Integrating biochar in anaerobic digestion: Insights into diverse feedstocks and algal biochar

This review article intends to report the advances in the production and application of biochar from macroalgae and microalgae and its utilization in anaerobic digestion (AD), aiming to achieve zero waste and promote a circular economy. Biochar, a carbon-rich material derived through pyrolysis or gasification, offers environmental and agricultural benefits due to its stability and porosity. By incorporating biochar into AD systems, improved process efficiency, enhanced microbial activity, and nutrient retention can be achieved. An integrated approach on its production and application can minimize biomass disposal impacts, generate renewable energy, and improve the soil and nutrient management. The use of macroalgae and microalgae for biochar production aligns with the sustainability principles, as these resources have high growth rates and there is no direct competition with the arable land. Thus, the focus of this article is to highlight the advances in algal biochar production with emphasis to the factors influencing biochar properties, structure, characterization, mechanism of biochar action, and the impact of biochar addition on AD. It also evaluates the economic and environmental benefits, featuring the role of this approach in achieving a zero-waste paradigm and supporting circular economy development. • Structural, functional and electrical characteristics of algal biochar have been discussed. • Algal biochar enhances methane production during AD through increased methanogenic activity. • Algal biochar increases DIET due to higher electrical conductivity. • Modification of algal biochar using organic acids may be more economic.