Not: Figürlerin, Tabloların ve Formüllerin daha yüksek çözünürlüklü görüntüleri için görsele sağ tıklayıp “resmi yeni sekmede aç” seçeneğini seçiniz

A. Samsunlu

 Istanbul Technical University, Faculty of Civil Engineering, Environmental Engineering Department,

 Maslak 80626, Istanbul, Turkey


Istanbul is one of the world’s most ancient cities. The present population is around 13 million. The population increase rate is more than twice the average of the country, and is due to migration. Each year roughly 400.000 new inhabitants settle in Istanbul. Insufficient water sources are surrounded by unplanned and uncontrolled urban and industrial development. Thus, problems such as treatment of drinking water, sewage and wastewater, as well as transportation etc. could not be solved easily.

Even though, efforts have been paid to solve these problems since 1920s, more successful activities have been realized after the establishment of Istanbul Water and Sewerage Administration (ISKI) in 1981.

ISKI is responsible for supplying and distributing potable water as well as collecting and treating wastewater and storm water. ISKI has become a branch of Greater Istanbul Metropolitan Municipality since 1984. 

As a result of applying economically and technologically available systems for wastewater treatment and discharge, Istanbul today has reached to a competitive and comparable stage with other NATO member countries. 

In this paper, a review on the prevailing condition of the wastewater and storm water collection and treatment systems will be done and brief information on wastewater management will be given. Within the context of the study, success gained by the application of ‘The Golden Horn Environmental Protection Project’ and the findings of Water Quality Monitoring Studies in Golden Horn will be discussed and evaluated.

Keywords: Istanbul Water and Sewerage Administration, Golden Horn Environmental Protection Project, Water Quality Monitoring


Istanbul being established as early as 658 B.C. is one of oldest cities inhabited in all the times. The geographical location and topography of the city is quite unique which made the sewerage works easy especially during the early times when no treatment was required. Sewerage projects of Istanbul are not well documented as the water projects.

The channels that have been built before and after the Ottoman Empire have served the city till 1950’s. In the past century, significant work has been realized regarding the city’s infrastructure. The most important ones may be listed accordingly;

Sewer projects prepared and implemented are presented in chronological order as French Sewers (1918-1920), Wild projects (1925-1935), Kehr projects (1959-1966), DAMOC master plan and its revisions (1966-1975) and finally master plan prepared by Istanbul Master Plan Consortium from 1992 to 1999.

In year 1957, Prof. Kehr from Hannover Technical University has been assigned to solve the sewerage and wastewater problems of the city. The Professor compared the mortality figures in the cities of Istanbul and Hannover resulting from typhoid. He indicated that the mortality ratios were 1/1000 in Istanbul whereas 5/100 000 in Hannover between years 1950-1957. It is reported that nowadays no death event from typhoid is registered as a result of ISKIs success in coping with the infrastructure problems.

  • ISKI and Its Responsibilities

Till 1981, the Istanbul Municipality dealt mainly with the preparation of the required wastewater management projects, and up to certain extend with the construction of urgent sewerage systems.

The main reason of not being successful in the infrastructure works of Istanbul was mainly due to financial constraints. Thus, the Central Government decided to form an independent association in the city to deal with wastewater management issues. Therefore, Water and Sewerage Administration of Istanbul (ISKI) has been established in 20.11.1981 under the law referenced as 2560 with the aim of constructing and operating any kind of water and sewerage plants in the province.

According to a Law established in 1984, the municipalities are divided into 2 groups. Those municipalities under the Greater Metropolitan Cities are benefited financially and are fully authorized. In 23.05.1984 under the law referenced as 3030, the administration is joined to the Istanbul Greater Metropolitan Municipality of the Province. Therefore, the mayor of the Province is authorized to act as the head of the Administrative Board of ISKI. The Administrative Board consists of a chairman and 5 members. The General Manager of ISKI and the vice manager with the maximum service period or else if the service periods are same among the vice managers the oldest become the natural members of the Board. The rest 3 members of the Board are selected by the proposal of the Mayor of the Province under the approval of the Ministry of Interior Affairs.

