The benefits of autotrophic nitrogen removal from high concentration of urea wastewater through a process of urea hydrolysis and partial nitritation in sequencing batch reactor

Keywords Urea wastewater; Intracellular hydrolysis; Free ammonia; Partial nitritation; Anammox Highlights * A novel biological nitrogen removal process for urea wastewater was investigated. * Autotrophic N removal with no alkalinity added was achieved for urea wastewater. * Intracellular urea hydrolysis and stable partial nitritation was integrated in SBR. * 81.45% of total N was removed by anammox with N removal rate of 1.05 kg N*m.sup.-3*d.sup.-1. Abstract For the sake of high efficiency and saving operational cost for high-concentration urea wastewater treatment, a novel two-stage partial nitritation (PN)-anammox process containing simultaneous urea hydrolysis and PN in sequencing batch reactor (SBR) was investigated. Although the influent urea concentration increased from 500 to 1200 mg/L, the SBR simultaneously achieved urea removal efficiency higher than 98% and stable PN with effluent NO.sub.2.sup.--N/NH.sub.4.sup.+-N ratio of 1.0--1.3 without any extra alkalinity addition. The intracellular hydrolysis was the dominant mechanism for urea removal and persistent free ammonia inhibition on nitrite-oxidizing bacteria was the main reason for nitrite accumulation of 97.92% in SBR. The subsequent anammox reactor showed efficient nitrogen removal performance with average ammonium removal efficiency, nitrogen removal efficiency and maximum nitrogen removal loading rate of 98.08%, 81.45% and 1.05 kg N*m.sup.-3*d.sup.-1 respectively. High-throughput sequencing results indicated Gemmatimonadetes became the most abundant bacterial phylum related to potential intracellular urea hydrolysis and displayed obvious ammonium-oxidizing bacteria enrichment and nitrite-oxidizing bacteria inhibition in SBR, and the dominant anammox bacteria (Candidatus_Kuenenia) in anammox reactor. The proposed process was proven to be promising for high-concentration urea wastewater treatment, facilitating the sustainable development of the urea industry in the future. Abbreviations AOB, Ammonium-oxidizing Bacteria; CANON, Completely autotrophic nitrogen removal over nitrite; DO, Dissolved oxygen; FA, Free ammonia; MLSS, Mixed liquor suspended solids; NAR, Nitrite accumulation rate; NOB, Nitrite-oxidizing Bacteria; NRE, Nitrogen removal efficiency; NRR, Nitrogen removal rate; TN, Total nitrogen; SBR, Sequencing batch reactor; URE, Urea removal efficiency Author Affiliation: (a) School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China (b) The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, 510006, China (c) Hua An Biotech Co., Ltd., Foshan, 528300, China * Corresponding author. School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China. Article History: Received 13 January 2021; Revised 18 April 2021; Accepted 19 April 2021 Byline: Yongxing Chen (a,b), Haochuan Chen (a,b), Zhenguo Chen (a,b,c), Haolin Hu (a,b), Cuilan Deng (a,b), Xiaojun Wang [cexjwang@scut.edu.cn] (a,b,c,*)