recovery process, where co-digestion and the two-stage process emerge as prominent methods. In this context, this study aimed at evaluating the co-digestion of sugarcane vinasse and molasse in a two-stage process using anaerobic fluidized bed reactors (AFBR), verifying the effect of increasing the organic loading rate (OLR) (5–22.5 kg COD.m−3.d−1) and temperature in the second stage methanogenic reactor. Regarding the two-stage process, sugarcane vinasse and molasses fermentation demonstrated the maximum energy potential (E.P) of 57.08 kJ.d−1 (7.5 g COD.L−1). Regarding the methanogenic sequential reactors, organic matter removal reached high values (up to 84.5 % in a thermophilic sequential reactor (TSR); up to 84.5 % in a mesophilic sequential reactor (MSR)). The highest CH4 yield (MY) of 306.77 ± 38.84 mL CH4.g−1 COD rem was observed in MSR (9 kg COD.m−3.d−1). Meanwhile, the maximum value of MPR (3.8 ± 0.5 L CH4.L−1.d−1) was observed in TSR (21 kg COD.m−3.d−1). Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be identified, in which the genera Methanobacterium and Methanothermobacter were the most abundant in MSR and TSR, respectively. This study demonstrates that anaerobic digestion of sugarcane vinasse and molasses enhances anaerobic treatment using two-stage AFBRs. It not only produces CH4 but also generates hydrogen and high-value products through an acidogenic reactor. This research marks a significant advancement in managing sugarcane processing by-products, offering promising approaches to maximize biogas production and improve pollutant removal efficiency.

Volatile fatty acid and methane production from vinasse and microalgae using two-stage anaerobic co-digestion.

The effects of adding vinasse (VIN) as a co-substrate on the stability and production of volatile fatty acids (VFA) and methane (CH4) during the anaerobic digestion (AD) of microalgal biomass (MB) were evaluated. The AD system consisted of an acidogenic reactor (AR) followed by a methanogenic reactor (MR). The experiment was divided into phase I-start-up and AD of VIN; phase II-MB+VIN co-digestion (50:50 based on chemical oxygen demand (COD)); and phase III-co-digestion of pretreated MB and VIN (PTMB+VIN, 50:50). In phase I, the total amount of VFA in the AR increased from 240 to 2126 mg/L. In the MR, the conversion of VFA into CH4 yielded an average of 71 ± 37 NmL CH4/g CODin. In phase II, the initial CH4 production was 246 ± 31 mL CH4/g CODin but it decreased to 63 mL CH4/g CODin due to the accumulation of longer chain acids. More stable conditions were achieved after two hydraulic retention cycles and the average CH4 yield in this phase was 183 mL CH4/g CODin. In phase III, when using PTMB, 197 ± 72 NmL CH4/g CODin were obtained, i.e., a 2.7- and 1.1-fold increases compared to phases I and II, respectively. The predominance of acetate producers and syntrophic organisms suggests acetoclastic methanogenesis, confirmed by the occurrence of Methanosaeta (10.5%).

Acidogenic gas utilization improves methane production in high-load digestion: Underlying mechanisms

High-load reactors face a significant challenge with fatty acid accumulation. Although injecting acidogenic gas (H2 and CO2) into methanogenic reactors improves biogas production, its mechanisms and stability enhancement remain unclear. Therefore, this study investigated the potential of using acidogenic gas to enhance methane production and system stability in a high substrate-loading co-digestion system with decreasing hydraulic retention time (HRT) and its regulatory role by considering biological pathways. Acidogenic gas injection effectively managed volatile fatty acid accumulation, with a concomitant increase in methane production from 0.042 to 0.066 L/L h as HRT decreased (16–8 days). However, the methane yield decreased from 611 to 460 mL/g volatile solids. Microbial community analysis revealed an increased abundance of hydrogenotrophic methanogens, along with several acidogenic and syntrophic fatty acid oxidizing consortia with decreasing HRT. The HRT10.67 sample exhibited the highest microbial species diversity and richness in the methanogenic reactor. Metabolomics analysis showed acidogenic gas reduced energy synthesis related to the tri-carboxylic acid cycle and oxidative phosphorylation while profoundly regulating the metabolism of amino acids, lipids, fatty acids, membrane transporters and inhibitory substances, thereby strengthening methane metabolism pathways. This study provides valuable insights into the roles of acidogenic gas in regulating energy metabolism to enhance methane production and offers potential opportunities for improving lipid and protein degradation.

