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This study proposes a novel anaerobic digestion (AD) strategy combining recyclable photoactivated nanomaterials with illumination to enhance electronic transfer for anaerobic microorganisms. Results showed that 7000 Lux illumination increased methane production yield and rate. Incorporating Fe 3 O 4 into graphite carbon nitride (g-C 3 N 4 ) created a recyclable Fe 3 O 4 /g-C 3 N 4 (FG) nanocomposite with improved light absorption, conductivity, redox properties, and methane promotion. The highest methane yield from corn straw was achieved with 7000 Lux and 1.5 g/L FG nanocomposite, 22.6% higher than the dark control. The AD system exhibited increased adenosine triphosphate content, improved redox performance, reduced electron transfer resistance, and higher photocurrent intensity. These improvements bolstered the microorganisms and key genes involved in hydrolysis and acidification, which in turn optimized the acetoclastic pathway. Furthermore, this strategy promoted microorganisms associated with direct interspecies electron transfer, fostering a favorable environment for methanogenic activities, paving the way for future anaerobic reactor developments., 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. 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.)

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.)

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.

The methane potential of nine varieties of fresh maize harvested at three different times and of maize silage was experimentally determined in batch assays. The ultimate methane productivity in terms of volatile solids (VS) was determined as 213.94-313.63, 195.88-334.81 mL/g VS from several fresh and silage maize in three stages, respectively. The average specific methane yield of wax ripeness stage for fresh maize and full ripeness stage for silage maize were higher than that of other stages, respectively. The high-oil varieties of fresh maize and silage varieties of ensiling maize could produce more methane than general varieties in the same ripeness stage. Methane yield of ensiled materials was higher than fresh material. The methane yields of fresh and silage maize in full ripeness stage were ranged 5656-7956 and 4633-8915 m(3)/ha, respectively. The corresponding maximum of methane yield came from fresh HO5580 and silage CAU No. 4., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

A microbial consortium MC1 was used to pretreat filter paper, office paper, newspaper, and cardboard to enhance methane production. The results of pretreatment indicated that sCOD of hydrolysates of the four substrates increased significantly in the early stage, and peaked on day 7. During pretreatment, ethanol, acetic acid, propionic acid, butyric acid, and glycerol were the predominant volatile organic products in hydrolysates. MC1 had strong degradation ability on the four substrates, and the weight loss of filter paper, office paper, newspaper, and cardboard reached 78.3%, 80.5%, 39.7%, and 49.7%, respectively. The results of anaerobic digestion showed that methane production yields and rates of the four substrates significantly increased after pretreatment. This study is the first attempt to explore the microbial pretreatment method for anaerobic digestion of waste paper and cardboard. Microbial consortium pretreatment could be an effective method for enhancing methane production of waste paper and cardboard into bioenergy., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The effect of temperature on the functionality of microbial community structure in a low temperature, anaerobic fixed-bed reactor was studied by decreasing the operating temperature from 18 °C to 5 °C. The reactor was productive within 20 days and produced stable methane content in biogas (above 77%) throughout the trial period. At 17 °C and 15 °C, chemical oxygen demand (COD) removal efficiency and biogas production of reactor were significantly reduced. These might be temperature thresholds when fixed-bed reactors are operated under low temperatures. The methanogen community composition was analyzed using 16S rRNA gene clone library screening and quantitative PCR. At low ambient temperatures, Methanomicrobiales were dominant methanogens, and they preferentially adhered to the carbon fiber carrier. The results indicated that 16S rRNA levels of Methanomicrobiales and Methanosaetaceae in adhering sludge were higher than in deposited sludge, and they all contributed to the efficient performance of the fixed-bed reactor at low operating temperatures., (Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.)

