Elimination of isothiazolinone biocides in reverse osmosis concentrate by ozonation: A two-phase kinetics and a non-linear surrogate model.

Wang WL, Chen Z, Du Y, Zhang YL, Zhou TH, Wu QY, Hu HY

Journal of hazardous materials

May 5, 2020

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Abstract

Elimination of commercial Kathon biocide (methyl-isothiazolinone (MIT) and chloro-methyl-isothiazolinone (CMIT) mixture) by ozonation was investigated in real RO influent and concentrate. MIT and CMIT had different reactivities (second-order-rate-constants) with molecular ozone and OH. Ozonation of biocides followed an instantaneous phase (16.6 %-36.9 % contributions) and then a gradual phase (33.6 %-78.8 % contributions). Newly developed kinetics including both phases demonstrated that O oxidation contributed 25.6 %-39.8 % and <10 % of MIT and CMIT eliminations, respectively, and OH oxidation contributed 60.2 %-74.4 % and >90 % of MIT and CMIT eliminations, respectively. OH oxidation at the instantaneous phase accounted 15.7 %-37.9 % of total OH oxidation. Mass ratios of O/DOC of 0.24 and 0.32 were needed for ∼80 % eliminations of MIT and CMIT in RO concentrate, respectively. The kinetics including both phases allowed a para-chlorobenzoic acid indicator model to predict MIT and CMIT elimination better than that including gradual ozonation only, with 58.9 %-96.0 % lower relative error. The attenuations of electron-donating-moiety indicated that O may preferentially react with chromophores through aromatic cleavage and electrophilic extraction, while OH may non-selectively react with chromophores through predominant electrophilic addition. A surrogate model for biocide elimination by UVA loss was proposed to be nonlinear rather than linear, which reduced 31.8 %-71.3 % surrogating error.

Affiliation

Environmental Simulation and Pollution Control State Key Joint Laboratory, State Environmental Protection Key Laboratory of Microorganism Application and Risk Control (SMARC), and School of Environment, Tsinghua University, Beijing 100084, China; Key Laboratory of Microorganism Application and Risk Control of Shenzhen, Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China.