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Two-stage anaerobic digestion (AD) is a promising method of converting organic waste into clean and sustainable energy. This work aimed to study the efficiency of a two-stage AD system with the production of hydrogen at the first acidogenic stage and methane in an electromethanogenic reactor. Two types of biocathodes based on carbon cloth were used in the electromethanogenic reactor: with and without retention of biomass on the electrode surface. A high applied voltage continuously supplied to the pair of electrodes was automatically maintained at 2.5 V. Hydrogen yield (0.11 NL/g volatile solids (VS) init or 2 mol H 2 /mol hexose) and hydrogen content in biogas (52%) were relatively high, even despite the extremely low pH (∼4.0). Improved retention of biomass on the surface of the carbon cloth-based biocathode led to greater stability of the AD process (no water electrolysis was observed) and a significant increase in the efficiency of electromethanogenesis, including the methane yield (by 40.5% up to 0.39 NL/g VS init), volumetric methane production rate (by 38.8% up to 1.16 NL/L/d) and current density (by 233% up to 0.56 A/m2). • T= 57.5 °C and pH ∼4 completely suppressed methanogenesis in the acidogenic reactor. • 2 mol H2/mol glucose during continuous dark fermentation of OF-MSW is achieved. • Better biomass attachment to the biocathode increased the current density by 233%. • Increase in CH4 yield by 40.5% and volumetric CH4 production rate by 38.8%. • A physical barrier is an effective tool to retain biomass on the biocathode surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Isolation of acetic acid-producing bacteria from fruit waste and cow dung. • Estimation of Acetic acid production by biological method for waste valorization. • Experimentation of Acetic acid production on different parameters. • Optimization of acetic acid yield by RSM and ANN models. In this study, acetic acid bacteria (AAB) are isolated from fruit waste and cow dung on the basis of acetic acid production potential. The AAB were identified based on halo-zones produced in the Glucose-Yeast extract-Calcium carbonate (GYC media) agar plates. In the current study, maximum acetic acid yield is reported to be 4.88 g/100 ml from the bacterial strain isolated from apple waste. With the help of RSM (Response surface methodology) tool, glucose and ethanol concentration and incubation period, as independent variable showed the significant effect of glucose concentration and incubation period and their interaction on the AA yield. A hypothetical model of artificial neural network (ANN) was also used to compare the predicted value from RSM. Acetic acid production through the biological route can be the sustainable and clean approach to utilizing food waste in circular economy approach [ABSTRACT FROM AUTHOR]

[Display omitted] • Batch test is a useful tool for predicting H 2 potential and hydrolysis constant. • Maximum H 2 production rate has been underestimated in batch test. • Thermoanaerobacterium is an effective thermophilic H 2 producer at a very low pH. • Both batch and semi-continuous experiments are needed to predict dark fermentation. The performance and kinetics response of thermophilic semi-continuous dark fermentation (DF) of simulated complex carbohydrate-rich waste was investigated at various hydraulic retention times (HRT) (2, 2.5, and 3 d) and compared with data obtained from biochemical hydrogen potential assay (BHP). A culture of Thermoanaerobacterium thermosaccharolyticum was used as the inoculum and dominated both in BHP and semi-continuous reactor. Both the modified Gompertz and first-order models described the DF kinetics well (R2 = 0.97–1.00). HRT of 2.5 d was found to be optimal in terms of maximum hydrogen production rate and hydrogen potential, which were 3.97 and 1.26 times higher, respectively, than in BHP. The hydrolysis constant was highest at HRT of 3 d and was closest to the value obtained in the BHP. Overall, BHP has been shown to be a useful tool for predicting H 2 potential and the hydrolysis constant, while the maximum H 2 production rate is greatly underestimated. [ABSTRACT FROM AUTHOR]

The direct relationship between thermodynamic entropy and economic scarcity is only valid for a thermodynamically isolated economy. References to the second law of thermodynamics in economics within the context of scarcity ignore the fact that the earth is not an isolated system. The earth interacts with external sources and sinks of entropy and the resulting total entropy fluctuates around a constant. Even if the mankind finally proves unable to recycle industrial waste and close the technological cycle, the economic disruption caused by the depletion of natural resources may happen while the total thermodynamic entropy of the ecosystem remains essentially at the present level, because the transfer of chemically refined products may not increase significantly the total entropy, but it may decrease their recyclability. The inutility of industrial waste is not connected with its entropy, which may be exemplified with the case of alumina production. The case also demonstrates that industrially generated entropy is discharged into surroundings without being accumulated in ‘thermodynamically unavailable matter’. Material entropy, as a measure of complexity and economic dispersal of resources, can be a recyclability metric, but it is not a thermodynamic parameter, and its growth is not equivalent to the growth of thermodynamic entropy. [ABSTRACT FROM AUTHOR]

[Display omitted] • AD of concentrated VFA is greatly enhanced by stainless steel mesh and carbon fiber. • Electrogenic Ureibacillus , Limnochordia, Coprothermobacter , Ca. Caldatribacterium. • Short thick pili-like structures 150 nm in width correlate with ECM and enhanced AD. Various conductive materials and their dielectric counterparts were used to get deeper insights into contribution of direct interspecies electron transfer (DIET) in improving methanogenesis from highly concentrated volatile fatty acids (12.5 g/L). Potential CH 4 yield, maximum CH 4 production rate and lag phase were significantly (up to 1.4, 3.9 and 2.0 times, respectively) improved with addition of stainless-steel mesh (SM) and carbon felt (CF) compared to both control and dielectric counterparts (p < 0.05). k app increased by 82% for SM and 63% for CF compared to control (p < 0.05). Short thick pili-like structures up to 150 nm in width were formed only in CF and SM biofilms, however, were more abundant for SM. Ureibacillus and Limnochordia specific for SM biofilms, and Coprothermobacter and Ca. Caldatribacterium for CF biofilms, were considered electrogenic. Promotion of DIET by conductive materials is governed by many factors, including specificity of electrogenic groups to material surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Suitability of various pretreatment methods for particular biomass. • Impact of pelletization, torrefaction & HTC on properties of biomass. • Effect of torrefaction & HTC on gasification for bio-H 2 yield improvement. • Framework of technoeconomic analysis of system for bio-H 2 production. • Knowledge gaps & challenges to improve process for enhanced bio-H 2 yield. Energy demands and immense environmental degradation have extorted for production of low-carbon and carbon–neutral fuels. Abundantly available lignocellulosic biomass is second-generation feedstock which has potential to produce biofuels. Among all biofuels, biohydrogen is carbon neutral and sustainable biofuel which can be produced by thermochemical conversion routes mainly gasification. However, there are still numerous unsolved challenges related to physicochemical properties of lignocellulosic biomass. To tackle these issues, physical, chemical and thermal pretreatment methods can be employed to improve these properties and further strengthen usability of biomass for biohydrogen production. Pelletization, torrefaction and hydrothermal carbonization pretreatment have shown significant results for treating biomass and biohydrogen enhancement. This study reviews physical and thermal pretreatment and its effect on biohydrogen yield. Framework of techno-economic analysis of processes is provided for examining feasibility of required pretreatments. This sustainable approach will help to reduce emissions and promote concept of bioenergy with carbon capture and storage. [ABSTRACT FROM AUTHOR]