Effect of lactose as a co-substrate in the biodegradation of an anionic surfactant “LAS” by anaerobic digestion

Sodium alkylbenzenesulfonate (LAS) is the most widely used anionic surfactant in the manufacture of commercial detergents due to its excellent detergent properties and low cost. However, they are highly polluting products due to their chemical composition, causing a serious problem of pollution and eutrophication in natural bodies of water, if the amount dumped and the frequency with which they are dumped is taken into account. In addition, damage to health and ecosystems by remaining in the environment for a long time, is a relevant issue of immediate attention. This article presents the results found when using lactose as a co-substrate on the simultaneous biodegradation of the LAS surfactant in an arrangement of UASB-type anaerobic reactors in two stages; with a hydraulic retention time of 0.25 days in the acidogenic reactor in which two surfactant concentration rates were evaluated: 200 ± 0.49 mg/L with an organic load of 5.92 ± 0.5 KgCOD/m3.d (experiments II, III and V) and 300 ± 0.05 mg/L with organic loading. of 6.8 ± 0.11 KgCOD/m3.d (experiment VI) and of one day, in the methanogenic reactor. The results showed that the acidogenic reactor was able to eliminate COD by 42.24% and biodegrade LAS by 86.65% (experiment V). At 300 mg/L (experiment VI), these values are reduced to 36.6 and 55% respectively. For its part, the methanogenic reactor fed with the effluent of the acidogenic reactor (experiment V) with a lower concentration of COD, LAS and organic load, showed a COD removal and LAS biodegradation efficiency of 83.17 and 13.85% respectively.

Valorization of fruit and vegetable waste in a novel three-stage hybrid anaerobic digester for enhanced biogas production: Performance study and microbial community analysis

The study proposes the performance of a three-stage hybrid mesophilic anaerobic digester comprising a suspended-growth hydrolytic reactor, a hybrid (suspended-growth + attached-growth) acidogenic down-flow reactor, and a hybrid methanogenic up-flow reactor, for enhanced biogas production. Commingled fruit and vegetable waste (FVW) – shredded to sizes 1 – 4 mm – plus 2.5 L of tap water served as the feedstock in 8 different batch combinations, where the weight of the waste was increased from 3.5 to 7 kg. Decoupling the three major anaerobic steps ensured desirable working pH ranges for the hydrolytic (4.02 – 6.79), the acidogenic (5.69 – 6.62), and the methanogenic stages (6.94 – 7.7). Triplicate studies of each batch type vis-à-vis all three stages were performed. The highest cumulative soluble chemical oxygen demand percentage removal of 96.3 % was noticed in the case of batch run 5. The maximum biogas yield of 781.8 ml/g CODremoved was corresponding to batch 7, with 6.5 kg FVW, whereas the lowest biogas yield, 735.8 ml/g CODremoved, was corresponding to batch 1. The produced biogas from the methanogenic digester was of high quality (≤ 0.01 % H2S) and constituted 58–62 % CH4 and 6–7 % H2. Microbial community analysis confirmed the presence of pertinent bacterial and archaeal groups, such as Firmicutes, Proteobacteria, Spirochaetes, and Methanothrix, including key homoacetogenic genera, such as Acetobacterium Woodii, Desulfotomaculum, and Desulfitobacterium.

Anaerobic treatment removing tetrabromobisphenol A and biota safety: How do tropical aquatic species respond to effluent toxicity over short- and long-term exposures?

