Evaluation of the sub-products from the chlorination process at the ？Lucio Baldó Soulés？ Water Treatment Plant

every process used to make water potable involves the addition of chemical substances to improve the physicochemical and bacteriological properties of water. chlorine is used in the disinfection process,step that guarantees the bacteriological quality of the water. when chlorine is added to water with a high content of organic matter, there are secondary reactions that generate ？organo-chlorinated？ compounds, which in some cases have proven carcinogenic, specifically the brominated tri-halogenated methanes. this study determined the concentration of tri-halogenated methanes in the water from the ？lucio baldó soulé？ water treatment plant. the pre-chlorination point was also modified, to evaluate if there was a relation between this point and the formation of tri-halogenated methanes (thm). a total of 8 samples collected during 4 sampling sessions carried out in a four-week period were analyzed. the thm concentration was determined by gas chromatography, using the liquid-liquid micro-extraction technique, and by capillary gas chromatography with an electron micro-capture detector (μecd). the concentrations of the following thm were determined: chloroform (chcl3), bromoform (chbr3), dibromochloromethane (chbr2cl) and dichlorobromomethane (chcl2br). some results showed that modifying the point where the chlorine was injected decreased the concentration of thm from 79.9 ± 0.8 μg/l to 12.5 ± 0.5 μg/l, a value substantially lower than the maximum permissible concentration established by the environmental protection agency in the united states 80 μg/l and by the marn (venezuelan environmental ministry) 460 μg/l for the total of the four thms.