Abstrait

Experimental Investigation into the Occurrence and Effects of Individual Parameters on THM Formation

Abbas S and Hashmi I

Disinfection of drinking water for removal of water borne microorganisms has been in use for past many years. Common disinfectant used is Chlorine. Reaction between chlorine and naturally occurring organic matter (NOM) results in formation of trihalomethanes (THMs) which are possible carcinogen to humans. This study presents the results of an experimental investigation on different parameters from two water supply systems in twin cities Islamabad and Rawalpindi, Pakistan. Research was carried out in two phases. In first phase factors affecting the formation behaviour of THMs were studies and in the second phase drinking water samples of the twin cities were investigated for likely occurrence of THMs. To identify factors that influence the THM formation, the chlorine decay and THM formation kinetics were carried out in laboratory experiments. Water quality characteristics that influence the formation of DBPs e.g. type and concentration of organic precursors, pH, temperature, and disinfectant were monitored. Gas chromatographic method was established to analyse the samples on GC apparatus. The present study also assessed that main factors influencing THM formation in the main water distribution system were the chlorine dose and presence of the naturally occurring organic matter (NOM) in water. The results of the study indicated that temperature and chlorine dosage tends to effect formation of trihalomethanes more as compare to pH. In the second phase of experimentation samples were collected from 20 different sampling sites of the twin cities including water filtration plants, underground water storage areas and consumer taps. The results showed occurrence of THMs in 90% of chlorine treated drinking water samples. Results from the investigation indicated the occurrence of Trihalomethanes in the water sample collected from 16 stations. Few sites met the standard value of 80 μg/L.