Desalination 226 (2008) 231–248

Presented at the 10th IWA International Specialized Conference on Diffuse Pollution and Sustainable BasinManagement, Istanbul, Turkey, 18–22 September 2006.

Critical evaluation of wastewater treatment and disposal strategies for Istanbul with regards to water quality

monitoring study results

Erdogan Okusa, Izzet Ozturkb*, Halil Ibrahim Sura, Ahsen Yukseka,Seyfettin Tasa, Asli Aslan-Yilmaza, Husne Altioka, Nuray Balkisa,

Ertugrul Dogana, Suleyman Ovezb, Ali Fuat Aydinb aInstitute of Marine Science and Management, University of Istanbul, Vefa 34470, Istanbul, Turkey

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

Tel. +90-212-285 3790; Fax +90-212-285 3781; email: iozturk@ins.itu.edu.tr

Received 27 December 2006; revised accepted 12 February 2007

Abstract

Urban Wastewater Treatment and Marine Outfall Facilities are being planned in accordance with IstanbulWater Supply and Wastewater Treatment and Disposal Master Plan prepared for Istanbul Water and SewerageAdministration (ISKI) in 1999. According to the Master Plan, ISKI initiated in 1996 the water quality monitoringprogram of receiving water bodies conducted by the Istanbul University (IU) Institute of Marine Sciences andManagement and Istanbul Technical University (ITU) Environmental Engineering Department. The monitoringprogram has been carried out for 10 years in 28 stations in the marine environment. In this paper, the results ofexperimental investigations conducted for parameters including dissolved oxygen, total organic carbon (TOC),particulate organic carbon (POC), Total-N, Total-P, chlorophyll a, structure of benthic community, turbidity andcoliforms have been critically analysed taking into consideration the marine outfall and surface water dischargesfrom Istanbul’s major wastewater treatment plants together with the transboundary pollution sourced by the BlackSea. The studies reveal that the water quality in the Marmara Sea is deteriorated more than anticipated before, andit is a necessity to develop international cooperation aimed for taking more effective measures in the area.

Keywords: Water quality; Biodiversity; Eutrophication; Monitoring; Transboundary effects; Two-layer flows

*Corresponding author.

0011-9164/06/$– See front matter © 2008 Published by Elsevier B.V.doi:10.1016/j.desal.2007.02.109

232 E. Okus et al. / Desalination 226 (2008) 231–248

1. Introduction

Istanbul is the largest city in Turkey currentlyhousing around 15% of the population and 30%of industrial activities in Turkey within theboundary of its metropolitan area. Istanbul islocated along the shores of the Marmara Sea andthe Istanbul Strait (Bosphorus). The Istanbul Met-ropolitan Area is the largest contributor of pollu-tion in the Marmara Basin. The prevention ofpollution of the Marmara Sea–Bosphorus Systemis possible only if appropriate treatment and dis-posal techniques are defined and implemented forwastewater sources discharging into the system.

Istanbul Water and Sewerage Administration(ISKI) has let Istanbul Master Plan Consortium(IMC) to prepare a Master Plan for solving thewater supply, wastewater and storm water prob-lems in the Istanbul Metropolitan Area [1]. TheMaster Plan, a result of intensive engineering

studies for 6 years, proposes that secondarystage biological treatment should be applied atthe first phase and tertiary biological treatmentat the second phase for wastewater discharges tothe Marmara Sea. For wastewaters dischargedinto the Bosphorus, preliminary treatment isrequired for the first stage and chemicallyenhanced primary treatment for the second stage.The Master Plan suggestions developed througha modeling study conducted by Danish HydraulicInstitute (DHI) for the Marmara Sea–BosphorusSystem water quality [2]. Oceanographic dataobtained by the Middle East Technical Univer-sity (METU) for years 1986–1989 [3], has beenused to a major extent. The existing situation ofthe wastewater treatment and marine outfallfacilities set in the ISKI Wastewater Master Planis summarized in Table 1. According to the table,more than 75% of the domestic and industrial

Table 1Proposed Wastewater Treatment Facilities by Istanbul Wastewater Treatment and Disposal Master Plan [2]

BMJ: Bosphorus–Marmara Junction, S: screening, U: upper level (surface discharge), P: preliminary (screening + aer-ated grid chamber), L: lower level, 2: secondary stage biological treatment, SD: surface discharge, 3: tertiary stage bio-logical treatment (BNR),acombined with Ambarli WWTP.

WWTP Discharge medium Treatment level Average design flow (m3/d) Present situation

Yenikapi BMJ (L) P 424,000 OperatingKadikoy BMJ (L) P 286,000 OperatingUskudar Bosphorus (L) S 44,000 OperatingKucuksu Bosphorus (L) P 118,000 OperatingBaltalimani Bosphorus (L) P 241,000 OperatingPasabahce Bosphorus (L)/SD P 17,000 Under constructionB. Cekmece Marmara (L) P 61,300 OperatingGuney K. Cekmece Marmara (L) P 41,000 OperatingTuzla Marmara (L) 2 274,000 OperatingAtakoy Marmara (L)/SD 2/3 174,000 Under biddingAmbarli Marmara (L)/SD 2/3 93,000 Under biddingKuzey K. Cekmecea Marmara (L)/SD 2/3 196,000 Under biddingIslands Marmara (L) P 4760 OperatingBeyond B. Cekmece Marmara (L) P 31,200 OperatingPasakoy Black Sea (U) 3 146,000 Operating

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wastewaters generated within the Istanbul Met-ropolitan Area are currently connected to pre-treatment and sea outfall systems. However, 25%of the wastewater of the total city population isdischarged via creeks into the Marmara Sea andBosphorus coastal waters. The construction ofthe mentioned major facilities is currently at thebidding stage.