Wastewater containing tetrabromobisphenol A (TBBPA), a commonly used flame retardant found in wastewater, can present significant toxic effects on biota, yet its impact on tropical freshwater environments is not well understood. This study explores the effectiveness of two independent anaerobic treatment systems, the acidogenic reactor (AR) and the methanogenic reactor (MR), for the ecotoxicity reduction of TBBPA-rich wastewater in four tropical freshwater species. Despite presenting good physicochemical performance and reduced toxicity of the influent for most species, AR and MR treatments remain acute and chronic toxicity. Overall, MR exhibited greater efficacy in reducing influent toxicity compared with AR. TBBPA bioaccumulation was observed in Chironomus sancticaroli after short-term exposure to 100% MR effluent. Multigenerational exposures highlighted changes in the wing length of C.sancticaroli, showing decreases after influent and AR exposures and increases after MR exposures. These findings underscore the need for ecotoxicological tools in studies of new treatment technologies, combining the removal of emerging contaminants with safeguarding aquatic biota. PRACTITIONER POINTS: Acidogenic and methanogenic reactors reduced the acute and chronic toxicity of wastewater containing tetrabromobisphenol A. Both treatments still exhibit toxicity, inducing short- and long-term toxic effects on four native tropical species. The aquatic species Pristina longiseta was most sensitive to effluents from acidogenic and methanogenic reactors. TBBPA concentrations recovered from Chironomus sancticaroli bioaccumulation analysis ranged from 1.07 to 1.35 μg g-1. Evaluating new treatment technologies with multiple species bioassays is essential for a comprehensive effluent toxicity assessment and ensuring aquatic safety.

Phase separation as a strategy to prevent sulfide-related drawbacks in methanogenesis: performance and energetic aspects.

The establishment of sulfate (SO42-) reduction during methanogenesis may considerably hinder the efficient energetic exploitation of methane, once removing sulfide from biogas is obligate and can be costly. In addition, sulfide generation can negatively impact the performance of methanogens by triggering substrate competition and sulfide inhibition. This study investigated the impacts of removing SO42- during fermentation on the performance of a second-stage methanogenic continuous reactor (R2), comparing the results with those obtained in a single-stage system (R1) fed with SO42--rich wastewater (SO42- of up to 400mg L-1, COD/SO42- of 3.12-12.50). The organic load (OL) was progressively increased to 5.0g COD d-1 in both reactors, showing completely discrepant performances. Sulfate-reducing bacteria outperformed methanogens in the consumption for organic matter during the start-up phase (OL = 2.5g COD d-1) in R1, directing up to 73% of the electron flow to SO42- reduction. An efficient methanogenic activity was established in R1 only after decreasing the OL to 0.625g COD d-1, after which methanogenesis prevailed by consuming ca. 90% of the removed COD. Nevertheless, high sulfide proportions (up to 3.1%) were measured in biogas. Conversely, methanogenesis was promptly established in R2, resulting in a methane-rich (> 80%) and sulfide-free biogas regardless of the operating condition. From an economic perspective, processing the biogas evolved from R2 would be cheaper, although the techno-economic impacts of managing the sulfur pollution in the fermentative reactor still need to be understood.

Brooklawnia propionicigenes sp. nov., a facultatively anaerobic, propionate-producing bacterium isolated from a methanogenic reactor treating waste from cattle farms.

Facultatively anaerobic bacterial strains were isolated from samples of a methanogenic reactor and, based on 16S rRNA gene sequences, found to be affiliated with the family Propionibacteriaceae in the phylum Actinomycetota. Four strains with almost-identical 16S rRNA gene sequences were comprehensively characterized. The most closely related species to the strains was Brooklawnia cerclae BL-34T (96.4 % sequence similarity). Although most of the phenotypic characteristics of the four strains were identical, distinct differences in some cellular and physiological properties were also detected. Cells of the strains were Gram-stain-positive, non-spore-forming, pleomorphic rods. The strains utilized carbohydrates and organic acids. The strains produced acetate, propionate and lactate from glucose, but the molar ratios of the products were variable depending on the strains. The strains grew at 10-40 °C (optimum at 35 °C) and pH 5.3-8.8 (optimum at pH 6.8-7.5.) The major cellular fatty acids of the strains were anteiso-C15 : 0, C15 : 0 and C15 : 0 dimethylacetal (as a summed feature). The major respiratory quinone was menaquinone MK-9(H4) and the diagnostic diamino acid in the peptidoglycan was meso-diaminopimelic acid. The genome size of the type strain (SH051T) was 3.21 Mb and the genome DNA G+C content was 65.7 mol%. Genes responsible for propionate production through the Wood-Werkman pathway were detected in the genome of strain SH051T. Based on the results of phylogenetic, genomic and phenotypic analyses of the novel strains, the name Brooklawnia propionicigenes sp. nov. is proposed to accommodate the four strains. The type strain of the novel species is SH051T (=NBRC 116195T=DSM 116141T).

