Reduction of Trihalomethanes Using Ultrasound as a Disinfectant

Ringer, Erin E

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Reduction of Trihalomethanes Using Ultrasound as a Disinfectant

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The emergence of pathogens that are more difficult to inactivate than bacteria, such as C. parvum and G. lamblia, has led to the enactment of more stringent drinking water regulations. The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), promulgated in January 2006, requires increased inactivation of C. parvum. However, increasing the disinfectant dose to enhance inactivation, especially when using chlorine, increases production of carcinogenic disinfection by-products (DBPs) such as trihalomethanes (THMs). As a result of the risks posed by DBPs, the Stage 2 Disinfectants and Disinfection By-Products Rule (Stage 2 D/DBP) was promulgated to limit exposure to DBPs by requiring systems to monitor concentrations at the worst cases locations in the distribution system. The purpose of this study was to evaluate sonication as an alternate disinfection strategy to reduce THM formation. Prior research has demonstrated the inactivation kinetics of sonication. Therefore, if sonication also reduces THM formation, this disinfection technology could help water utilities simultaneously comply with the Stage 2 D/DBP Rule and the LT2ESWTR. Water samples were prepared with varying concentrations of natural organic matter (NOM). THM formation potential reduction was evaluated by treating the water samples with sonication at 20 kHz for 0 seconds, 30 seconds, 60 seconds, 5 minutes and 10 minutes. After treatment, the samples were chlorinated and incubated at 20â€žaC to form THMs. After incubation times from 1 to 7 days, THMs were extracted, and gas chromatography with electron capture detection was used to quantify THM concentrations in treated and control samples. For experimental water with an NOM concentration of 1 mg/L that was dosed with 6 mg/L of NaOCl, the average THM formation potential reduction was 40% for sonication times of 30 seconds, 5 minutes and 10 minutes. The data for 60 seconds of treatment do not follow the same trends as the other data. Additional study is necessary to increase precision of the experimental data; however, this study supports sonication as a potential method of THM reduction.

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