Removal of Steroid Estrogens and Total Nitrogen by Denitrification Biofilter with UV/Peracetic Acid Pretreatment: Performance, Microbial Characteristics, and Mechanism

Total nitrogen (TN) and steroid estrogens (SEs) in secondary effluent challenge widely used denitrification biofilter (DNBF) in achieving the regulated limit value in water reuse, as well as toxicity reduction. Herein, we first use UV/peracetic acid (PAA) as a pretreatment of DNBF for advanced wastewater treatment, followed by an evaluation of its effectiveness in removing TN and SEs from low C/N wastewater. The results showed that UV/PAA-biofilter significantly improved the removal of TN and SEs compared to conventional DNBF. Under the conditions of [PAA]0 = 15 mg/L, UV = 1250 mu W/cm2, photoreaction time of 30 min, and biofilter hydraulic retention time (HRT) = 3 h, the SE removal rates could reach more than 95% and the effluent TN maintained less than 10 mg/L. Furthermore, UV/PAA-biofilter improved the reduction of estrogenic activity but not of acute toxicity. Increased extracellular polymeric substance (EPS) content and relative abundance of napA gene were observed in DNBF pretreated with UV/PAA, and Azospira was identified as the core microorganism for denitrogenation. Our investigations confirmed the feasibility of the UV/PAA-biofilter to remove SEs and TN simultaneously, highlighting the great potential of its application in the advanced purification of secondary effluent for safe wastewater reuse.