A review of biochar properties and their roles in mitigating challenges with anaerobic digestion

Anaerobic digestion (AD) is an established organic waste management technology, producing biogas and organic fertiliser as end-products. Despite being an established technology, AD still faces key challenges, including process inefficiencies due to substrate-induced instability and product quality assurance; inability to digest highly lignocellulosic biomass without pre-treatment; and management of effluents and emissions. Commercial grade carbon-based materials have been employed as stabilising agent to improve process efficiency. Biochar, a by-product from biomass pyrolysis, has recently been identified as a sustainable alternative material to commercial grade carbon-based adsorbent used in AD. This review highlights the challenges with the AD process and the limitations of the various conventional approaches in its management. An exposition of the characteristics of biochar and the physico-chemical properties of biochar, that can simultaneously promote AD process stability, increase biomethane yield rate and the agronomic quality of digestate, are presented and discussed.