High synthetic cost-amino acids reduce member interactions of acetate-degrading methanogenic microbial community.

The cooperation among members of microbial communities based on the exchange of public goods such as 20 protein amino acids (AAs) has attracted widespread attention. However, little is known about how AAs availability affects interactions among members of complex microbial communities and the structure and function of a community. To investigate this question, trace amounts of AAs combinations with different synthetic costs (low-cost, medium-cost, high-cost, and all 20 AAs) were supplemented separately to acetate-degrading thermophilic methanogenic reactors, and the differences in microbial community structure and co-occurring networks of main members were compared to a control reactor without AA supplementation. The structure of the microbial community and the interaction of community members were influenced by AAs supplementation and the AAs with different synthetic costs had different impacts. The number of nodes, links, positive links, and the average degree of nodes in the co-occurrence network of the microbial communities with AAs supplementation was significantly lower than that of the control without AAs supplementation, especially for all 20 AAs supplementation followed by the medium- and high-cost AAs supplementation. The average proportion of positive interactions of microbial members in the systems supplemented with low-cost, medium-cost, high-cost, all AAs, and the control group were 0.42, 0.38, 0.15, 0.4, and 0.45, respectively. In addition, the ecological functions of community members possibly changed with the supplementation of different cost AAs. These findings highlight the effects of AAs availability on the interactions among members of complex microbial communities, as well as on community function.

Biomethane and biohydrogen production from an anaerobic sludge used in the treatment of rice parboiling effluent: Specific methanogenic and hydrogenic activity

This study evaluated the biomethane and biohydrogen production capacity of an anaerobic sludge collected from a rice parboiling industry. Three main parameters were assess from an experimental batch with varying substrate-inoculum ratios (S/I): the final mass production, the maximum generation rate, and the reactors’ biomethane and biohydrogen yield. From the analysis of the final production and the maximum generation rate, the best S/I ratios found for the methanogenic and hydrogenic reactors were, respectively, 1.4 and 3.8 gCOD/gVSS. These proportions produced 102.65 mgCH4/gVSS and 27.96 mgH2/gVSS, reaching the following maximum generation rates: 32.91 mgCOD CH4/gVSS.h and 12.63 mgCOD H2/gVSS.h. In contrast to the methanogenic microorganisms of the studied sludge, the acetogenics allow the use of higher organic loads in the systems. However, the lowest S/I ratio (0.1 gCOD/gVSS) resulted in both the best biomethane and biohydrogen production yield, around 2.33 mol CH4/mol glucose and 2.46 mol H2/mol glucose. Compared to the maximum theoretical yields, whereas the sludge produced biohydrogen more effectively under high S/I ratios, biomethane was generated more efficiently in low S/I ratios. Finally, the anaerobic sludge can be employed as a satisfactory inoculum in anaerobic digestion and dark fermentation processes designed for biomethane and biohydrogen production.

Metabolism of novel potential syntrophic acetate-oxidizing bacteria in thermophilic methanogenic chemostats.

Acetate is a major intermediate in the anaerobic digestion of organic waste to produce CH4. In methanogenic systems, acetate degradation is carried out by either acetoclastic methanogenesis or syntrophic degradation by acetate oxidizers and hydrogenotrophic methanogens. Due to challenges in the isolation of syntrophic acetate-oxidizing bacteria (SAOB), the diversity and metabolism of SAOB and the mechanisms of their interactions with methanogenic partners are not fully characterized. In this study, the in situ activity and metabolic characteristics of potential SAOB and their interactions with methanogens were elucidated through metagenomics and metatranscriptomics. In addition to the reported SAOB classified in the genera Tepidanaerobacter, Desulfotomaculum, and Thermodesulfovibrio, we identified a number of potential SAOB that are affiliated with Clostridia, Thermoanaerobacteraceae, Anaerolineae, and Gemmatimonadetes. The potential SAOB possessing the glycine-mediated acetate oxidation pathway dominates SAOB communities. Moreover, formate appeared to be the main product of the acetate degradation by the most active potential SAOB. We identified the methanogen partner of these potential SAOB in the acetate-fed chemostat as Methanosarcina thermophila. The dominated potential SAOB in each chemostat had similar metabolic characteristics, even though they were in different fatty-acid-fed chemostats. These novel syntrophic lineages are prevalent and may play critical roles in thermophilic methanogenic reactors. This study expands our understanding of the phylogenetic diversity and in situ biological functions of uncultured syntrophic acetate degraders and presents novel insights into how they interact with methanogens.IMPORTANCECombining reactor operation with omics provides insights into novel uncultured syntrophic acetate degraders and how they perform in thermophilic anaerobic digesters. This improves our understanding of syntrophic acetate degradation and contributes to the background knowledge necessary to better control and optimize anaerobic digestion processes.

