Recent trends in biochar integration with anaerobic fermentation: Win-win strategies in a closed-loop

Abstract

Anaerobic fermentation (AF) is a widely used process for the transformation of organic waste into biogas. However, despite its ubiquitous use, it has several limiting factors, including low yield, redox imbalance, high concentration of inhibitors, and a long retention time. Integration of pyrolysis with AF improves efficiency and facilitates effective biomass utilization in a closed-loop approach. Research trends emphasize the inclusion of biochar derived from biomass to improve the stability and efficiency of AF and facilitate biogas up-gradation (H2S removal). However, there is a lack of consolidated scientific understanding regarding the complex interactions of biochar and AF microbial communities, in addition to its potential amendment advantages. Therefore, this review summarizes biomass utilization for biochar production using various pyrolysis methods and its use as an effective inclusion material to improve AF performance. Specifically, the influence of biochar amendments in AF is discussed in terms of microbial colonization, direct interspecies electron transfer, minimization of organic load, and buffering maintenance. Moreover, the role of AF digestate biochar in nutrient recycling and utilization as a soil conditioner is elaborated. The progressive integration of pyrolysis and AF offers the complete decoupling of biomass, enhances AF performance, and promotes the establishment of a sustainable bioprocess by inducing the circular bioeconomy.