Together with the ISKI Wastewater MasterPlan, water quality monitoring program hasbeen initiated in year 1996 in order to guideMaster Plan applications and especially investi-gate the pre-treatment level and implementationschedule through regularly monitoring the effectof Istanbul discharges on receiving water bod-ies. In the study conducted with the joint effortsof the Istanbul University (IU) Institute ofMarine Sciences and Management and IstanbulTechnical University (ITU) Environmental Engi-neering Department, basic oceanographic, waterquality and biological parameters have beenmonthly monitored for water column for a totalof 28 stations. This paper presents a criticalevaluation of the action plan and implementa-tion schedule for Wastewater Treatment and SeaOutfall Facilities proposed in the ISKI MasterPlan with regards to the water quality monitor-ing program conducted for a period of 10 yearsbetween 1996 and 2006.

2. Properties of Marmara Sea and the Turkish Straits system

The most significant characteristic of theTurkish Straits system that consists of Dar-danelle and Bosphorus is the two layered flowseparated by the terminating “pycnocline”. Lesssaline upper layer waters of the Black Sea flowthrough the Straits System to the Aegean Sea,while more saline Mediterranean Sea watersflow to the Black Sea via the lower layer in theopposite direction.

With the assumption of the two-layered StraitsSystem, the average water transfer between topand lower layers could be estimated with amodel that takes into account the water and salin-ity budgets. Water transfers based on the annualaverage salinity values are presented in Fig. 1 [4].Ratio of upper to lower layer of Bosphorusremains almost 2/1 averagely. On the otherhand, when the strong northern winds areobserved in the region, this ratio reaches 9/1 [5].As it is seen from Fig. 1, some part of wastewa-ter discharged into lower layer of BosphorusMarmara Junction (BMJ) and Bosphorus waterreturns to Marmara Sea by mixing with theupper layer.

The basic criterion that determines the flowsin a Strait is the difference in the water levels ofthe two ends of the Strait. According to average

Fig. 1. Turkish Straits system flow structure.

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sea level, when the difference varies from +45to −10 cm, top and lower flows could beblocked out totally. The occurrence percentagesof such blockages (especially the lower layerblockage) present significance in evaluating therisks created by wastewater discharges. Existinginformation specify that the lower layer block-age is observed in approximately less than 10%of the year. Based on the monthly flow measure-ments conducted since 1999, the lower layerflow reaches near blockage conditions only 2times for 7 years [5].

3. Evaluation of pollution loads

3.1. Sources polluting the Marmara Sea

3.1.1. Point sources

Pollutant loads including industrial effluentsdischarged to the Marmara Sea from Istanbulmetropolitan area is given in Table 2. Shares ofpolluting loads discharging from Istanbul metro-politan area into Marmara Sea, Bosphorus–Mar-mara Junction and Bosphorus are 31%, 21% and48%, respectively. By considering the existing

wastewater and marine outfall facilities and dataobtained in 2005, it can be assumed that 45% ofthe discharges from Istanbul reach Black Seaand the rest remains in the Marmara Sea. Waste-water transfer to the Black Sea could be much inthe future as a result of discharging into lowerlayer of Marmara Sea instead of lower layer.BOD load resulting from Istanbul constitutes70% of the total BOD load discharged into theMarmara Sea [6]. Today the share of Istanbul onthe pollution of Marmara Sea is not less than 2/3of the total pollution. Therefore, it can be con-cluded that the Marmara Sea will be secured to amajor extent when the pollution from Istanbulalone is controlled.

3.1.2. Diffuse sources

In a study conducted on the pollution load ofstormwaters resulting from the residential areaswithin Istanbul’s provincial boundaries, resultswere obtained using US EPA Storm Water Man-agement Model (SWMM) in 1995 and are pre-sented in Table 3 [7]. Pollution load havingapproximately 1 × 109 m3/year of flowrate froma settlement area of 130,000 ha has been dis-charged into the Marmara Sea and Strait waters.In year 2032, by which all of the planned devel-opment areas of Istanbul are expected to reachsaturation, stormwaters resulting from residen-tial areas will reach 1.8 × 109 m3/year. By year2032, pollution loads carried by stormwaterswill reach 120%, 20%, 40% and 30% consecu-tively for parameters of SS, BOD5, Total-N, andTotal-P. Therefore, it is essential that the pollution

Table 2Polluting loads discharging from Istanbul into MarmaraSea and Bosphorus (2005 data)

BMJ: Bosphorus–Marmara Junction.

Pollution source Polluting loads (t/day)

BOD5 SS Total-N Total-P

Marmara (31%) Upper layer 133.2 159.7 20.0 4.0 Lower layer 27.9 33.4 12.7 2.4

BMJ (21%) Upper layer – – – – Lower layer 109.7 131.7 35.5 3.5

Bosphorus (48%) Upper layer 4.9 5.9 0.7 – Lower layer 178.9 214.5 28.5 5.8 Total 454.6 545.2 97.4 15.7

Table 3Diffuse pollution loads resulting from stormwater inresidential areas (t/day)

Year SS BOD5 Total-N Total-P

1995 246 32 10 1.2

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resulting from the storm water collection systemtogether with domestic wastewaters should beeffectively managed.

