Methanogenic Reactor Research Articles

Demand-driven biogas production from Upflow Anaerobic Sludge Blanket (UASB) reactors to balance the power grid

Future energy systems necessitate dispatchable renewable energy to balance electrical grids with high shares of intermittent renewables. Biogas from anaerobic digestion (AD) can generate electricity on-demand. High-rate methanogenic reactors, such as the Upflow Anaerobic Sludge Blanket (UASB), can react quicker to variations in feeding as compared to traditional AD systems. In this study, experimental trials validated the feasibility of operating the UASB in a demand-driven manner. The UASB was operated with leachate produced from a hydrolysis reactor treating grass silage. The UASB demonstrated a high degree of flexibility in responding to variable feeding regimes. The intra-day biogas production rate could be increased by up to 123% under 4 hours in demand-driven operation, without significant deterioration in performance. A model based on kinetic analysis was developed to help align demand-driven operation with the grid. The findings suggest significant opportunities for UASBs to provide positive and negative balance to the power grid.

The production of bio-silica from agro-industrial wastes leached and anaerobically digested rice straws

Silicon extraction from rice straw (RS) has gained attention due to its increasing demand for various applications. This study investigated the potential for producing bio-silica from RS digestates, and RS leached with agro-industrial waste, such as corn-steep liquor (CSTL) and cassava-steep wastewater (CSWW). The results indicated that pretreated (PT) and digested methanogenic RS ash (RSA) samples contain amorphous silica, as confirmed by SEM, EDX and XRD analysis. The EDX results showed high levels of silica with minimal inorganic elements, while the XRD showed that the RSA from methanogenic reactors contained amorphous silica, indicated by a broad peak at 2Ɵ ranging from 160 to 280. The leaching potential of CSTL and CSWW was confirmed through SEM and EDX, with the XRD results indicating that CSWW was a more effective leaching agent than CSTL. The CSWW-leached RSA samples showed slight amorphousness with a broad peak at 2Ɵ between 160 and 250.

Evaluation of biogas production and pollutant removal efficiency of two-phase anaerobic digestion treating slaughterhouse effluent

Treatment of slaughterhouse and other agro-processing industry effluent has become important due to continuous global population growth and meat demand, particularly in developing countries, for sustainable biowaste management as well as value additions such as biofuel. Therefore, the objective of the study was to evaluate the performance of two-phase anaerobic digestion of slaughterhouse wastewater in terms of biogas production, methane yield, and removal efficiencies of organic matter, total nitrogen, and total phosphorus. Two consecutively connected 40 L galvanized metal anaerobic batch bioreactors were used to conduct the experiment. The total phosphorus removal efficiencies of hydrolytic-acidogenic reactor and methanogenic reactor were 13.34% and 16.58%, respectively. Total chemical oxygen demand, soluble chemical oxygen demand, biological oxygen demand, total dissolved solids, total solids, total suspended solids, volatile solids, and turbidity had overall removal efficiencies of 82.87, 88.53, 93.32, 75.35, 95.55, 98.95, 97.42 and 98.06%, respectively. Biogas production of 189.45 mL/day with methane and carbon dioxide compositions of 67.69% and 29.9%, respectively, was also achieved. It was concluded that the two-phase anaerobic digestion of slaughterhouse wastewater shows substantial organic matter removal efficiencies and biogas production.

Genome-centric metagenomic insights into the role of Chloroflexi in anammox, activated sludge and methanogenic reactors

BackgroundThe phylum Chloroflexi is highly abundant in a wide variety of wastewater treatment bioreactors. It has been suggested that they play relevant roles in these ecosystems, particularly in degrading carbon compounds and on structuring flocs or granules. Nevertheless, their function is not yet well understood as most species have not been isolated in axenic cultures. Here we used a metagenomic approach to investigate Chloroflexi diversity and their metabolic potential in three environmentally different bioreactors: a methanogenic full-scale reactor, a full-scale activated sludge reactor and a lab scale anammox reactor.ResultsDifferential coverage binning approach was used to assemble the genomes of 17 new Chloroflexi species, two of which are proposed as new Candidatus genus. In addition, we recovered the first representative genome belonging to the genus ‘Ca. Villigracilis’. Even though samples analyzed were collected from bioreactors operating under different environmental conditions, the assembled genomes share several metabolic features: anaerobic metabolism, fermentative pathways and several genes coding for hydrolytic enzymes. Interestingly, genome analysis from the anammox reactor indicated a putative role of Chloroflexi in nitrogen conversion. Genes related to adhesiveness and exopolysaccharides production were also detected. Complementing sequencing analysis, filamentous morphology was detected by Fluorescent in situ hybridization.ConclusionOur results suggest that Chloroflexi participate in organic matter degradation, nitrogen removal and biofilm aggregation, playing different roles according to the environmental conditions.

