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Gradient anaerobic digestion reactor (GADR) can improve substrate utilization efficiency by solving the problem of the "short circuit" of materials. However, the substrate's composition significantly affects the reactor's performance. This study investigated the impact of food waste (FW) levels on corn straw's dry anaerobic digestion (AD) in a novel GADR. The results show that biomethane production can be improved by coupling urban and agricultural solid waste recycling. The mechanism is to increase the hydrolysis and acid production efficiency, and the abundance of enzymes related to methanogenesis. The maximum methane yield (494.2 mL CH 4 /g VS) and the highest anaerobic biodegradability (85.7 %) were obtained when the FW was added at 60 %. The co-digestion of FW and straw can improve the hydrolysis and acid production efficiency and methane yield, which improves the buffering capacity and stability of the system compared with the single digestion of FW., 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 © 2024 Elsevier Ltd. All rights reserved.)

Ensilage is a commonly used method of preserving energy crops for biogas production. However, aerobic deterioration of silage is an inevitable problem. This study investigated the effect of aerobic deterioration on methane production and microbial community dynamics through anaerobic digestion (AD) of maize stalk silage, following 9days air exposure of silage. After air exposure, hydrolytic activity and methanogenic archaea amount in AD were reduced, decreasing the specific methane yield (SMY); whereas lignocellulose decomposition during exposure improved the degradability of silage in AD and enhanced SMY, partially compensating the dry matter (DM) loss. 29.3% of the DM and 40.7% of methane yield were lost following 0-9days exposure. Metagenomic analysis showed a shift from Clostridia to Bacteroidia and Anaerolineae in AD after silage deterioration; Methanosaetaceae was the dominant methanogenic archaea., (Copyright © 2017. Published by Elsevier Ltd.)

Fe is widely used as an additive in anaerobic digestion, but its bioavailability and the mechanism by which it enhances digestion are unclear. In this study, sequential extraction was used to measure Fe bioavailability, while biochemical parameters, kinetics model and Q-PCR (fluorescence quantitative PCR) were used to explore its mechanism of stimulation. The results showed that sequential extraction is a suitable method to assess the anaerobic system bioavailability of Fe, which is low and fluctuates to a limited extent (1.7 to -3.1wt%), indicating that it would be easy for Fe levels to be insufficient. Methane yield increased when the added Fe 2+ was 10-500mg/L. Appropriate amounts of Fe 2+ accelerated the decomposition of rice straw and facilitated methanogen metabolism, thereby improving reactor performance. The modified Gompertz model better fitted the results than the first-order kinetic model. Feasibility analysis showed that addition of Fe 2+ at ≤50mg/L was suitable., (Copyright © 2017. Published by Elsevier Ltd.)

The ready formation of scum in vertical reactors has been a bottleneck in the digestion of lignocellulosic materials for biogas production. This study describes a single vertical reactor that integrates the acidogenic and methanogenic phases of this process. The effects of two types of maize stover feedstock (fresh and silage) and two mixing intensities (20 and 70rpm) on methane yield were orthogonally determined. Fresh maize stover yielded approximately 14% more methane than silage maize stover. Mixing at 20rpm contributed to methane yield, while mixing at 70rpm blurred the phase boundary, resulting in accumulation of volatile fatty acids and loss of methanogens. The upper and lower phases clearly constituted a two-phase fermentation system. Clostridiales occupied the acidogenic phase, while the predominant bacteria in the methanogenic phase were Bacteroidetes, Chloroflexi, and Synergistetes. The absolute predominance of Methanosaetaceae clearly demonstrated that aceticlastic methanogenesis was the main route of methane production., (Copyright © 2017. Published by Elsevier Ltd.)

