Marmara Denizi'nde su kalitesinin korunması doğrultusunda yenikapı atıksu arıtma tesisinin tasarımına esas olacak arıtılabilirlik çalışması
Treatability study based on the design of yenikapi wastewater treatment plant for the protection of water quality in the Marmara Sea
Yazar: ŞEYDA DUBA
Danışman: PROF. DR. SEVAL SÖZEN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
İstanbul'da artan nüfusa bağlı olarak, Marmara Denizi'nde su kalitesinin korunması amacı doğrultusunda derin deniz deşarjı ile sonlandırılan ön atıksu arıtma tesislerinde arıtma stratejisinin yeniden gözden geçirilmesi ihtiyacı doğmuştur. Yenikapı Atıksu Ön Arıtma Tesisi, İstanbul'un Fatih, Zeytinburnu, Sultangazi, Gaziosmanpaşa, Esenler, Bayrampaşa, Güngören, Eyüp, Kâğıthane, Bakırköy ve Bahçelievler ilçelerinden kaynaklanan kentsel atıksuyun ön arıtma prosesleriyle arıtılarak derin deniz deşarjı ile sonlandırıldığı atıksu arıtma tesislerinden biridir. 
Mevcut durumda Yenikapı Atıksu Ön Arıtma Tesisi, ızgara ve kum tutucudan oluşan bir yapıya sahiptir. Bu tesisin deşarjının İstanbul Boğazı karışım bölgesine yapılması ve bu bölgenin "az hassas" olarak tanımlanmış olmasından hareketle arıtma uygulamasının organik madde ve askıda katı madde giderimine yönelik bir düzene dönüştürülmesi gerekmektedir. Bu çerçevede mevcut alanın kısıtlı olması da dikkate alınarak uygulanabilecek arıtma düzenini ortaya koymak üzere deneysel çalışmalar yürütülmüştür.
Atıksuların arıtımında uygun stratejinin belirlenmesi için öncelikle anlamlı parametreler dikkate alınarak karakterizasyon çalışmasının yapılması gerekmektedir. Bu nedenle Yenikapı Atıksu Ön Arıtma Tesisi'nden alınan 24 saatlik kompozit numuneler üzerinde yaklaşık 55 gün boyunca karakterizasyon çalışması yürütülmüştür. Arıtılabilirlik çalışmalarının ilk aşamasında atıksudaki organik maddenin ve askıda katı maddenin sadece basit çöktürme ile hedeflenen düzeylere indirilip indirilemeyeceği araştırılmıştır. 
Askıda katı madde ve organik içeriği yüksek olan evsel atıksuların arıtımında genel olarak biyolojik arıtma sistemleri kullanılmaktadır. Fakat biyolojik arıtma sistemlerinin karmaşık mekanizmalar içermesi, birincil arıtma yöntemlerine kıyasla prosesler üzerinde daha fazla kontrol gerektirmesi, çamur kabarması sorunu gibi işletme zorluklarına sahip olmasının yanı sıra alan ve enerji ihtiyacı fazladır. Yenikapı Atıksu Ön Arıtma Tesisi'nin özellikle alan kısıtına sahip olmasının, ön arıtmadan daha ileri seviyede bir arıtım stratejisinin belirlenmesi açısından engel teşkil ettiği bilinmektedir. Gelişmekte olan ülkeler için kimyasal destekli çöktürme uygulamalarının tavsiye edilmeye ve uygulanmaya başlanması nedeniyle, Yenikapı Atıksu Ön Arıtma Tesisi'nden alınan numunelerde kimyasal destekli çöktürme deneylerine ağırlık verilmiştir. Bu amaçla, yaygın olarak kullanılan koagülantlar yardımıyla kimyasal destekli çöktürme uygulaması ile mümkün olabilecek en küçük hacimde çıkış suyu kalitesi araştırılmıştır. Evsel atıksu arıtımında en sık kullanılan koagülantlar olan FeCl3, Alum ve PAC ile kimyasal destekli çöktürme denemeleri yapılmıştır. İlk olarak her bir koagülant için optimum dozu belirlemek üzere ön deneyler gerçekleştirilmiş ardından belirlenen dozlar ile Jar test deneyleri yürütülmüştür. Optimum dozların belirlenmesi aşamasında, üst fazdaki KOİ, TP ve TN gideriminin yanı sıra çamur miktarları da göz önünde bulundurulmuştur. Sonuç olarak, koagülant ilavesiyle ham atıksuda ortalama %68 KOİ, %19 TN, %80 TP ve %92 AKM giderimi sağlanabilmiştir.