Wet Anaerobic Codigestion of Sewage Sludge and OFMSW in Pilot-Scale Continuously Stirred Tank Reactors: Focus on the Reactor Microbial Communities

Dark fermentation (DF) is a simple method for hydrogen (H2) production through the valorization of various organic wastes that can be used as feedstock. In particular, an organic fraction of municipal solid waste (OFMSW) is a fermentation substrate that can easily be gathered and provides high yields in biogas and value-added organic compounds such as volatile fatty acids (VFAs). DF is coupled with a methanogenic reactor to enhance biogas production from the OFMSW. In this study, a two-stage reactor was conducted and monitored to optimize the methane yield by reducing the HRT at the DF reactor. A focus of the functional inference based on a next-generation sequence (NGS) metabarcoding analysis and comparison of microbial communities that populate each reactor stage was performed. Concerning gas quality, the two-stage system observed a hydrogen-rich biogas in the first fermentative reactor (on average 20.2%) and an improvement in the methane content in the second methanogenic digester, which shifted from 61.2% obtained for the one-stage experiment to 73.5%. Such increases were due to the improvement in substrate hydrolysis. As for the specific biogas production, the results showed an overall increase of 50%.

Proteiniphilum and Methanothrix harundinacea became dominant acetate utilizers in a methanogenic reactor operated under strong ammonia stress.

Microorganisms in anaerobic digestion (AD) are easily affected by ammonia, especially acetoclastic methanogens. Thus, in ammonia-suppressed AD systems, acetate degradation is reported to be carried out mainly by the cooperation of syntrophic acetate oxidizers and hydrogenotrophic methanogens. Previous studies have revealed ammonia inhibition on microbial flora by AD performance, but the effect mechanism of ammonia on microbial metabolism remains poorly understood. In this study, we constructed a mesophilic chemostat fed with acetate as the sole carbon source, gradually increased the total ammonia nitrogen (TAN) concentration from 1 g L-1 to 6 g L-1, and employed the 16S rRNA gene, metagenomics, and metatranscriptomics analysis to characterize the microbial community structure and metabolic behavior. The results showed that even at the TAN of 6 g L-1 (pH 7.5), the methanogenesis kept normal, the biogas production was approximately 92% of that at TAN of 1 g L-1 and the acetate degradation ratio reached 99%, suggesting the strong TAN tolerance of the microbial community enriched. 16S rRNA gene analysis suggested that the microbial community structure changed along with the TAN concentration. Methanothrix predominated in methanogens all the time, in which the dominant species was gradually replaced from M. soehngenii to M. harundinacea with the increased TAN. Dominant bacterial species also changed and Proteiniphilum showed a significant positive correlation with increased TAN. Meta-omics analysis showed that the absolute dominant microorganisms at TAN of 6 g L-1 were M. harundinacea and Proteiniphilum, both of which highly expressed genes for anti-oxidative stress. M. harundinacea and the second dominant methanogen Methanosarcina highly expressed both acetate cleavage and CO2 reduction pathways, suggesting the possibility that these two pathways contributed to methanogenesis together. Proteiniphilum and some other species in Firmicutes and Synergistetes were likely acetate oxidizers in the community as they highly expressed genes for syntrophic acetate oxidization, H2 generation, and electron transfer. These results suggested that Proteiniphilum as well as M. harundinacea have strong ammonia tolerance and played critical roles in acetate degradation under ammonia-suppressed conditions. The achievements of the study would contribute to the regulation and management of the AD process.

