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Despite its numerous advantages, the aerobic granular sludge (AGS) process faces several challenges that hinder its widespread implementation. One such challenge is the requirement for high organic load ratios (OLR), which significantly impacts AGS formation and stability, posing a barrier to commercialization. In response to these challenges, this study investigates the granulation and treatment efficacy of the AGS process for treating high-concentration wastewater under various OLR and settling time. Three sequential batch reactors (R1, R2, R3) were operated at OLRs of 0.167, 0.33, and 1 kg COD/m3·day. The study focuses on analyzing key parameters including sludge characteristics, extracellular polymeric substances (EPS) content, PN/PS ratio, and microbial clusters. Results demonstrate that reducing settling time from 90 to 30 min enhances sludge settleability, resulting in a maximum 50.8 % decrease in SVI30 (from 98.1 to 122.8 mL/g to 51.9-81.3 mL/g), thereby facilitating the selection of beneficial microorganisms during granulation. Particularly, at R2, the PN/PS ratio was 4.3, and EPS content increased by 1.52-fold, leading to a 1.41-fold increase in sludge attachment. This observation suggests a progressive maturation of AGS. Additionally, analysis of microbial diversity and cluster composition highlights the influence of OLR variations on the ratios of Proteobacteria and Bacteroidetes. These findings emphasize the significant impact of SBR operational strategies on AGS process performance and biological stability, offering valuable insights for the efficient operation of future high-concentration wastewater treatment processes.

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The organic loading rate (OLR) is a critical parameter affecting the stability of dry anaerobic digestion (AD) of kitchen waste (KW), and significantly impacting the variations in physicochemical parameters and microbial communities. However, the evolution of quorum sensing (QS) and their role on anaerobic biochemical metabolism during the increase in OLR in dry AD remain unknown. Therefore, this study systematically elucidated the matter through multi-omics analysis based on a pilot-scale dry AD of KW. The results demonstrated that fluctuations in the OLR significantly influenced the microbial QS in dry AD. When the OLR ≤4.0 g·VS/L·d, the system operated stably, and methane production increased. The enrichment of Proteobacteria was crucial for sustaining high levels of functional genes associated with various types of QS, including acyl-homoserine lactones (AI-1), autoinducer-2 (AI-2), autoinducer-3 (AI-3), and gamma-aminobutyric acid (GABA). This enabled cooperative communication among microbes under low OLR. Furthermore, most genes associated with these QS processes positively affected hydrolysis, acidogenesis, and methanogenesis. When the OLR increased to 6.0 g·VS/L·d, the fatty acids and hydrogen partial pressure increased significantly. The autoinducing peptides (AIP)-type became the predominant QS and was positively correlated with fatty acids abundance. Syntrophaceticus and Syntrophomonas may promote syntrophic oxidation of acetate at high OLR through AIP-type QS. These findings provided new insights into the QS processes of microbes during dry AD of KW and a theoretical foundation for optimizing biochemical metabolic processes in dry AD through QS.

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Organic loading rate (OLR) is crucial for determining the stability of dry anaerobic digestion (AD). Digestate recirculation contributes to reactor stability and enhances methane production. Nevertheless, the understanding of how OLR and digestate recirculation affect the abundance and diversity of antibiotics and antibiotic resistance genes (ARGs), as well as the mechanisms involved in the dissemination of ARGs, remains limited. This study thoroughly investigated this critical issue through a long-term pilot-scale experiment. The metabolome analyses revealed the enrichment of various antibiotics, such as aminoglycoside, tetracycline, and macrolide, under low OLR conditions (OLR ≤ 4.0 g·VS/L·d) and the reactor instability. Antibiotics abundance decreased by approximately 19.66-31.69 % during high OLR operation (OLR ≥ 6.0 g·VS/L·d) with digestate recirculation. The metagenome analyses demonstrated that although low OLR promoted reactor stability, it facilitated the proliferation of antibiotic-resistant bacteria, such as Pseudomonas, and triggered functional profiles related to ATP generation, oxidative stress response, EPS secretion, and cell membrane permeability, thereby facilitating horizontal gene transfer (HGT) of ARGs. However, under stable operation at an OLR of 6.0 g·VS/L·d, there was a decrease in ARGs abundance but a notable increase in human pathogenic bacteria (HPB) and mobile genetic elements (MGEs). Subsequently, during reactor instability, the abundance of ARGs and HPB increased. Notably, during digestate recirculation at OLR levels of 6.0 and 7.0 g·VS/L·d, the process attenuated the risk of ARGs spread by reducing the diversity of ARGs hosts, minimizing interactions among ARGs hosts, ARGs, and MGEs, and weakening functional profiles associated with HGT of ARGs. Overall, digestate recirculation aids in reducing the abundance of antibiotics and ARGs under high OLR conditions. These findings provide advanced insights into how OLR and digestate recirculation affect the occurrence patterns of antibiotics and ARGs in dry AD.

