Pre-treatment of Industrial Wastewater: ISKI’s Approach in Turkey

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Pre-treatment of Industrial Wastewater: ISKI’s Approach in Turkey

Prof. Dr. Ahmet Samsunlu

Istanbul Technical University, Faculty of Civil Engineering, Department of Environmental Engineering, Maslak 34469, Istanbul, Turkey



The industries whose wastewater are not allowed to be directly discharged to the sewer system, and those whose wastewater are not seen appropriate to be discharged to the sewer system due to their wastewater characterization by the authorities have to install and operate pre-treatment systems in a way so as to meet the current limits given in the Water Pollution Control Regulation and in the related local regulation. 

Water supply and wastewater disposal of industries have not been properly achieved in Turkey. The limited number of regulations is not efficiently obeyed due to the inadequate infrastructure of the municipalities, inadequate number of trained technical personnel, and to political expectations. Consequently, the industries do not construct and/or postpone the pre-treatment plants required according to the Water Pollution Control Regulation.

Some local water and sewerage administrations under the Greater Metropolitan Municipalities behave more sensitively on pre-treatment requirements and in the disposal of industrial wastewater. ISKI (Istanbul Water and Sewerage Administration) is one of these organizations and it has a leading position in Turkey. ISKI has been established on 20 November 1981 under the law dated 20.11.1981 with a reference number 2560. The aims of this organization are to construct, operate and manage the services of water and sewerage systems.

The industries in Istanbul are controlled and monitored according to the ‘Discharge to Sewer Systems Regulation’ of ISKI that has been prepared under the light of Water Pollution Control Regulation. Those industries that do not comply with the stated limits are asked to construct their pre-treatment plants. 

In this paper, information will be given about ISKI which is the oldest and the largest metropolitan infrastructure organization. Besides, the discharge of industrial wastewater to sewerage systems, pre-treatment approach, payments and applications of ISKI will be referred. Additionally, the distribution of industries among sectors, and their establishment of pre-treatment plants have been studied. The wastewater treatment methods that are used in the established treatment plants have been evaluated.


ISKI, Discharge of industrial wastewater to sewer system, Discharge Criteria, Pre-treatment, Payments.


The industries with inappropriate wastewater characterization and with those that are not allowed to directly discharge their influent to sewer systems by the administrations like residential site officials, municipalities, and water and sewerage authorities have to install and operate their pre-treatment plants both in developed countries and Turkey so as to comply with the limits and standards stated in the related regulations.

Water supply and wastewater discharges are regulated and monitored separately by the 16 Greater Metropolitan municipalities and 3215 municipalities. This application is found to be economically expensive, and difficulties are faced regarding their operation and maintenance (Samsunlu, 2005).

It is known that industrial activities have a major share in water pollution of Istanbul. Industries active in Istanbul constitute more than 50% of the country’s overall industrial potential. Istanbul is an example of a province with a big area having scattered constructions and residential sites. The industries established within this big area are scattered around in an unplanned manner. The main sources of pollution identified in the province are due to industries, and these industries lead to great and negative impacts on the environment compared to conventional pollutants like BOD and COD (Orhon, 1991).

Even though the terminology of industrial pollution has come to the scene so late, it has recently gained interest as Turkey is at the accession stage to join EU. Istanbul is the leading province of the country in the sense of industrial pollution, however, the Water and Sewerage Administration of Greater Metropolitan Istanbul (ISKI) has set its ‘Wastewater Monitoring and Control’ department in 1986. The regulations on industrial pollution have been stated in 1984. At these days, the number of pretreatment wastewater treatments systems was about 5-10, this figure has increased to 1568 in year 2005.

The industrial wastewater control and related penalties are defined in the Wastewater Discharge to Sewers regulation of ISKI. In the calculation of monetary payments to be taken from the industries are formulated quite easily compared to individual formulations of each polluter system valid in Ruhrverband region of Germany.

Limited information is present on how the sludge generated from the pretreatment systems is disposed. The sludge generated from the pre-treatment systems is not controlled by ISKI.


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.

In 23.05.1984 under the law referenced as 3009, the administration is joined to the Greater Metropolitan Municipality of the Province. Therefore, the mayor of the Province acts 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 referenced 5216 instead of 3030, 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. In addition to this new boundary, one district, 14 sub-districts and 173 villages are also included to the service area of ISKI. The overall area is 6504 km2 with a population of 12 million.

Figure 1. ISKI’s service area

Among the duties of ISKI,

  • Supply of domestic and industrial water,
  • Collection and discharge of wastewater and storm water,
  • Protection of water resources like seawater, lake, river coasts and groundwater from pollution with used water and industrial wastewater can be counted.

The list of materials that should not be disposed to sewer lines as well as the precautions to be taken to protect the drinking water watersheds of the Province are dictated in ISKI’s law and regulations.

