Enhanced nutrient removal from mixed black water by a microbial ultra-low weak electrical stimulated anaerobic-two stage anoxic/aerobic process

Efficient nutrient removal from mixed black water is under challenge in the context of global pollution control and circular economy. The anaerobic-anorexic-aerobic process is a widely used biological nutrient removal technology for wastewater treatment, yet its denitrification capacity is limited by the low biodegradable organics to nitrogen (C/N) ratio due to prior degradation of mixed black water. We have previously proved that weak electrical of 0.2 V could stimulate microbial denitrification of black water using an external electrical supply to ensure voltage stability. To reduce the dependence on additional electrical and to ensure a stable voltage output, we built a microbial fuel cell (MFC) and a microbial electrolytic cell (MEC) embedded in the anaerobic-two stage anoxic/aerobic (A-(A/O)²) system in this study, where the MFC degrades organic matter and generates electricity first. Then, the electroactive bacteria in the MEC catalyze denitrification at low carbon levels, which is affected by microbial ultra-low weak electrical stimulation (MUlWES) generated by MFC. Results showed that the removal rates of total nitrogen (TN) and total phosphorus (TP) were up to 91.3% and 98.3% respectively at a stimulation voltage of 0.1 V. Fluorescence spectroscopy revealed the formation of aromatic proteins and an increase in tightly bound-extracellular polymeric substances (TB-EPS), suggesting the involvement of these compounds in electron transfer. Community analysis disclosed the activation of autotrophic denitrifying bacteria and the inhibition of most heterotrophic denitrifying bacteria.