The assembly of Greater Metropolitan Municipality is responsible to act as ISKI’s General Board.

The activities of the Administration are limited to Greater Metropolitan boundaries. By means of the new law established in 2005, referenced 5216, the boundaries of the Greater Metropolitan Municipality is extended up to the boundaries of the Province. The service area stated by the old and new law is shown in Figure 1. The Old Service Area has been 1.976 km2 while in year 2005 the entire area is extended till the administrative boundary of the city by the change in the Law No: 5216. The overall area now is 6504 km2 with a population of 12 million. In addition to this new boundary, one district, 14 sub-districts and 173 villages are also included to the service area of ISKI.

Figure 1. The service area of ISKI

Since the establishment of ISKI 24 years ago, the administration has managed to solve the infrastructure problems of the old service area, and now faces the responsibility of continuing its successful activities within the extended service area. As seen from Figure 2, as a result of extending the service area of the city and in turn, the population increase, decreased the annual amount of treated wastewater.

Figure 2. Daily amount of wastewater treated according to years

  • ISKI Wastewater Treatment and Discharge Systems

ISKI serves to a total area of 6,504 km2, where the total population is 12 million. ISKI has 3.8 million clients. The length of the water distribution and sewerage collection lines are 14.045 and 11.343 km, respectively. The annual amount of water resources are 1.170 million m3, and 2.000.000 m3/year water is supplied to the city. The total volume of the water resources is 1.317.280 m3. The total budget of ISKI was 1.3 billion dollars in 2006 while the total investment costs in the same year were 778 million dollars.

Wastewater Collection, Treatment and Disposal system of Istanbul is shown in Figure 3.

The separate sewerage systems are collected and treated initially in preliminary treatment plants and the effluent are either discharged to the sea as marine discharge systems or else are further treated biologically. Table 1 shows the existing infrastructure and wastewater treatment systems in Istanbul.

Figure 3. Wastewater Collection, Treatment and Disposal system in İstanbul

Table 1. Completed Wastewater Investments

Investment Total
Pre-Treatment Plant 7
Biological Treatment Plant 7
Pumping Stations 17
Tunnel 54 km.
Collector 387 km.
Pipe – Jacking 31 km.
Land Pipeline 17 km.
Sea Outfall 17 km.
Wastewater Network 11.343 km.
Creek Rehabilitation 48 km.

Location and some characteristics of wastewater treatment plants which are currently in use are given in Figure 4 and Table 2, respectively.

Figure 4. Location of Wastewater Treatment Plants 

There are 14 wastewater treatment plants in Istanbul. The urban wastewater treatment is achieved by means of 2 advanced treatment, 5 biological treatment and 7 marine outfall systems (nowadays 2 advanced treatment (3%), 4 biological treatment (14%) and 7 marine outfall system (83%)). The total capacity of these plants is 3.846.100 m3/day. The planned projects of ISKI for the next year are 6 wastewater treatment plants (tender stage), biological treatment plants to be added to 2 already existing marine discharge plants having pre-treatment units, 5 new marine discharge plants having pre-treatment units, and new treatment plants for plenty of villages.

In 2005, 571 million m3 wastewater and 89 million m3 storm water has been treated (ISKI, 2006). Table 3 gives the average effluent values of ISKIs Wastewater Treatment Plants.

Table 2. Characteristics of wastewater treatment plants

  Name of Facility Year Commissioned Capacity (m3/day) Average Amount of Treated Wastewater per day in 2006 (m3 )
1. Yenikapı Pre-Treatment Plant 1988 864,000  495,567
2. Üsküdar Pre-Treatment Plant 1992 77,760  26,224
3. Ataköy Biological Treatment 1996 7,650   5,576
4. Baltalimanı Pre-Treatment Plant 1997 625,000  366,425
5. Tuzla Biological Treatment 1998 150,000  242,789
6. B.Çekmece Pre-Treatment Plant 1998 155,120 30,544
7. Paşaköy Advanced Biological 2000 125,000  56,134
8. Terkos Advanced Biological 2000 1,700 811
9. K.Çekmece Pre-Treatment Plant 2003 354,000 113,106
10. Kadıköy Pre-Treatment Plant 2003 833,000 346,266
11. Küçüksu Pre-Treatment Plant 2004 640,000 117,667
12. Bahçeşehir Biological Treatment 2004 7,400 6,442
13. Çanta Biological Treatment 2005 1,600 1,254
14. Silivri Biological Treatment 2006 1,330 1,254
Total 3,843,560 1,703,926

