The ins and outs of photo-assisted microbial electrochemical systems for synchronous wastewater treatment and bioenergy recovery

Abstract

Wastewater, as the used water, carries huge energy that is frequently ignored and unexploited. Microbes, as bioelectrocatalysts in microbial electrochemical systems (MESs), can convert chemical energy stored in biodegradable matrixes from wastewater to bioelectricity and chemicals. However, due to sluggish wastewater treatment rates and bioenergy production, wider applications have been hampered. Currently, photo-assisted MESs, combined electrochemical/photochemical driving force with microbial catalysis, have emerged as a sustainable platform to enhance pollutants degradation and bioenergy recovery from wastewater with the aid of solar light, accompanied by reasonable energy investment and minimal environmental disturbance. Nevertheless, the development of photo-assisted MESs is still in its infancy. This work broadly concludes present photo-assisted MESs wastewater treatment technologies and their overall limitations in terms of performance and the future advancements that will be necessary to make them more widely applicable. Herein, crucial factors influencing the performance of these photo-assisted MESs, such as the reactor types (bioanode-photocathode, photoanode-biocathode, photomicrobial electrode, and photosynthetic bacteria/algae MESs), the bandgap of semiconductor and microbe species are discussed. Furthermore, prominent research accomplishments of photo-assisted MESs with an emphasis on eliminating contaminants (initial concentration, removal efficiency, and removal rate) and recovering bioenergy (product types, production rate, and current density) from various wastewaters are systematically summarized. Finally, present challenges and prospects in the field of photo-assisted MESs technology are discussed, mainly including the optimization of electrode materials, screening and culture of microorganisms, scale-up of bioreactors, intermittency of solar energy, and other complications overarchingly shared with photo-assisted microbial electrochemical wastewater treatment and bioenergy recovery.