Unveiling the hidden diversity and functional role of Chloroflexota in full-scale wastewater treatment plants through genome-centric analyses

Abstract The phylum Chloroflexota has been found to exhibit high abundance in the microbial communities from wastewater treatment plants (WWTPs) in both aerobic and anaerobic systems. However, its metabolic role has not been fully explored due to the lack of cultured isolates. To address this gap, we use publicly available metagenome datasets from both activated sludge (AS) and methanogenic (MET) full-scale wastewater treatment reactors to assembled genomes. Using this strategy, 264 dereplicated, medium- and high-quality metagenome-assembled genomes (MAGs) classified within Chloroflexota were obtained. Taxonomic classification revealed that AS and MET reactors harbored distinct Chloroflexota families. Nonetheless, the majority of the annotated MAGs (166 MAGs with >85% completeness and < 5% contamination) shared most of the metabolic potential features, including the ability to degrade simple sugars and complex polysaccharides, fatty acids and amino acids, as well as perform fermentation of different products. While Chloroflexota MAGs from MET reactors showed the potential for strict fermentation, MAGs from AS harbored the potential for facultatively aerobic metabolism. Metabolic reconstruction of Chloroflexota members from AS unveiled their versatile metabolism and suggested a primary role in hydrolysis, carbon removal and involvement in nitrogen cycling, thus establishing them as fundamental components of the ecosystem. Microbial reference genomes are essential resources for understanding the potential functional role of uncultured organisms in WWTPs. Our study provides a comprehensive genome catalog of Chloroflexota for future analyses aimed at elucidating their role in these ecosystems.

Solving the seasonality issue in sugarcane biorefineries: High-rate year-round methane production from fermented sulfate-free vinasse and molasses

Anaerobic digestion (AD) has been recently highlighted as the most efficient approach to manage vinasse in sugarcane biorefineries, providing both a renewable energy source (biogas) and a mineralized and nutrient-rich effluent suitable for agricultural use. However, the high sulfate concentrations (ca. 2 g L−1) present in vinasse and its seasonal availability (7–8 months) hinder the maximization of methane production in AD plants. This study investigated the use of sulfate-free vinasse (season) and molasses (off season), both pre-fermented in fermentative-sulfidogenic systems, as substrates to obtain enhanced year-round methane production in sugarcane biorefineries. Two second stage methanogenic structured-bed reactors operated at different temperatures (30 °C and 55 °C) were subjected to increasing organic loading rate (OLR) levels (1.0–20.0 kg COD m−3 d−1) in an experimental simulation of sequential periods of season, off season and season. An efficient start-up strategy enabled achieving operating stability in the full load project (10.0 kg COD m−3 d−1) in 37 d, which means anticipating the maximization of bioenergy production. Pre-fermenting vinasse and molasses was imperative for maintaining efficient organic matter conversion (80–90 %) into methane, regardless of the significant differences in lactate and phenols availability. A methane content in biogas ≥ 80 % and methane yield ≥ 330 NmL CH4 g−1COD were observed in both reactors, with no apparent observation of organic overloads. The results point towards a highly efficient strategy to maintain year-round high-rate biogas production from sugarcane vinasse, although the relatively high molasses demands can trigger an internal competition (with ethanol production) for substrate.

