Simultaneous carbon, nitrogen, and phosphorus removal and energy recovery from wastewater in a zero-energy microbial electrochemical system with algal-bacterial biocathode

Addressing the challenge of high energy consumption in conventional wastewater treatment, this study develops a zero-energy microbial electrochemical system (MES) featuring an algal-bacterial symbiotic biocathode. Under simulated day-night cycles, this configuration achieves simultaneous and efficient removal of carbon, nitrogen, and phosphorus pollutants while recovering electrical energy. During the illuminated phase, algal photosynthesis generates oxygen to sustain a stable voltage output (∼600 mV) without external aeration. In the dark phase, the system promotes denitrification, thereby enabling effective nitrogen removal. A petal-like NiO-modified carbon felt biocathode was fabricated, significantly enhancing the cathode's specific surface area and active sites, thereby effectively promoting the formation of a microbial-algal composite biofilm and cathodic reduction reaction. This innovative design and operational strategy enable zero-energy wastewater treatment coupled with resource recovery, offering a promising pathway toward energy self-sufficiency and carbon neutrality in practical wastewater treatment applications.