Presence and formation of disinfection by-products in Cairo residential water supply

Abstract

A sampling program was conducted in a residential community in Cairo, Egypt in order to determine the presence of chlorine disinfection by-products (DBPs) in treated water and to observe the impact of the distribution system on DBP levels. Five campaigns were conducted over a 15-month period during 2005–2006. Trihalomethanes (THMs) and haloacetic acids (HAAs) exceeded local and international limits depending upon the season. Tap water concentrations of THMs were considerably higher in summer than during the rest of the year. In the Summer 2005 event, the average for the 20 tap water locations was 158 μg/l Total-THMs, well in excess of the U.S. EPA limit of 80 μg/L and the current Egyptian standard of 100 μg/l; all 20 locations exceeded the 100 μg/l limit. For the following event in late Fall 2005, the average dropped to 84 μg/l with 11 and 6 sites exceeding the U.S. EPA and Egyptian limits, respectively. HAA levels tended to be complementary to Total-THM values in that they were lower in summer but higher during fall and spring. The U.S. EPA limit on a select set of 5 HAAs (HAA5) is 60 μg/l (Egypt does not currently regulate HAAs). The average for HAA5 in the Summer 2005 event was 52 μg/l with 8 of the 20 tap samples equalling or exceeding the 60 μg/l standard. By contrast, in Fall 2005, the HAA5 average increased to 89 μg/l, with 15 of 20 sites exceeding the limit. THM and HAA concentrations generally increased with distance from the WTP along a targeted distribution main, while chlorine and natural organic matter tended to decrease.