OCCURRENCE AND CONSEQUENCES OF DISINFECTION BY-PRODUCTS IN DRINKING WATERS AS RELATED TO WATER SHORTAGE PROBLEMS IN ISTANBUL METROPOLITAN CITY

摘要

As expected for the majority of South Europe countries, Turkey would also face serious problems related to water shortage conditions particularly for drinking water. Istanbul is one of the mega cities of the world with a population of 13 million. Considering both European and Asian sides, average water demand is 3 × 10~5 m~3/day. Existing raw water sources display quite different characteristics in relation to raw water quality. Besides basic parameters set by the local as well as the international standards, daily monitoring of pesticides, taste and odor compounds, bromide and bromate levels also followed for all of the finished water samples before being introduced to the distribution system. Considering the major concern as disinfection by-products (DBPs) among all of the chlorinated by-products trihalomethanes (THMs) constitute the main group of interest. The major surrogate parameter of DBPs is mainly the natural organic matter (NOM) content of water either expressed as total organic carbon (TOC) or dissolved organic carbon (DOC). Therefore the control of DBPs primarily relies on the efficiency of DOC removal from drinking waters through the application of conventional treatment methods as well as by the use of disinfection alternatives such as ozonation, chlorine dioxide or UV-irradiation. Preoxidation either by prechlorination or by preozo-nation is applied to surface water sources of Istanbul. Following a conventional treatment scheme, post chlorination is applied as a final step in all of the treatment plants. Therefore existence of chlorinated DBPs as well as the other DBPs in drinking waters could possibly pose a public health risk. However, as monitored by the local authorities the THM levels are reported to be well below 100 μg/L. Water shortage and drought conditions lead to adverse changes in water quality parameters mainly in terms of NOM characteristics. The major consequence of the diverse conditions related to the occurrence and distribution of allochthonous and autochthonous organic matter contents would be observed in the process efficiencies as well as on the DBPs formed via the action of oxidizing agents. This paper addresses the occurrence and consequences of disinfection byproducts in drinking waters as related to the water shortage problems in Istanbul Metropolitan City. Detailed information would be presented regarding the speciation and characteristics of NOM, removal efficiencies, application of conventional and novel treatment schemes in relation to the formation of DBPs and THMs.