Synergy of anaerobic digestion and pyrolysis processes for sustainable waste management: A critical review and future perspectives

Abstract

The worldwide growing population, challenged by an ever-increasing global demand for food production, is also concomitant with increased waste production, particularly organic wastes. During the last decades, several waste processing technologies have been developed such as anaerobic digestion and pyrolysis. Recently, there has been an increased interest in creating industrial synergies by combining technologies in order to increase the efficacy of the process and improve waste management in the circular economy. In this review, we report on the importance of coupling anaerobic digestion and pyrolysis while providing evidence on the synergistic effects that may occur within such a combined waste bi-functional process. Specific attention has been paid to multiple symbiosis features that exist when coupling both processes, mainly 1) maximizing energy recovery through pyrolysis of solid digestate or feeding of the aqueous bio-oil phase in anaerobic digestion, 2) biogas purification by biochar or activated biochar, and 3) improving anaerobic digestion process stability by biochar addition to the system. In addition, the effects of coupling anaerobic digestate with biochar on soil biochemical properties and crop production were also presented. Improving the dual symbiosis of coupling anaerobic digestion and pyrolysis is likely to be a sustainable based approach that holds promise for wiser and more eco-efficient processing of organic wastes for versatile applications.