Enhancing nitrogen removal from real oxytetracycline pharmaceutical wastewater via partial nitrification and post-denitrification (PNPDE) process: Insights into performance, mechanism, and application

Abstract

Economically and efficiently removing nitrogen from oxytetracycline pharmaceutical wastewater (OPW) is a challenging problem. To address this, this study established an anaerobic-oxic-anoxic sequencing batch reactor, integrating a process involving partial nitrification (PN) and post-denitrification (PDE) to treat OPW (PNPDE). When the average total nitrogen in the influent was 110 mg/L, the effluent nitrogen level, nitrite accumulation ratio, and nitrogen removal efficiency were 12.7 mg/L, 95.1 %, and 88.7 %, respectively. Extracellular polymeric substances (EPS) played a crucial role in PNPDE stability and oxytetracycline degradation; EPS increased from 34.1 to 66.3 mg/gVSS during operation. In a typical cycle, exogenous denitrification, simultaneous nitrification-denitrification, and endogenous denitrification were the main nitrogen removal pathways, contributing 19.8 %, 21.3 %, and 48.7 %, respectively, of nitrogen removal. Meanwhile, 41.2 % of oxytetracycline was degraded, generating eight low-toxic biotransformation products. High-throughput sequencing results indicated that functional microorganisms, such as Nitrosomonas, Ellin6067, OLB8, Candidatus_Competibacter, Persicitalea, and Thauera, played a crucial role in removing nitrogen and degrading OTC. PNPDE provides a novel solution for effective and energy-saving OPW treatment.