3.2. Transboundary pollution carried by the Bosphorus upper flow

A significant amount of nutrients taken bythe big rivers ending up in the Black Sea andpollution loads of the wastewater discharges inthe western and northern coasts of the Black Seaare carried down to the Bosphorus through pre-vailing natural geostrophic currents in the region.The Black Sea has been exposed to high levelsof pollution mainly through Danube and DnieperRivers. As a result of this fact, a significant amountof pollution is being continuously fed to theMarmara Sea through upper current of the Bos-phorus. Data from K0 station, which is BlackSea inlet of Bosphorus, and average values ofTOC, POC, Total-N and Total-P of upper andlower layers of Marmara for the years 1996,2000, 2005 are given in Table 4. According toTable 4, transboundary polluting loads in Mar-mara Sea, originated from the Black Sea, are4470 t TOC/year (6150 t BOD5/year), 84 t Total-N/year and approximately 17 t Total-P/year,respectively. This means, transboundary pollu-tion from Black Sea is 14, 0.9 and 1.1 times oftotal polluting loads of discharges from Istanbul

into Marmara Sea in terms of BOD5, Total-Nand Total-P, respectively. Pollution generatedfrom the Marmara Sea carried by the lower layerflow of Bosphorus to Black Sea is 1418 t TOC/year, 1950 t BOD5/year, 81 t Total-N/year and3 t Total-P/year. As it is given in Fig. 1, a flowof 19,100 m3/s and 9600 m3/s is accepted asaverage of upper and lower layer of Marmara inthe calculation of pollution loads. Since, theratio between pollution loads generated in BlackSea and carried to the Black Sea is approxi-mately 3.2, transboundary pollution loads fromthe Black Sea threatens the quality of MarmaraSea significantly.

The lower current from the Marmara Sea headsbelow the halocline layer of the Black Sea start-ing at the outlet of the Bosphorus. Since almostthere is not any material transfer at the Black Seabetween layers below and above the halocline,The Black Sea top layer water quality remainsunaffected except for a limited area at the outletof the Marmara Sea. As it is known, the lowerlayer of the Black Sea, constituting 90% of thetotal volume, is anoxic for many years.

3.3. Extent of pollution

Dissolved oxygen concentration of the 10 cmthick top layer of the Marmara Sea is close tothe saturation limit. In the lower layer that is 30 mbelow the surface, there exists a chronic defi-ciency of dissolved oxygen (20–30% of saturationlevel). However, in the Marmara Sea, which hasan average dissolved oxygen concentration of2 mg/L, the minimum dissolved oxygen valuehas not dropped below 1 mg/L at any location[8]. The pycnocline layer between 10 and 30 mis a transition area where dissolved oxygengradually decreases.

Low dissolved oxygen concentrations at thelower layer is due to the excess consumption ofoxygen during biochemical decomposition ofthe detritus (organic material, N and P based)formed through primary production process.

Table 4Polluting parameters average for upper and lower layersin the Black Sea side of Bosphorus (Station K0)

Station K0 Year Parameters (μg/L)

TOC POC Total-N Total-P

Upper layer 1996 2770 240 188.7 11.1 2000 2660 210 202.3 11.0 2005 2710 – 50.9 10.0

Lower layer 1996 1260 90 180.7 32.0 2000 1330 140 275.7 32.0 2005 1710 – 98.2 47.4

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The total primary production is equivalent to 1.2million tons of carbon in overall Marmara, ofwhich 20–30% passes down to layers belowhalocline to be decomposed at a percentage of85% [1]. This situation could be observed in allsummer months at which the dissolved oxygenconcentrations are between 1 and 2 mg/L. In thewinter period, the dissolved oxygen concentra-tions are above 1.5 mg/L.

In the north of Bosphorus surface waters,fecal coliform concentrations are very low. How-ever, as going south, the fecal coliform numbersreach 500/100 mL at the Ahirkapi-Kadikoy region.The high coliform values (100–5000/100 mL)in the lower layers of the Bosphorus are due toIstanbul marine outfalls at Yenikapi, Kadikoy,Uskudar, Baltalimani and Kucuksu.

Near the outlet of the Black Sea and theBosphorus, nitrogen and phosphorus formshave been measured. In these measurements,nitrate concentrations reach maximum values at50–150 m depths. In deeper regions, both thesurface and lower layer concentrations aredeclining. The decrease in the layers below thehalocline is due to the denitrification of oxidizednitrogen transforming into nitrogen gas inanoxic conditions. Therefore, ammonia and H2Sproductions start at these depths. Phosphorusconcentrations increase below 100 m depths andreach 5 μg/L in the anoxic layer [1].

Nitrate in the lower layer is considered to bea buffer between limited dissolved oxygen andanoxic bottom parts where denitrification couldtake place. An important reason of the high con-centrations at the lower layer is the nutrientsresulting from the decomposition of the detritusthat settle down from the top layer. The sedimentsat the bottom are another depot for nutrients.

The Marmara Sea remains to be a sedimenta-tion basin for particulate organic carbon (POC)generated through primary production. Daily andannual primary production and the change ofchlorophyll a in the period of 1985–1989 havebeen calculated by METU [3] as 0.2–0.3 gC/m2

for average primary production. This amount isequivalent to 1 millions tons of carbon per yearand is close to 1% of the carbon producedthrough primary production in the Black Sea.About 70–80% of this organic load resultingfrom primary production mineralizes in the toplayer and the remaining portion settles down tolayers below the halocline where they can bemineralized. Among the 20–30% of the organicload that passes through the layers below halo-cline, 85% of it mineralizes and the nutrientsmight be recycled back to the top layer. Finally,the remaining 12% can be buried in the sediment.

