Mutually trading off biochar and biogas sectors for broadening biomethane applications: A comprehensive review

The biogas sector has been in the limelight among renewable energy sources with its eco-friendly and carbon capturing characteristics for more than a century. Over the years, the sector has expanded into three major subsidiaries, namely, “biogas production,” “upgradation,” and “bottling and dissemination” for energy applications. This review emphasizes exploring the opportunities of the carbonaceous material “Biochar” on how it can play a crucial role in all the three subsidiaries imparting a positive advancement in the biogas sector. The contribution of different biochar properties in the biogas sector to negotiate the challenges faced explicitly for the biogas production, syntrophic microbial activity, interspecies electron transfer, biomethane enrichment, and high-pressure bottling are extensively discussed from systematically selected literature. According to the study, the properties such as adsorption capacity, high pH, cation exchange capacity, electrical conductivity etc., enhanced the various subsidiaries of the biogas sector. Results suggest that incorporating biochar in the biogas sector could unravel new opportunities in terms of biomethane applications. High-quality biochar is expected from the slow pyrolysis process from the lignin-rich substrate, while easily biodegradable substrate could be utilized for biogas production for mutual trade-offs between the sectors. Thus, a self-resource sufficient biochar-biogas closed-loop system can be developed to utilize waste biomasses efficiently. The techno-economics and sustainability of the proposed concept are also discussed. The study further gives a conclusive outlook on research gaps and future directions over the use of biochar for methane enhancement and enrichment from the biogas and its low-pressure storage.