Kimyasal destekli çöktürme uygulamalarının performansını belirlemek üzere Jar test sonrası üst fazlardan alınan numunelerde, 30 dakikalık basit çöktürme sonrası üst fazdan alınan numunede ve ham numunede Partikül Boyut Dağılımı (PBD) analizi gerçekleştirilmiştir. Kimyasal destekli arıtılabilirlik çalışmalarının sonuçları, PBD ile ilişkilendirilerek kimyasal destekli çöktürmenin hangi dane boyutları üzerinde etkin olduğu ortaya konmuştur. PBD deneyleri ham atıksuda KOİ'nin %72'sinin partiküler olarak, %28'inin ise çözünmüş formda bulunduğunu göstermiştir. 
Optimum dozlar ile gerçekleştirilen PBD deneyleri sonucunda 50 mg/L FeCl3 dozu ile kimyasal destekli çöktürmenin sağlandığı durumda üst fazdaki KOİ'nin %36'sının partiküler formda ve %64'ünün çözünmüş formda bulunduğu; 100 mg/L alum dozu ile kimyasal destekli çöktürmenin sağlandığı durumda üst fazdaki KOİ'nin %45'inin partiküler formda ve %55'inin çözünmüş formda bulunduğu; 25 mg/L PAC dozu ile ise kimyasal destekli çöktürmenin sağlandığı durumda üst fazdaki KOİ'nin %36'sının partiküler formda ve %64'ünün çözünmüş formda bulunduğu gözlenmiştir. 
PBD deneylerinin sonuçlarına ek olarak çıkış KOİ, TP, TN, AKM konsantrasyonları ve çamur hacimleri birlikte değerlendirildiğinde optimum koagülant ve dozunun 25 mg/L PAC olduğu sonucuna varılmıştır. 
Biyolojik arıtılabilirliğin anlaşılması açısından önemli bir referans olan Oksijen Tüketim Hızı deneyleri yürütülerek atıksuyun kimyasal destekli çöktürme prosesinin yanı sıra biyolojik arıtma proseslerindeki davranışı karakterize edilmiştir. Oksijen Tüketim Hızı deneyi sonuçları, literatürde verilen değerler ile karşılaştırıldığında Yenikapı kum tutucu çıkışından alınan atıksudaki kolay ayrışabilir KOİ'nin toplam KOİ içerisinde düşük bir yüzdeye sahip olduğu görülmüştür. Atıksu içerisindeki inert çözünmüş KOİ fraksiyonu %12 olarak bulunmuştur, bu değer literatürde evsel atıksu için verilen orana göre yüksek bulunmuştur. Bu durumda, biyolojik arıtma gerçekleştirilse dahi arıtma çıkışında KOİ konsantrasyonunun 75 mg/L altında olamayacağı sonucuna varılmıştır.

Abstract:
In the early 1970s, giving the wastewater to receiving environments by deep-sea discharge without treatment was an approach that started to become widespread in the USA and Europe. Based on this approach, DAMOC Project was completed in 1971 to solve the problems arising from insufficient water resources and wastewater in Istanbul. Within the scope of this project, it was foreseen that the discharges made to the Bosphorus lower stream would be transported to the Black Sea and the deep sea discharge application was adopted. It was proposed to give the wastewater to the lower stream at a depth of 25 meters after pre-treatment. Following the DAMOC project, the Camp-Tekser (1975) Master Plan revised the work on increasing the depth of deep-sea discharge to 50 meters and adopting biological treatment especially for Küçükçekmece, Büyükçekmece, Adalar, and Terkos. In 1992, a new master plan for Istanbul was started to be prepared by the Istanbul Water and Sewerage Administration (ISKI). The Master Plan determined different treatment degrees depending on whether the discharge was done to the lower stream of the Marmara Sea or the Bosphorus in these regions. The Master Plan has suggested the implementation of treatment systems in these regions in a defined timetable.
