The interaction of natural organic matter and disinfectants such as chlorine and chloramine tend to produce a suite of toxic chemicals, such as haloacetic acids (HAAs), which are currently under the Stage I and II Disinfectants/Disinfection Byproducts Rule by the United States Environmental Protection Agency (EPA). This study investigated the removal of HAAs using pyrogenic carbonaceous matter (PCM)-modified reductive electrochemical membranes (REMs) to enhance their adsorption. More importantly, we reported for the first time that PCM could accelerate the degradation kinetics of three HAAs, namely Br3AA, BrCl2AA, and Br2ClAA, at pH 7. Detailed characterization of the degradation kinetics of Br3AA and its subsequent product formation were performed in the absence and presence of our PCM model graphite. Br3AA followed a pseudo-first order decay with a rate constant (kobs) of (1.92 ± 0.29) × 10-3 h-1 in the absence of graphite, which corresponds to a half-life (t1/2) of 360.94 ± 2.39 h at pH 7.1. Graphite powder accelerated the degradation of Br3AA with a shortened kobs of (8.41 ± 0.70) × 10-3 h-1 and t1/2 of 82.40 ± 0.99 h. Product characterization indicated a 1-to-1 molar transformation of Br3AA to CHBr3, its corresponding trihalomethane. The formation of CHBr3 suggests that the transformation of Br3AA involves the decarboxylation pathway, where the deprotonated form of Br3AA could dissociate into carbon dioxide and CHBr3. To understand the role of PCM in accelerating the degradation of Br3AA, the activation energy (Ea) of Br3AA with and without graphite was quantified by measuring the Br3AA degradation kinetics from 15°C to 45°C. Our results suggest that graphite significantly lowered the activation energy for the decarboxylation of Br3AA to CHBr3 from 25.7 ± 3.2 kcal/mol to 13.6 ± 2.2 kcal/mol, thus enabling the conversion of Br3AA. These findings improve our understanding of the activity of HAAs with PCM under ambient temperatures and neutral pH, though the specific reactive sites on PCM require further characterization.

Enhanced tribromoacetic acid (Br3AA) degradation using pyrogenic carbonaceous matter (PCM)

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.