A two-phase digestion system for treating agricultural waste is beneficial for methane production. This study explored the effect of solid content, temperature, and mixing mode on the process of hydrolysis and acidification using rice straw and cow dung launched in non-airtight acidogenic system. The results showed that the substrate could be hydrolyzed efficiently in the initial stage, the hydrolysis coefficient (k) of maximum cellulose and hemicellulose can be increased by 217.9% and 290.5%, respectively, compared with those of middle and last stages. High solid content played a leading role in promoting hydrolysis, resulted in hydrolysate content (sCOD) that was significantly higher than in treatments with low solid content (P<0.01), and led to organic acids accumulation up to 5.8 and 6.7g/L at mesophilic and thermophilic temperatures. Thermophilic temperature stimulated the hydrolysis and acidification of low solid content (P<0.05), and improved organic acid accumulation of high solid content only during the middle stage (P<0.01). Mixing mode was not a major factor, but increasing the mixing time was necessary for organic acid accumulation during the last stage (P<0.05). In addition, the study comprehensively analyzed a series of corresponding relationships among each operating parameter during the whole treatment process using canonical correspondence analysis., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Silage and dry are the two typical cornstalk forms. Either form could be used as substrate in biogas plants and might be replaced by another when shortage occurred. This study focused on the feeding sequence of these two kinds of feedstocks, aiming to discuss their specific methane potential (SMP). A 15-day hydraulic retention time was chosen for semi-continuous experiments based on the batch test results. In semi-continuous experiments, before and after feedstocks were exchanged, the significantly decreased and comparable SMPs of silage and dry cornstalks indicated that a basis of unstable digestion would result in incomplete methane release from the subsequent digestion. A higher similarity of bacterial community structure and greater quantity of bacteria were shown in acidified silage cornstalk digestion through band similarity analysis. Methanosaetaceae and methanomicrobiales were the predominant methanogens, and aceticlastic methanogenesis was the main route for methane production. The different feeding sequences affected the hydrolysis course and further influenced the methanogenic proliferation. Our work suggests that silage cornstalk digestion should be conducted before dry cornstalk digestion.

Silage efficiency is crucial for corn stalk storage in methane production. This study investigated characteristics of dynamic changes in materials and microbes during the silage process of corn stalks from the initial to stable state. We conducted laboratory-scale study of different silage corn stalks, and optimized silage time (0, 2, 5, 10, 20, and 30days) for methane production and the endogenous microbial community. The volatile fatty acid concentration increased to 3.00g/L on Day 10 from 0.42g/L on Day 0, and the pH remained below 4.20 from 5.80. The lactic acid concentration (44%) on Day 10 lowered the pH and inhibited the methane yield, which gradually decreased from 229mL/g TS at the initial state (Day 0, 2) to 207mL/g TS at the stable state (Day 10, 20, 30). Methanosaeta was the predominant archaea in both fresh and silage stalks; however, richness decreased from 14.11% to 4.75%., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Molasses is a typical feedstock for fermentation, but the effluent is hard to treat. In this study, molasses containing a high concentration of organic matter was treated by a two-stage Fix-bed reactor system with an increased organic loading rate (OLR). The results indicated at high molasses loading rate, the two-stage system was more efficient (i.e. organic matter removal, the COD of effluent and biogas production) than the single-stage system. The relative abundance of Anaerolineaceae and W5_norank was higher in the first stage (R1), where these organisms digest carbohydrates, while the second stage (R2) had higher relative abundance of Synergistaceae and SB-1_norank , which digest VFAs and decomposition-resistant compounds to produce compounds used by hydrogen methanogens. The qPCR analysis demonstrated that the Methanosaetaceae dominated the archaeal community in the first stage (R1), while Methanomicrobiales and Methanobacteriales were predominant in the second stage (R2), where they were involved in hydrogen production. [ABSTRACT FROM AUTHOR]

Microbial pretreatment is beneficial in some anaerobic digestion systems, but the consortia used to date have not been able to effectively increase methane production from cotton stalk. In this study, a thermophilic microbial consortium (MC1) was used for pretreatment in order to enhance biogas and methane production yields. The results indicated that the concentrations of soluble chemical oxygen demand and volatile organic products increased significantly in the early stages of pretreatment. Ethanol, acetic acid, propionic acid, and butyric acid were the predominant volatile organic products in the MC1 hydrolysate. Biogas and methane production yields from cotton stalk were significantly increased following MC1 pretreatment. In addition, the methane production rate from the treated cotton stalk was greater than that from the untreated sample. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ensiling EWS with acetic acid or heterofermentative LAB addition was first studied. • Ensiling EWS with additives enhanced acetic acid fermentation. • Ensiling EWS with additives preserved hemicellulose and cellulose content. • Ensiling EWS with additives changed the homo-fermentation to hetero-fermentation. • Ensiling EWS with additives improved the methane yield by 17.7–23.9%. Ensiling is an effective storage strategy for agricultural biomass, especially for energy crops (mainly energy grasses and maize). However, the ensiling of excessively wilted crop straw is limited due to material characteristics, such as a high lignocellulosic content and low water-soluble carbohydrate and moisture contents. In this study, acetic acid or hetero-fermentative lactic acid bacterial community (hetero-fermentative LAB) were employed as silage additives to improve the ensiling process of excessively wilted wheat straw (EWS). The results showed that the additives inhibited the growth of Enterobacteriaceae and Clostridium_sensu_stricto_12 , whose abundances decreased from 55.8% to 0.03–0.2%, respectively. The growth of Lactobacillus was accelerated, and the abundances increased from 1.3% to 80.1–98.4% during the ensiling process. Lactic acid fermentation was the dominant metabolic pathway in the no additive treatment. The additives increased acetic acid fermentation and preserved the hemicellulose and cellulose contents, increasing the methane yield by 17.7–23.9%. This study shows that ensiling with acetic acid or hetero-fermentative LAB is an effective preservation and storage strategy for efficient methane production from EWS. [ABSTRACT FROM AUTHOR]

