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

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.