title: Formation Potential of Disinfection Byproducts from Quaternary Ammonium Surfactants During Ozonation with Subsequent Chlor(am)ination
Creators: name: Baguma, Gabson
Publisher: name: University of Nevada, Las Vegas
publisherIdentifier: https://ror.org/0406gha72
publisherIdentifierScheme: ROR
Year: 2024

description: Quaternary ammonium-based surfactants (QAS) are ubiquitous in daily life, found in products ranging from disinfectants and fabric softeners to food preservatives and personal care products. Their widespread use, especially during the COVID-19 pandemic due to their antimicrobial properties, has made them indispensable in modern hygiene and public health practices. However, their prevalence is not without concerns. When these compounds enter wastewater treatment plants, they are not fully degraded by the conventional treatment methods used, due to variations in their structural properties. As a result, QAS residues persist and accumulate in treated wastewater effluents, ultimately affecting water sources. These residues end up in water treatment plants where they are transformed into potentially harmful disinfection byproducts (DBPs) through methods such as ozonation and subsequent chlorination/chloramination.This necessitated a comprehensive investigation into the reaction of these compounds with common water treatment disinfectants including chlorine, monochloramine, and ozone. This study examined the formation potential of disinfection byproducts (DBPs) namely haloacetic acids (HAAs), haloacetonitriles (HANs), N-nitrosamines (NOAs), and trihalomethanes (THMs) from ten distinct quaternary ammonium-based surfactants (QAS) including allyltrimethyl ammonium chloride (ATMAC), benzalkonium chloride (BAC), benzethonium chloride (BTC), cetylpyridinium chloride monohydrate (CPC), Cetyltrimethylammonium chloride (CTMAC), diallyldimethyl ammonium chloride (DDAC), dodecyltrimethylammonium chloride (DTMA), didecyldimethylammonium chloride (DDEC), polydiallyldimethylammonium chloride solution (polyDADMAC), tetramethylammonium chloride (TMAC). These compounds were selected based on their prevalent use in commonly available consumer products and structural variations such as the presence or absence of a benzene ring, chain length, and saturation level of the carbon chains. They were prepared to a target concentration of 0.1 mM and subjected to simulated water treatment processes, including chlorination/chloramination, and ozonation followed by
chlor(am)ination.
Controlled formation potential tests were meticulously conducted at a controlled pH of 7, with precisely targeted residual chlorine concentrations maintained at 1.0±0.4 mg/L as free Cl2 over a three-day period and 2.5±0.5 mg/L as total free Cl2 over five days. The results demonstrated significant increases in the formation of DBPs, particularly HANs, HAAs, and THMs. Notably, DCAN molar yields peaked at 45.6 μmol/mol during chloramination alone and later increased to 479 μmol/mol following ozonation and subsequent chloramination. Similarly, DCAA molar yields ranged from 197 μmol/mol to 750 μmol/mol post-chlorination and from 193 to 1980 μmol/mol after ozonation with subsequent chlorination. Total trihalomethanes (TTHM) displayed a substantial variation, with molar yields ranging from 124 to 6910 μmol/mol post-chlorination, and from 187 μmol/mol to 39000 μmol/mol post-chloramination.
A critical observation was the significant enhancement of N-nitrosodimethylamine (NDMA) formation, where molar yields increased to a peak of 5330 μmol/mol during ozonation with subsequent chloramination in compounds containing aromatic ring structures such as BAC, BTC, CPC, and polyDADMAC, compared to a peak of 510 μmol/mol during chloramination alone. This marked increase highlights the catalytic role of ozonation in elevating NDMA formation.
Pre-ozonation effectively transformed QAS precursors, reducing their potential to form HAAs and HANs during subsequent chlorination. However, it also increased the reactivity of certain compounds, such as BTC, CPC, and BAC, leading to elevated levels of TCAA, DCAA, and DCAN. These observations highlight the dual role of ozonation in water treatment, demonstrating its capacity to both mitigate and enhance DBP formation under specific conditions.
These findings highlight the need for careful management of these compounds prior to their discharge via treated wastewater into the environment to mitigate potential DBP formation during drinking water treatment. The study identifies significant gaps in our understanding of the specific pathways through which QAS transform to form intermediate products that act as DBP precursors, emphasizing the necessity for continuous monitoring and adaptive management in water treatment practices to minimize risks associated with DBP formation from QAS precursors.