Table 3.  Mean effluent values of some parameters (mg/L)

Parameters Ataköy Tuzla Paşaköy Terkos Bahçeşehir
BOD5 30 139 33 12 22
COD 83 241 49 35 58
NH4-N 34 124 16 5 15
Total-N     73 13,6  
Total-P     12 1,8  

Information on Wastewater Sea outfalls are given in Table 4. 

Table 4. Wastewater Sea Outfalls

Name Year Commissioned Length (m) Diameter (mm) Depth (m)
1. Yenikapı 1988 2,360 2 x Ø1600 – 60
2. Üsküdar 1992 275 Ø1200 – 47
3. Baltalimanı  1997 700 2 x Ø1727 – 70
4. Tuzla 1998 2,203 Ø2200 – 46
5. B.Çekmece  1998 1,803 Ø1600 – 40
6. K.Çekmece 2003 1,650 Ø1600 – 36
7. Kadıköy 2003 2,308 Ø2200 – 52
8. Küçüksu 2004 363 Ø2172 – 67
9. Büyükada 1989 2,200 Ø600 – 62
10.Burgazada P2 1988 890 Ø315 – 30
11.Kınalıada 1997 1,100 Ø315 – 52
12.Heybeliada 1999 1,020 Ø450 – 62
13.Anadolu Kavağı 1991 120 Ø315 – 32
Total 16,992    

While ISKI collects the wastewater originating from the city, it also decides whether preliminary treatment is required for some industries or not. In Turkey, in early years when the wastewater management programs were implemented and applied, the industrial plants were asked to install their individual treatment plants to treat their wastewater up to domestic wastewater character as there were no urban wastewater treatment plants. Today, in Metropolitan cities owning urban wastewater treatment plants accept wastewater from industries obeying the discharge to sewers and/or discharge to urban wastewater treatment plants.

  • Storm Water Discharge

At the time of establishment, ISKI was not directly in charge of storm water collection and disposal like the rehabilitation of rivers. The related law states that unless the financial needs fro the storm water collection and disposal are paid by the municipality, ISKI may be involved in constructing the corresponding facilities. Therefore, ISKI constructs such facilities in the main branches of the Metropolis and does not get involved with the district municipalities as it is not paid by the local authorities.

The main storm water lines of ISKI are almost 237 km. However, the existing lines may not be sufficient enough to cover the loads of the city. The length of main branches of the city that is not installed with the storm water facilities and that complain about flooding is about 304 km.

The length of storm water lines for the main branches of the city is around 1.577 km. If the deficient parts are constructed, the city will have a total storm water collection pipeline with a length of 1.814 km.

As can be understood from the prevailing situation, the local municipalities do not fulfil the storm water pipeline constructions.

After heavy rains, flooding becomes one of the major problems of the city. The difficulties are especially due to variety of coordination units, and lack of collaboration between authorities. This situation may be corrected by changing the Law of ISKI and by passing all the responsibility to ISKI.

  • River Rehabilitation

Even though the river rehabilitation activities are within the duties of State Hydraulic Works (DSI), it has become the responsibility of Greater Metropolitan Municipalities by Law no: 3030. For long periods of time, ISKI, DSI, and Metropolitan Municipality of Istanbul worked together in the river rehabilitation projects.

There have been a total number of 68 creeks in Istanbul that joined to Istanbul Strait and Sea of Marmara. The total length of these creeks together with their arms is around 615 km. During years 1981-2004 the total length of rivers that have been rehabilitated jointly by ISKI, DSI and by the Greater Metropolitan Municipality and the local municipalities is 203 km. 65 km. more rehabilitation continued till October 2005 (ISKI, 2005). On the other hand, it is stated in the Master Plan of the city that there are 106 more rivers with a total length of 772 km. are still waiting to be rehabilitated (Master Plan, 1999).

