A moderately thermophilic Gram-positive chemo-organotrophic bacterium, strain SP2, was isolated by serial dilutions with crotonate and yeast extract as substrates from a butyrate-degrading methanogenic enrichment obtained from thermophilically digested sludge of the Kuryanoskaya wastewater treatment plant (Moscow, Russia). Cells of strain SP2 are spore-forming rods, sometimes occurring in short chains. The bacterium is an obligate anaerobe that grows at temperatures from 20 to 70 °C (55–60 °C optimum) within a pH range of 3.5–8 (7.5 optimum) and with NaCl concentrations of up to 2.5%. The strain utilized yeast extract and simple sugars as carbon and energy sources. Thiosulfate was used as an electron acceptor when grown on sucrose, resulting in the formation of hydrogen sulfide and the accumulation of elemental sulfur globules inside the cells. Strain SP2 is phylogenetically related to Biomaibacter acetigenes strain SK-G1T as revealed by comparison with the 16S rRNA gene (99.9% identity) and genome (ANI 99%, dDDH 90%) of both strains. It is interesting that strain SP2 was capable of syntrophic conversion of glycerol and lactate when co-cultivated with hydrogenotrophic methanogen, which was not previously shown for the SK-G1T type of strain. The isolation and in-depth study of new facultatively syntrophic microorganisms is important for wastewater treatment ecotechnologies due to their ability to switch to an alternative source of carbon and energy and therefore greater resistance to changing environmental conditions in bioreactors.

The use of energy (and renewable energy, in particular) plays an important role in agriculture, where technologies are also being improved from year to year—agricultural production is growing, and machinery and systems are becoming more autonomous and robotic, where it is no longer possible to do without complex computing, optimization, planning, and working with large amounts of data [...]

In anaerobic digestion (AD), butyrate is degraded by syntrophic consortium, but can accumulate in highly loaded AD systems. The effect of butyrate on the AD process attracts much less attention than propionate or acetate. In this work, an enrichment culture of the thermophilic butyrate-oxidizing syntrophic consortium was obtained by gradually increasing the initial butyrate concentration from 20 to 170 mM. Surprisingly, even the highest butyrate concentration did not significantly inhibit the methanogenic community, and the stage of acetate degradation was the limiting overall rate of the process. At 170 mM butyrate, the bacterial community changed towards the dominance of syntrophic acetate-oxidizing (SAO) bacteria related to Syntrophaceticus (42.9%), Syntrophomonas (26.2%) and Firmicutes (26.2%), while the archaeal community experienced a sharp decrease in the abundance of Methanosarcina thermophila (from 86.0 to 25.0%) and increase in Methanothermobacter thermautotrophicus (from 3.2 to 53.1%) and Methanomassiliicoccus (from 3.2 to 21.9%). Thus, the shift from acetoclastic methanogenesis to SAO coupled to hydrogenotrophic methanogenesis occurred as an adaptive strategy to overcome high acetate (~200 mM) build-up. Bioaugmentation with the obtained enrichment culture was effective in mitigating the butyrate-dominated VFA build-up during the AD of readily biodegradable waste, increasing the methane production rate, methane yield and volatile solids removal by more than 3.5, 6.2 and 2.9 times, respectively. Our study revealed that the thermophilic butyrate-oxidizing consortia as bioaugmented culture could be the potential strategy to alleviate the high organic load and VFA stress of AD.

The ability of microorganisms to carry out interspecies electron transfer during the degradation of organic substances under anaerobic conditions opens up new possibilities for a controlled increase in the efficiency of the methanogenic decomposition of organic waste. This review presents the main principles of the effects of a direct electric current on the anaerobic degradation of organic substances, process parameters, changes in the composition of the microbial community, and factors affecting the optimization of the hybrid systems comprising microbial electrolysis cell (MEC) and anaerobic digester (AD), i.e., the performance of the MEC-AD system. The research in this field has been analyzed for the subsequent application of electromethanogenesis, which represents a new energy-efficient biotechnology for anaerobic wastewater treatment and organic waste digestion.

