Master of Science in Engineering (MSE)
Civil and Environmental Engineering and Construction
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Disinfection of drinking water is crucial for providing a safe potable water supply. Some of the most common disinfectants employed are chlorine, chloramines and ozone. While these disinfectants successfully inactivate pathogenic microorganisms, they simultaneously react with inorganic or organic precursors to form toxic byproducts, most commonly referred to as disinfection byproducts (DBPs). While there is a wide variety of organic matter and disinfection byproducts known, in this study we have looked into the potential of certain quaternary ammonium compounds (QACs) to act as precursors to form DBPs, namely trihalomethanes (THMs), haloacetonitriles (HANs) and nitrosamines.
The ubiquitous nature of QACs in municipal, hospital and industrial wastewater has motivated the need to investigate the potential of these compounds to form DBPs upon reaction with chlorine, monochloramine and ozone. Seven QACs, namely benzalkonium chloride (BZK), benzethonium chloride (BEC), tetraethylammonium chloride (TEAC), tetramethylammonium chloride (TMAC), cetylpyridinium chloride (CPC), dodecyltrimethylammonium chloride (DTMA), and cetyltrimethylammonium (CTMA), were considered in this study based on their structural differences as well as their presence in consumer products. Due to incomplete removal during wastewater treatment, these QACs end up in wastewater effluent, and, ultimately, in surface waters serving as drinking water sources.
When these seven QACs spiked at 0.1 mM were subjected to reaction with free chlorine (5 mg/L as Cl2), trichloromethane was the dominant THM that was formed in the order ofiv TMAC
In the case of HANs, dichloroacetonitrile was the dominant species formed upon reaction between the seven QACs spiked at 0.1 mM and monochloramine (140 mg/L as Cl2) in the order of TMAC
Formation of N-nitrosodimethylamine (NDMA) was observed only during chloramination. Of the seven QACs included in this study, benzethonium chloride and benzalkonium chloride were the only compounds that yielded detectable concentrations of NDMA. This is the first time the NDMA yield for benzethonium chloride has been reported as a result of chloramination, and the yield is approximately 3 times higher compared to the yield from the widely studied benzalkonium chloride. No other nitrosamines were detected, even though TEAC could potentially form N-nitrosodiethylamine.
This is the first study that shows that during the process of disinfection, BEC, CPC and BZK could form HANs, BEC and CPC could form THMs, and BEC could form NDMA. This study also investigated the potential of QACs to form brominated disinfection byproducts during disinfection treatment in the presence of bromide. Lastly, the prediction of DBP concentrations formed during the disinfection of water containing environmentally relevant concentrations of QACs was also performed. THMs and HANs formed either due to chlorination or chloramination of all of the 7 QACs (400 µg/L) was relatively low, i.e., less than 2 µg/L and 1 µg/L respectively, based on the prediction. The predicted concentration of NDMA formed due to chloramination of BEC and BZK are in the range of 22-50 ng/L. Although the DBPs formed due to the reaction of QACs with disinfectants is of lower concentration compared to regulations, it will still contribute to the total DBPs formed in a water treatment facility. Hence, care must be taken for proper removal of these QACs prior to discharge of wastewater effluent or disinfection of drinking water.
Chloramination; Chlorination; Disinfection Byproducts; Quaternary Ammonium Compounds; wastewater; Water
Civil Engineering | Engineering | Environmental Engineering
University of Nevada, Las Vegas
Krishnaswamy, Padmanabhan, "Quaternary Ammonium Compounds as Precursors to Disinfection Byproducts" (2021). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4299.
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