Transforming rice straw waste into biochar for advanced water treatment and soil amendment applications

The global rice industry produces an estimated 700 million tonnes of rice straw annually, with more than 100 million tonnes being burned openly in the fields. This practice significantly contributes to air pollution and greenhouse gas emissions. Each kilogram of burned straw releases approximately 0.29-0.38 kg of CO2-equivalents, posing substantial environmental and public health risks, such as respiratory and cardiovascular diseases. In order to tackle these challenges, it is essential to focus on creating new, cost-effective, and sustainable approaches for managing rice straw. This review comprehensively examines the recent advances in the valorization of rice straw, focusing on production, optimization (surface area, pore structure, surface functional groups, and modification techniques), and application of rice straw biochar (RSBC) for wastewater treatment and soil amendment applications. Further, this study explored the composition and morphological analysis of rice straw, along with its management strategies, highlighting their merits and demerits. In addition, this review delves into the benefits of integrating RSBC into biofuel production, particularly in reducing methane emissions. Notably, it also discusses the advantages of utilizing leftover digestate (a by-product of biofuel production), which can be further processed into biochar, thus adding value to environment restoration. Therefore, this review guides future researchers to optimize RSBC properties, enhance biochar and digestate potential, and scale up for broad environmental applications within circular economy principles.