Especially the Marmara surface water eco-logical system is intensely affected by the plank-tons carried from the Black Sea upper layerthrough the Bosphorus. The relatively highprimary production and chlorophyll a valuesresulting by the effect of the Black Sea graduallydecreases towards the Canakkale Strait. Themeasurements concerning trophic conditions inthe Marmara Sea, the Black Sea, and variousother seas around the world is given in Table 5.

4. Objectives and strategies of Istanbul Wastewater Master Plan

Istanbul Master Plan Consortium consistingof international and local engineering and con-sultancy firms has prepared in 1993–1999 theWater Supply and Wastewater Treatment/Dis-posal Master Plan to determine water supply andwastewater treatment demands of Istanbul forthe period of 2000–2040 for the Istanbul Waterand Sewerage Administration [1]. The funda-mental targets and strategies of the Master Planis summarized in the following sections.

4.1. Protection of Marmara Sea

4.1.1. Beneficial use

Commercial and recreational use of theMarmara Sea has evolved over the years. Otherbeneficial use of this interior sea can be listed as

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swimming, water sports, fishery, production ofaquatic products, transportation, harbour services,fresh water supply and wastewater disposal.

Master Plan propose wastewater treatmentand disposal strategies that make possible tocontrol the pollution of Marmara Sea up to itsnatural assimilation capacity.

4.1.2. Water quality objectives

Water quality objectives listed below set thebasis to sustain commercial and recreational useof receiving water body in the future:

Microbial quality: Total coliform concentra-tions will be less than 1000/100 mL and fecalcoliform will be less than 200/100 mL in the90% of water body samples from the protectionzone as specified by the EU Bathing WaterDirective [9] and the National Water PollutionControl Regulation [10].

Dissolved oxygen concentration: Maintainingthe dissolved oxygen concentration at the requiredlevel in the receiving body, as continuing fisheryand rehabilitation of unacceptable septic condi-tions in some parts of the shoreline is essential.

Eutrophication control: In the dischargedwastewater, N and P should be under the control

in order to improve fishery, hold the reductiontendency of dissolved oxygen concentration andamend the esthetical view of Marmara Sea.

4.1.3. Water quality standards

Discharge limits, given in Table 22 andTable 25 of Water Pollution Control Regulation[10], will be satisfied after preliminary and pre-treatment of wastewater discharging into Bos-phorus. On the other hand, biological treatmentof discharges into Marmara Sea will satisfy thelimits as defined in Table 22 and Table 21.3(BOD5 = 45 mg/L, SS = 30 mg/L) of the sameRegulation. In addition, objective of the MasterPlan is to satisfy standards of EU Urban Waste-water Treatment Directive [11] for the dischargesinto sensitive zones starting from 2010.

4.2. Modelling study on receiving water body

A modelling study was conducted by ISKI in1993 for the purpose of investigating the impactsof discharge alternatives on the ecosystems ofthe seas surrounding Istanbul. The model namedas System 3 had been developed by DanishHydraulic Institute (DHI) as a 3D hydrodynamic

Table 5Comparison of trophic condition of Marmara Sea with the other water bodies (considering 2005 data)

a1990 figures.

Location Chlorophyll a (μg/L) Total-P (μg/L) Total-N (μg/L) Secchi disk depth (m)

Marmara SeaUpper layer 0.5–15.4 (2.7) 7.7–106.6 (23.2) 11.8–266 (53.6) 1.8–16.5Lower layer 0.06–4.8 (0.8) 10.5–87.4 (35.0) 12.0–468 (82.5)

BosphorusUpper layer 0.5–1.5 (0.9) 4.3–26.6 (10.5) 16.7–119.6 (49.0) 3.3–13.8Lower layer 0.04–1.2 (0.6) 16.7–80.2 (48.9) 28.6–221.6 (94.7)Dardanelles 0.2–1.7 (0.7)a 1.95–20.2a 16–110a

Black Sea Upper layer 0.45–2.2 (1.1) 4.0–11.2 (8.1) 20.9–74.5 (65.8) 6.8–15.6Lower layer 0.25–1.4 (0.5) 5.3–44.6 (18.0) 19.3–186.6 (70.6)

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model [2]. System 3 is used to analyse the impactsof discharge alternatives on receiving waterbodyby means of the focal points listed below: • Determination of the stratification and mix-

ing conditions within the period of hydrody-namic simulation run for the typical flow.

• Simulation of coliform concentration in thereceiving waterbody for varying pollutionload and discharges.

• Simulation of BOD5 and dissolved oxygenconcentration in the waterbody for varyingpollution load and discharges.

• Simulation of general trophical state of theMarmara Sea for varying pollution load anddischarge scenarios.

4.2.1. Results of modelling studies

As a result of modelling study, informationregarding the discharges from Istanbul to the seahas been obtained. Results of DHI ModellingStudy [2] are summarized below:

Risk of discharges returning back to the Mar-mara with surface flows should be minimized.When the discharge depth is 60 m, it is esti-mated that the 10% of the discharge returns.When discharging from Kadikoy, almost 100%of the discharged material returns to MarmaraSea due to reverse subflows and blockage by thewind (Table 6).

After biological treatment, all discharges intoMarmara Sea will satisfy the standards of EUUrban Wastewater Treatment Directive [11].

