Mutual symbiosis of electroactive bacteria (EAB) and denitrifier may be the key for solving the refractory carbon and residual nitrogen in wastewater treatment plant effluent. However, its application is hampered by unclear co-metabolic model and uncertain electron transfer. Here, we achieved 3-5 times increase in refractory carbon degradation, 40 % improvement in denitrification, and 36.0 % decrease in N