Biorefinery of anaerobic digestate in a circular bioeconomy: Opportunities, challenges and perspectives

With the ever-increasing size of anaerobic digesters (AD), the management and disposal of digestate have become a challenging task for AD operators. Anaerobic digestate is rich in nutrients and contaminants; thus, a suitable treatment is required to meet environmental legislation and protect the receiving environment. There has been a thrust among the research efforts in anaerobic digestate management in the last decade. Volarization of digestate into high-value products is necessary to make the AD process more cost-effective. Moreover, digestate utilization helps in recycling the already mined resources. Efforts have been made to use digestate as a feedstock to recover energy and value-added products such as nutrients (N, P), biochar, biofuels, polyhydroxyalkanoates (PHAs), and algal cultivation, which can arguably help to enable the circular economy in modern communities. This communication thoroughly examines the anaerobic digestate-based biorefinery concept and its linkages with the circular bio-economy. This review comprehensively summarized digestate management practices; recovery of renewable fuels and other value-added products from digestate, including bottlenecks and perspectives altogether in digestate management and treatment. The state-of-the-art of commercialization of anaerobic digestate valorization technologies has also been provided. Overall, this review could support decision-makers in identifying environmentally sound and sustainable solutions ahead of time.