A novel route for urea abatement in UPW production: Pre-chlorination/VUV/UV under acidic circumstances and its enhancement mechanisms

Qi Wang; Nan Huang; Wenlong Wang; Zhuowei Zhang; Yu Qiu; Xiaowen Chen; Ao Xu; Yinhu Wu; Zhuo Chen; Hongying Hu

doi:10.1016/j.jhazmat.2024.134836

A novel route for urea abatement in UPW production: Pre-chlorination/VUV/UV under acidic circumstances and its enhancement mechanisms

J Hazard Mater. 2024 Aug 15:475:134836. doi: 10.1016/j.jhazmat.2024.134836. Epub 2024 Jun 15.

Authors

Qi Wang¹, Nan Huang², Wenlong Wang³, Zhuowei Zhang¹, Yu Qiu¹, Xiaowen Chen¹, Ao Xu⁴, Yinhu Wu⁵, Zhuo Chen⁵, Hongying Hu⁶

Affiliations

¹ Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), School of Environment, Tsinghua University, Beijing 100084, China.
² National Engineering Laboratory for Advanced Municipal Wastewater Treatment and Reuse Technology, Beijing University of Technology, Beijing 100124, China. Electronic address: huangnan@bjut.edu.cn.
³ Key Laboratory of Microorganism Application and Risk Control of Shenzhen, Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Institute of Environment and Ecology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China.
⁴ Research Institute for Environmental Innovation (Suzhou), Tsinghua University, Suzhou 215163, China.
⁵ Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), School of Environment, Tsinghua University, Beijing 100084, China; Beijing Laboratory for Environmental Frontier Technologies, Beijing 100084, China.
⁶ Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), School of Environment, Tsinghua University, Beijing 100084, China; Beijing Laboratory for Environmental Frontier Technologies, Beijing 100084, China. Electronic address: hyhu@tsinghua.edu.cn.

PMID: 38889471
DOI: 10.1016/j.jhazmat.2024.134836

Abstract

Urea abatement has been a prominent challenge for UPW production. This research proposed a productive strategy combining pre-chlorination and VUV/UV processes under acidic conditions to settle this problem. This study first revealed the reaction kinetics between urea and free chlorine in a large pH range from 2.5 to 9.6, where the reaction constant rate varied from 0.06 to 0.46 M^-1·s^-1. Substitution reaction mediated by Cl₂ was the dominant process at low pH (pH<3). The differences of dominant pathways resulted in the differences in reaction products: The detected concentration of dichloramine at pH 2.5 was twice that at pH 4.5 and 6.5. Further, this study found that pre-chlorination/VUV/UV process could achieve the thorough removal of 2-mg/L urea with chlorination of less than 5 min and VUV/UV irradiation of less than 200 mJ/cm². Chloride ions, low pH, and higher chlorine dosage were found to be the positive factors to improve urea removal efficiency in pre-chlorination/VUV/UV process. The reaction rate constants between chlorourea with·OH and·Cl were calculated to be 3.62 × 10⁷ and 2.26 × 10⁹ L·mol^-1·s^-1, respectively.·Cl,·OH and photolysis contributed 60.5 %, 22.9 % and 16.6 % in chlorourea degradation, respectively. Pre-chlorination/VUV/UV achieved a DOC removal efficiency of 78.5 %. And nitrogen in urea was converted into inorganic nitrogenous compounds. Finally, compared with direct VUV/UV/chlorine and VUV/UV/persulfate processes, this process saved more than 70 % of energy in VUV/UV unit.

Keywords: Chlorine; Chlorourea; Ultrapure water; Urea; VUV/UV.