Yenikapı Pre-Treatment Plant is one of the wastewater treatment facilities where domestic wastewater originating from Fatih, Zeytinburnu, Sultangazi, Gaziosmanpaşa, Esenler, Bayrampaşa, Güngören, Eyüp, Kağıthane, Bakırköy and Bahçelievler districts of Istanbul is collected and pretreated by screening and grit chamber. The discharge of this facility was directed to the mixing area of the Bosphorus. This area was defined as "less sensitive" by the Ministery of Environment and Forestry within the legislation of Urban Wastewater Treatment Regulation. This definition requires that a carbon removing treatment scheme should be implemented. Starting from this point, extensive efforts were devoted to the implementation of a carbon removal system. Considering the very limited area available for the wastewater treatment plant, the most suitable compact alternative was preferred to be chemically enhanced primary treatment.
Generally, biological treatment systems are used in the treatment of domestic wastewater with high suspended solids and organic content. However, biological treatment systems have many operational difficulties as well as the need for space. Considering such problems caused by biological treatment systems, chemically enhanced precipitation practices have started to be recommended for developing countries. In this framework, studies based on chemically enhanced primary treatment have been carried out to reveal the treatment scheme that can be applied, taking into account the limited space available.
To develop an appropriate treatment strategy, a comprehensive characterization study was conducted on 24-hour composite samples taken from Yenikapı Wastewater Treatment Plant for 53 days. Statistical evaluations showed that the average flow rate received by the plant constitutes approximately 70% of its capacity. It was observed that Chemical Oxygen Demand (COD) values showed a profile between 250 mg/L and 825 mg/L, while the 50 and 70 percentile values correspond to the concentrations of 540 mg/L and 580 mg/L, respectively. While the total COD is on average 530 mg/L values, dissolved COD concentration corresponds to 27% of this value.
During the characterization studies, the minimum and maximum concentrations measured for the Total Nitrogen (TN) parameter varied between 30 mg/L and 102 mg/L, while a profile varying between 2.3 mg/L and 8.9 mg/L concentrations was found for the Total Phosphorus (TP) parameter. It was found that the 50 and 70 percentile values for the TN parameter correspond to 74 mg/L and 79 mg/L. For the TP parameter, the 50 and 70 percentile values correspond to 4.8 mg/L and 5.5 mg/L, respectively. TN and TP parameters have an average value of 72 mg/L and 5 mg/L, respectively. Approximately 55% of TN is NH4+-N, 1.2% is NO3--N and the remaining part is in the form of organic nitrogen. 
While Suspended Solids (SS) value varies around the value of 310 mg/L, approximately 70% of SS is composed of Volatile Suspended Solids (VSS). The differences in wet and dry weather conditions reflected that the flow rate differs by about 22%, although the pollution loads in wet air are almost equal to the pollution loads in dry air.
Standard deviation values show that the concentration of the conventional parameters varied widely. This variability is expected, as it is known that pre-treatment plants with only screening and grit chamber do not have stable output values like biological treatment systems. 
In the first stage of the treatability studies, it was investigated whether the organic matter and suspended solid matter in wastewater could be reduced to the targeted levels with only plain settling. For this purpose, plain settling experiments were carried out in 1-liter sample volume at a settling time of 15, 30, 60, 90, 120, 180, and 240 minutes. COD and SS experiments were carried out in the supernatant to understand to what extent the COD and SS were reduced by plain settling. It was observed that the plain settling for more than 60 minutes did not reflect any meaningful increase in SS and COD removal. 30 minutes settling was identified as the most suitable period at a reduction rate of approximately 25-35% for COD and 44% for SS. It resulted that solely the plain settling did not satisfy the effluent quality desired
Beyond that, the quality of the effluent was investigated with the application of chemically enhanced precipitation with commonly used coagulants. FeCl3, alum, and PAC are chosen for conducting coagulation-flocculation experiments. Preliminary Jar test experiments were done to determine the optimum dosage for each coagulant. Dosages of 50, 100, 150, and 200 mg/L were applied for alum and FeCl3 coagulants while lower dosages of 25, 50, 100, and 150 mg/L were applied for PAC. Chemical sludge volumes were measured after each experiment and COD, TN, TP, TSS tests were performed on samples taken from the upper phases. Preliminary Jar test results were evaluated in terms of removal efficiencies and sludge volumes, it was decided that 50 mg/L for FeCl3, 100 mg/L for alum, and 25 mg/L for PAC were the optimum dosages. For alum and FeCl3, trials were made with the addition of 1 mg/L cationic polyelectrolyte and it was observed that the polyelectrolyte did not affect the removal efficiency. However, it has been observed that precipitation can be achieved at a shorter time with the addition of polyelectrolytes. For keeping the amount of sludge produced and the chemical used as a minimum, the lowest doses were applied.