Temperature and hydraulic retention time (HRT) control are crucial for mitigating the "short-circuit" issue and enhancing methane production in continuous stirred-tank reactors. This study focuses on the combined effects of temperature and HRT on methanation via operating the reactors at different temperatures (35 °C, 45 °C, and 55 °C) and HRT (30, 25, and 20 d) for 116 days. The results demonstrated that the digester conducted at 45 °C and an HRT of 30 d unexpectedly yielded the maximum average methane production of 296.08 ml/g volatile solids (VS). In contrast, the optimal HRT for the 35 °C and 55 °C digesters were 25 and 30 d, with a methane yield of 241.88 ml/g VS and 240.9 ml/g VS, respectively. High-throughput sequencing shows that Firmicutes, Bacteroidetes, Themotogae, Chloroflexi, and Acidobacteria dominated 90–98 % of the total bacteria. Temperature exhibited a significant influence on shaping microbial ecosystems, indicating that temperature, rather than HRT, is the primary factor to consider. Additionally, metagenomic analysis reveals that the levels of genes involved in acetoclastic and hydrogenotrophic methanogenic pathways were enhanced at 45 °C, probably improving methane yield. These findings provide new insights into "short-circuit" mitigation and strategies to strengthen methane generation from biomass. • The digester at 45 °C exhibited a higher methane yield than those at 35 °C and 55 °C. • The optimal HRT for the 35 °C, 45 °C, and 55 °C digesters were 25, 30, and 30 d, respectively. • Temperature showed more influence on microbial regulation than HRT. • The enhanced acetoclastic methanogenesis path exhibited at 45 °C. [ABSTRACT FROM AUTHOR]

Ensiling is a widely used method for preserving crop stalks as biogas feedstock. However, secondary fermentation of silage is an inevitable problem that causes significant mass and energy losses. In this study, the effect of different lactic acid bacteria (LAB) inoculants on the fermentation pattern, aerobic stability, and methane production of maize stover was investigated. Maize stover was ensiled for 50 days with or without different LAB inoculants, followed by 10 days of air exposure. Methane production from the stover after the two processes was determined through batch anaerobic digestion (AD) tests. Lactiplantibacillus plantarum enhanced the homo-fermentation and reduced the pH of silage. Lentilactobacillus buchneri improved the hetero-fermentation of hexose, while causing higher dry matter loss (DML) than other inoculants. Limosilactobacillus fermentum enhanced pentose hetero-fermentation and increased both lactic acid and acetic acid production with minor DML. All the tested inoculants reduced the DML, improved the aerobic stability, and increased the methane yield of maize stover after ensiling (by up to 18.8%) and after air exposure (by up to 41.0%), with Limosilactobacillus fermentum exhibiting superior performance. The Limosilactobacillus fermentum treatment showed smaller variations in the bacterial community in AD than other treatments during air exposure. Ruminococcaceae , SHA-31 , SB-1 , Lachnospiraceae , Marinilabiaceae, and Erysipelotrichaceae showed positive correlations with water-soluble components, whereas Anaerolinaceae was positively correlated with cellulose or hemicellulose. [Display omitted] • Maize stover was ensiled with different lactic acid bacteria for methane production. • All the inoculants improved the aerobic stability and reduced dry matter loss. • The inoculants led to up to 41% higher methane yield after air exposure. • Limosilactobacillus fermentum enhanced pentose hetero-fermentation into acetic acid. • Limosilactobacillus fermentum showed superior performance in methane preservation. [ABSTRACT FROM AUTHOR]