Untreated wastewater discharges into Mar-mara Sea will lead reduction of dissolved oxy-gen concentrations. Especially at Tuzla andKucukcekmece discharge points where currentvelocity is too slow, reduction of dissolved oxy-gen concentrations is too high at the primarymixing zone.

Dissolved oxygen concentration of theMarmara Sea will be slightly affected from thelower layer biologically treated wastewaterdischarges.

Table 6Ratio of discharges entering the Bosphorus and carried down to the Marmara Sea

Holding level: depth of submerged wastewater field.

Scenario Best conditionsreflecting two-layer flow (%)

The design periodrepresenting the summer season (%)

The worse blockage condition where the leveldifference of the Marmara andthe Black Sea > 0.40 m (%)

Averagestablecondition(%)

Discharge to the Black Sea Bosphorus lower discharge

Scenario 0 holding level — 50 m<0.1 34 100 11

(Alternative holding level — 60 m)(inside the channel)

(<0.1) −10 −33 −3

Discharge to Bosphorus Kadikoy (lower layer, holding at

35 m) Scenario 6 8 33 100 15

Yenikapi discharge, holdinglevel — 40 m

3 28 90 13

Baltalimani/Goksu discharge, holding level — 40 m

<0.1 12 40 4

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4.2.2. Wastewater treatment and disposal strategies proposed by the Master Plan

Short-term strategies (2000–2010): Someexisting data and DHI Model reveals that it ispossible to develop short-term wastewater dis-posal alternatives for Istanbul.

Modelling study shows that it is adequate toapply preliminary treatment (screening and aer-ated grid removal unit) for large-scale facilities(Yenikapi, Baltalimani, Kadikoy) and physicaltreatment (screening) for small-scale facilities(Uskudar, Kucuksu, Pasabahce) before discharg-ing into the lower layers of the Strait.

For the discharges into lower layers of Mar-mara Sea, it is much better to treat wastewaterbiologically (conventional activated sludge sys-tem as an initial stage) for especially eutrophica-tion control.

Medium and long-term strategies (after 2010):Tertiary biological treatment before discharg-ing into Marmara will be necessary to controleutrophication in Marmara Sea, which is acceptedas sensitive water body, and to decrease oxygenconsumption of pretreated wastewater discharg-ing to the Marmara Sea and Strait. The IMCMaster Plan proposes upgrading of pre-treatmentlevels to chemically enhanced primary treat-ment for WWTP's using the lower flows of theBosphorus as the final discharge environmentfor the medium-term.

4.3. Implementation of Wastewater Master Plan

Wastewater treatment and marine outfall sys-tems in the Istanbul Wastewater Master Plan final-ized in 1999 by IMC [1] are approved by ISKI.Fig. 2 shows the all the facilities of the systems.

Fig. 2. Sea discharge facilities of Istanbul according to Master Plan.

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In the Master Plan, before the discharginginto the lower layers of Strait, preliminary treat-ment (screening and aerated grid removal unit)at Kadikoy, Yenikapi, Baltalimani WastewaterTreatment Facilities, physical treatment (screening)at Uskudar and Pasabahce Wastewater TreatmentFacilities is recommended to be in compliancewith the short and medium-term master planstrategy. However, it is recommended to applyprimary treatment (primary settling tanks, sludgethickening, anaerobic sludge digestion andmechanical sludge dewatering) at Kadikoy andYenikapi located on the Marmara Sea inlet ofthe Strait where it is likely that almost 30% ofdischarged wastewater returns to the MarmaraSea in 5% of the year according to the modelresults. Except Pasabahce Wastewater TreatmentPlant, all facilities have been constructed andthey are in the operation.

Secondary stage biological treatment (conven-tional active sludge systems) before discharginginto the bottom layer of Marmara Sea is rec-ommended for Tuzla, Kucukcekmece, Atakoy,Ambarli and Buyukcekmece Wastewater Treat-ment Plants for medium-term. According to theresults of water quality monitoring studies of themarine environment, in the long run these facili-ties will be converted into tertiary biologicaltreatment plants where nutrient removal is done.Secondary stage biological treatment is sug-gested for Pasakoy and Tepeoren WastewaterTreatment Plants in the medium-term, and ter-tiary biological treatment in long-term. On theother hand, Pasakoy Wastewater Treatment Planwas constructed as tertiary biological treatmentplan. In addition to this, ISKI has recentlydecided to construct the two new WWTP's(Atakoy and Ambarli WWTP's) as tertiary bio-logical treatment and the general tendency ison the direction of implementing EU UrbanWWT directive limits to sensitive waters. Flowand pollution loads of wastewater treatmentplants proposed in the Master Plan are given inTable 1.

Atakoy, Ambarli, Pasabahce and Kucukcek-mece Wastewater Treatment Facilities havebeen constructed and facilities are planned to beoperated soon. By the end of 2005, 75% ofmunicipal wastewater has been connected towastewater treatment and disposal system.

5. Water quality monitoring study

Starting from 1996, ISKI has initiated awater quality monitoring program for guidingthe ISKI Wastewater Master Plan through moni-toring and assessment of environmental effectson the receiving waterbody resulting fromwastewater treatment and marine outfall facilities,and wastewaters discharged into the IstanbulStrait and the Marmara Sea. In the monitoringprogram conducted by the IU Institute of MarineSciences and Management and ITU Environ-mental Engineering Department, the variation ofoceanographic, biological, ecological, bacterio-logical and water quality parameters with depthtogether with the upper and lower layer currentvelocity profiles of the Bosphorus were investi-gated in monthly samples at a total of 28 sta-tions (Fig. 3).

