Principles and advancements in improving anaerobic digestion of organic waste via direct interspecies electron transfer

Abstract

The inefficiency of interspecies electron transfer between syntrophic bacteria and methanogens typically restricts the reaction rates and methanogenesis efficiency of anaerobic digestion (AD) of organic waste. Direct interspecies electron transfer (DIET) has been proposed as a pathway that may enhance AD performance by increasing electron transfer efficiency. This paper comprehensively reviews the main principles and mechanisms of DIET between syntrophic bacteria and methanogens in AD, summarizes strategies for the regulation and enhancement of DIET in AD, and discusses the role of DIET in improving AD efficiency. Literature research demonstrate that c-type cytochromes and e-pili are two major functional components for the cell-to-cell electron transfer and the supplementation of ethanol-enriched substrates along with conductive materials have been proven to be efficient for DIET establishment. It is also confirmed that DIET has the great potential for shortening the start-up period, promoting organic degradation, and enhancing methane production in the AD of organic waste. Furthermore, the main knowledge gaps in the profound understanding of DIET, including the effect of multimedia environment, the establishment of mathematical model and the realization of engineering application, are identified, and the future perspectives are proposed for DIET applications in the AD of organic waste. This paper thus highlights important references and directions that will support research to enhance the DIET pathway and therefore the AD of organic waste.