an evaluation of thms in drinking water and a method of its removal

chlorination of natural water containing humic compounds, produce significant amount of disinfectant by - products. the most important of such compounds are thlvis and halo acetic acids, suspected to cause cancer in animals and human. studies showed that under usual processes of water treatment plants, thms can not be removed effectively. since chlorination is the final process of treatment, it is necessary to suggest a method for removing such compounds. the primary goal of this research was to study the possibility of the presence of thms in the drinking water and the procedures for its removal. in the first phase of this study which was done in 1996, the quality of raw and fmished water in the case of total thms were studied for ahwaz, isfahan, bandar- abbas, shiraz, mashhad and tehran. the thms determination was done for three months in all cities, but for tehran, fulfilled ten months for raw and seven months for the tap waters. total thm concentrations were determined by liquid-liquid extraction and gas chromatography. results varied from less than 5µgr/lit (the lowest concentration detectable by the method) to 732 µgr/lit (thm.f.p. in for bandarabbass tap water). four samples out of 185, showed that total thm concentrations were above the 100 µgr/lit (mcl). in the second phase of the study, granular activated carbon was used to determine its ability to remove the thm, from the water. tap water was spiked to 500 µgr/lit using bromoform and chloroform, and then passed through the activated carbon filter. the effluent and influent of the filter were analyzed periodically to determine the concentration of thms. after 1360 liter of spiked water was passed through, breakthrough was measured. gac absorption follows frendlich isotherm. k and n parameters were determined.