In order to evaluate and present the broaddatabase obtained through the water qualitymonitoring program in a more simple and mean-ingful manner, the upper and lower layer aver-ages have been selected for the critical qualityparameters (DO, TOC, POC, Total-N, NO3

−,Total-P, PO4

3−, chlorophyll a and Secchi diskdepth) measured in a total of 8 stations (K0,B13, B2, M3, M23, MBC1, MY1, MKC) repre-sentative of the Bosphorus and the Marmara Seafor years 1996, 2000, and 2005. The results of thementioned water quality monitoring programare given in Table 7. The variation of valuesobtained in years 1996, 2000 and 2005 is alsoshown by a bar diagram in Figs. 4 and 5 for abetter understanding. The overall evaluation ofthe water quality monitoring results in terms ofselected parameters is presented below [12–14].

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5.1. Dissolved oxygen (DO)

The DO level in the upper layer is above7.5 mg/L and inclining in all stations. On theother hand, the lower level DO values are gener-ally within a range of 1.5–3.0 mg/L (average2.0 mg/L) with the minimum value of 1.0 mg/Lrecorded in 1996 at the M8 station. The 2005DO figures for lower levels are around 2 mg/Lwhich is equal to the long-term DO figure forthe Marmara Sea. The MKC and MY1 Stationsthat present low deep flow (current) velocitiesare of critical importance (Fig. 4(a)).

5.2. TOC and POC

In all stations the upper layer TOC level isapproximately 2.5 mg/L (≈3.4 mg BOD5/L). Inthe upper layer POC values from stations M23,MBC1 and MY1, increases that reach up to 50%compared to the stations in the Black Sea andthe Bosphorus. The difference could be a result

of the transition of Marmara Sea discharges andmarine outfalls at M23 and MY1 Stations intothe upper layer. The lower layer TOC values areconstant throughout the stations with approxi-mately 1.2 mg/L. The POC figures reach up to 50%greater than the Marmara Sea values (≈1.0 mg/L)near the Black Sea entrance as a result of mainlyIstanbul discharges (Fig. 4(b) and (c)).

5.3. Total-N and -NO3-

Values of total nitrogen are 200 μg/L on theaverage in the upper layer and 250 μg/L inlower layer at the Bosphorus and Marmara sta-tions; there is no significant difference betweenstations. Levels of NO3

− are 5 μg/L in upper layerof all stations due to high photosynthesis reactions.Lower layer NO3

− values have been decreasedup to 30 μg/L in the recent years. Similarly,upper layer NO3

− values at the Bosphorus andMarmara stations do not reflect major differences.The existence of aerobic conditions in lower

Fig. 3. Location of the stations.

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layers unable the formation of a suitable envi-ronment for denitrification (Fig. 4(c) and (d)).

5.4. Total-P and -PO43-

The upper layer total phosphorus values arelower in Bosphorus stations than Marmara.Nearly 200% high values (like 20 μg/L) areobserved in Marmara especially at MBC1 andMY1 stations compared to Bosphorus. Lowerlayer total phosphorus values are 40 μg/L in allstations and important increase in concentra-tions are observed in recent years. PO4

3− concen-trations are concurrent with total phosphorousconcentrations. Reason of the increase in totalphosphorus and PO4

3− concentrations in lowerlayers is the large amounts of wastewater dis-charged from Istanbul marine outfall facilities(Fig. 5(a) and (b)).

5.5. Chlorophyll a and Secchi disc depth

Chlorophyll a concentrations present rapidincrease starting from the entrance of Bosphorusdown to Dardanelles, similar to the case of POC.In MKC1 and MY1 Stations, the upper layerchlorophyll a concentrations are 2–4 times higherthat of Bosphorus. This situation is the reflectionof rapid primary production in the Marmara Seaand it is of concern in terms of eutrophication.Secchi disc depth has reverse correlation withchlorophyll a concentrations. Lower layer chloro-phyll a concentrations are approximately 0.5 μg/Lthroughout all stations (Fig. 5(c) and (d)).

5.6. Bacteriological quality

Analysis of total coliform, fecal coliform andfecal streptococci were conducted in samples ofsea water taken from surface discharge points in

Table 7Results for ten years of water quality monitoring studies

Station number Parameters

Dissolved O2 (mg/L) TOC (mg/L) POC (mg/L) Total-N (µg/L)