The paper mainly focuses on the application of the ‘Discharge of Wastewater to Sewer Systems’. Besides, in cases where this regulation is not addressed, the ‘Water Pollution Control Regulation’ will be referred and based.

ISKI recently operates 2 advanced wastewater treatment (3%), 4 biological wastewater treatment systems (14%), and 7 marine discharge systems with pre-treatment (83%).

In these plants, 571 million m3 of wastewater and 89 million m3 storm water has been treated in year 2005.


The industries and enterprises established in Istanbul have to obey the ‘Discharge of Wastewater to Sewer Systems’ and those industries that do not comply with the discharge limits given in Table 1 are required to construct their pre-treatment systems. The values referred in this table are prepared under the light ‘Water Pollution Control Regulation’. Besides, detailed information is also given in Item 9 of this regulation on the list of materials that are not allowed to be disposed into sewer lines and/or to receiving water bodies (ISKI, 2004).

In the ISKI’s discharge of wastewater to sewer system has brought certain exceptions related to pre-treatment that will be explained below.

If in a wastewater collection catchment area, there exist a biological treatment system or designed, only the industrial wastewaters consisting of conventional polluting sources with COD parameter     < 4000 mg/lt does not necessarily need to install a pre-treatment system prior to discharge to sewers by complying with Item 9 of the regulation.

Industrial wastewater in wastewater catchments with < 0.5 m3 /day or equal to this amount does not require individual pre-treatment. Precautions like water curtain, hammer, etc. is required. In case of no precautions taken, ‘polluter pays principle’ (KOP) is applied. After the allowed period if no improvements are realized, the industrial activities are ceased.

Table 2 is an operation evaluation table of industries active under the control of ISKI (ISKI, 2005). The evaluations are based on the water sample measurements.

Table 1. ISKI’s Discharge Limits to Sewer System

Parameters (mg/lt) Values
COD 800
Suspended matter 350
Total Nitrogen 100
Total Phosphorous 10
Oil/grease 100
Arsenic 10
Antimony 3
Tin 5
Boron 3
Cadmium 2
Total chromium 5
Copper 5
Lead 3
Nickel 5
Zinc 10
Mercury 0.2
Silver 5
Total Cyanide 10
Phenol 10
Fish Bioassay (48 hours tolerance limit) 100%
Sulphate 1700

In the column of ‘No requirement for a wastewater treatment plant’, some of the industries transporting their wastewater to another wastewater treatment plants and those that have already taken the proposed precautions by ISKI are also given. Table 3 gives information on the methodology of treatment applied on the listed industries.

Table 2. Evaluation of industries and enterprises of Istanbul according to sectors

Sector Active Generating industrial wastewater With wastewater treatment plant Requiring wastewater treatment plant No requirement for a wastewater treatment plant
Food industry 279 166 61 14 90
Metal industry 1831 760 540 90 225
Chemical industry 889 343 168 23 151
Textile industry 844 515 373 45 95
Leather industry 49 15 7 8
Petroleum and coal based industry 1383 1088 204 43 840
Mineral industry excluding metals 471 355 193 33 121
Wood based industry 110 23 9 32 14
Others 215 21 13 5 5
TOTAL 6071 3286 1568 285 1549

Table 3. Applied Treatment Methodology in the Industries of Istanbul

Type of Treatment % distribution
Mechanical 14
Chemical 57
Biological 8.6
Chemical + biological 4.9
Mechanical + chemical 3.4
Neutralization 7.6
Evaporation 8.3


The conditions of payments required from the industrial discharges will be referred below:

The effluent of the industrial wastewater is controlled by ISKI regarding the stated limits. To those industries that have already installed their treatment plants and to those that do not require installing a wastewater treatment system are identified and their ‘Discharge Quality Control Licence’ (DKKR) are given. The licence is valid for 3 years and must be renewed after this period. 

DKKR payment = 1,5FbQKmax

is calculated by the formula given above, where

F      : flow rate factor = 2400 (constant value)

b      : cost coefficient = 452 YTL/m3

This coefficient is fixed every year by the Administrative Board of ISKI. The value given here is valid for year 2006.

Kmax: a coefficient on pollution prevention share.

This coefficient is fixed for each sector by the Administrative Board of ISKI. The values are stated in the Annexes of ‘Discharge of Wastewater to Sewer Systems’ regulation of ISKI.

In the applications of the western countries, the payments of the industries are accepted as investment shares of new treatment systems and as operation and maintenance cost shares. ISKI, on the other hand, joins these to contributions in a single item and takes it from the users under ‘wastewater payment’ (Uslu, 1991).

