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Cu is widely present in the feedstocks of dark fermentation, which can inhibit H 2 production efficiency of the process. However, current understanding on the inhibitory mechanisms of Cu, especially the microbiological mechanism, is still lacking. This study investigated the inhibitory mechanisms of Cu 2+ on fermentative hydrogen production by metagenomics sequencing. Results showed that the exposure to Cu 2+ reduced the abundances of high-yielding hydrogen-producing genera (e.g. Clostridium sensu stricto), and remarkably down-regulated the genes involved in substrate membrane transport (e.g., gtsA, gtsB and gtsC), glycolysis (e.g. PK, ppgK and pgi-pmi), and hydrogen formation (e.g. pflA, fdoG, por and E1.12.7.2), leading to significant inhibition on the process performances. The H 2 yield was reduced from 1.49 mol H 2 /mol-glucose to 0.59 and 0.05 mol H 2 /mol-glucose upon exposure to 500 and 1000 mg/L of Cu 2+ , respectively. High concentrations of Cu 2+ also reduced the rate of H 2 production and prolonged the H 2 -producing lag phase., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

This study systematically evaluated and compared different inoculum pretreatment methods to quickly select dark fermentative bacteria from anaerobic sludge for the bioconversion of food waste. The hydrogen (H 2 ) production rate was found to be highest for 'heat + CO 2 ' treated inoculum at 140.75 ± 2.61 mL/L/h compared to control experiments (60.27 ± 2.61 mL/L/h). At the same time, H 2 yield was found to be highest for alkali-treated inoculum at 157.25 ± 7.62 mL/g of volatile solids (VS) added compared to control experiments (91.61 ± 1.93 mL/g VS). Analysis of organic acids suggests a Clostridial-type fermentation with acetate (0.52 to 1.60 g/L) and butyrate (1.69 to 2.42 g/L) being the major by-products. The microbial data analysis showed that Firmicutes (63.64-90.39%), Bacteroidota (1.16-21.88%), and Proteobacteria (2.09-9.93%) were dominant at the phylum level, whereas genus-level classification showed Clostridium sensu stricto 1 (6.37-42.63%), Streptococcus (1.87-28.96%), Prevotella (0.57-16.59%), and Enterococcus (0.56-14.51%) dominated under different experimental conditions., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The aim of this study is to evaluate the effect of leachate recirculation at a ratio of 0%, 25%, 50% or 75% of collected leachate from the Leach Bed Reactor (LBR) on food waste digestion efficiency and its subsequent methane production in the second phase of a two-phase anaerobic system. Higher hydrolysis-acidogenesis efficiency and lower energy loss were achieved in LBR with higher leachate recirculation ratio. Better biochemical balance between metabolic products and microorganisms in leachate was revealed under 50% leachate recirculation ratio, which leads to the highest hydrogen production yield in LBR resulting the highest methane production yield in the corresponding methanogenic phase which was at least 15% higher than that in other conditions. This provides an easy approach to enhance the hydrolysis efficiency and in the same time a biochemical balanced leachate to enhance methanogenic reaction of a two-phase anaerobic digestion., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Potential of methane production by co-digestion of food waste with saline sludge produced from sewage receiving seawater toilet flushing was investigated to determine its suitability for food waste management in Hong Kong by making use of excess design capacity of sludge digesters. High salinity of saline sludge (12.8 mS/cm) affected degradation of organic compounds resulting in an increase in sCOD by 135% as compared to an increase by 283% in treatments with non-saline sludge (4.2 mS/cm) co-digestion. This inhibitory effect was also evident by lower VS removal efficiency of 32.65% for saline versus 54.23% for non-saline sludge based co-digestion. Furthermore, non-saline sludge gave a 3.4-fold higher methane yield than saline sludge co-digestion. It is concluded that co-digestion of food waste with both sludges could be adopted as a potential strategy to make use of excess digestion capacity of existing wastewater treatment facilities but is more viable for non-saline sludge., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Food waste (FW) is a valuable resource which requires sustainable management avenues to reduce the hazardous environmental impacts and add-value for better economy. Anaerobic digestion (AD) is still reliable, cost-effective technology for waste management. Conventional AD was originally designed for sewer sludge digestion, is not effective for FW due to mainly high organics and volatile fatty acid (VFA) accumulation, hence better technical aptitudes and biochemical inputs are required for optimal biogas production. Besides, to overcome these challenges, FW co-digestion with complementary organic waste e.g. sewage sludge (SS) mixed which complement each other for better process design. The main aim of this article is to summarize the recent updates and review different holistic approaches for efficient anaerobic co-digestion (AcoD) of FW and SS to provide a comprehensive review on the topic. Moreover, to demonstrate the status and perspectives of AcoD at present scenario for Hong Kong and rest of the world., (Copyright © 2018. Published by Elsevier Ltd.)