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Levulinic acid (LA) is a polymer with a vast industrial application range and can be co-produced as a minor by-product during the biological production of polyhydroxyalkanoates (PHA). However, the influence of key parameters as tools for favouring the production of LA over PHA is still unclear. In this study, we investigated how several critical operational conditions, i.e., carbon-nitrogen ratio (C/N), organic loading rate (OLR) and airflow, can be optimised to favour LA accumulation over PHA production by a mixed microbial culture (MMC), using synthetic grape pomace (GP) hydrolysate as the substrate. The results showed that it was possible to direct the MMC towards LA accumulation instead of PHA. The maximum LA yield was 2.7 ± 0.2 g LA/(L·d) using a C/N of 35, an airflow of 5 L/min and an OLR of 4 g sCOD/(L·d). The OLR and, to a lesser extent, the C/N ratio were the main factors significantly and positively correlated with the biological synthesis of LA.

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Anaerobic digestion (AD) of microalgae is an intriguing approach for bioenergy production. The scaling-up of AD presents a significant challenge due to the systematic efficiency losses related to process instabilities. To gain a comprehensive understanding of AD behavior, this study assessed a modified version of the anaerobic digestion model No1 (ADM1) + Contois kinetics to represent microalgae AD impacted by overloading. To this end, two new inhibition functions were implemented: inhibition by acetate for acidogenesis/acetogenesis and total volatile fatty acids for hydrolysis. This proposed ADM1 modification (including Contois kinetics) simulated AD behavior during the stable, disturbed and recovery periods, showing that the inhibition functions described in the original ADM1 cannot explain the AD performance under one of the most common perturbations at industrial scale (overloading). The findings underscore the importance of refining the inhibitions present in original ADM1 to better capture and predict the complexities of microalgae AD against overloading.

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The feasibility of anaerobic co-digestion in semicontinuous mode of two major urban biowaste, food waste (FW) and garden and park waste (GPW) (75 % FW and 25 % GPW) as well as the co-digestion of FW with the process water originated from the hydrothermal carbonization of GPW (95 % FW and 5 % process water), both on a COD basis, has been assessed. The effect of varying organic loading rate (OLR) from 1.5 to 3.5 g COD/L·d on methane yield, gross energy recovery, and microbiome population was evaluated. For comparison, anaerobic digestion of FW was also conducted to determine the best strategy for sustainable biowaste management. This study showed an optimal OLR of 2.5 g COD/L·d. Acetic and propionic acid content increased as OLR raised for each condition studied, while methane yield decreased at the highest OLR tested indicating overloading of the system. The anaerobic co-digestion of FW and process water showed a 10 % increase on methane production compared to anaerobic digestion of FW (324 vs. 294 mL CH4 STP/L·d). Moreover, it enhances the process due to a greater abundance and diversity of hydrolytic and acidogenic bacteria belonging to Bacterioidota, Firmicutes, and Chloroflexi phyla, as well as promotes the hydrogenotrophic pathway under higher propionic concentrations which is not usually favoured for methane production. The integration of hydrothermal carbonization of GPW with the anaerobic co-digestion of 95 % FW and 5 % of process water results in the highest potential energy recovery and could be a good strategy for sustainable management of urban biowaste.