Upgrading ADM1 by Addition of Lag Phase Sub-model to Simulate Acidic Inhibition of Methanogenic Reactor

This study is aimed at improving calculation quality for IWA Anaerobic Digestion Model No.1 (ADM1) to simulate acidic failure of the methane fermentation systems and its performance recovery. The methanogen collected from digestate at a municipal wastewater treatment plant was cultivated in a lab-scale continuous reactor receiving acetate as a sole organic source. By varying the influent concentration during 400 days of operation, 6 datasets of acidification events were obtained to simulate the concentrations of acetate, VSS, pH, and the methane production rate. The ADM1 equipped with either pH sub-model or undissociated acetate sub-model could reproduce the deterioration of reactor performance in the acidic failure but totally failed to simulate the recovery in the subsequent lowered volumetric loading rate. The statistical analysis revealed both ADM1 models had relatively low correlation coefficient (Nash-Sutcliffe model efficiency coefficient (NSE)) of 0.31–0.38 although these were considerably improved from that without parameter calibration (NSE = −0.04). To cope with the mismatch, a lag phase sub-model was developed. The sub-model is composed of the remaining relative activity of the microorganism at which the inhibition peaked, and the half-saturation coefficient to express the specific length of lag phase. By adding the sub-model into the calibrated ADM1, NSE was significantly improved to 0.49–0.53.

Biomethane recovery through co-digestion of cheese whey and glycerol in a two-stage anaerobic fluidized bed reactor: Effect of temperature and organic loading rate on methanogenesis

Anaerobic digestion for CH4 recovery in wastewater treatment has been carried out with different strategies to increase process efficiency, among which co-digestion and the two-stage process can be highlighted. In this context, this study aimed at evaluating the co-digestion of cheese whey and glycerol in a two-stage process using fluidized bed reactors, verifying the effect of increasing the organic loading rate (OLR) (2–20 g-COD.L−1.d−1) and temperature (thermophilic and mesophilic) in the second stage methanogenic reactor. The mesophilic methanogenic reactor (R-Meso) (mean temperature of 22 °C) was more tolerant to high OLR and its best performance was at 20 g-COD.L−1.d−1, resulting in methane yield (MY) and methane production (MPR) of 273 mL-CH4.g-COD−1 and 5.8 L-CH4.L−1.d−1 (with 67% of CH4), respectively. Through 16S rRNA gene massive sequencing analysis, a greater diversity of microorganisms was identified in R-Meso than in R-Thermo (second stage methanogenic reactor, 55 °C). Firmicutes was the phyla with higher relative abundance in R-Thermo, while in R-Meso the most abundant ones were Proteobacteria and Bacteroidetes. Regarding the Archaea domain, a predominance of hydrogenotrophic microorganisms could be observed, being the genera Methanothermobacter and Methanobacterium the most abundant in R-Thermo and R-Meso, respectively. The two-stage system composed with a thermophilic acidogenic reactor + R-Meso was more adequate for the co-digestion of cheese whey and glycerol than the single-stage process, promoting increases of up to 47% in the energetic yield (10.3 kJ.kg-COD−1) and 14% in organic matter removal (90.5%).

Two-stage thermophilic anaerobic digestion of cheese whey: Process optimization, comparison with single-stage, and full-scale estimation

The purpose of this study was to determine whether a single-stage or two-stage system of an anaerobic sequencing batch and fed-batch biofilm reactor (AnSBBR) would be more efficient for thermophilic whey treatment and bioenergy production. The best results were achieved at 55 °C and 15 kg-COD.m−3.d−1 with organic matter removal of 96%, methane productivity of 142.9 mol-CH4.m−3.d−1, and yield of 10.3 mol-CH4.kg-COD−1. In addition, temperature strongly impacted the microbial community diversity and had an inverse relation with the genus Methanosarcina. To treat all of the whey produced by a dairy industry, which generates 3.4 × 103 m3-whey.year−1, a single-stage anaerobic digestion system of 80.0 m³ would be required, generating a power of 75.1 kW and an energy yield of 9.89 MJ.kg-COD−1. A two-stage system designed for the same industry would have a total working volume of 134.9 m³, combining thermophilic acidogenic reactors and mesophilic methanogenic reactors, with a power of 39.1 kW and energy yield of 5.14 MJ.kg-COD−1. The single-stage system would need an investment cost of U$$ 271,681.00, which is 42% cheaper compared to the two-stage system and would be able to supply 23.5% of the energy demand required by the dairy industry.

