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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. [ABSTRACT FROM AUTHOR]

Pretreatment prior to anaerobic digestion is an effective option for increasing the biodegradability of organic waste. Vortex layer apparatus (VLA) is considered one of the promising types of equipment for pretreatment. In this work, confectionery wastewater (CW) was pretreated in VLA for 1 and 3 min before dark fermentative hydrogen production in anaerobic upflow biofilters. The pretreatment resulted in a slight increase in soluble chemical oxygen demand (COD), soluble sugars and acetic acid, and a decrease in the concentration of propionic, butyric and caproic acids. Due to the abrasion of steel needles in VLA, the concentration of iron in the pretreated CW increased by 2.57 times. Hydraulic retention time in anaerobic upflow biofilters was gradually reduced from 5.6 to 1.8 and 1.3 days, which corresponded to organic loading rate of 2.0, 6.3 and 8.8 kg COD/(m3 day). Although the highest hydrogen yield (96.2 ± 8.1 ml/g COD) was obtained for non-pretreated CW, the pretreatment contributed to a significant increase in methane yield (39.2 ± 2.5 ml/g COD), possibly due to higher iron content (1.8 ± 0.3 mg/L). The highest energy production rate (4407 J/(L day)) was achieved after 3 min CW pretreatment. Thus, pretreatment in VLA can be a promising method for improving the biohythane production process. [ABSTRACT FROM AUTHOR]

The article analyzes the world experience in the use of solar energy in anaerobic bioconversion systems, determines the necessary heat and electricity supply for a biogas plant, as well as the composition and location of solar modules of various designs for its energy supply. Various arrangements of solar modules of photovoltaic, thermal and photovoltaic thermal constructions on the surfaces of a container for a biogas plant are considered. Various modes of energy generation for power supply of a biogas plant are proposed - to ensure the minimum power generation mode in parallel operation with the network and the power generation mode for a daily power consumption with batteries, as well as the minimum power generation mode in parallel operation with the network to control the power generation schedule. [ABSTRACT FROM AUTHOR]

The hydrogen-producing bacterium SP-H2 was isolated from a thermophilic acidogenic reactor inoculated with municipal sewage sludge and processing a carbohydrate-rich simulated food waste. Based on the 16S rRNA gene sequence, the bacterium was identified as Thermoanaerobacterium thermosaccharolyticum. The maximum growth rate was observed at 55–60 °C and pH 7.5. The H 2 -producing activity of the bacterium was studied using mono-, di- and tri-saccharides related to both hexoses (maltose, glucose, mannose, fructose, lactose, galactose, sucrose, raffinose, cellobiose) and pentoses (xylose and arabinose), as well as using real wastewaters (cheese whey, confectionery wastewater, sugar-beet processing wastewater). The highest H 2 yield was observed during dark fermentation (DF) of maltose (1.91 mol H 2 /mol hexose or 77.8 mmol H 2 /L). The maximum H 2 production rate was observed during DF of xylose (13.3 ml H 2 /g COD/h) and cellobiose (2.47 mmol H 2 /L/h). The main soluble metabolite products were acetate, ethanol and butyrate. The acetate concentration had a statistically significant positive correlation with the H 2 content in biogas and the specific H 2 yield. Based on the results of the correlation analysis, it was tentatively assumed that in the formic acid (mixed-acid) type fermentation, the rate of H 2 production was higher than in the butyric acid type fermentation. With regard to real wastewater, cheese whey and confectionery wastewater were distinguished by a higher H 2 yield (152 ml H 2 /g COD) and H 2 production rate (0.57 mmol H 2 /L/h), respectively. The highest concentrations of confectionery wastewater and cheese whey, at which the DF process took place, were 5915 and 7311 mg COD/L, respectively. At the same time, SP-H2 dominated in the microbial community, despite the presence of indigenous microorganisms in wastewater. Thus, T. thermosaccharolyticum SP-H2 is a promising strain for DF of carbohydrate-rich unsterile wastewater under thermophilic conditions. [ABSTRACT FROM AUTHOR]