Search

Sub-moderate temperature (ranging from low to moderate temperature) anaerobic digestion (AD) could balance fermentation efficiency and energy input. We investigated biogas production and the microbial community in wastewater AD at sub-moderate (15 °C, 20 °C, and 25 °C) and moderate (35 °C; control group) temperatures with the organic loading rate (OLR) incrementally increased over 200 days. The impact of temperature on biogas production was found to be minimal at a low OLR but became more significant at a high OLR. Notably, a temperature threshold ranging from 15 °C to 20 °C exerted a strong inhibitory effect on biogas production and disrupted the microbial community. And, SMT-AD is deemed by this study to be the optimal application strategy of wastewater with low temperature and low OLR. Bacterial richness was positively and linearly related to temperature. There is a relevance between methane production and archaeal diversity under the influence of temperature and OLR. Temperature and OLR shaped the ecological function of predominant bacteria. Anaerolineales, Thermotogales, and Lactobacillales were strongly influenced by temperature. Synergistales had a synergistic relationship with Desulfovibrionales. Clostridiales was responsible for acetate and butyrate production and closely related to Lactobacillales. Acetoclastic Methanosaetaceae was the predominant methanogen. Methanogens could survive and maintain their population even though methanogenesis was limited under high OLRs and low temperatures. [ABSTRACT FROM AUTHOR]

[Display omitted] • • The novel reactor allows dry anaerobic digestion of food waste (FW) and straw. • • The methane yield of FW and straw co-digestion could reach 494.2 mL CH 4 /g VS. • • FW significantly improved the anaerobic biodegradability of the substrate (85.7%). • • Co-digestion can improve hydrolysis and acid production efficiency. • • The acetotrophic methanogenic pathway significantly affects the methane yield. 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. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of temperature rises and falls on anaerobic digestion was assessed. • 45 °C exhibits optimal methanogenic performance during temperature rises and falls. • An effective equilibrium between hydrolysis and methanation is achieved at 45 °C. • The shortest recovery time was 2 days following temperature fluctuation. This study implemented five successive temperature stages (35 °C–45 °C–55 °C–45 °C–35 °C) in a continuous stirred tank reactor, designated as D35-1, D45-1, D55, D45-2, and D35-2, respectively. The objective was to probe the mechanism of temperature transformations on methanogenesis performance, microbial community, and metabolic pathways. The suitability of 45 °C for anaerobic digestion (AD) under varying temperatures was emphatically expounded. Intriguingly, optimal methanogenesis performance was attained at 45 °C, with methane production reaching 238.51 mL/g VS/d in D45-1 and 245.91 mL/g VS/d in D45-2, signifying increases of 17.66% and 21.32% contrasted with D35-2, respectively. Additionally, considerable resistance to temperature shocks at 45 °C was also manifested, as evidenced by a recovery time of 2 days in D45-2. At 45 °C, an effective balance between hydrolysis and methanogenesis was observed, maintaining a dynamic equilibrium between acetoclastic and hydrogenotrophic methanogenesis. The primary drivers in D45-1 were Caldicoprobacter , Bathyarchaeia , and Methanosarcina , while Anaerolinea and Methanosarcina were the key determinants in D45-2. By contrast, methanogenesis was suppressed at other stages. Therefore, 45 °C emerges as a viable alternative to conventional temperatures when confronted with temperature fluctuations to optimize energy efficiency. The results provide novel insights into AD temperature management and pave the way for engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two-stage anaerobic digestion affects the hydrolysis-methanogenesis process. • Aerobic or micro-aerobic hydrolysis results in carbon loss from the substrate. • Substrate type significantly affected biogas yield and microbial community. • The gradient anaerobic digestion process (GADP) improved the biogas yield. • GADP enhanced carbon recovery of substrate and synergies of microorganisms. The destruction of the synergistic effect of the hydrolysis-methanogenesis process (HMP) of substrate may lead to the serious carbon loss of substrate and low biogas yield in traditional straw biogas engineering. In this study, the influence of substrate composition on anaerobic digestion (AD) was investigated under pilot conditions, and the relationship between HMP was further investigated under full-scale plants. The results showed that straw with a high content of soluble substances had the highest methane yield (264.25 L/kg VS) and degradation rate (59.32 %). At HRT = 20 d, the full-scale plant achieved the highest biogas yield (576.92 L/kg VS, 3.47 L/L/d) and degradation rate (67.50 %). Microbial analysis showed that substrate composition affected microbial community and methanogenic metabolic pathway. The analysis results of PICRUSt2 confirm that gradient AD guarantees the synergistic relationship of HMP. This study provides the theoretical basis and engineering guidance for improving the AD process in traditional straw biogas engineering. [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]