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The Anaerobic Baffled Reactor (ABR) is an effective solution for landfill leachate treatment using an anaerobic fermentation process, which helps to reduce operating costs and sludge volume. To better understand the biological, chemical, and physical processes involved, especially when combining the ABR with an aerobic component, the study aimed to investigate the performance of an Anaerobic-Aerobic Hybrid Baffled Reactor (AABR) that includes an Anaerobic Filter (AF) for treating landfill leachate. This research utilized two glass reactors. The first reactor, designated as AABR-AF, consisted of six independent rectangular glass chambers arranged side by side. The third and sixth chamber designed for aerobic treatment and AF, respectively. The second reactor was used as a control reactor and did not include any aerobic chamber. The highest Removal Efficiencies (REs) for turbidity, COD, BOD, TP, TKN, nitrate, TOC, and TSS in the AABR-AF and ABR-AF were found to be (65.4% and 56.3%), (98.3% and 94.1%), (98.1% and 93.2%), (86.4% and 65%), (89.2% and 76.7%), (81.2% and 64.4%), (88.2% and 79.4%), and (72.4% and 68.5%), respectively. These optimal REs were achieved at an HRT of 48 h and an OLR of 10 kg/m3.d. Also, the highest and the lowest REs in Heavy Metals (HMs) were 89.57% for manganese in AABR-AF and 6.59% for nickel in ABR-AF, in an OLR of 10 kg/m3.d, respectively. The effective removal of Organic Matters (OMs) from landfill leachate using the AABR-AF and ABR-AF was found to be strongly influenced by HRT and OLR. The AABR-AF configuration, featuring a single aerobic chamber in the reactor, exhibited a higher efficiency in removing OMs compared to the ABR-AF configuration.

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The two-stage anaerobic digestion (AD) for biohythane production is a sustainable solution, but it is sensitive to organic shock load that disrupts reactors and inhibits biohythane production. This study investigated biohythane production, reactor performance, and the possibility of post-failure restoration in a two-stage AD system designed for treating high-strength organic wastewater. Sudden shock load was applied by increasing the OLR threefold higher after reaching steady state phase. During shock load phase, hydrogen content, hydrogen yield and methane production rate (MPR) reached its peak values of 62.61 %, 1.641 mol H2/mol glucose, and 1.003 L CH4/L⋅d respectively before declining significantly. Interestingly, during the restorative phase, hydrogen production sharply declined to nearly zero, while methane production exhibited a resilience and reached its peak methane content of 52.2 %. The study successfully demonstrated the system's resilience to sudden shock load, ensuring stable methane production, while hydrogen production did not exhibit the same capability.

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The semi-continuous anaerobic co-digestion (AcoD) of thermal and thermal-alkali pretreated organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) was studied under varying hydraulic retention times (HRT) and organic loading rates (OLR Three semi-continuous digesters were operated under control (non-pre-treated), thermally pretreated (125 °C), and thermal-alkali pretreated (125°C-3g/L NaOH) conditions at variable OLRs at 2.5, 4.0, 5.1, and 7.6 kgVS/m3.d and corresponding HRTs of 30, 20, 15, and 10 days. The 10 and 43% higher methane yield (0.445 m3/kgVS) and 11 and 57% higher VS removal (52%) was achieved for thermal-alkali pretreated digester at 5.1 kgVS/m3.d OLR over thermally pretreated (0.408 m3/kgVS, 45% VS removal) and control digesters (0.310 m3/kgVS, 33% VS removal), respectively. Thermal and thermal-alkali digesters failed on increasing the OLR to 7.6 kgVS/m3.d, whereas the control digester becomes upset at 5.1 kgVS/m3.d OLR. The metagenomic study revealed that Firmicutes, Bacteroidetes, Chloroflexi, Euryarchaeota, Proteobacteria, and Actinobacteria were the predominant bacterial population, whereas Methanosarcina and Methanothrix dominated the archaeal community. Energy balance analysis revealed that thermal alkali pretreatment showed the highest positive energy balance of 114.6 MJ/ton with an energy ratio of 1.25 compared with thermally pretreated (81.5 MJ/ton) and control samples (-46.9 MJ/ton). This work pave the way for scaleup of both thermal and thermal-alkali pre-treatment at 125 °C to realize the techno-economic and energy potential of the process.