Following the preliminary Jar tests, experiments were carried out with optimum dosages to determine the best coagulant. With the addition of the optimum FeCl3 dosage, 68% COD, 19% TN, 83% TP and 93% TSS removal were achieved and 178 mg/L COD, 50 mg/L TN, 1.0 mg/L TP, 29 mg/L SS concentrations were measured in the effluent. 62% COD, 18% TN, 67% TP and 88% TSS removal rates for alum and 74% COD, 21% TN, 90% TP and 94% TSS removal rates for PAC were found. Jar test carried out with the optimum dosage of alum resulted in an average effluent quality of 215 mg/L COD, 51 mg/L TN, 1.9 mg/L TP, and 45 mg/L SS. Applying the optimum dosage found for PAC, with an average of 144 mg/L COD, 49 mg/L TN, 0.6 mg/L TP and 22 mg/L SS effluent quality was achieved.
Chemically enhanced treatability studies were associated with the particle size distribution to determine the particle size on which chemical precipitation is effective. Sequential filtration/ultrafiltration experiments were initiated by passing samples through 1600 nm (Millipore AP40), 450 nm (Durapore HV, polyvinyl fluoride (PVDF)), and 220 nm (Durapore GV, PVDF) filters. Subsequently, the obtained 220 nm filtrates were passed through membrane discs with a molecular weight cut-off (MWCO) of 100, 30, 10, 3, and 1 kDa. It is known that the molecular weight cut-off (MWCO) values of 100, 30, 10, 3 and 1 kDa correspond to particle sizes of 13 nm, 8 nm, 5 nm, 3 nm, and 2 nm, respectively. For this reason, Total Organic Carbon (TOC) and COD concentrations corresponding to the mentioned particle sizes were determined. Particle Size Distribution experiments have shown that 72% of the COD in raw wastewater are particulate and 28% are dissolved.
In addition to the raw wastewater, particle size distribution experiments were performed in the upper phases after optimum dose applications. After the addition of 50 mg/L FeCl3, 36% particulate and 64% dissolved COD were found in the upper phase. For the optimum dosage of Alum, 45% particulate and 55% dissolved COD were determined while application of 25 mg/L PAC resulted in 36% particulate and 64% dissolved COD in the upper phase. It has been found that similar removal rates of around 80% can be achieved in >450 nm COD by 50 mg/L FeCl3 and 25 mg/L PAC dose applications. In the >450 nm size range, COD removal provided by the addition of 100 mg/L alum is 75% and is lower than other coagulants. It was observed that the dissolved COD removal in the size range < 450 nm could be achieved by 21% with 50 mg/L FeCl3, 22% with 100 mg/L alum, and 26% with 25 mg/L PAC.  The concentration of 111 mg/L COD in the 2-450 nm size range was reduced to 69 mg/L with the addition of PAC, 77 mg/L with the addition of alum, and 79 mg/L with the addition of FeCl3. These values show that 38%, 31%, and 29% COD removal can be achieved with the additions of PAC, alum, and FeCl3 in the size range of 2-450 nm, respectively. In all coagulant dosing, low amounts of COD removal were observed in the size range < 2 nm, which is presumed to be due to adsorption. 
When the results of the Particle Size Distribution experiments and the COD, TP, TN, and sludge analyzes are evaluated together, the optimum coagulant and dosage are found as 25 mg/L PAC. 
Oxygen Uptake Rate experiments were performed to characterize the distribution of the COD fractionation in terms of size and biodegradation characteristics of raw wastewater. Oxygen Uptake Rate experiments were done by using an online respirometer. Modeling was accomplished using the curve fitting method with the OUR curve obtained as a result of the respirometer. COD fractions were determined as well as kinetic and stoichiometric parameters. It was observed that approximately 7% of the biodegradable COD was easily degradable, approximately 14% was rapidly hydrolyzable COD, and the remaining part was slowly hydrolyzable COD. As a result of the modeling, it was found that the total dissolved inert COD is %12 of total COD which is higher than normally found in domestic wastewater.