Analysing the mechanism of food waste anaerobic digestion enhanced by iron oxide in a continuous two-stage process

The food waste (FW) digestion performance can be enhanced by introducing iron oxide (IO) into digesters. However, the role of IO in continuous two-stage digesters in enhancing the FW anaerobic digestion remains unclear. In this study, the effect of IO on the bioenergy recovery from a two-stage digestion process was investigated. The bioenergy recovery was significantly increased by up to 208.43 % with IO addition. The activities of dehydrogenase, α-amylase, and protease increase by 0.82–1.44, 7.24–14.56 and 7.97–20.45 times, respectively, as compared with that of the blank. With IO addition, the metabolic pathway in hydrolytic–acidogenic (HA) reactor shifted from lactic acid fermentation to butyric fermentation, which promoted stable methane production in methanogenic (MG) reactor. The activity of coenzyme F420 increased by 19.19–39.01 times, indicating that IO facilitated FW digestion by promoting hydrogenotrophic methanogenesis. The enhancement in the enzyme activity was attributable to the Fe2+ generated by dissimilatory iron reduction. According to the microbial analysis, IO enhanced interspecies hydrogen transfer between Methanobacterium and Syntrophomonas. Furthermore, IO improved direct interspecies electron transfer between Geobacter sulfurreducens and Methanosarcina. The effluent recirculation strategy greatly facilitated the hydrolysis and acidification of FW, which was critical for improving the two-stage process performance.

Iron and Nickel Supplementation Exerts a Significant Positive Effect on the Hydrogen and Methane Production from Organic Solid Waste in a Two-Stage Digestion

Two-stage anaerobic digestion and trace metals (TM) supplementation are promising techniques to improve biogas production. Fe2+ and Ni2+ can improve process stability since they are part of the cofactors of enzymes and microorganisms’ growth. This work attempted to evaluate the effect of Fe2+ and Ni2+ addition on H2-rich biogas production from organic solid waste and the CH4-rich biogas production from the acidogenic effluents (AEs) enriched with TM. The TM concentrations that enhanced the hydrogen yield in the batch were 0.25 mg/L of Ni2+ and 334 mg/L of Fe2+. These concentrations were evaluated in a two-stage system. The substrate for the batch tests and fermentative reactor (first stage) was OSW. The AE generated in the first stage was the substrate to produce CH4-rich biogas in the second stage. In the first stage, the productivity achieved was 1823 ± 160 mL H2/L/day. However, TM supplementation decreased productivity by 65% since the VS removal increased. Megasphaera genus predominated in the first stage. Regarding the methanogenic reactor, the undiluted AE without TM caused the fast decay of the process. Nevertheless, the reactor operated stably after using AE enriched with TM as a substrate, and CH4 yields increased by 42%. The highest productivity achieved in the second stage was 1278 ± 42 mL CH4/L/day, operating with an organic loading rate of 2.8 gVS/L/day. The genera Proteiniphilum, Thermovirga, DMER64, Anaerovorax, and Syntrophomonas predominated in the second stage. In conclusion, AE enriched with TM can be used to recover the stability of anaerobic digesters, increasing methane production.

A hybrid bioelectrochemical system coupling a zero-gap cell and a methanogenic reactor for carbon dioxide reduction using a wastewater-derived catholyte

A hybrid bioelectrochemical system coupling a zero-gap cell and a methanogenic reactor for carbon dioxide reduction using a wastewater-derived catholyte

Bioenergy production from pretreated rice straw in Nigeria: An analysis of novel three-stage anaerobic digestion for hydrogen and methane co-generation