The industries that have already installed their wastewater treatment plants or those that do not need to install such plants have to pay 1.5 YTL/m3 of clean water and in addition to that amount, 1.5 YTL/m3 for wastewater discharges.

In the regulation of ISKI, it is stated that industries with wastewater discharges above the minimum amount stated and/or with wastewater characteristics high above the discharge limits to sewer system are required to install pre-treatment systems. The industries that are required to install pre-treatment systems, or those having pre-treatment systems but not operating it, or those that have not installed the pre-treatment systems in the allowed time limit, or those that have installed the pre-treatment systems but still not complying with the stated limits have to pay pollution prevention shares  till the limits are obeyed or else till the activity ceases. Same conditions hold true for those who prefer to construct septic tanks.

The formula used for various conditions of pollution prevention share is described below:

  1. Pollution prevention share of those industries that have not installed their pre-treatment systems:



KOP: share of pollution prevention (YTL)

T      : period for the payments (day). This period is calculated according to related items of the regulation.

B      : unit payment (YTL/m3) (0.2 YTL/m3) (decided by the Administrative Board)

Q     : flow rate of industrial wastewater

Kmax: coefficient of the share of pollution prevention payment (the coefficient is decided by the Administrative Board of ISKI under the light of all technical and scientific based calculations for the parameters of each sector or sub-sector).

Also, for the industries whose wastewater characterization cannot be done, the calculation method of the Kmax is described in the regulation.

  1. The  is calculated according to the below given formula for cases where there exist a pre-treatment or treatment system with insufficient treatment or in cases where they are not under operation:

KOP = 30 BQKa


Q     : flow rate of the industrial wastewater (m3/day)

30    : T (time) applied average time when two sequencing analysis results do not comply with the limits (time/day)

Ka = (Ca – Ct)

Ca    : average concentration of two sequencing analysis results giving the maximum (Ca – Ct)/Ct ratio that form the basis for non-compliance (mg/lt)

Ct     : limit value given in the Discharge Limits to Sewer System or in the Water Pollution Control Regulation (mg/lt)

The Ka value is taken as,

Ka = Ka when Ka <   Kamax

Ka = Kamax when Ka >Kamax

 and Kamax values are stated in the regulation. cannot be taken by the evaluation of only one set of sampling analysis. The flow rate of industrial wastewater that forms the basis for KOP is defined in the regulations as well as the calculation methods. pH is the prerequisite parameter that should be satisfied. For those industries not satisfying the pH parameter are given an extra time of 15 days to fulfil the pH requirement. If the industry still does not meet the limits by evaluating the average of the sequential analysis results, then a written notice is delivered to the industry. Moreover, if the same situation is continued for the following two sequential analysis results, the industry has to cease operation.

  1. If the existing wastewater treatment is not operated due to a trouble, or if the industry directly discharges its wastewater without treatment either to the sewer system or directly to a receiving water body, an extra 2 months to recover the system is given to the industry. In case of no change in the system after the termination of the allowed time, the industry is asked to cease its operation. Till the industry recovers itself in the calculation of , 1 is added to Kamax value.

In the annexes of the ‘Discharge to Sewer System’ regulation, the Kamaxvalues for various important industrial sectors are dictated. For example, this coefficient is taken as 1 for non-alcoholic drinks industry, whereas it is taken as 5 for washing, processing of raw leather industry and for electro plating industry. In this manner, the pollution strength of wastewater is taken into account.

In Germany, in the Ruhrverband region the below mentioned formulations are considered, however this methodology is not favoured by ISKI due to its difficulty in monitoring and control.

Ruhrverband authorities have decided to follow the below given expressions for the calculation of the payments to be asked from the industries (Bode, 1998; Grunebaum 2002). In the formula not only the domestic wastewater load of 60 g/BOD5/day is considered. The other related parameters like COD, reduced nitrogen (Norganic + NH4-N), oxidized nitrogen, inorganic suspended matter (SSmin), and total phosphorous are also taken into account. Also, some other properties of the plant are considered. An example to that fact is considering heavy metals in metal finishing industries.


E            : evaluation in the form of evaluation equivalents, roughly corresponding to the load caused by the domestic sewage of one inhabitant

Qa        : sewage quantity

COD   : organic substances, fixed as chemical oxygen demand

BOD5  : organic substances, fixed as biochemical oxygen demand

SSmin    : mineral proportion of suspended solids   

Ptotal    : phosphorus total  

Nred      : reduced nitrogen  

NOXN: nitrate and nitrite nitrogen  

F(COD/BOD): correction function

The individual expenditures for wastewater and sludge treatment are assigned to the specified treatment targets and to the above given criteria. Prerequisite for this approach is a precise definition and weighting of treatment objectives as well as their translation into cost-relevant items. In principle, the most efficient tool to succeed on this route is to manage an entire catchment area and to use the resulting synergy effect [Bode and Grünebaum, 2000]. Against this background it becomes evident that it may be helpful to also evaluate cost aspects in any planned or required effort to reduce emissions. Under average conditions, the expenses for municipal sewage treatment can be assessed as substance-related variables. Accordingly, the costs incurred in German municipal sewage treatment plants may be quantified as follows [Grünebaum, 2001]:

