The presence of metal ions in drinking water treatment and distribution systems may affect the disinfection process of organic matter, which had aroused people's concern. L-tyrosine can complex with metal ions through carboxyl, carbonyl, and amino groups and affect its chemical reactions. In this paper, the complexation of L-tyrosine with common metal ions was studied and the influence of complexation on chlorination with different experimental factors was investigated. It was inferred that L-tyrosine complexed with metal ions by single dentate ligand or double dentate chelation in a ratio of 2:1. The degradation of L-tyrosine-metal complex followed the pseudo-first-order reaction kinetic. TCM, DCAA, and TCAA were the main species DBPs in the chlorination of L-tyrosine. Compared with L-tyrosine, the reaction rate constants of complex increased by 5.6%, the formation of trihalomethane production decreased by 21.5% and the formation of haloacetic acids production increased by 26.9% at the state of metal complexation. The effect of metal complexation on chlorination was more obvious than that of metal coexistence. For different metal complexation, the order of inhibition on trihalomethane production was Ca2+> Fe3+> Mn2+ and the order of promotion on haloacetic acids production was Mn2+> Fe3+> Ca2+. Moreover, it was found that alkaline conditions were favorable for the formation of DBPs due to the hydroxyl radical. The combination of ultraviolet and chlorine disinfection promoted L-Tyrosine degradation and DBPs generation, and the promotion efficiency follow the order: UV/Cl2> UV-Cl2> Cl2.
Bingliang Zhang,Cong Wang,Fuyao Tong,Meixue Chen,Xiaojuan Liu,Xifeng Shi
UV-based advanced oxidation processes (UV-AOPs) show great potential for municipal wastewater advanced treatment. Although chlor(am)ine-based UV-AOPs have been widely investigated, discrepancies in chlorinated byproduct (Cl-BP) formation and biotoxicity risks among UV/chlorine (UV/Cl 2 ), UV/chloramine (UV/NH 2 Cl), vacuum ultraviolet/ultraviolet/chlorine (VUV/UV/Cl 2 ), and VUV/UV/chloramine (VUV/UV/NH 2 Cl) processes for municipal secondary effluent treatment remain poorly understood. Herein, gas chromatography, Fourier transform ion cyclotron resonance mass spectrometry, and Vibrio fischeri were employed to reveal the formation characteristics of Cl-BPs and acute toxicity variations during these treatments. The results indicated that UV/Cl 2 process produced the highest levels of total organic chlorine (TOCl), known Cl-BPs, calculated cytotoxicity, and acute toxicity. In contrast, VUV/UV/NH 2 Cl treatment exhibited the lowest values for these parameters, with reductions of 61.3%, 96.3%, 99.7%, and 28.0% relative to UV/Cl 2 system. UV/Cl 2 treatment yielded the largest number of unknown Cl-BPs with high saturation, while VUV/UV/NH 2 Cl process generated the fewest Cl-BPs, consisting of more unsaturated CHONCl compounds. Mass difference analysis revealed that Cl 2 -based AOPs had the most precursors and precursor-product pairs, with oxygenation, chlorine substitution and addition as the principal reactions, whereas NH 2 Cl-based ones were dominated by nitrogen-related reactions. Considering Cl-BP and biotoxicity mitigation, VUV/UV/NH 2 Cl process emerges as the most promising technology for advanced treatment of municipal secondary effluent. Overall, this study provides fundamental insights and technological guidance for applying (VUV/)UV-AOPs to real municipal wastewater.
Lin Deng,Wei Luo,Xiao Chi,Tingting Huang,Longjia Wen,Huiyu Dong,Mingxian Wu,Jun Hu
The UV/Cl 2 process is commonly used to achieve a multiple-barrier disinfection and maintain residuals. The study chose methylamine as a precursor to study the formation of high-toxic halonitromethanes (HNMs) in the presence of bromide ions (Br − ) during UV/Cl 2 disinfection. The maximum yield of HNMs increased first and then decreased with increasing concentration of Br − . An excessively high concentration of Br − induced the maximum yield of HNMs in advance. The maximum bromine incorporation factor (BIF) increased, while the maximum bromine utilization factor (BUF) decreased with the increase of Br − concentration. The maximum yield of HNMs decreased as pH value increased from 6.0 to 8.0 due to the deprotonation process. The BUF value remained relatively higher under an acidic condition, while pH value had no evident influence on the BIF value. The maximum yield of HNMs and value of BUF maximized at a Cl 2 :Br − ratio of 12.5, whereas the BIF value remained relatively higher at low Cl 2 :Br − ratios (2.5 and 5). The amino group in methylamine was first halogenated, and then released into solution as inorganic nitrogen by the rupture of C-N bond or transformed to nitro group by oxidation and elimination pathways. The maximum yield of HNMs in real waters was higher than that in pure water due to the high content of dissolved organic carbon . Two real waters were sampled to verify the law of HNMs formation. This study helps to understand the HNMs formation (especially brominated species) when the UV/Cl 2 process is adopted as a disinfection technique.
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