Enhanced removal of nitrogen and phosphorus from expressway service area wastewater using step-feed multi-stage Anoxic/Oxic membrane bioreactor optimization process

To address nitrogen and phosphorus removal challenges in expressway service area wastewater (ESAW) with high influent shock loads and low carbon-to-nitrogen ratios, a step-feed multi-stage A/O-MBR optimization process was proposed. After operating with actual wastewater for 263 days, regulating the influent flow distribution ratio to 7:3 and adding sponge iron (S-Fe0) to aerobic chamber resulted in effective pollutants removal and strong resistance to influent shock loads. Enzyme activity analysis indicated that ammonia monooxygenase, hydroxylamine oxidoreductase, nitrate reductase, and nitrite reductase activities in aerobic chamber with S-Fe0 were 1.99, 2.57, 2.71, and 2.45 times higher than the control group, respectively. Microbial community structure revealed that heterotrophic nitrification and aerobic denitrification microorganisms with an overall relative abundance of 41.74 %, dominated by Acinetobacter and Acetoanaerobium, contributed to 57.69 % nitrogen removal. FAPROTAX analysis confirmed a 25.77 % enhancement in nitrogen removal functionality. This study provides a high-efficiency, shock-resistant, and low-maintenance nitrogen and phosphorus removal strategy by innovatively introducing S-Fe0 into ESAW treatment.