Year: 1996 2000 2005 1996 2000 2005 1996 2000 2005 1996 2000 2005

K0 8.982.43

9.392.62

10.062.64

2.771.26

2.661.33

2.711.71

0.240.09

0.210.14

188.7180.7

202.3275.7

50.998.2

B13 8.982.86

9.152.45

9.762.58

2.601.25

2.461.08

2.461.24

0.230.08

0.210.12

166.0179.0

201.8287.4

47.494.1

B2 8.852.52

8.352.11

9.592.74

1.821.04

2.341.15

2.511.16

0.100.11

0.160.07

190.6193.4

228.5263.3

44.887.6

M3 8.153.12

7.612.93

9.505.10

2.831.75

2.511.36

2.402.47

0.170.03

0.160.07

232.0136.5

216.5204.3

43.387.5

M23 7.911.65

8.441.75

10.022.27

2.761.07

2.391.35

3.491.54

0.240.03

0.270.02

191.6160.2

171.7253.8

49.081.0

MBC1 8.561.59

9.962.12

2.321.09

2.400.99

0.300.04

247.9327.7

42.085.2

MY1 8.901.91

9.811.71

3.000.98

2.491.15

0.340.05

255.8305.8

54.1107.9

MKC 9.846.90

2.551.84

63.160.2

E. Okus et al. / Desalination 226 (2008) 231–248 243

addition to selected stations, especially for mon-itoring bacteriological pollution in coastal waters.Analysis results show that bacteriological qualityis provided within the required limits of the WaterPollution Control Regulation [10] and EU BathingWater Quality Directive [9] in wide coastal areasexcept for the close impact zone of surface dis-charges [15]. Criteria of bacteriological qualityin surface discharges carried through some creeksis satisfied except for Baltalimani, Kucuksu,Goksu, Atakoy, Ambarli and North Kucukcekmece(Fig. 6). In this respect, wastewater treatmentand marine outfall facilities of ISKI present animportant role in Istanbul especially after 1994.

5.7. Benthic community structure

A total of 95 species from 13 groups weredistinguished at monitoring stations. There is a

notable separation of among species composi-tion and diversity between regions, due to dif-ferences in hydrodynamic processes, substratumand perturbation by man. Bosphorus stationsreceiving great pollutant loads of marine outfalldischarges have high diversity due to dominanthydrodynamic processes. On the other hand,coastal Marmara stations with weak waterexchange capacity, got polluted from the sur-face discharges especially, and benthic life hasvanished in the following years. According toBellan’s (1985) classification, only MY1 andM3 can be classified as zone I (deprived of allanimals), whereas other Marmara stations arein zone II (presence of few polycaeta species)and some (M8 and M14) in zone III (subnormalzone) [16]. Benthic studies reveals that dischargedwastewater quality should be improved atMY1 station where discharges from Tuzla and

NO3− (μg/L) Total-P (μg/L) PO4

3− (μg/L) Chlorophyll a (μg/L) Secchi depth (m)

1996 2000 2005 1996 2000 2005 1996 2000 2005 1996 2000 2005 1996 2000 2005

19.1102.3

3.942.4

6.828.7

11.132.0

11.032.0

10.047.4

5.329.2

3.920.3

4.131.7

1.60.4

3.10.8

0.70.6

7.5 8.1 9.9

20.788.7

5.044.9

7.127.9

12.732.2

10.739.1

10.654.5

5.323.2

3.519.7

5.033.1

1.60.6

2.40.6

0.90.6

7.4 7.6 8.1

18.1103.1

4.849.5

8.428.6

20.330.5

16.932.8

12.147.9

19.629.9

4.718.7

5.234.2

1.50.2

2.40.7

1.10.5

6.8 5.7 6.3

13.358.6

4.618.5

7.420.5

13.528.8

21.528.6

10.731.3

8.131.3

5.313.5

5.117.3

2.10.4

1.80.6

1.40.7

6.0 7.7

10.5124.9

4.6102.2

3.727.8

15.336.0

13.024.5

11.434.5

7.931.9

4.316.8

4.118.4

1.90.1

2.10.4

1.60.1

7.6 8.2

3.080.8

7.637.7

19.032.3

17.939.8

4.923.3

6.827.2

4.70.6

2.40.2

6.4 7.4

2.657.8

6.233.4

18.936.7

17.545.9

4.424.3

6.035.5

2.90.3

2.30.3

6.8 7.7

8.411.8

39.728.8

12.512.0

4.51.1

5.3

244 E. Okus et al. / Desalination 226 (2008) 231–248

Dissolved oxygen (upper)

0123456789

1011

K0 B13 B2 M3 MB M23 MBC1 MY1 MKC

1996 average DO (mg/L) 2000 average DO (mg/L) 2005 average DO (mg/L)

0123456789

1011

K0 B13 B2 M3 MB M23 MBC1 MY1 MKC

Dissolved oxygen (bottom)

1996 average DO (mg/L) 2000 average DO (mg/L) 2005 average DO (mg/L)

(a)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

TOC (upper layer)

0

0.501.00

1.502.00

2.503.00

3.50

1996 average TOC (mg/L) 2000 average TOC (mg/L) 2005 average TOC (mg/L)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

TOC (bottom layer)

0

0.501.00

1.50

2.00

2.503.00

3.50

1996 average TOC (mg/L) 2000 average TOC (mg/L) 2005 average TOC (mg/L)

(b)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

POC (upper layer)

0

0.05

0.10

0.150.20

0.250.30

0.35

0

0.05

0.10

0.150.20

0.250.30

0.35

1996 average POC (mg/L) 2000 average POC (mg/L) 2005 average POC (mg/L)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

POC (bottom layer)

1996 average POC (mg/L) 2000 average POC (mg/L) 2005 average POC (mg/L)

(c)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

TN (upper layer)

0

50

100

150

200

250

300

350

1996 average TN (µg/L) 2000 average TN (µg/L) 2005 average TN (µg/L)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

TN (bottom layer)

0

50

100

150

200

250

300

350

1996 average TN (µg/L) 2000 average TN (µg/L) 2005 average TN (µg/L)

(d)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

NO3 (upper layer)

0

20

40

60

80

100

120

140

1996 average NO3 (µg/L) 2000 average NO3 (µg/L) 2005 average NO3 (µg/L)

K0 B13 B2 M3 M23 MBC1 MY1 MKC

NO3 (bottom layer)

0

20

40

60

80

100

120

140

1996 average NO3 (µg/L) 2000 average NO3 (µg/L) 2005 average NO3 (µg/L)

(e)

Fig. 4. Changes in selected parameters at the monitoring stations during the study.

