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Samonte PRV, Li Z, Mao J, Chaplin BP, Xu W. Pyrogenic carbon-promoted haloacetic acid decarboxylation to trihalomethanes in drinking water. WATER RESEARCH 2022; 210:117988. [PMID: 34959066 PMCID: PMC9195562 DOI: 10.1016/j.watres.2021.117988] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Revised: 12/16/2021] [Accepted: 12/17/2021] [Indexed: 06/14/2023]
Abstract
Drinking water disinfection by chlorination or chloramination can result in the formation of disinfection byproducts (DBPs) such as haloacetic acids (HAAs) and trihalomethanes (THMs). Pyrogenic carbonaceous matter (PCM), such as activated carbon (AC), is commonly used as an ostensibly inert adsorbent to remove HAAs from water. HAA degradation has been mainly attributed to biological factors. This study, for the first time, revealed that abiotic HAA degradation in the presence of PCM could be important under water treatment conditions. Specifically, we observed complete destruction of Br3AA, a model HAA, in the presence of powder AC at pH 7 within 30 min. To understand the role of PCM and the reaction mechanism, we performed a systematic study using a suite of HAAs and various PCM types. We found that PCM significantly accelerated the transformation of three HAAs (Br3AA, BrCl2AA, Br2ClAA) at pH 7. Product characterization indicated an approximately 1:1 HAA molar transformation into their respective THMs following a decarboxylation pathway with PCM. The Br3AA activation energy (Ea) was measured by kinetic experiments at 15-45 °C with and without a model PCM, wherein a significant decrease in Ea from 25.7 ± 3.2 to 13.6 ± 2.2 kcal•mol-1 was observed. We further demonstrated that oxygenated functional groups on PCM (e.g., -COOH) can accelerate HAA decarboxylation using synthesized polymers to resemble PCM. Density functional theory simulations were performed to determine the enthalpy of activation (ΔH‡) for Br3AA decarboxylation with H3O+ and formic acid (HCOOH). The presence of HCOOH significantly lowered the overall ΔH‡ value for Br3AA decarboxylation, supporting the hypothesis that -COOH catalyzes the C-C bond breaking in Br3AA. Overall, our study demonstrated the importance of a previously overlooked abiotic reaction pathway, where HAAs can be quickly converted to THMs with PCM under water treatment relevant conditions. These findings have substantial implications for DBP mitigation in water quality control, particularly for potable water reuse or pre-chlorinated water that allow direct contact between HAAs and AC during filtration as well as PAC fines traveling with finished water in water distribution systems. As such, the volatilization and relative low toxicity of volatile THMs may be considered as a detoxification process to mitigate adverse DBP effects in drinking water, thereby lowering potential health risks to consumers.
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Affiliation(s)
- Pamela Rose V Samonte
- Department of Civil and Environmental Engineering, Villanova University, 800 E. Lancaster Ave., Villanova, PA 19085, United States
| | - Zhao Li
- Department of Civil and Environmental Engineering, Villanova University, 800 E. Lancaster Ave., Villanova, PA 19085, United States
| | - Jingdong Mao
- Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, United States
| | - Brian P Chaplin
- Department of Chemical Engineering, University of Illinois at Chicago, 929 W. Taylor St., Chicago, IL 60607, United States; Institute of Environmental Science and Policy, University of Illinois at Chicago, 1603 W. Taylor St., Chicago, IL 60612, United States; Department of Civil, Materials, and Environmental Engineering, University of Illinois at Chicago, 842 W. Taylor St., Chicago, IL 60607, United States
| | - Wenqing Xu
- Department of Civil and Environmental Engineering, Villanova University, 800 E. Lancaster Ave., Villanova, PA 19085, United States.
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