The transition of livestock production to industrial processes and the concentration of animals associated with this process on large farms and complexes has caused a sharp increase in the volume of manure that must be disposed of without pollution. One of the ways of processing organic waste (biomass) is its anaerobic digestion in biogas plants through the vital activity of microorganisms (methanogenesis).Biogas obtained using microbiological processing of biomass can be used as a raw material for heat and electric energy. Annually, 0.17% of the total livestock manure produced at Russian agricultural enterprisesis used for biogas production.The main component of a biogas plant is a manure fermentation reactor, the required volume of which is determined by the daily output of manure from the livestock farm, the temperature and the hydraulic retention time of treatment. This research explored thermal energy consumption of biogas plants, using the example of a biogas plant of a modular design that depended on the average annual outdoor temperature. Based on the calculations, the thermophilic mode was found to be more energy-efficient than the mesophilic one; thus, with the thermophilic mode, the specific energy consumption needed for the plant was lower at the average annual outdoor temperatures of all the constituent entities of the Russian Federation. At the same time, the specific biogas yield in the thermophilic regime was 20-50%higher than in the mesophilic regime. Keywords: anaerobic processing, agricultural waste, thermophilicmode, mesophilicmode, energy costs, energy rationale

A relatively high (0.2-4.3) digestate recirculation ratio (RR) is typically adopted to raise the pH and provide the dark fermentation reactor (DF) with alkalinity and hydrogen-producing microorganisms in a two-stage anaerobic digestion process. This study examined the production of bio-H2 and bio-CH4 from readily biodegradable organic waste in a large scale recirculated two-stage thermophilic anaerobic system to determine the effect of low RR on biofuel and bioenergy recovery. The performance of the two-stage system was evaluated at 2 hydraulic retention times (HRT) (1.1 and 2.5 d) in DF and 4 RR (0, 0.11, 0.18 and 0.25). The pH in DF was not controlled and ranged from 3.8 to 4.2. Hydrogen yield was negatively affected by digestate recirculation, while CH4 yield, as well as H2 and CH4 production rates, first tended to increase and then decrease with increasing RR. Overall, biofuel and bioenergy were best recovered at an RR of 0.11, namely 1.48 L H2/L/d, 0.88 L CH4/L/d, 106.2 mL H2/g VSinit.,161.3 mL CH4/g VSinit., 7.7 kJ/g VSinit. and 88.2 kJ/L/d were obtained depending on HRT in DF. It has been shown that a low RR can improve the performance of the two-stage anaerobic digestion process. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

This paper considers the production of biohydrogen in a two-stage process of anaerobic bioconversion of organic matter (OM) of liquid waste with recirculation of digester effluent into an anaerobic bioreactor for dark fermentation (ARDF). The values of the average biohydrogen specific yield (BSY) and the average volumetric biohydrogen production rate (VBPR) were obtained at 4 recirculation ratios (RR) of the digester effluent (1, 1.1, 1.18, 1.25) and 2 hydraulic retention times (HRT) ( 1 and 2.5) in ARDF. Organic loading rate (olr) varied from 7.96 to 21.6 g OM / (l ∙ day). The pH value in ARDF practically did not depend on RR and HRT, and ranged from 3.8 to 4.16. The maximum BSY was 0.108 l / (day ∙ g OMin) with a RR of 1.11 and a HRT of 2.5 days. The maximum VBPR was observed at RR 1 and HRT 1 day and amounted to 1.67 l / (l ∙ day). The methane content in biohydrogen-containing biogas at modes providing maximum BSY and VBPR was no more than 0.01%, but it increased sharply at higher values of RR and HRT. The hydrogen content in biogas averaged 50-52% for all combinations of RR and HRT, but it sharply decreased to 46.7% with HRT 2.5 and RR 1.25. In general, with RR 1.11 and HRT 1 day, an increase in BSY by 9.05% was observed, while the VBPR decreased by 1.04% (compared with RR 1.0 and HRT 1 day). In general, the experi- mental data obtained allow us to speak of a RR equal to 1.11 as the most effective for both HRTs in the studied range of RR.