E. Okus et al. / Desalination 226 (2008) 231–248 245

pre-treatment outlet from Kucukcekmece Bayreach.

6. Concluding remarks

Results and suggestions in the light of scien-tific findings from the water quality monitoringstudy of IU and ITU since 1996 in order to mon-itor environmental impacts of the pre-treatment

and marine outfall facilities proposed in theWastewater Treatment and Removal MasterPlan of ISKI [1] on the Marmara Sea and theBosphorus, together with current surface dis-charges and transboundary pollutants generatedin the Black Sea, are listed below: • Around 2–4 times deterioration occurred in

trophic conditions in the upper layer ofthe Marmara Sea compared to 1990, due to

TP (upper layer)

0

10

20

30

40

50

60

1996 average TP (µg/L) 2000 average TP (µg/L) 2005 average TP (µg/L) 1996 average TP (µg/L) 2000 average TP (µg/L) 2005 average TP (µg/L)

(a)

1996 average PO4 (µg/L) 2000 average PO4 (µg/L) 2005 average PO4 (µg/L) 1996 average PO4 (µg/L) 2000 average PO4 (µg/L) 2005 average PO4 (µg/L)

(b)

Chlorophyll a (upper)

0

1

2

3

4

5

1996 average 2000 average 2005 average (µg/L)

Chlorophyll a (bottom)

0

1

2

3

4

5

1996 average 2000 average 2005 average (µg/L)

(c)

(d) Secchi disc

02468

1012

1996 average 2000 average 2005 average

K0 B13 B2 M3 M23 MBC1 MY1 MKC

TP (bottom layer)

0

10

20

30

40

50

60

K0 B13 B2 M3 M23 MBC1 MY1 MKC

PO4 (bottom layer)

05

10152025303540

K0 B13 B2 M3 M23 MBC1 MY1 MKC

K0 B13 B2 M3 M23 MBC1MY1 MKC

K0 B13 B2 M3 M23 MBC1 MY1 MKC

K0 B13 B2 M3 M23 MBC1 MY1

PO4 (upper layer)

05

10152025303540

K0 B13 B2 M3 M23 MBC1 MY1 MKC

MKC

Fig. 5. Changes in selected parameters at the monitoring stations during the study.

246 E. Okus et al. / Desalination 226 (2008) 231–248

preliminary treatment and marine outfall facil-ities proposed as short-term implementationsof the ISKI Master Plan, surface dischargeson coastal waters (equivalent to 25% Istanbul’spopulation) and transboundary pollution loadcoming from Black Sea.

• Level of dissolved oxygen in the lower layerof the Marmara Sea has never decreasedbelow 1.0 mg/L and is at the level of 2.0 mg/Lin general. Therefore, no suitable anoxic con-ditions exist for denitrification in MarmaraSea’s lower layer.

• Significant upgrading for bacteriological andphysical/aesthetics quality of coastal waterwere provided with preliminary treatmentand marine outfall facilities in Istanbul.

• Tuzla and Kucukcekmece marine outfallfacilities where deep current velocities are low,have negative impact on the water qualityand ecological life at the initial mixing zone.

• The query that the lower flow of Bosphorusreaches the Black Sea has proven to be irrele-vant. Complete blockage of lower flow is

observed only two times during the time spanof the monitoring program initiated in 1996.The lower flow reaches the Black Sea conve-niently in more than 95% of the time.

• Transboundary pollution from the Black Seadown to the Marmara Sea has not increasedin the past 10 years, however it still has sig-nificance [17]. The transboundary pollutiondetermined in terms of BOD5, Total-N andTotal-P parameters are 14, 0.9 and 1.1 timesthe load of pollution for Istanbul in 2005,respectively. The ratio of BOD5 loads carriedfrom the Black Sea and the Marmara throughthe upper and lower flows of the Bosphorusis 3.2 and transboundary pollution from theBlack Sea source (via the upper layer flowsof the Bosphorus) has great impact on thetrophic state of the Marmara Sea.

• Strategies and application schedule of ISKI’sWastewater Treatment and Disposal MasterPlan has been re-evaluated with scientificfindings of the current water quality monitor-ing program. In this sense, the pre-treatment

Fig. 6. Fecal coliform distribution of coastal stations along the strait of Bosphorus.

E. Okus et al. / Desalination 226 (2008) 231–248 247

facilities must be increased to tertiary biologicaltreatment (BNR process) until 2012 in Tuzla,and planned Ambarli, South Kucukcekmeceand Atakoy wastewater treatment plants.Therefore, all surface discharges into theMarmara Sea will be prevented. This situationpresents critical importance in terms eutro-phication and bacteriological quality of thecoastal waters in the Marmara Sea and theBosphorus. In addition, preliminary treatmentlevels must be upgraded to chemically-enhanced primary treatment in Yenikapitreatment plant until 2015. Finally, preliminarytreatment level of Buyukcekmece wastewatertreatment plant must be upgraded to tertiarybiological treatment, and preliminary treat-ment levels of Kadikoy and Baltalimaniwastewater treatment plants must be increasedto chemically enhanced-primary treatmentlevel until 2020.

Acknowledgements

We are grateful to ISKI, as the financer ofthe water monitoring program in the marineenvironment, in letting us publish and share thevaluable project outcomes. We also express ourgreat sorrow for the loss of dear scientist andfriend, Prof. Erdogan Okus, in a tragic sea acci-dent on 09/04/2006.

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