Hybrid technologies for enhanced microbial fermentation process for production of bioenergy and biochemicals

Anaerobic digestion (AD) is a mature technology that has been extensively employed worldwide for biomass waste minimization and bioenergy recovery, but some intrinsic drawbacks, such as limited hydrolysis/methanogenesis rates and impurities in biogas, still necessitate further advancement and optimization of conventional AD systems. Microbial electrochemical technologies, typically including microbial electrolysis cells (MECs), which harness the power of certain electroactive microorganisms to catalyze the electrochemical reactions converting the energy in waste biomass into other forms such as methane, share the similar targets with conventional AD systems, thus offering an excellent example of technology integration. This chapter focuses on the recent progress of the hybrid systems integrating MEC into AD for enhanced bioenergy and biochemical production. The mechanisms of such hybrid systems are outlined, and the specific performances are compared and summarized. Through the incorporation of MEC into AD, the anodic oxidation assisted by electroactive bacteria improves the decomposition of organics, while the enhanced electron transfer and enriched methanogens facilitate the cathodic carbon dioxide reduction for methane synthesis. Hydrogen sulfide removal from the yielded biogas and phosphorus recovery in the electrode precipitate and sludge sediment are also expected in the hybrid MEC-AD systems. The significance of hybrid MEC-AD systems has been well documented in lab-scale studies, but more efforts are required to be devoted to the engineering aspect in practical industrial application on the basis of detailed technoeconomic assessment.