Recent Advances in Bioethanol Production from Rice Straw: Strategies, New Concepts, and Challenges

Second-generation bioethanol has garnered considerable interest among researchers due to its utilization of lignocellulosic biomass, such as rice straw, which is both cost-effective and readily available. Nonetheless, the economic viability of large-scale production of second-generation bioethanol remains a significant challenge. There is an urgent need for cost efficiency across three critical stages: pretreatment, hydrolysis, and fermentation. This paper reviews recent advancements in bioethanol production from rice straw and proposes a novel approach to enhance economic feasibility. The inherent recalcitrance of rice straw necessitates the implementation of an appropriate pretreatment method, as this step is crucial for the success of the hydrolysis process. While chemical pretreatment is frequently employed, it often results in increased waste generation and maintenance costs, thereby elevating the overall production expenses. Optimizing reactor configurations for enzyme production, hydrolysis, and fermentation can lead to substantial reductions in production costs. Although enzymatic hydrolysis utilizing commercial enzymes is the predominant method, on-site enzyme production has demonstrated significant cost advantages. Consolidated bioprocessing (CBP) integrates enzyme production, hydrolysis, and fermentation within a single reactor using a single strain or microbial consortium. However, the productivity of bioethanol production from rice straw via CBP is currently low. The proposed novel CBP aims to address the limitations of the original CBP by integrating pretreatment, enzyme production, hydrolysis, and fermentation in a single reactor with a microbial consortium. This innovative approach is expected to minimize contamination risks and reduce equipment installation costs, thereby improving cost-effectiveness. Nevertheless, the implementation of the novel CBP presents challenges, including the establishment of a stable and efficient microbial consortium and the determination of optimal process parameters. Addressing these challenges is essential for the successful application of the novel CBP at an industrial scale.