Planning of wastewater treatment and disposal systems of Istanbul metropolitan area

Current and future wastewater treatment and disposal strategies of Istanbul city are presented. Istanbul is the largest city of Turkey and has a popul ation of 10 million that may reach about 20 million in 2032. The city is di vided into Asian and European sides by the Bosphorus Strait. The Sea of Mar mara is an enclosed sea, connected to the Black Sea and Aegean Sea by the s traits of Bosphorus and Dardanelles, Therefore, there is very strong and pe rmanent stratification in the Sea of Marmara throughout the year, lower lay ers carrying Mediterranean and the upper layers carrying Black Sea water. T his unique coastal structure of Istanbul necessitated a detailed study to d etermine the level of wastewater treatment and the location and depth of ma rine outfalls. A comprehensive three-dimensional water quality modelling study concluded t hat tertiary treatment including nitrogen and phosphorus removal is require d for the effluent discharges into the Marmara Sea. However, enhanced prima ry or even primary treatment has been found satisfactory for discharges int o the lower layers of the Bosphorus and into the Black Sea. Provisions for upgrading to secondary treatment were recommended. The status of existing a nd planned wastewater treatment plants and sea outfalls of Istanbul city ar e also presented. Although the amount of treated wastewater was only 63 per cent in 1998, a target of 95 percent treatment level by the end of 2000 has been adopted in implementation plans. All treatment plants are located at or close to the coast except Pasakoy WWTP which is in the catchment area of Omerli Reservoir, the major source of drinking water for Istanbul city. Th e Pasakoy WWTP has been designed to treat wastewaters collected from the ca tchment area of Omerli Reservoir to tertiary level before ultimate disposal . The implementation programme together with the cost estimates are given. Total investment on water, wastewater and stormwater projects up to year 20 32 is estimated at about 10 billion US Dollars. The share of the wastewater projects in this total is increasing with time. The financial analysis con cluded that investments for a Higher Demand Scenario can be realised by rai sing the water tariffs to 1.0 $/m(3) for Phase 1 and 0.9 $/m(3) for Phase 2 .