Biochar from anaerobic digestates: Production, characteristics and applications in wastewater remediation

Anaerobic digestate, a byproduct of biogas production, poses significant challenges related to its disposal and environmental impacts. Converting this waste into biochar offers a sustainable solution by transforming the digestate into a value-added product with diverse applications. This review reports the production of biochar from different anaerobic digestates, focusing on its modifications, characteristics and potential applications. The characteristics of the digestate which can influence the biochar characteristics are first discussed. Various biochar production methods and the processes used to modify the biochar characteristics are compared. The reported applications of digestate-derived biochar specifically for the removal of different classes of contaminants including heavy metals, dyes, nutrients and organic micropollutants, in addition to its use in the anaerobic treatment process, are then discussed. This review shows that while the use of digestate-derived biochar appears promising, several critical gaps remain. Further studies on its long-term applications using real water/wastewater, standardising and optimising the biochar production process, and cost-benefit analysis are needed to scale up its use in practical applications.