Biochar regulates enzymes activity and interspecies electron transfer to promote bioenergy recovery from a continuous two-stage food waste anaerobic digestion process

The influence of biochar on the performance of food waste anaerobic digestion in a continuous two-stage process was examined. Biochar was added to a methanogenic (MG) reactor, with 50% of its effluent recirculated to a hydrolytic–acidogenic (HA) reactor. The addition of biochar in the MG reactor simultaneously enhanced the performance of both reactors, and the energy recovery efficiency increased by 25.01–70.99%. Biochar improved the activities of protease and α-amylase in the HA and MG reactors by 1.08–2.23 and 0.46–1.21, and 13.65–15.76 and 8.73–13.64 times, respectively. The enhancement of these hydrolytic enzymes' activity in the HA reactor was correlated to the effluent recirculation from the MG reactor, contributing to the improved hydrolysis of food waste. Furthermore, the activity of coenzyme F420 in the MG reactor increased by 11.47%, 18.81%, and 27.03%, respectively, indicating that biochar can promote hydrogenotrophic methanogenesis. Microbial analysis revealed that the presence of biochar promoted interspecies hydrogen transfer between Syntrophomonas and hydrogenotrophic methanogens. Additionally, biochar triggered direct interspecies electron transfer between Geobacter sulfurreducens and acetotrophic methanogens, enabling effective methanogenesis.

Optimization of operating parameters for biogas production using two-phase bench-scale anaerobic digestion of slaughterhouse wastewater: Focus on methanogenic step.

The objective of the present study was an optimization of operating parameters and the performance of the methanogenesis reactor in phased anaerobic digestion (AD) of slaughterhouse wastewater at 37.5°C. Accordingly, the feedstock of the methanogenic reactor was effluent from the hydrolytic-acidogenic reactor operating at HRT of 3-days and OLR of 1789 mg/L. The methanogenesis phase was also investigated at different hydraulic retention time (HRT) values ranging from 12 to 3days at 3-day intervals, and organic loading rates (OLR) of 149, 199, 298, and 596mg of COD/L. The methanogenesis reactor effluent concentrations of TN, TP, PO4-3, SO4-2, and S2-2 were ranging between 424-464, 83-117, 63-86, 130-197, and 0.98-1.02mg/L, respectively. The removal efficiencies of TN and TP were vary from 10-17% to 17-21%, respectively. The average biogas production was 125 ± 16, 150 ± 10, 185 ± 4, and 154 ± 17mL at HRT of 12, 9, 6, and 3days, respectively. Methane quality (%) and yield (mg/L of COD) were 55-67% and 0.02-0.03, respectively. Furthermore, the average stability indicator parameter values of (total volatile fatty acid (TVFA) = 520 ± 19mg/L, total alkalinity (TotA) = 1424 ± 10mg/L, TVFA:TotA. Ratio = 0.36, salinity = 1172mg/L, pH = 6.92) and performance indicator parameters removal efficiency (RE) for (chemical oxygen demand (COD) = 81%, volatile solid (VS) RE = 95%, biogas production = 185 ± 4mL, methane yield = 0.03 per mg COD consumed) were achieved at HRT of 6days and OLR of 298mg of COD/L. Low removal efficiencies of TP and TN at all HRT/OLR were observed for the methanogenic reactor signifying further treatment system.