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The effects of heterogenous (anaerobic sludge from treating distillery sewage, ASDS) and homologous (anaerobic sludge from treating swine wastewater, ASSW) inocula on anaerobic digestion and the microbial community in an up-flow anaerobic sludge blanket treating swine wastewater were compared. The highest chemical oxygen demand removal efficiencies with ASDS (84.8%) and ASSW (83.1%) were obtained with an organic loading rate of 15 kg COD/m3/d. For ASSW compared with ASDS, methane production efficiency was 15.3% higher and excess sludge production was 73.0% lower. The abundance of the cellulose hydrolyzing bacterium Clostridium sensu stricto_1 with ASDS (36.1%) was 1.5 times that with ASSW, while that of Methanosarcina with ASSW (22.9%) was > 100 times that with ASDS. ASDS reduced the content of pathogenic bacteria by 88.0%, while ASSW maintained a low level of pathogenic bacteria. ASSW greatly improved the methane production efficiency of wastewater and is more suitable for treating swine wastewater.

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Performance of an anaerobic moving bed biofilm reactor (AnMBBR) was evaluated for pretreatment of real textile desizing wastewater at organic loading rate (OLR) of 1±0.05 to 6.3±0.37 kgCOD/m3/d. After OLR optimization, the performance of AnMBBR was evaluated for biodegradation of reactive dyes. AnMBBR was operated under a mesophilic temperature range of 30 to 36 °C, while the oxidation-reduction potential (ORP) and pH were in the range of 504 to 594 (-mV) and 6.98 to 7.28, respectively. By increasing the OLR from 1±0.05 to 6.3±0.37 kgCOD/m3/d, COD and BOD5 removal was decreased from 84 to 39% and 89 to 49%, respectively. While the production of biogas was increased from 0.12 to 0.83 L/L·d up to an optimum OLR of 4.9±0.43 kgCOD/m3/d. With increase in the dye concentration in the feed, COD, BOD5, color removal and biogas production reduced from 56, 63, 70% and 0.65 L/L·d to 34, 43, 41% and 0.08 L/L·d, respectively. Based on the data obtained, a cost-benefit analysis of AnMBBR was also investigated for the pretreatment of real textile desizing wastewater. Cost estimation of anaerobic pretreatment of textile desizing wastewater indicated a net profit of 21.09 million PKR/yr (114,000 €/yr) and a potential payback period of 2.54 years.

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Currently, the phenomenon of direct interspecies electron transfer (DIET) is of great interest in the technology of anaerobic digestion (AD) due to potential performance benefits. However, the conditions for the occurrence of DIET and its limits on improving AD under conditions close to real have not been studied enough. This research is concentrated on the effect of conductive carbon cloth (R3), in comparison with a dielectric fiberglass cloth (R2) and control (R1), on the AD performance in large (90 L) thermophilic reactors, fed with a mixture of simulated organic fraction of municipal solid waste and sewage sludge. While organic loading rate (OLR) was gradually increased from 2.4 to 8.66 kg VS/(m3 day), a statistically significant (p < 0.05) difference in biogas production was observed between R1 and both R2 and R3. However, at a maximum OLR of 12.12 kg VS/(m3 day) in R3, an increase in biogas production (p < 0.05) was observed both compared to R1 (by 8.97%) and R2 (by 4.24%). The content of volatile fatty acids in R3 as a whole was the lowest, especially at the maximum OLR. Biofilm on carbon cloth was rich in syntrophic microorganisms of the genera Tepidanaerobacter, as well as Defluviitoga, capable of DIET in mixed cultures with Methanothrix, which was the most abundant methanogen in biofilm. Suspended Bifidobacterium, Fervidobacterium and Anaerobaculum were negatively affected, while Defluviitoga, Methanothermobacter and Methanosarcina, on the contrary, were positively affected by the increase in OLR and showed, respectively, a negative and positive correlation (p < 0.05) with the main AD performance parameters.

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A high amount of easily degradable organics and the absence of trace metals (TMs) in household food waste (HFW) lowered the stability and efficiency of anaerobic digestion (AD) of HFW. Leachate addition to the AD of HFW can provide ammonia nitrogen and TMs to address the accumulation of volatile fatty acids and the lack of TMs. To study the effect of leachate addition on increasing organic loading rate (OLR), both mono-digestion of HFW and AD of HFW with leachate addition were evaluated using two continuously stirred tank reactors. The OLR of the mono-digestion reactor only reached 2.5 g COD/L/d. However, with the addition of ammonia nitrogen and TMs, the OLR of the failed mono-digestion reactor increased by 2 and 3.5 g COD/L/d, respectively. The specific methanogenic activity increased by 94.4% and the hydrolysis efficiency increased by 135%. Finally, the OLR of mono-digestion of HFW reached 8 g COD/L/d, with a hydraulic retention time (HRT) of 8 days and methane production rate of 2.4 L/L/d. In the leachate addition reactor, the OLR reached 15 g COD/L/d, while the HRT and methane production were 7 days and 3.4 L/L/d, respectively. This study demonstrates that leachate addition substantially improves the AD efficiency of HFW. The two main mechanisms of increasing the OLR of an AD reactor are the buffer capacity of ammonia nitrogen and the stimulation of methanogen by TMs from leachate.

