Citation:

Mezgebe, B., E. Sahle-Demessie, AND G. Sorial. Disinfection ByProducts in Drinking Water: Formation, Characterization, Control Technologies. Chapter 7, CONTAMINANTS IN OUR WATER: IDENTIFICATION AND REMEDIATION METHODS. ACS Publications, Washington, DC, 1352:119-142, (2020). https://doi.org/10.1021/bk-2020-1352.ch007

Impact/Purpose:

Chlorinated disinfectants used in water distribution systems to destroy pathogenic microbes. Disinfectants react with natural organic matter, that are found in surface waters and produce a range of byproducts, which include trihalomathane (THMs). Different physical and chemical techniques including aeration are used to control THMs from drinking water. This study proved that aeration is an effective approach to investigate a low cost technique, aeration as a method for controlling THMs from drinking water storage tanks.

Description:

Chlorination of water is a highly reliable and effective disinfection method. However, it results in the formation of trihalomethanes (THMs), which can cause serious health problems from chronic exposure (long-term ingestion). Although precursor removal and changes in disinfection practices are the primary measures for lowering the formation of THMs, the need to further lower residual levels has brought aeration as an alternative approach. Following the disinfection of water, diffused-air aeration is one of the methods used to control THMs after long-term water storage. The effectiveness of bench-scale bubble diffused aeration in reducing three THMs, namely, dichlorobromomethane (DCBM), dibromochloromethane (DBCM), and bromoform (BF), was studied. In the study, the THM concentrations were held constant while different gas flow rates were investigated. Differences in the percentage THM removals were assessed, including the impacts on their Henry’s law constants. The removal efficiencies of these THMs from an initial concentration of 100 µg/L at an air flow rate of 2 L/min were 99%, 97%, and 88% for DCBM, DBCM, and BF, respectively. The predicted values of the Henry’s law constants obtained for DCBM, DBCM, and BF from the experiments were 0.0883 ± 0.008, 0.0502 ± 0.003, and 0.0291 ± 0.003, respectively. Computational methods were used to understand the effects of temperature, flow rate, initial THM concentration, and Henry’s law constant. A quantitative health risk analysis for chloroform (CF) from different streams was also performed. The reduction of CF from chlorinated finished water using aeration was assessed based non-carcinogenic substances hazard quotient (HQ). The assessment found on individual excess lifetime cancer risk (IELCR) estimates confirmed that aeration could reduce risk to an acceptable range.

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