Bioenergy recovery from two-stage mesophilic-thermophilic anaerobic digestion of cheese whey

Among renewable energy sources, hydrogen and methane are gaseous fuels that have a higher energy density than petroleum-derived gasoline and diesel. In recent years, there has been increasing interest in converting existing anaerobic digestion systems to a two-stage process that produces hydrogen in the first stage and then methane in the second stage and is characterized by increased recovery of biofuels and bioenergy. In this study, an assessment of the energy recovery from two-stage mesophilic-thermophilic anaerobic digestion of cheese whey (CW) was carried out. After appropriate dilution, CW was fed at three COD levels of 6.8, 9.2 and 13.8 g O 2 /L to a mesophilic acidogenic reactor with a hydraulic retention time (HRT) of 10 h. The acidogenic reactor effluent was then fed to three thermophilic methanogenic reactors, which operated at different HRTs: 72, 48, and 24 h. Polyurethane foam was used to immobilize the anaerobic acidogenic and methanogenic sludge. The heating value (HV) was determined according to the experimental method using a bomb calorimeter for modes with the highest methane content and with the highest hydrogen content, as well as a calculation method based on the content of combustible gases in biohythane. The obtained deviations of the calculated from the experimentally determined HV of biohythane (4.84–7.60%) may be due to the fact that the HV of biohythane is probably not equal to the sum of the HV of pure hydrogen and methane. While an increase in the hydrogen content in biohythane leads to a decrease in the deviation of the calculated HV of biohythane from the experimental one. The maximum energy production rate was 53.2 kJ/(L d) at a COD level of 13.8 g O 2 /L, HRT in an acidogenic reactor of 10 h, and HRT in a methanogenic reactor of 48 h. The maximum energy yield of 14.42 kJ/g COD was obtained at a COD level of 9.2 g O 2 /L, HRT in an acidogenic reactor of 10 h and HRT in a methanogenic reactor of 72 h.

Effect of initial pH and substrate to inoculum ratio on the production of methane and hydrogen from food waste

“Anaerobic co-digestion of food waste, cow dung, and sludge solution is experimented by varying the pH to produce hydrogen and methane as a source of renewable energy. The substrate to inoculum ratio (v/v) of 1:1(S1), 1:2(S2), 1:3(S3), 1:4(S4) and 1:5(S5) are investigated in separate fermentative and methanogenic reactors. A maximum hydrogen and methane concentration of 19.73% and 64.81% respectively are obtained in S3. The methane concentration of 53.67%, 64.81% and 59.64% is observed at the pH variation of 6.5, 7, and 7.5 respectively. The obtained result shows the substrate to inoculum ratio of 1:3 to be the optimal combination for the highest methane and hydrogen production during the anaerobic co-digestion process”.

Two-phase (acidogenic-methanogenic) anaerobic fixed bed biofilm reactor enhances the biological domestic sewage treatment: Perspectives for recovering bioenergy and value-added by-products.

The organic matter bioconversion into methane during anaerobic digestion (AD) comprises different steps, the acidogenic and methanogenic phases being clearly distinct in terms of metabolic activities. In this work, new configurations of anaerobic fixed bed biofilm reactors (AFBBR) were operated under conventional methanogenic conditions (single phase - SP-AFBBR, M1R), and in a sequential two-phase system, acidogenic reactor followed by methanogenic reactor (TP-AFBBR, AcR+M2R), in order to verify the impact of the AD phase separation on the overall system performance in operational, kinetics and microbiological aspects. The results indicated that feeding the methanogenic reactor with the acidogenic effluent stream provided a shorter operating start-up period (11 and 32 days for SP and TP-AFBBR, respectively), a greater alkalinity generation (0.14 and 0.41g-CaCO3·g-CODremoved-1 for M1R and M2R, respectively), and the optimization of biomethane production (methane yield of 95 and 154N-mLCH4·g-CODremoved-1 for M1R and M2R, respectively). The COD removal kinetics was also favored in the TP-AFBBR (k1-COD=1.4 and 2.9 h-1 for M1R and M2R, respectively), since the soluble fermentation products were readily bioavailable to the biomass in the reactor. Hydrogenotrophic methanogenesis was the predominant pathway in the M2R, while the Methanosaeta-driven acetoclastic pathway predominated in the M1R. The greater diversity of Bacteria and Archaea in M2R denotes a better balance between the species that degrade volatile organic acids from AcR (i.e. Syntrophorhabdus, Syntrophus and Syntrophobacter) and the hydrogenotrophic methanogens (Methanoregula, Methanolinea and Methanospirillum) that consume the biodegradation products. The estimated bioenergy generation potential (range of 0.39-0.64kWh·m-3-sewage considering the COD removed) for full-scale TP-sewage treatment plants evidences the feasibility of energetic recovery in the domestic sewage anaerobic treatment.