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This study proposed fresh leachate treatment with anaerobic membrane bioreactor (AnMBR) based on the on-site investigation of the characteristics of fresh leachate. Temperature-related profiles of fresh leachate properties, like chemical oxygen demand (COD), were observed. In addition, AnMBR achieved a high COD removal of 98% with a maximum organic loading rate (OLR) of 19.27 kg-COD/m3/d at the shortest hydraulic retention time (HRT) of 1.5 d. The microbial analysis implied that the abundant protein and carbohydrate degraders (e.g., Thermovirga and Petrimonas) as well as syntrophic bacteria, such as Syntrophomonas, ensured the effective adaptation of AnMBR to the reduced HRTs. However, an excessive OLR at 36.55 kg-COD/m3/d at HRT of 1 d resulted in a sharp decrease in key microbes, such as archaea (from 37% to 15%), finally leading to the deterioration of AnMBR. This study provides scientific guidance for treating fresh leachate by AnMBR and its full-scale application for high-strength wastewater.

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Salt-tolerant aerobic granular sludge (SAGS) technology has shown potentials in the treatment of ultra-hypersaline high-strength organic wastewater. However, the long granulation period and salt-tolerance acclimation period are still bottlenecks that hinder SAGS applications. In this study, "one-step" development strategy was used to try to directly cultivate SAGS under 9% salinity, and the fastest cultivation process was obtained under such high salinity compared to the previous papers with the inoculum of municipal activated sludge without bioaugmentation. Briefly, the inoculated municipal activated sludge was almost discharged on Day 1-10, then fungal pellets appeared and it gradually transitioned to mature SAGS (particle size of ∼4156 µm and SVI30 of 57.8 mL/g) from Day 11 to Day 47 without fragmentation. Metagenomic revealed that fungus Fusarium played key roles in the transition process probably because it functioned as structural backbone. RRNPP and AHL-mediated systems might be the main QS regulation systems of bacteria. TOC and NH4+-N removal efficiencies maintained at ∼93.9% (after Day 11) and ∼68.5% (after Day 33), respectively. Subsequently, the influent organic loading rate (OLR) was stepwise increased from 1.8 to 11.7 kg COD/m3·d. It was found that SAGS could maintain intact structure and low SVI30 (< 55 mL/g) under 9% salinity and the OLR of 1.8-9.9 kg COD/m3·d with adjustment of air velocity. TOC and NH4+-N (TN) removal efficiencies could maintain at ∼95.4% (below OLR of 8.1 kg COD/m3·d) and ∼84.1% (below nitrogen loading rate of 0.40 kg N/m3·d) in ultra-hypersaline environment. Halomonas dominated the SAGS under 9% salinity and varied OLR. This study confirmed the feasibility of direct aerobic granulation in ultra-hypersaline environment and verified the upper OLR boundary of SAGS in ultra-hypersaline high-strength organic wastewater treatment.

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A two-stage anaerobic digestion process utilizing food waste was investigated in this study, without any additive and co-digestion. Solid content, temperature and pH value were key controlling factors for hydrolysis, which results the optimized food waste hydrolysate with COD/VSfood waste of 2.67. Efficient biogas production was maintained in long-term operation (>150 d) without any additive, and methane production yields up to 699.7 mL·gVS-1·d-1 was achieved under organic loading rate (OLR) of 31.0 gVS·d-1. Methane production can be recovered (70.4 %) after temperature shock within 30 days. This study confirmed the possibility to establish two-stage food waste anaerobic digestion system under high organic load. pH, OLR, and temperature are key factors to maintain stable biogas production, while pH control was performed as a in situ sulfide control technology (75.8 % sulfide reduction). This study provides practical strategies for food waste utilization and decreasing carbon footprint.

