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Rice straw is an abundant lignocellulosic biomass used to produce biogas. However, its resistant structure hinders biogas production. In this study, three pretreatments, microwave, ammoniation, and microwave-assisted ammoniation (MAA), were evaluated for their use in improving biogas production from rice straw. After an 18-day digestion, methane production by rice straw pretreated with MAA was 281.56 mL/g (volatile solids of substrate), which was 25.43%, 7.96%, and 18.18% more than that produced following the control, microwave, and ammoniation pretreatments, respectively. These increases were mainly attributed to the change in the resistant structure of rice straw following the MAA pretreatment and a more stable anaerobic digestion system. The degradation rate for the volatile solids of the rice straw pretreated with MAA during anaerobic digestion was 71.20%, which was 4.71%, and 4.86% higher than the rates observed using microwave and ammoniation pretreatments, respectively. In addition, the MAA method had a T90 fermentation cycle of 6 days, which was 33.3%, 25.0%, and 33.3% shorter than those for the control, microwave, and ammoniation methods, respectively. This technology shows the potential to enhance biogas production from the anaerobic digestion of rice straw. [ABSTRACT FROM AUTHOR]

Biogas production by anaerobic digestion is an attractive approach to producing clean fuel biomethane and reducing environmental pollution. However, many fluctuations in production occur during a batch digestion period. This study investigated the dynamics of microbial communities involved in biogas production during a 20-day digestion of rice straw (RS) at 35 °C. The results demonstrated roughly consistent trends in biogas and methane production and revealed distinct stages of production. The lowest and peak methane yields were 82 ± 19.9 mL/(L•day) at day 3 and 328.5 ± 0.9 mL/(L•day) at day 8, respectively, whereas most (97.1%) of the methane was produced in the first 14 days of digestion. Ultimately, the biogas potential of RS reached 393.2 ± 13.6 mL/g added volatile solids (CH4% = 57.1%), and the logistic model best fitted actual methane production compared to the modified Gompertz, first-order kinetic, and Cone models. The microbial communities at different critical stages are a clear reflection of the biochemical dynamics in digesters. The bacterial genera Bacteroides and Clostridium_sensu_stricto_1 were the dominant microorganisms at the early stage of digestion, while the archaeal genus Methanosarcina was significantly more abundant at the peak stage of methane production than at other times during the digestion. This study demonstrates the detailed micro- and macro-conditions that exist during the fluctuating and constant digestion of RS, which will benefit industrial applications during the anaerobic digestion of RS. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-digestion of 45.7% BPS, 26.2% SCB and 28.1% CM produced 186.5 mL/g VS methane. • This co-digestion strategy provided a synergistic effect of 37.1% on methane yield. • A higher microbial diversity was found in co-digestion due to the balanced nutrition. • The predominant microorganisms in co-digestion were Choroflexi with a proportion of 39.3%. • Enriched hydrogenotrophic Methanobacterium and Methanolinea were found at high OLR. Balanced nutrition is important for maximizing anaerobic digestion (AD) performance. Herein, the strategy of balancing sugar-fiber-nitrogen nutrients was first established for improved methane production by co-digesting two agricultural and one livestock wastes with complementary compositional properties, such as banana pseudo-stem (BPS), sugarcane baggage (SCB), and chicken manure (CM) having high sugar, fiber and nitrogen contents, respectively. The maximum methane yield was 186.5 mL/g VS added with a mixture of 45.7% BPS, 26.2% SCB and 28.1% CM (with 1: 11.3: 0.3 of sugar to fiber to nitrogen ratio), increasing by 16.1%, 53.3%, 122.6% than those of mono- BPS, SCB, and CM, respectively. The co-digestion process remained stable under an organic load of 4 g VS/(L·day), which was attributed to the predominant presence of Bacteroidetes, Proteobacteria, Thauera , uncultured_bacterium_p_Aegiribacteria , and hydrogenotrophic methanogens. This study provides a deeper understanding of the co-digestion with agricultural and livestock wastes from the perspective of nutrient balance. [ABSTRACT FROM AUTHOR]

The sustainability of biogas production from straws is limited by the collection, transportation, storage, and pretreatment of feedstocks. To address these constraints, this study investigated briquetting as a pretreatment strategy for rice straw (RS) to increase bioenergy generation. The results indicated that briquetted RS yielded 205.4 mL/g VS of methane, which was 11.7% higher compared to that produced by the untreated RS. The economic analysis revealed that the briquetting process had positive effects with a payback time of 3.4 y and an internal rate of return of 23.4%. It also reduced feedstock transportation and storage costs by 42.6%. Adding a NaOH treatment to the briquetting process increased methane production by 26.4% compared to untreated RS. However, the integration of briquetting with NaOH treatment might be an unprofitable method for processing RS. This became apparent when examining the production cost, which stood at 1.13 $/kg biomethane with an internal rate of return of 16.2%, representing an 8.7% increase and a 7.2% decrease, respectively, compared to the mono briquetting method. These results revealed that briquetting as a source pretreatment strategy can improve the productivity of straw biogas plants, thereby advancing the industry towards cleaner production. [Display omitted] • Briquetting, a source pretreatment strategy, improved straw biogas production. • The briquetting strategy integrates the collection and pretreatment of rice straw. • The proposed strategy reduced straw transportation and storage costs by 42.6%. • Adding an NaOH treatment reduced the profitability of a straw biogas plant. [ABSTRACT FROM AUTHOR]

• High moisture content is a prominent feature of banana pseudo-stems (BPS). • The effect of squeezing pretreatment on methane production from BPS was evaluated. • Methane production increased by 41.2% after pretreating BPS by squeezing. • Most phenols were lost with the BPS juice during squeezing. • Energy output from squeezed BPS exceeded energy consumption during pretreatment. Banana pseudo-stems (BPS) are an abundant and low-lignin-content lignocellulosic biomass for methane production. However, the high-water content in BPS increases the transport costs, and the resistant structure of BPS hinders methane production. In this study, squeezing of BPS as a pretreatment was evaluated for improving anaerobic digestion (AD). After 20-d digestion, methane production from squeezed BPS was 204.2 ± 6.2 mL/(g volatile solids (VS) of feedstock), which was 41.2% more than that from untreated BPS. This increase was mainly attributed to the improvement of physical properties (e.g. water absorbing capacity) and the change in the resistant structure of BPS after squeezing, which promoted good contact between microbes and substrate during AD. The measured methane production was described using a modified Gompertz model and the results showed that anaerobic process would take less time and occur faster when pretreated BPS was used as the substrate. The energy produced during AD of squeezed BPS, after deducting the energy used by the squeezer, resulted in an energy surplus of 26.2%. [ABSTRACT FROM AUTHOR]