Is bioelectrochemical energy production from wastewater a reality? Identifying and standardising the progress made in scaling up microbial electrolysis cells

Abstract

Bioelectrochemical systems (BESs) have the potential to produce energy from wastewater. However, they are far from ready to be applied into industry. The development of large and pilot-scale systems to harness energy and value-added chemicals is widely regarded as one of the greatest research challenges in this field. There are several reasons for this: i) they are expensive, ii) they are difficult to engineer, iii) the data that can be derived from them is often limited, rarely in duplicate, and is disproportionate to the time commitment. Given these restrictions, systematic reviews of large and pilot-scale systems can be helpful in determining the direction of future research. These reviews need to standardise very different reactor set-ups, operational conditions, and methods of reporting data. Here we present an analysis of the energy production from semi-pilot and pilot-scale BESs, and benchmark their performance against existing wastewater treatment. The parameters used include complexity of wastewater; chemical oxygen demand (COD) loading rate; conductivity; reactor depth; volumetric treatment rate; effluent quality; energetic treatment balance; and temperature. We find that factors which are perceived to be problematic, such as low conductivities and temperatures, have been overcome by BESs at pilot-scale, and that these systems have met the regulatory requirements for discharge standards. We identify reactor depth and volumetric treatment rate as the areas for future research to focus on. The first of these issues will need an engineering solution, while the second is likely to come from improved understanding of the complex microbial digestion pathways. Material science may help both. Importantly, these pilot studies have shown that renewable energy production from wastewater is possible, and with targeted future research, could become a reality.