The response to Nigeria's energy inadequacies and waste management issues is projected in this research to be achieved with hydrogen and methane co-produced from pretreated (PT) rice straw (RS) in a three-stage digestion process. This study also demonstrated a novel pretreatment (PTM) agent to improve biological energy recovery from RS. The objectives were accomplished using acidogenic and methanogenic procedures in batch, semi-continuous and continuous systems after pretreating RS with chemical/potash extract (PE) followed by a biological agent. At the same time, the energy assessments were done using data from the laboratory study and the literature. The research findings indicated that at the acidogenesis stage, specific hydrogen yield was insignificant when chemical agents and PE were employed alone. However, the daily H2 production increased when the PT RS residues were enzymatically hydrolysed with NaOH-PT (114 NmL H2 g−1 TS d−1) and PE-PT (103 NmL H2 g−1 TS d−1) RS substrates having the highest values at steady states and raw RS producing the least (30 NmL H2 g−1 TS d−1). In the methanogenesis phase, chemical/ PE PTM followed by enzymatic hydrolysis of RS improved the daily specific methane production by 18%, 31.7% and 41.5% for HCl, PE and NaOH-PT RS residues. The methane production efficiency was 80% for NaOH, 75% for PE, and 68% for HCl RS PT samples, while the raw RS was 48%. The total output energy expressed in electricity and thermal production using combined cooling, heat, and power (CCHP) showed that NaOH and PE-PT RS digesters gave the highest electricity (892.43 and 852.00 KWhelect. tonne-1 TS) and thermal (1194.10 and 1140 KWhtherm. tonne-1 TS) yield respectively. Similarly, the cooling fluid in KWhcool produced per tonne of TS RS was 835.57, 798.00 and 741.66 for NaOH, PE and HCl PT RS samples. Finally, whereas the Firmicutes, especially the Clostridium, Ruminococcus and Thermoanaerobacterium, were the dominant microbial community in acidogenic digestates, the Euryarchaeota typified by Methanobacterium, Methanosarcina and Methanosaeta were the principal phyla for most methanogenic reactors.

Metabolic Functional Profiles of Microbial Communities in Methane Production Systems Treating Winery Wastewater

This study investigated the impact of process configuration and conditions on microbial communities and metabolic pathways in the anaerobic digestion of winery effluents. Four system configurations were analyzed for taxonomic and functional profiles using 16S rRNA gene sequencing and Tax4Fun2. Sporolactobacillus, Prevotella, and Acetobacter dominated (> 70%) in the acidogenic reactor with 5277 conserved functions across configurations. In the methanogenic reactor, methane production relied on Methanosaeta in the single-stage configuration (13%) and five archaea genera in the two-stage configuration (18%). Thermophilic conditions favored syntrophic acetate oxidation and hydrogenotrophic methanogenesis by Methanothermobacter (65%), significantly changing due to temperature. The two-stage configuration exhibited 3.0 times higher functional redundancy than the single-stage configuration. Mesophilic conditions displayed 2.5 times greater functional redundancy than thermophilic conditions. High organic loading rate and short hydraulic retention time reduced functional redundancy by 1.5 times. Assessing microbial functionality beyond their composition is crucial to understand stability and performance of anaerobic digestion systems.

Anaerobic co-digestion of agro-industrial wastes using anaerobic sequencing batch reactor for bio-energy recovery: Focus on process performance and stability of the methanogenic step

Anaerobic co-digestion of tannery wastewater (TWW) with dairy wastewater (DWW) using a two-phase anaerobic sequencing batch reactor (ASBR) was evaluated. For this purpose, laboratory-scale anaerobic digesters, one for acidogenesis and the other for methanogenesis, with 0.4 and 0.6 L of working volume, respectively, operated in semi-continuous mode, were used. The results showed that a methanogenic reactor treating the effluent acidogenic reactor (50 % TWW and 50 % DWW) exhibits the best process performances in terms of daily biogas (64.7 mL/day), methane production (461 mL/day), specific methane yield (892 mL CH4/g COD), methane content (71.2 %), and total chemical oxygen demand (TCOD) removal efficiency (85.6 %) when operated at a hydraulic retention time (HRT) of 15 days. This indicated that the addition of DWW improves the anaerobic co-digestion process, increasing biogas production (64.7 mL/day) by about 41 % as compared with anaerobic co-digestion of 100 % TWW (27.4 mL/day). The process stability of the methanogenic stage of the two-stage anaerobic digestion process was also evaluated, and the obtained result showed suitable pH (6.70), no total volatile fatty acid (TVFA) accumulation (VFA/alkalinity: 0.363), alkalinity (3350 mg CaCO3/L), and ammonia (231 mg/L) within the optimum operating range. Furthermore, high overall performance efficiency in terms of TCOD reduction (88.8 %) in the two-phase (acidogenesis and methanogenesis) anaerobic digester of 50:50 (TWW:DWW) was obtained when operated at a HRT of 18 days (3 days for acidogenesis and 15 days for methanogenesis). Anaerobic co-digestion of TWW with DWW generally resulted in increased process stabilities and performances compared to mono-digestion of TWW.