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The kinetics of chlorine decay of the pre-treated water collected once a month from the Gilau Water Treatment Plant after one of the sand filters was investigated. The chlorine species reacts with ABTS (2,2-azinobis( 3-ethylbenzothiazoline)-6-sulfonicacid-diamonium salt) to yield a green colour product that is measured at 405 nm wavelength with a spectrophotometer. The second method used for the investigation of chlorine consumption was by means of DPD (N,N-diethyl-p-phenylenediamine), where chlorine oxidizes DPD which takes on a red colour. The absorption is measured with a spectrophotometer at a wavelength of 515 nm. Both methods are useful for the determination of chlorine consumption in the treated water from distribution systems. [ABSTRACT FROM AUTHOR]

Chlorine is one of the most used water disinfectant agent used on the world. The use of chlorine in the treatment of drinking water has virtually eliminated waterborne diseases, because chlorine can kill or inactivate most microorganisms commonly found in water. The majority of drinking water treatment plants in Romania use some form of chlorine to disinfect drinking water: to treat the water directly in the treatment plant and/or to maintain a chlorine residual in the distribution system to prevent bacterial regrowth. Unfortunately it's used results in formation of some disinfection by products (DBPs) that are suspected from harmful effects on humans. Such of disinfection byproducts are trihalomethanes (THMs). Trihalomethanes are a group of volatile organic compounds that can form when the chlorine used to disinfect drinking water reacts with naturally occurring organic matter (e.g., decaying leaves and vegetation). The preliminary results presented in this paper shown that the THMs levels from Gilau Water treatment Plants and Cluj-Napoca distribution system. The results have higher values in the summer period relative to other seasons. [ABSTRACT FROM AUTHOR]