Upon the proposal of Greater Metropolitan Municipality, in the meeting held at 11.10.2004 and resolution no: 817, the below mentioned decisions are declared and put into force;

* River rehabilitation works will be undertaken by ISKI,

* Maintenance, cleaning and operation of these systems will be under the responsibility of ISKI, and

* It has been decided that ISKI is responsible for construction of required wastewater and storm water collectors and river rehabilitations as there is a high risk potential of flooding.

  • Sludge Disposal

ISKI has been quite successful in wastewater treatment. On the other hand, similar success has not been achieved in sludge treatment. The sludge generated in the wastewater treatment plants of Istanbul are disposed to two existing solid waste disposal landfills. The disposed amounts of year 2005 was 56 593 tonnes. The disposal site and the disposed amounts arising from the pre-treatment systems of certain industries are still not known and not controlled. It is assumed that part of this sludge is transferred to İzaydas, whereas the rest is disposed to illegal sites. The planned constructions of two incineration plants (Tuzla and Ambarlı) and another hazardous waste storage facility in Trakya will highly contribute to the solution of this specific problem (Samsunlu, 2006).

  • Quality Measures of ISKI

ISKI emphasizes on the quality measurements in the Sea of Marmara and the Black Sea as it wishes the coasts of the city to be used for swimming. Thereffore, monthly measurements are conducted on 40 parameters in the samples collected from different depths. The measured parameters are listed in Table 5. The important indicator parameters of fecal coliform and fecal streptococci also take palce within the list of measured parameters.

Table 5. Controlling parameters

Temperature Total Org. N
Salinity Total N
Viscosity Ortho-Phosphate
Current Total P
Secchi Depth Particulate P
Air Temperature Dissolved Si
Wind Speed and Directions Poly Aromatic Hydrocarbons
Pressure Detergent
Dissolved Oxygen Fe/Mn/Cu/Hg/Pb/Zn in SSM
Suspended Solid Mat. Fe/Mn/Cu/Hg/Cd/Pb in Water
Total Org. Carbon Chl-a
Particulate Org. Carbon Phytoplankton
NO2-N Zooplankton
NO3-N Fecal Coliform
Org. N Benthic Organisms
  • Water Quality Monitoring Studies in the Golden Horn

ISKI monitors sea water quality at various stations in the Sea of Marmara, the Bosphorous and the Bosphorous Discharge Area in the Black Sea.

  • Water Quality Monitoring studies are conducted by the Institute of Marine Sciences at Istanbul University.
  • Monthly and seasonal measurements of pollution levels are detected by means of sampling at different depths from a total of 45 monitoring stations; 40 different parameters in these samples are studied.
  • As a result of investments made in the last 8 years, there have been major improvements in the water quality level of the Golden Horn, the Bosphorous and the Sea of Marmara in comparison with previous years.

The distribution of fecal coliform and fecal streptococci values measured in the Strait of Istanbul and Sea of Marmara are given in Figure 5.a, Figure 5.b and Figure 6.a and Figure 6.b.

Figure 5.a. Distribution of fecal coliform and fecal streptococci in the Strait of Istanbul and Sea of Marmara (Asian Side, December 2002)

Figure 5.b. Distribution of fecal coliform and fecal streptococci in the Strait of Istanbul and Sea of Marmara (Asian Side, 17 May 2006)

Figure 6.a. Distribution of fecal coliform and fecal streptococci in the Strait of Istanbul and Sea of Marmara (European Side, 24 December 2002)

  • In the past, nearly all wastewater of Istanbul was discharged into sea, rivers and water resources.
  • There were “forbidden to swim” signboards all around the city coasts of Istanbul.
  • 80 points in the Istanbul coast are permitted to be used for swimming  as a result of the treatment investments
  • Today out of 234 km coastline, swimming is allowed along the 161 km. 