Recently, efficient disposal of food waste (FW) with potential resource recovery has attracted great attentions. Due to its easily biodegradable nature, rich nutrient availability and high moisture content, FW is regarded as favorable substrate for anaerobic digestion (AD). Both waste disposal and energy recovery can be fulfilled during AD of FW. Volatile fatty acids (VFAs) which are the products of the first-two stages of AD, are widely applied in chemical industry as platform chemicals recently. Concentration and distribution of VFAs is the result of acidogenic metabolic pathways, which can be affected by the micro-environment (e.g. pH) in the digester. Hence, the clear elucidation of the acidogenic metabolic pathways is essential for optimization of acidogenic process for efficient product recovery. This review summarizes major acidogenic metabolic pathways and regulating strategies for enhancing VFAs recovery during acidogenic fermentation of FW., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Lactate accumulation occurs frequently during the hydrolysis and acidogenesis of food waste and produces an unfavorable substrate for anaerobic digestion. The objective of the present study was to reduce lactic acid production during the hydrolysis and acidogenesis of food waste in leachate bed reactor for establishment of the two-phase anaerobic digestion system. The results showed that the hydrolysis and acidogenesis of food waste in batch feeding mode underwent two consecutive stages, namely lactic acid fermentation and mixed acid fermentation. In the lactic acid fermentation stage, lactate constituted 74.4-96.8% of the total organic acids in the leachate. However in semi-continuous mode the content of lactate in the leachate could be reduced less than 0-2% for leach bed reactors operated at feeding loads of 50-150g/d although lactate accumulation occurred at a feeding load of 200g/d. Furthermore the organic acid shifted to acetate and butyrate, providing ideal substrates for anaerobic digestion., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

This study investigated the effects of 12.6psi (T1), 6.3psi (T2), 3.3psi (T3) and ambient (T4) headspace pressure on the metabolic pathways in the acidogenic leach bed reactor (LBR) and overall methane recovery during two-phase anaerobic digestion of food waste. Diversion of biogas from LBR enhanced COD and soluble product generation in T2, T3 and T4 whereas, high pressure (T1) resulted in comparatively higher lactate production and low protein degradation. A pressure of 3-6psi (T2 and T3) improved the production of COD by ∼22-36%, soluble products by ∼9-43%, volatile solid reduction by ∼14-19%, and CH 4 production by ∼10-31% compared with control. Besides, ∼3-6psi headspace pressure positively influenced the composition of soluble products resulting in enhanced methane recovery adding advantage to the two-phase system. A headspace pressure of ∼3-6psi is recommended to enhance the hydrolysis-acidogenesis; however, the actual hydrogen concentration should be considered., (Copyright © 2017. Published by Elsevier Ltd.)

Microbial electrolysis cells (MECs) are a promising technology for biological hydrogen production. Compared to abiotic water electrolysis, a much lower electrical voltage (~0.2V) is required for hydrogen production in MECs. It is also an attractive waste treatment technology as a variety of biodegradable substances can be used as the process feedstock. Underpinning this technology is a recently discovered bioelectrochemical pathway known as "bioelectrohydrogenesis". However, little is known about the mechanism of this pathway, and numerous hurdles are yet to be addressed to maximize hydrogen yield and purity. Here, we review various aspects including reactor configurations, microorganisms, substrates, electrode materials, and inhibitors of methanogenesis in order to improve hydrogen generation in MECs., (Copyright © 2017 Elsevier Inc. All rights reserved.)