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Examining the relationship between total chlorine residual to Disinfection By-Products production and microbial control
Citation:
Donohue, M. Examining the relationship between total chlorine residual to Disinfection By-Products production and microbial control. 2019 Gordon Research Conference on Water Disinfection, Byproducts and Health, Holyoke, MA, July 28 - August 02, 2019.
Impact/Purpose:
To determine the relationship between Disinfection By Products and pathogen occurrence.
Description:
Public water utilities use a chemical residual (chlorine or monochloramine) within distributed water to protect humans from harmful microbial growth or regrowth. This protective measure does control the microbial population. Yet, these chemical disinfectants are reactive and can oxidize with other organic and inorganic matter to form disinfection by products (DBP). One class of DBP is known as Trihalomethanes (THMs). These DBPs are primarily composed of four chemicals (chloroform, bromoform, bromodichloramethane, and dibromochloromethane) known to be harmful to human health. This study examines the relationship between total chlorine residuals (TClR) to both microbial control and THM generation within water taken from point-of-use taps. One hundred and forty-two samples were taken at various taps across the US. Diethyl-p-phenylenediamine (DPD) total chlorine test was used to measure the total chlorine residual. EPA Method 551.1 was used to provide the total Trihalomethanes (TTHM) amount. Heterotopic plate counts (HPC) (Standard Methods 9215B) were used to quantitate the microbial density and qPCR was used to detect the presence of Legionella pneumophila. THM data were quartile base on concentration, first quartile has least amount, fourth quartile has the highest concentrations. Mann-Whitney T-test was used to determine statistical significance. The TClR measured at taps ranged from 0 to 8 mg/L with an average of 1.3 mg/L. The amount of TTHMs varied greatly from 0 to 85.4 ug/L with the average concentration of 26.3 mg/L. A high residual did not necessarily mean a high TTHM concentration (no statistical significance was determined). The water with the highest TTHM (4th quartile) (44.5-85.4 mg/L) had an average total chlorine residual (TClR) of 1.2mg/L. The lowest TTHM quartile (0 - 4.6 mg/L) had an average of 1.3 mg/L TCLR. HPC and TTHM were correlated. The higher the TTHM concentration (44.5-85.4 mg/L), the more bacteria (average 4.0 103/ml) were present in the water samples. This was not the case for L. pneumophila, the higher detection frequencies (33%) were observed for the 2nd TTHM quartile (4.7-22.9mg/L). The relationship between TClR to TTHM and microbial control HPCs/L. pneumophila was complex, but it was necessary to understand the underlying chemical and microbial dynamics to develop strategies that will reduce exposure to these harmful constituents.