This article presents the results of the start-up of continuous production of biohydrogen from cheese whey (CW) in an anaerobic filter (AF) and anaerobic fluidized bed (AFB) with a polyurethane carrier. Heat and acid pretreatments were used for the inactivation of hydrogen-scavengers in the inoculum (mesophilic and thermophilic anaerobic sludge). Acid pretreatment was effective for thermophilic anaerobic sludge to suppress methanogenic activity, and heat treatment was effective for mesophilic anaerobic sludge. Maximum specific yields of hydrogen, namely 178 mL/g chemical oxygen demand (COD) and 149 mL/g COD for AFB and AF, respectively, were obtained at the hydraulic retention time (HRT) of 4.5 days and organic load rate (OLR) of 6.61 kg COD/(m3 day). At the same time, the maximum hydrogen production rates of 1.28 and 1.9 NL/(L day) for AF and AFB, respectively, were obtained at the HRT of 2.02 days and OLR of 14.88 kg COD/(m3 day). At the phylum level, the dominant taxa were Firmicutes (65% in AF and 60% in AFB), and at the genus level, Lactobacillus (40% in AF and 43% in AFB) and Bifidobacterium (24% in AF and 30% in AFB).

When mixed organic waste is used for hydrogen production by dark fermentation, the microbial community which is most adapted to the actual biopolymer composition of the substrate is auto-selected. In this research, six substrates simulating different biopolymers (proteins, fats, carbohydrates) and their mixtures were used to enrich hydrogen-producing bacteria adapted to these substrates from non-pretreated sewage sludge. Phylum Firmicutes dominated in the microbial community (67-100%) regardless of the substrate used, as was shown by high-throughput sequencing. Microbial diversity was low when using carbohydrate-rich substrates and the microbial community was mainly represented by Ruminococcus (26-90%) and Thermoanaerobacterium (6-67%). Dark fermentation of fats and proteins was characterized by higher microbial diversity. Thermoanaerobacterium (21%), Thermobrachium (19%), Tepidiphilus (16%) and Acetomicrobium (14%) dominated when using fats, while Thermobrachium (34%), Acetomicrobium (16%) and Clostridium sensu stricto 7 (12%) dominated when using proteins, as substrate. Different microbial communities and substrates resulted in diverse process performance and metabolic pathways. Dark fermentation of starch achieved the maximum hydrogen yield of 138 mL/g volatile solids with 60.4% hydrogen content in biogas. The dominance of genus Ruminococcus was thought to be responsible for the highest hydrogen production. Minor quantities of methane from proteins and fats were produced by Methanothermobacter and Methanosarcina. Based upon the stable 13C isotope analysis, the hydrogenotrophic pathway was a slightly more predominant methane formation route than the others considered. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

— Anaerobic digestion of municipal and other organic waste is a microbial process for conversion of complex organic substances to biogas (a renewable energy source) comprising a mixture of methane and CO 2 , and a stabilized sludge, which may be used as an organic fertilizer. Diverse groups of the methanogenic microbial community degrade complex organic compounds into simple fermentation products such as hydrogen, formate, acetate, short-chained volatile fatty acids, ethanol, etc. These low-molecular mass products act as the substrates and carriers involved in biogas production by syntrophic bacteria and methanogenic archaea at the methanogenesis stage, the last stage of the anaerobic process. The present review discusses syntrophic interactions between the microorganisms involved in anaerobic degradation of organic substances, as well as two types of interspecies electron transfer (IET): indirect IET (IIET, Indirect Interspecies Electron Transfer) and direct IET (DIET, Direct Interspecies Electron Transfer). DIET-based syntrophic interactions between microorganisms may be stimulated by adding conductive materials into anaerobic digesters, which may have the potential for practical applications.

This is the study of efficiency of anaerobic reject water treatment and of changes in the relative abundance of the major microbial groups involved in nitrogen removal at increase in nitrogen and COD (chemical oxygen demand) load. A two-reactor laboratory system carried out anammox and partial nitrification, with the biomass immobilized on a brush carrier and water recycling. Nitrogen concentration in the water varied from 50 to 250 mg N-NH4/L, while COD varied from 50 to 1650 mg О2/L. Efficiency of the process was assessed by monitoring the concentrations of N-NH4, N-NO2, N-NO3, COD, dissolved oxygen, and pH in the inflowing and treated sludge liquor. The efficiency of nitrogen removal was 75‒90%. Active development of anammox bacteria and first step nitrifiers was observed in the anammox reactor, while almost no second step nitrifiers were present. Elevated content of organic matter in sludge liquor was shown to cause a significant decrease in the water purification degree due to lower abundance of anammox bacteria and the first step nitrifying Nitrosomonas species, while the abundance of the second step nitrifying Nitrospira species increased. The major microbial groups involved in nitrogen removal were better represented in biofilms than in free-floating sludge (flocs and granules). While the size of the granules and flocs did not change at increased load, their color changed from gray-red to a darker one.

