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The production of biogas from lignocellulose by anaerobic digestion (AD) has attracted much attention recently. However, the over-acidification phenomenon and low biogas yield often occur during the AD of lignocellulose. In this work, the liquid-state fermentation mode using pretreatment liquor from dilute acid treated rice straw without detoxification for continuous biogas production in a 100 L internal circulation reactor was studied. The highest biogas yield reached 0.66 m3/kg CODconsumption while the methane yield was 0.38 m3/kg CODconsumption. The pH values of outlet were maintained at 6.9–7.4, and even the inlet pH values were lower than 6.0. Furthermore, from the second day to the end of fermentation, the COD removal rates were more than 90%, even though the inlet COD was close to 20000 mg/L. The organic substances from acid pretreated rice straw were efficiently degraded by AD, which was confirmed by substrate metabolism analysis. These results indicated that the whole fermentation process of AD was very stable and showed great potential for industrial application. [Display omitted] • AD of pretreatment liquor from dilute acid treated rice straw without detoxification. • The COD removal rate during the AD process was more than 85%. • The sugars and organic acids could be utilized efficiently. • Continuous biogas production in a 100 L IC reactor was investigated. [ABSTRACT FROM AUTHOR]

Traditional solid-state biogas production from lignocellulosic biomass has some issues such as relatively low methane yield, instability of fermentation system, etc., and these might be solved by changing solid-state mode to completely liquid-state mode using lignocellulosic hydrolysates as substrate for biogas production. However, the potential and possibility of this new technology for industrial application is still unclear. In this study, semi-pilot scale long-term biogas production using various lignocellulosic hydrolysates (acid hydrolysates of bagasse, rice straw, and corncob) as substrate was carried out in a 100 L up-flow anaerobic bioreactor (internal circulation reactor, IC) for 76 days. During operation, biogas was generated almost immediately when the substrate was pumped into bioreactor and the start-up can be finished in short period. Throughout the fermentation process, most COD (>85%) of lignocellulosic hydrolysates was utilized for biogas production. High biogas yield (0.549 ± 0.058 m 3 /kg COD consumption ), methane yield (0.381 ± 0.043 m 3 /kg COD consumption ) and CH 4 content in biogas (69.6 ± 5.6%) can be obtained respectively when the fermentation system was stable. Variations of inlet pH value and types of lignocellulosic hydrolysate showed little influence on the operation performance of this fermentation system. Overall, the fermentation scale, operation period, COD removal, biogas yield, CH 4 content in biogas, and operation performance with various inlet pH value and different kinds of substrate shows that this technology has great potential and possibility of industrialization. [ABSTRACT FROM AUTHOR]

• Anaerobic digestion of elephant grass hydrolysate was evaluated. • Efficient COD removal and biogas production were fulfilled. • Most inlet organic materials could be utilized or degraded efficiently. • Almost no VFAs were accumulated and the operation was stable. • COD and color of outlet effluent of anaerobic digestion were removed efficiently. Elephant grass (Pennisetum purpureum) acid hydrolysate was used as substrate for anaerobic digestion for the first time. Within short period (ten days), the organic materials (sugars and organic acids) in the elephant grass hydrolysate could be utilized efficiently for stable biogas production that the COD removal, biogas yield, and CH 4 content were 91.3 ± 2.0%, 0.561 ± 0.014 m3/kg COD consumption, and 68.1 ± 4.6%, respectively throughout this bioprocess. During anaerobic digestion, almost no volatile fatty acids (VFAs) was accumulated (merely <0.1 g/L acetic acid was found) and the outlet pH was very stable (7.3 ± 0.1). Meanwhile, the furans including furfural and 5-hydroxymethylfurfural (HMF) existing in the inlet substrate could be degraded. After anaerobic digestion, the outlet effluent was treated by combination of Fe-C micro-electrolysis and Fenton reaction to remove 93.1% of residual COD and 98.6% of color. Considering the performance, cost, operation, and environmental influence, this technology is suitable for industrial treatment of waste elephant grass. [ABSTRACT FROM AUTHOR]

Biogas is one of the important renewable energy sources, which is expected to significantly contribute not only for the successful achievement of a low carbon transition but also to achieve global climate change policy targets. Private investment is identified as a critical factor for biogas sector to fulfill its expected role. Hence, this paper emphasizes on identifying private stakeholder’s investment criteria in order to increase its active involvement for biogas in China. This study focused on banks, insurance companies, pension funds, private equity funds and high network individuals as the primary stakeholders. It applies an SWOT-AHP-TOWS analysis, in which the Strengths, Weaknesses, Opportunities, and Threats (SWOT) of stakeholders are identified and then prioritized by using the analytical hierarchy process (AHP). Finally, the TOWS matrix supports the development of private investment strategies, which serve as a foundation for Chinese policy makers to promote private investments in the biogas sector. The following strategies have been identified as the most important ones: (1) Promoting financial tailored biogas products in terms of volume, interest rate and duration for banks; (2) Permitting insurance companies and pension funds directly investing into biogas equity; (3) Encouraging public-private partnerships and (4) Improving project cooperation by introducing professional guidance. [ABSTRACT FROM AUTHOR]