Statistical analysis of trihalomethanes in treated-water tanks: seasonality, local variability and correlations

Abstract

Chlorine was accepted as an effective disinfectant for drinking water in early 1900s. Because of
 chlorination, chlorine has dramatically reduced the incidence of waterborne diseases. An unwanted side
 effect is the formation of harmful by-products upon chlorination. The most significant group of disinfection
 by-products formed during chlorination is the trihalomethanes (THMs).
 In this reason, European Union initiated the maximum contaminant level (MCL) of total concentration of
 THMs to 100 μg L-1. Because of this regulation, operational parameters of the WTP and raw water quality
 characteristics need to be studied in depth in order for THMs to be minimised. Statistical analysis is
 necessary for this purpose employing the parametric two-way ANOVA for the concentrations of chloroform
 (CHCl3) and dichlorobromomethane (CHCl2Br) and the analysis of variance on data ranks of
 chlorodibromomethane (CHClBr2) concentration. Chlorine dose, postchlorination, bromide levels, reaction
 temperature, reaction duration and dissolved organic carbon levels as well as pH of raw water, are the
 factors that affect the rate of THMs formation and the total THMs yield. Athens Water Supply and
 Sewerage Company (EYDAP SA), as the water supplier of a city with 3.5 million inhabitants, makes
 continuous attempts to improve water quality.