Document Type : Original Articles
Department of Environmental Planning, Faculty of Environment, University of Tehran
During recent years, surface water resources supplying Tehran's potable water – Karaj, Lar and Jajrood Rivers – are contaminated with different microorganisms due to population growth. Additionally, the amount of organic materials generating odor, taste and color in the surface water has increased sharply. By considering the trihalomethane (THM) production potential of dissolved chlorine in reaction with innocuous humic substances, future use of chlorine as a disinfectant in Tehran's drinking water is clouded in uncertainty. Accordingly, the use of ozone as another alternative was taken in to consideration for disinfection of drinking water in this mega city. In order to evaluate advantages and disadvantages of water ozonation a pilot with a generating capacity of 4 gr ozone per hour was designed. This study was performed between April and September 2005 and Tehran Pars water treatment plant in the Northeast of Tehran was chosen for the case study. Bacteria removal was considered to be at highest level in all monthly samples. Different ozone contact times and dosages were tested in the deactivation of nematodes and the results showed the perfect removal in specified periods. Although the initial investment for construction and implementation of the required apparatuses is relatively high, since the raw material for ozone generation is air, the use of ozone is financially justifiable during the predicted time of operation. Moreover, the transfer and storage of ozone is much easier in comparison with chlorine which is currently in use. Unlike chlorine, the use of ozone as a disinfectant does not have the potential of THMs generation. On the other hand, ozone must be generated on site and is instable in water. Therefore, a continuous and precise monitoring and maintenance process must be taken in to consideration. Furthermore, due to high corrosive potential of ozone, special resistant materials must be used in the applied instruments.