[Display omitted] • The Continuous stirred-tank reactor (CSTR) has a "short-circuit" problem. • The Gradient anaerobic digestion reactor (GADR) can solve the problem of CSTR. • GADR can stably carry out semi-continuous dry anaerobic digestion. • GADR can improve the biogas yield of straw raw materials that are unique to China. • The biogas production efficiency and microbial community were analyzed. In China, the problem of low biogas yield of traditional biogas projects has become increasingly prominent. This study investigated the effects of different hydraulic retention times (HRTs) on the biogas production efficiency and microbial community under pilot conditions. The results show that the "Gradient anaerobic digestion reactor" can stably carry out semi-continuous dry anaerobic digestion and improve biogas yield. The highest volatile solids (VS) biogas yield (413.73 L/kg VS and 221.61 L CH 4 /kg VS) and VS degradation rate (48.41%) were observed at an HRT of 25 days. When the HRT was 15 days, the volumetric biogas yield was the highest (2.73 L/L/d, 1.43 L CH 4 /L/d), but the VS biogas yield and degradation rate were significantly decreased. Microbial analysis showed that HRT significantly affected microbial community. It provides basic data support for the development of a new anaerobic digestion process and the practical application of the straw biogas project in China. [ABSTRACT FROM AUTHOR]

• The interval temperature digester exhibited the highest methane yield. • The decomposition rate of organic matter increases with increasing temperature. • Methanogenesis, rather than hydrolysis, is limited at the thermophilic temperature because of the loss of Methanosarcina. • Efficient methanogenesis occurs under the balance between hydrolysis and methanogenesis at interval temperature. • Our findings may provide insight into the temperature control in AD systems. Anaerobic digestion (AD) at mesophilic and thermophilic interval temperatures has received increasing attention due to an unexpectedly higher methane yield. However, there is no general consensus and the mechanisms of microbial regulation under interval temperature remain unclear. Therefore, this study evaluated the effect of conventional and interval temperatures on methanogenesis performance and microbial regulation in continuous AD of wilted corn straw. The results demonstrated that the hydrolysis rate increased with increasing temperatures, probably due to the predominant Firmicutes and Proteobacteria, whose abundance in D55 was more than 72% and 19%, respectively. However, in the stable period (31–55 d) experiments, digesters D35, D45, and D55 achieved an average methane yield of 224 ± 34, 311 ± 55, and 261 ± 49 N mL/g VS/d, respectively. Interval temperature substantially enhanced methane yield by 39.4% and 19.0% compared to that from mesophilic and thermophilic digesters, respectively. A higher proportion of Methanosarcina (94.42–94.73%) promoted the acetoclastic methanogenesis at interval temperature, implying that methanogenesis, rather than hydrolysis, is limited at the thermophilic temperatures because of the loss of Methanosarcina. Furthermore, a high abundance of essential genes involved in methane metabolism was found to stimulate methane production in the interval temperature digester. These findings revealed that the interval temperatures may be a balanced zone between hydrolysis and methanogenesis for achieving higher methane yield and provided a new perspective strategy for AD. [ABSTRACT FROM AUTHOR]

Adopting anaerobic digestion (AD) of lignocellulosic biomass to produce biomethane is an effective approach to meet the urgent demand for clean and sustainable energy in energy transition. The pretreatment kinetic mechanism is the key to enhance the lignocellulosic carbon conversion and significantly improve the efficiency of AD. Various pretreatment strategies have been proposed in the literature, while a systematical summarization of these strategies based on different driving forces is still lacking. The purpose of this review is to classify and analyze the current technologies and research achievements on lignocellulose pretreatment technologies according to different driving forces including single ones and combined ones. Features, as well as fundamental modes of conventional and recently emerged pretreatments, have been introduced. Single pretreatment methods driven by physical, chemical, or biological forces have obvious advantages and limitations for the anaerobic transformation of lignocellulosic feedstocks. Recently emerged combined pretreatment technologies powered by multiple forces have synergistic treatment effects which hold greater application potential than those driven by single forces. Besides, a comprehensive evaluation of combined pretreatments is carried out on the basis of pretreatment efficiency, cost, energy consumption, and environmental impact to detect their potential applications in the actual biogas industry. By comprehensively summarizing the current features of single and combined technologies, this review finally provides future research perspectives for biomass pretreatment. [Display omitted] • Features of different pretreatments driving by different forces were analyzed. • Conventional pretreatments driven by single forces have obvious shortcomings. • Rational integration of multiple driving forces has synergistic pretreatment effect. • Combined pretreatment strategies have greater potential than single ones. • Physical-chemical methods are most promising based on comprehensive evaluations. [ABSTRACT FROM AUTHOR]