Characteristic drivers of biochar and nanomaterials in anaerobic digestion across all stages for augmented methane-rich biogas production

Abstract

Anaerobic digestion (AD) is a widely adopted technology for biogas production using organic waste across rural, industrial, and municipal sectors. To meet the rising renewable energy demand, the process efficiency of AD must be stratagically enhanced. Recalcitrant feedstock, accumulation of toxicants, such as ammonia, organic acids, and diminished methanogenic activity compromise digester performance. Biochar and nanomaterials have received wide attention as additives to boost biogas production. However, insights into their point of action and the underlying mechanism at each AD stage remain largely shattered. In this review, the characteristic drivers and controlling factors through which biochar and nanomaterials influence AD are delineated. A comprehensive discussion of interlinks between the physicochemical properties of each of the additives and the undergoing reactions in AD at various stages is provided. This review suggests that biochar with high alkalinity, minerals, electron donating capacity, oxygen-containing functional groups, and porosity are superior in enhancing biogas production and methane content. Chemical properties over physical properties are decisive factors in biochar application. Metal impregnation and chemical modifications assist in tuning biochar properties for enhanced AD performance. Further, nanoparticles can work as an electron conduit to boost methanogen activity. Additionally, these nanoparticles, especially iron, nickel, and cobalt can act as a source of micronutrients to enhance microbial growth and support as a cofactor in enzymatic activities. To some extent, nickel nanoparticles can accelerate disintegration of the intermediate compounds and thus improve the hydrolysis rate. This review presents valuable data and insights for designing effective biochar and nanomaterials to ensure maximum conversion of feedstock into methane-rich biogas.