Excessive extracellular polymeric substances induced by organic shocks accelerate electron transfer of oxygen reducing biocathode

Highlights: • The autotrophic biocathode adaptively adjusted to glucose shocks. • The maximum current increased by 5.5 times after 100 mg/L glucose shock. • Agglomerates with proteins and polysaccharide accumulated in biocathodes. • Agglomerates wrap additional redox shuttles that accelerated the electron transfer. • Glucose mainly promoted Actinomycetes in cathodic microbial community. Electrotrophic bacteria on cathodes are promising substitutes to precious metals as oxygen reduction reaction catalysts in bioelectrochemical systems (BESs). Leading the anodic effluent to the biocathode has additional benefits of neutralizing pH and removing residual pollutants. However, the overflow of excessive organic pollutants inhibits the activity of autotrophic biocathodes. Adding glucose as an organic shock, we confirm that the startup time of biocathodes is initially prolonged by 1.2 times with a decrease in current. However, the currents inversely surpass the control in glucose-added BESs when the biofilm is mature, and the maximum current density increase by 5.5 times with a relatively stable performance. This increase is mainly attributed to the production of agglomerates dominated by polysaccharides and proteins as extracellular polymeric substances. These agglomerates wrap additional redox shuttles that accelerated the electron transfer between electrotrophic bacteria and the cathode. This study demonstrates for the first time that organic shocks enhance the electroactivity of autotrophic biocathodes and provides insights into the feedback mechanisms of electrotrophic microbial community to environmental changes.