An overview of complementary microbial electrochemical technologies for advancing anaerobic digestion

Abstract

Abstract Anaerobic digestion (AD) is considered an attractive option for diversion of organic waste from landfills as well as the treatment of high-strength wastewater. Biomethane generated from AD can be used to meet on-site heat or electricity needs. However, the operation of AD facilities faces many challenges, including slow process kinetics, poor process stability due to inhibition by high ammonia level and organic acids accumulation, and low methane content in biogas. Therefore, further advancements in AD regarding process kinetics and robustness is a critical industry need. In recent years, considerable research interest focused on coupling microbial electrochemical systems with AD. The integration of microbial electrochemical systems, such as microbial electrolysis cells (MECs) with digesters, usually referred to as MEC-AD, can enhance process kinetics by stimulating electro-methanogenesis along with conventional methanogenesis pathways. The electro-methanogenesis represents an energetically favorable methanogenesis pathway where electrons are directly utilized for carbon dioxide reduction to methane. In addition to improving process kinetics, promoting electro-methanogenesis can provide high-quality biogas. Moreover, different configurations of microbial electrochemical systems have also been explored as a separate unit operation for biogas upgrading through carbon dioxide reduction to methane and hydrogen sulfide recovery as elemental sulfur. Also, various engineering approaches on integrating microbial electrochemical systems within AD facilities have been successfully demonstrated for monitoring volatile fatty acids concentrations in digester effluent to assess methanogenic activity, chemical production for pre-hydrolysis of complex feedstock, and control of ammonia inhibition through in situ nitrogen recovery. This book chapter provides an overview of these recent developments toward promoting the next-generation of anaerobic digestion facilities through the application of various microbial electrochemical technologies.