Operating strategies to optimize a membrane bioreactor enriched in nitrite-dependent anaerobic methane-oxidizing bacteria

The use of N-damo bacteria, which can simultaneously remove nitrite and dissolved methane, could represent a cost-effective and sustainable alternative to minimize the environmental impact of effluents from methanogenic reactors treating domestic sewage. The operation of N-damo bacteria reactors is often not stable, and their activity decrease with no proven reason over time. This study aims to optimize the nitrite removal capacity of a lab-scale MBR by using different operating strategies for 878 days. The reactor was operated in continuous mode and with biomass highly enriched in these microbes. It was found that adjustments in the mineral medium concentration (reduction of Ca, P, and K) and composition (EDTA addition, increasing the Cu and Fe bioavailability), contributed to achieving remarkable and prolonged nitrite removal rates of up to 285.7 mg NO2–-N/L/d. N-damo bacteria dominated the culture, up to 57 %. To the best of our knowledge, the rates attained are the highest reported in an N-damo bacteria enrichment.

Effect of nitrite on hydrolysis-acidification, biogas production and microbial community in semi-continuous two-phase anaerobic digestion of sewage sludge

Previous study found that the pre-treatment of sewage sludge with nitrite improves the biogas production during the mono/two-phase anaerobic digestion (AD) using batch biochemical methane potential tests. In this study, the effects of nitrite on hydrolysis-acidification, biogas production, volatile solids destruction and microbial composition in semi-continuous two-phase AD of sewage sludge were investigated. The addition of nitrite promotes sludge organic matter solubilization (+484%) and VFAs production (+98.9%), and causes an increase in the VS degradation rate during the AD process (+8.7%). The comparison of biogas production from the acidogenic and methanogenic reactors with or without the addition of nitrite implies that the nitrite has no significant effect on the overall biogas production of two-phase sludge AD process. High-throughput sequencing analysis shows that the microbial communities of bacteria and archaea in two-phase AD reactors significantly changes after the addition of nitrite. Vulcanibacillus (bacteria) and Candidatus Methanofastidiosum (archaea) become the dominant genera in the acidogenic and methanogenic reactors with the nitrite respectively. These findings provide new insights about using nitrite to promote the organic matter degradation of sewage sludge in a semi-continuous two-phase AD system.

Sessile and Planktonic Microbial Taxonomy of a Methanogenic Cellulolytic Enrichment Reactor Sourced from the Organic Fraction of Municipal Solid Waste

The bacterial, archaeal, and fungal taxonomies of a semi-batch-fed, lab-scale cellulolytic enrichment reactor inoculated by the organic fraction of municipal solid waste were explored using 16SrRNA and internal transcribed spacer (ITS) sequencing. Biomass samples were partitioned into total, planktonic, and sessile (biofilm) fractions using a centrifugation separation technique developed to quantify sessile biomass growth on cellulose particles during anaerobic digestion. The relative abundances of bacteria and archaea taxa were determined over a 1-day period. The sessile and planktonic biomass fractions showed significantly different relative abundances for 13 taxa, with the sessile biomass having 10 times lower relative abundance of Unclassified Firmicutes, nearly 20 times higher relative abundance of Methanothrix spp., double the relative abundance of Hydrogenispora spp., and 44.3% higher relative abundance of an uncultured Leptospira sp. than the planktonic biomass. This study shows how a relatively simple physical separation method can be employed to add another dimension to taxonomic studies. Better understanding the microbial communities in these systems is a key first step toward achieving performance improvements such as enhanced cellulose solubilization rates and other microbial biotransformations through process, genetic, and/or other manipulations.