  • 4 to 8 € per kg of eliminated nitrogen (Ntotal)
  • 2 to 5 € per kg of eliminated nitrate-nitrogen (Noxidised)
  • 8 to 20 € per kg of eliminated phosphorus (Ptotal)
  • 0.2 to 1 € per kg of eliminated organics, determined as chemical oxygen demand

These cost data must be added up so that a genuine monetary comparison of achieved environmental benefits – expressed as load reductions of the above listed pollutants – can be established.

Impacting variables are for one thing the conditions already outlined above, and for another in particular the specified targets with regard to the treatment performance of the wastewater treatment plant. At this point it should be noted that any effort to eliminate the ‘very last milligram’ of loads would increase the cost. The above listed substance-related costs comply with the European Urban Wastewater Directive for sensitive areas.


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 amount of year 2005 was 56 593 tones. The disposal site and the disposed amounts arising from the pretreatment systems are 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).


The industrial plants located in Istanbul have to effectively fully treat/partially their industrial wastewater in a way to prevent the environment from further pollution. The existing Environmental Law, and the regulations on ‘Water Pollution Control’, ‘Discharge limits to Sewer Systems’ and the ‘Protection and Control of Drinking Water Catchments’ state the corresponding limits. ISKI has taken under control almost all existing industrial plants in Istanbul and only there are 285 industrial plants requiring pretreatment systems.

Most of the established pretreatment systems are chemical treatment systems followed by mechanical and biological systems. The industries with efficient wastewater treatment systems and the ones that have no necessity to install treatment plants have to pay wastewater cost in the same amount as they pay for the water supply. Both water and wastewater costs are paid at the same time.

The industries that have a pretreatment system and the ones that need to install pretreatment systems have to pay . ISKI has already initiated a simple and easy formulation to calculate  quite different from the application in western countries where each polluting parameter is considered in detail.

The disposal methods and sites of sludge arising from pretreatment systems are unknown. In order to solve this problem, ISKI has planned to construct two incineration plants and one hazardous waste disposal site in Istanbul. It is very urgent to establish these plants.

ISKI has already taken almost all the existing industries under control in Istanbul by applying the ‘Discharge Limits to Sewer Systems’, however, should frequently control and monitor these industries and in the long run, the discharge limits must become more stricter like in EU countries for industries like metal finishing industry whose influent highly pollutes the surface waters.

ISKI has also to rearrange its legal enforcements so as to undertake the responsibility of controlling and monitoring the influents of Organized Industrial Districts (OID). The OIDs are active according to a special law and thus, their discharges are not controllable by ISKI.


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Bode, H. and Grünebaum, T. (2000) The cost of municipal sewage treatment – structure, origin, minimization of fair cost comparision allocation, Water Science and Technology, 41(9), 289-298.

Grünebaum, T. (2001) Approaches to monetary evaluation of pollutant loads in waterbodies, IWA World Water Congress, Berlin, October 15-19th 2001.

Grünebaum, T. (2002). Overview of International Best Practice Concerning Organizational Structure and Cost Recovery Systems for Large Wastewater Treatment Plants, SamPraCor International Conference “Wastewater Management from a Thai Perspective”  Bangkok, 4 March 2002.

Orhon, D. (1991). Design of Pretreatment Systems, Pretreatment of Industrial Wastewaters, Turkish Committee on Water Pollution Research- Istanbul Chamber of Industry publication, Istanbul. (in Turkish).

Samsunlu, A. (2005). Regional Management Associations and Infrastructure Plants, 6th Environmental Engineering Congress, Turkish Chamber of Engineers and Architects- Environmental Engineers Publication, Ankara. (in Turkish).

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Uslu, O. (1991). Evaluation of the various proposals for ‘Discharge Limits to Sewer Systems of ISKI’, Turkish Committee on Water Pollution Research- Istanbul Chamber of Industry publication, Istanbul. (in Turkish).

“Environmental Law”, Official Newspaper dated: 09.08.1983, Reference number: 2872.

Regulation of “Water and Sewerage Administration of Istanbul” (ISKI), 2004.

“Regulation on Urban Wastewater Treatment”, Ministry of Environment and Forestry, Official Newspaper dated: 08.1.2006, Reference number: 26047.

“Water Pollution Control Regulation”, Ministry of Environment and Forestry, Official Newspaper dated: 31.12.2004, Reference number: 25687.

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