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The present study aimed to investigate the application of a multilayer quartz sand substrate horizontal subsurface flow constructed wetland (HSFCW) for campus sewage treatment. It aimed to assess the pollutant removal efficiency and anti-clogging performance under the suggested maximum organic loading rate (250 g/m2/d). The results of the multilayer HSFCW (CW6) were compared to the mololayer HSFCW (CW1) for the removal of the chemical oxygen demand (COD), solid accumulation, and microbial communities. During operation, the combination conditions of high hydraulic loading rate (HLR) with low COD concentration were better for COD removal under a high organic loading rate (OLR) of 200-300 g/m2/d. The maximum removal rate reached 80.4% in CW6 under high HLR, which was 13.8% higher than that in CW1, showing better adsorption and biodegradation ability of organic matter. Impressive clogging resistance capacity was found in CW6 due to the lower contents of the insoluble organic matter (IOM) that are prone to clogging, indicating full degradation of organic matters, particularly IOM, in CW6 under high HLR. Less abundance of unclassified Chitinophagaceae (under low HLR), Pedobacter and Saccharibacteria_genera_incertae_sedis (under high HLR) in CW6, which contributed to aerobic membrane fouling, helped to prevent clogging. Moreover, Brevundimonas, Cloacibacterium, Citrobacter, Luteimonas contributed to IOM degradation, thus further enhancing the anti-clogging performance. In view of the better clogging resistance performance, the application of CW6 operated under high HLR and low COD concentrations was recommended to achieve economical, efficient, and steady COD removal for domestic sewage treatment in long-term operation.

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pH is one of the major parameters that influence the granulation and long-term operation of aerobic granular sludge (AGS). In hypersaline wastewater, the impact of pH on granulation and the extent of organic loading rate (OLR) that AGS can withstand under different pH are still not clear. In this study, AGS was cultivated at 3% salinity in three sequencing batch reactors with influent pH values of 5.0, 7.0, and 9.0, respectively, and the OLR was stepwise increased from 2.4 to 16.8 kg COD/m3·d after the granules maturation. The results showed the satisfactory granulation and organic removal under different influent pH conditions, in which the granulation was completed on day 43, 23, and 23, respectively. Neutral influent was the most appropriate for development of salt-tolerant aerobic granular sludge (SAGS), while acidic environment induced the formation of fluffy filamentous granules, and alkaline environment weakened the granule stability. Metagenomic analysis revealed the similar microbial community of neutral and alkaline conditions, with the predominance of genus Paracoccus_f__Rhodobacteraceae. While in acidic environment, fungus Fusarium formed the skeleton of filamentous granules and functioned as the carrier of bacteria including Azoarcus and Pararhodobacter. With the elevation of OLR, SAGSs were found to maintain the compact structure under OLRs of 2.4, 7.2, and 2.4 kg COD/m3·d, and obtain high TOC removal (>95.0%) under OLRs of 7.2, 14.4, and 14.4 kg COD/m3·d, respectively. For hypersaline high-strength organic wastewater, satisfactory TOC removal could also be obtained at broad pH ranges (5.0-9.0), in which neutral environment was the most suitable and acidic environment was the worst. This study contributed to a better understanding of SAGS granulation and treatment of hypersaline high-strength organic wastewater with different pH values.

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This study provided novel insights into the effects of organic loading rate (OLR) and hydraulic retention time (HRT) on thermophilic anaerobic co-digestion of food waste and sewage sludge. The obtained maximum methane (CH4) yield of 328 ± 4 mL CH4/g CODfed at HRT of 15 days (OLR = 5.8 g VS/L/d) was partly attributable to the enhanced acidogenesis, acetogenesis, and methanogenesis phases. The increased key enzyme activities, particularly acetate kinase (improved by 5.2-fold), providing substantial methanogenic substrates for efficient CH4 production. The functional syntrophs that were related to syntrophic decarboxylation, novel acetate oxidation & reductive acetyl-CoA, and ß-oxidation pathways could drive trophic interactions with methanogens. This markedly stimulated hydrogenotrophic Methanoculleus thermophilus metabolism and concomitantly enriched mixotrophic Methanosarcina thermophila. The distinctive cross-feeding interspecies interactions significantly affected the assembly and dynamics of thermophilic consortia. These findings shed light on the physicochemical and microbial mechanisms of HRT- and OLR-dependent enhancement of methanogenesis.

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