Microbiological processes occurring in the course of controlled thermophilic composting of dehydrated wastewater sludge anaerobically digested in a reactor at the Lyubertsy waste treatment plant (Moscow, Russia) were studied. Dynamics of the concentrations of nitrogen species in the presence of microorganisms of the nitrogen cycle (ammonifying, nitrifying, denitrifying, and nitrogen-fixing) was studied at the changed temperature modes at sequential stages of long-term composting (98 days). During the active stage of composting, considerable emission of ammonia (553–861 mg m–3) and nitrogen oxide (67–86 mg m–3) were observed on days 6–10; these values significantly exceeded the accepted allowances for atmospheric emissions. Abundance of culturable heterotrophic microorganisms, CFU numbers of nitrogen-fixers, and the presence and activity of cultured nitrifying and denitrifying microorganisms were determined using microbiological techniques. The data of real-time PCR and NGS profiling by the 16S rRNA genes were used to analyze the taxonomic diversity of the microorganisms involved in composting (bacteria, archaea, and fungi); the patterns of succession within the microbial community during this process were established. Laboratory experiments revealed the potential for further decomposition of organic matter of digested sludge, which was probably unavailable to microorganisms under anoxic conditions, but could be degraded by the aerobic microbiota, resulting in a product stimulating plant growth and containing 2.3% of total nitrogen and containing ammonium and nitrate nitrogen (890 and 3750 mg kg–1, respectively).

Pretreatment of the organic fraction of municipal solid waste ( OFMSW ) is a necessary step to accelerate the process of anaerobic digestion in order to avoid rapid acidification and inhibition of methanogenesis. This work shows for the first time the effect of pretreatment in a vortex-layer apparatus ( VLA ) on the physicochemical properties and characteristics of the anaerobic thermophilic, two-phase fermentation of OFMSW. Pretreatment in a VLA led to a decrease in the amount of fat, an increase in pH, a slight increase in the amount of protein in dry matter, and a change in the density and dry matter content. OFMSW processing in a VLA for 2 min increased the specific yield of biogas and methane by 11.6 and 15.8%, respectively.

The microbial community of a laboratory-scale bioreactor based on the anammox process was investigated by using metagenomic approaches and fluorescent in situ hybridization (FISH). The bioreactor was initially inoculated with activated sludge from the denitrifying bioreactor of a municipal wastewater treatment station. By constantly increasing the ammonium and nitrite load, a microbial community containing the novel species of anammox bacteria “Candidatus Jettenia ecosi” developed in the bioreactor after 5 years when the maximal daily nitrogen removal rate reached 8.5 g/L. Sequencing of the metagenome of anammox granules and the binning of the contigs obtained, allowed a high quality draft genome of the dominant anammox bacterium, “Candidatus Jettenia ecosi” to be assembled. Annotation of the 3.9 Mbp long genome revealed 3970 putative protein-coding genes, 45 tRNA genes, and genes for 16S/23S rRNAs. Analysis of the genome of “Candidatus Jettenia ecosi” revealed genes involved in anammox metabolism, including nitrite and ammonium transporters, copper-containing nitrite reductase, a nitrate reductase complex, hydrazine synthase, and hydrazine dehydrogenase. Autotrophic carbon fixation could be accomplished through the Wood Ljungdahl pathway. The composition of the community was investigated through a search of 16S rRNA sequences in the metagenome and FISH analysis of the anammox granules. The presence of the members of Ignavibacteriae, Betaproteobacteria, Chloroflexi and other microbial lineages reflected the complexity of the microbial processes in the studied bioreactor performed by anammox Planctomycetes, fermentative bacteria, and denitrifiers.