Improving the Biogas Potential of Rice Straw Through Microwave-Assisted Ammoniation Pretreatment During Anaerobic Digestion

Abstract

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 T 90 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.

Sewage sludge pretreatment: current status and future prospects

“…Another commonly used method of pretreatment involves microwaves, where the generated heat causes disintegration of compounds via hydrogen bond cleavage due to changes in dipole orientation at the polarized side chains in the cell membranes of macromolecules (Park et al 2004 , Serrano et al 2016 ). Microwave is considered a promising pretreatment method and is normally used in crop straw pretreatment (Liu et al 2021a ). It is a rapid heating source, promoting thermal and nonthermal effects, resulting in enhanced biogas production, and it is regarded a supporting method for chemical treatment (Xu, 2015 ; Zaidi et al 2019 ).…”

“…The possibility of biomass fermentation increases in the presence of bases due to lignin degradation (Patinvoh et al 2016 ). However, alkaline treatment decreases the degree of polymerization of lignocellulosic biomass compounds, promoting lignin removal, and increases organic matter solubility in sludge and easier cellulose degradation by enzymatic and microbial impact (Liu et al 2021a ). Thus, alkaline treatment method is a promising and efficient way to lignocellulosic biomass decomposition.…”

“…In some industries, protein content in dairy wastewater is over 40% of total oxygen demand, but the addition of carbohydrate matter can increase protein conversion in the sewage sludge. Moreover, pH influences methane production through the composition of VFA (Liu et al 2021a ). The use of sludges rich in protein sources, such as keratin wastes (e.g., feathers), contains over 90% of crude protein instead, or mixed with sewage sludge may provide higher biogas production.…”

Rice straw for energy and value-added products in China: a review

“…Rice straw is produced in large quantities in China, with an annual output of 230 million tons (Liu et al 2021a ). Regrettably, a significant portion of this rice straw remains unused and subsequently disposed of or burned in the open fields, resulting in ecological predicaments, such as atmospheric and aquatic contamination, in addition to soil deterioration (Alengebawy et al 2022c ).…”

“…Therefore, utilizing this waste for energy production is essential to achieving renewable energy goals (Londoño-Pulgarin et al 2021 ). China, an agriculture-based country, produces over 1.04 billion tons of agricultural waste annually, which is almost one-third of the global yield (Liu et al 2021a ). Considerable amounts of this waste, which has a high energy potential, are lost through disposal or direct burning in open fields, resulting in negative environmental impacts from fine particulate matter as well as elemental and organic carbon (Su et al 2021 ).…”