Figure 6.b. Distribution of fecal coliform and fecal streptococci in the Strait of Istanbul and Sea of Marmara (European Side, 18 May 2006)

5.2. The Golden Horn Project

Due to wrong city planning, Golden Horn was turned to an industrial region in the past years. In 1985, about 700 industrial facilities and over 2000 offices were established. It was impossible to visit the Golden Horn because of pollution and unpleasant odour. It was highly polluted in a short period of time due to rapid and unplanned of industrialization.

Some strategic works was then done to save the Golden Horn:

  • Wastewater formerly being discharged directly to the Golden Horn is collected and transferred to treatment plants,
  • The sludge that had accumulated in the course of time was dredged and collected in a convenient place,
  • Rehabilitation of the Golden Horn and its environment is realized.

The dredged material is stored in an area that may be later used for sports activities and/or the sludge may be used as filling material in other works.

After the rehabilitation activities, 33 species of fish started to reside in the Golden Horn, and it has been observed that the Sea Horse, once almost extinct, is growing in numbers nowadays.

The materials carried by Kağıthane and Alibeyköy creeks in rainy weathers gradually spoil the bottom of Golden Horn, which was cleaned from industrial sludge. To prevent this problem, ISKI dredges the sludge in the Golden Horn after heavy rains.

As a result of the works completed in the Golden Horn, the oxygen level has increased up the saturation level, while the sea transport, which had stopped 20 years ago, has restarted, and International Boat Races are organized again in the Golden Horn

The Golden Horn region has now turned to be a cultural site, Feshane and Miniaturk have already been established, and the construction of Sütlüce Culture Centre is still ongoing.

The Golden Horn Environment Protection Project was awarded by the First Prize in 2002 by the World Metropolitan Municipality Association, where there were 84 municipalities competing for the award.

6. Istanbul and some other NATO cities

Table 6 and 7 show the population served by municipalities, the amount of annual treated wastewater together with the ratio of treated wastewater to distributed amounts.

Table 6. The Percentage of the Population benefited from Sewerage System (%)

Cities Population (%)
Berlin 100
London 100
Madrid 100
New York 100
Paris 100
İstanbul 90

Table 7. The Amount of Wastewater Treated Annually (m3/year) and the Ratio of Wastewater Treated Annually to the Water Distributed (%)

Cities The Volume of Wastewater Treated Annualy (m3/year) The Ratio of Wastewater Treated Annually to Water Distributed (%)
New York 1.780.983.650 100
London 1.608.000.000 100
Paris 100
Madrid 560.000.000 100
Berlin 230.000.000 97
İstanbul 637.000.000 80

      6.  Conclusions

Environmental issues have become one of the major titles of the country that is on the way to join European Union. EU countries pay attention to increase the living standards of the inhabitants and approach to the subject of concern very sensitively. They especially emphasize on reducing the surface urban run-off, increase Greenland and fill the highways with natural material as much as possible. In order to increase the standard of living, the rivers, creeks and other aquatic environments must comply with the standards.

ISKI has been quite successful in constructing and operating the infrastructure of the city, thus, the coasts of the city have now become convenient environments for swimming.

However, the same success has not been achieved in realizing the storm water collection and disposal systems as well as in river rehabilitation works. Only the urgent rehabilitations have been completed, and the rest of the rivers will be rehabilitated in the near future. Most of the flooding problems are decreased after the rehabilitation works. That is why emphasis is now given to river rehabilitations

Legal arrangements must be done in order to accelerate the construction and operation of storm water systems as is the case in most of the EU countries. ISKI has now reached to a state comparable with most of the other NATO membership cities in the world after the establishment of ISKI.


[1]     Samsunlu, A. (2006) “Ruhr Union approach in Germany and ISKI approach in Turkey to the treatment of industrial wastewater”, ITÜ Industrail Pollution Control Symposium, İTÜ Department of Environmental Engineering, İstanbul (in Turkish)

[2]     İstanbul Water and Sewerage Administration 2004, İSKİ Annual Report

[3]     İSKİ Publications


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