Methane production from lignocellulosic feedstock through high solid anaerobic digestion is a huge potential technology. However, the shortage of an efficient reactor has become a major bottleneck in developing the technology. The continuous feeding and discharge of lignocellulosic feedstock with high solids is difficult to complete. Methane production from the feedstock is low in practice. Thus, it is important to develop a new reactor with efficient feeding and discharge feedstock equipments and improve methane production by an optimized operation process. Based on synthesizing the merits of a number of techniques home and abroad, a novel anaerobic reactor was designed in this study. The reactor had two spiral equipments to implement continuous feeding and discharge feedstock with high solid content and had a high bearing capability of organic loading rate (OLR) to improve methane production. In order to provide a technology and some reliable operating parameters to efficiently produce methane from lignocellulosic feedstock, the continuous anaerobic co-digestion tests were conducted at three total solid contents of 10%, 15% and 20% using corn stalk and dairy manure as feedstock. An integrated two-phase division digestion system was constructed by controlling stirring intensity (h/d) and feeding intensity (d). The methane volumetric production rate (MVPR) of different OLRs was compared. Effects of the total solid (TS) of feedstock, stirring, feeding intensity on height, pH of function divisions, and MVPR were discussed in detail. The results showed that function divisions, including the acidification division of upside and methanogenic division of underpart in the vertical reactor, were obviously formed when TS were 10% and 15%, MVPR gradually increased, and methane content stabilized around 52% with OLR increasing. The highest MVPR reached 1.62 and 1.66 m3/(m3·d) respectively when OLR was 13.44 kg/(m3·d) at 10% TS and 20.17 kg/(m3·d) at 15% TS. MVPR significantly decreased when OLR was 20.17 kg/(m3·d) and 30.0 kg/(m3·d), respectively, which might be caused by the accumulation of volatile fatty acids. MVPR stabilized around 0.98 m3/(m3·d) with OLR increasing, then it dramatically decreased and anaerobic digestion failed when OLR reached 30.0 kg/(m3·d) at 20% TS. The results of two factors interacting declared the highest MVPR at 1.63-1.69 m3/(m3·d) The efficient acidification division and methanogenic division were formed, and the height ratio of both was 1.1-1.6:1 when stirring intensity, feeding intensity, and TS were 6-12 h/d, 6.5-10 d, and 10%-15%, respectively. In summary, the process of continuous feeding and discharge at 10%-20% TS of lignocellulosic feedstock was feasible in the anaerobic digestion reactor. The reactor was more efficient and stable to produce methane at 10% and 15% TS compared to 20% TS, and MVPR could be improved by adjusting stirring intensity and feeding intensity. Therefore, this technology has a promising prospect for industrial scale application. [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]

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]

Highlights: [•] Effect of microbial pretreatment on methane production of LMSW was evaluated. [•] Soluble substrates in hydrolysate increased obviously after microbial pretreatment. [•] CH4 production yields and rates significantly increased after microbial pretreatment. [Copyright &y& Elsevier]

[Display omitted] • Anaerobic digestion by-products were used to pretreated corn straw. • Methane production was improved by 50.97% after CO 2 -liquid digestate pretreatment. • The dense structure of straw could be effectively destroyed after pretreatment. • Pretreatment at 170 ℃ hindered methane production due to formation of inhibitors. • Mechanism behind CO 2 -liquid digestate pretreatment was elucidated. The development of biogas projects feed by lignocellulosic biomass has been constrained by the high cost of pre- and post-treatment. In this study, a novel strategy for pretreatment by using two by-products, i.e., CO 2 and liquid digestate (LD), generated from anaerobic digestion (AD) was developed to overcome these shortcomings. Results showed that corn straw pretreated in LD pressurized under 1 Mpa CO 2 at 55 ℃ resulted in increased glucose and xylose contents and a 9.80% decrease in cellulose crystallinity. After 45 days of AD conversion, the methane yield increased by 50.97% compared with untreated straw. However, pretreatment in LD pressurized under 1 Mpa CO 2 at 170 ℃ produced 5-hydroxymethylfurfural and furfural, which led to a decrease in methane production from the straw in the subsequent AD conversion. The alteration of the microbial community in the pretreated slurry at 55 °C was another potential contributor to the enhanced performance of AD. [ABSTRACT FROM AUTHOR]