Scale-up and energy estimations of single- and two-stage vinasse anaerobic digestion systems for hydrogen and methane production

This study evaluated the full-scale vinasse anaerobic digestion for industrial application. Twelve scenarios were simulated, considering single (methanogenic reactor) and two-stage systems (acidogenic + methanogenic reactors), raw and concentrated vinasse, thermophilic and mesophilic conditions for methanogenesis and usage of acidogenic or methanogenic reactor effluent to dilute vinasse. A single-stage anaerobic digestion system of 17,433 m³ necessary to treat all the raw vinasse produced by a mill with a grinding capacity of 3.3 million tons of sugarcane per season can generate a power of 11.1 MW with an energy yield of 4.6 MJ/kg CODremoved. Two-stage system scenarios where vinasse was diluted with acidogenic reactor effluent had worse energetic recoveries than the single-stage system. Nonetheless, the usage of the methanogenic reactor effluent to dilute vinasse and its own influent in a two-stage system achieved an energetic recovery at least 34% higher than that of the single-stage system. In the best two-stage scenario, the total working volume was 19,666 m³, combining thermophilic acidogenic reactors and mesophilic methanogenic reactors, with an energy yield of 7.0 MJ/kg CODremoved. The different combinations of temperatures allow for a safer and more economic operation. The proposed novel industrial configuration can be divided into two parallel acidogenic reactors of 1,800 m³ each, and those reactors are in series with eight parallel methanogenic reactors of 2,828 m³ each. The electricity produced by the full-scale system can supply an energy demand of 24 thousand inhabitants per harvest season (9.7 kWh per ton of sugarcane). This study presents a novel discussion for sugarcane industry decision makers, such as plant managers, process and project engineers, providing a trade-off between highest energy production, optimal COD removal and lowest reactor volume (CAPEX investment) that better fits their needs.

Unravelling capability of two-stage thermophilic anaerobic membrane bioreactors for high organic loading wastewater: Effect of support media addition and irreversible fouling

This study investigated the effects of adding polyvinyl alcohol (PVA) beads on the performance of methanogenic reactors and the fouling behavior of a two-stage thermophilic anaerobic membrane bioreactor (ThAnMBR) for treating wastewater at a feed chemical oxygen demand (COD) of 10 g/L. The PVA-added methanogenic reactor exhibited stable operation performance and offered a relatively low volatile fatty acid concentration effluent with a higher COD removal than the system without PVA addition. The predominant microbial communities in both methanogenic reactors were similar and were assigned to the genus Methanosaeta, followed by Clostridia, which was the predominant genus in the hydrolytic reactor. Ultrafiltration in the PVA-added system offered higher effluent quality and lower fouling resistance. The system was able to operate with hydraulically removable fouling, without any chemical cleaning requirements; however, an elevated flux caused the system to suffer from hydraulically irreversible fouling. PVA beads exhibit their structural stability over long-term operation.

Prevotella herbatica sp. nov., a plant polysaccharide-decomposing anaerobic bacterium isolated from a methanogenic reactor.

An obligately anaerobic bacterial strain (WR041T) was isolated from a plant residue sample in a methanogenic reactor. Cells of the strain were Gram-stain-negative, non-motile, non-spore-forming rods. Prevotella paludivivens JCM 13650T was the closest species of the strain based on 16S rRNA gene sequencing (98.9 % similarity). Genome analysis of strain WR041T indicated that the genome size of the strain was 3.52 Mb and the genomic DNA G+C content was 37.5 mol%. Although the 16S rRNA gene sequence similarity of strain WR041T with the closest species was higher than the threshold value of the recommended species delineation (98.7 %), the average nucleotide identity and the digital DNA-DNA hybridization value between them were 91-92 and 45.5 %, respectively, suggesting that strain WR041T represents a novel species in the genus. Strain WR041T essentially required haemin and CO2/Na2CO3 for growth. The strain was saccharolytic and decomposed various polysaccharides (glucomannan, inulin, laminarin, pectin, starch and xylan) and produced acetate and succinate. The optimum growth conditions were 35 °C and pH 6.8. The major cellular fatty acids were branched-chain fatty acids such as anteiso-C15 : 0 and iso-C15 : 0. Menaquinones MK-11 and MK-12 were the major respiratory quinones. Many protein-coding genes which were not found in the genome of P. paludivivens as orthologous genes were detected in the genome of strain WR041T. Based on the differences in the phylogenetic, genomic and physiological characteristics between strain WR041T and related species, the name Prevotella herbatica sp. nov. is proposed to accommodate strain WR041T (=NBRC 115134T = DSM 112534T).