Simultaneous nitrogen removal and energy recovery of synthetic swine wastewater by the coupled system of microbial electrolysis and shortcut nitrification

A novel process of continuous stirred tank reactor, microbial electrolysis cell, and shortcut nitrification and denitrification (CSTR-MEC-SND) was developed for synthetic swine wastewater treatment. This process achieved effective nitrogen removal and energy recovery with an average hydraulic retention time (HRT) of 36 h. Benefited from the synergy between fermentative bacteria (e.g., Acholeplasma) and electroactive bacteria (e.g., Desulfovibrio), the CSTR-MEC achieved a chemical oxygen demand (COD) (2050 ± 60 mg L⁻¹) removal efficiency of 85 ± 2 %, accompanied by a cathode electron recovery efficiency (r_Cat) of 79 ± 6 % and an energy efficiency (η_E) of 119 ± 9 %. The NH₄⁺-N was oxidated in SN with an ammonia oxidation ratio (AOR) of 98.7 ± 0.9 % under the dilution of the reflux fluid. The dominance of AOB (Nitrosomonas) in nitrifying sludge contributed to an average nitrite accumulation rate (NAR) of 84.6 ± 0.3 %. Effluent indexes of this coupled process including COD (23 ± 8 mg L⁻¹), NH₄⁺-N (0.9 ± 0.3 mg L⁻¹) and TN (43 ± 6 mg L⁻¹) all complied with the “Discharge standard of poultry cultivation industry pollutant (the exposure draft)”. The energy contained in the biogas offset the energy consumption with positive energy feedback of 1.24 kWh m⁻³, promising a feasible approach for carbon and nitrogen removal, as well as collaborative resource recovery from swine wastewater.