Yüksek hızlı aktif çamur sistemlerinden oluşan fazla çamurun mezofilik çürütülmesi
Mesophilic digestion of high rate activeted sludge system excess sludge
Yazar: İSA IŞIK
Danışman: PROF. DR. İZZET ÖZTÜRK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Biyogaz = Biogas ; Biyogaz sistemleri = Biogas systems ; Çamur = Sludge ; Çamur arıtma = Sludge treatment

Özet:
Arıtma çamurlarının çürütülmesi bunun yanında organik atıklarla enerji geri kazanım oranın artırılması amacıyla Baltalimanı Atıksu Arıtma Tesisi deşarjından alınan ön arıtmaya tabi tutulmuş atıksu, pilot ölçekli yüksek hızlı aktif çamur sisteminde arıtılmıştır. Oluşan fazla çamurun mezofilik şartlarda 20 günlük çamur yaşıyla 90 günlük iki işletme döneminde laboratuvar ortamında çürütülmüştür. Ayrıca mutfak öğütücülerinin kullanıldığı bir sistemin etkilerinin görülmesi amacıyla ikinci işletme döneminde ise İTÜ yemekhanesinden alınan organik katı atıklar öğütülerek pilot tesis arıtma sistemine dahil edilmiştir. Bu sayede sisteme giren organik yükün artmasıyla oluşan çamurun biyometan potansiyeli aynı işletme koşulları altında bir önceki durumla karşılaştırılmıştır. Oluşan biyogaz miktarı ve metan içeriği ile birlikte özellikle Uçucu Katı Madde (UKM) ve kimyasal oksijen ihtiyacı (KOİ) giderim verimleri incelenmiştir.
Yapılan çalışma sonucunda pH değişimleri incelendiğinde ilk dönem için 7,2 – 7,9 aralığında değiştiği görülmüştür. İkinci işletme döneminde pH değişimi daha az görülmüş olup 7,2 ile 7,4 arasında değişmiştir. Redoks Potansiyeli -430 ile –480 mV arasında değişmiştir. Organik yükleme hızı 2,5 – 2,9 kg KOİ/m3.gün arasında değişmiştir.
TKM giderim verimi ilk dönemde ortalama % 56 iken ikinci işletme döneminde % 40 olarak gerçekleşmiştir. UKM giderimi verimi ilk işletme dönemi boyunca ortalama % 58 ikinci dönemde ise ortalama % 59 olarak gerçekleşmiştir. KOİ giderim verimi birinici ve ikinci işletme dönemlerinde sırasıyla ortalama % 62 ve % 63 olarak gerçekleşmiştir. İşletme dönmeleri boyunca çKOİ sonuçlarına bakıldığında reaktör içerisinde 700 – 2000 mg/L arasında değişim gösterdiği görülmüştür. Oluşan biyogaz içinde ilk işletme döneminde % 67 metan içeriği varken ikinci işletme döneminde bu oran % 73'e yükselmiştir. İlk döneme ait ortalama metan verimi 282 L CH4/kg UKMgiderilen olmuştur. Arıtma sistemine organik atık ilavesinden sonra alınan fazla çamurun çürütülmesi sırasında ise metan verimi 373 L CH4/kg UKMgiderilen olmuştur.  Metana döneşen KOİ miktarı ve 0,60 g KOİmetan/g KOİeklenen olarak hesaplanmıştır. Zeta potansiyeli ve partikül boyut dağılımları (P) incelenmiştir. İlk işletme döneminde belirgin bir değişim görülmemiştir. İkinci işletme döneminde ise çürütme sonrası boyut azalması görülmüştür. Amonyum azotu konsatrasyonu ilk işletme döneminde 1000 – 1300 mg/L arasında ikinci dönemde ise 600 – 730 mg/L arasında değişmiştir. 
Yüksek hızlı aktif çamur sistemi sayesinde düşük O2 tüketimi düşük bekletme süreleri ile arıtma tesisinin elektrik sarfiyatı konvansiyonel sistemlere göre düşüktür. Buna ek olarak oldukça yüksek olan A-kademesi çamurunun anaerobik çürütülmesiyle elde edilen biyogaz önemli bir enerji kaynağıdır. Yüksek enerji potansiyeli olan A-kademesi fazla çamuruna ayrıca organik atıkların ilavesi ile bu potansiyel artırılabilir. Organik atıkların doğrudan çürütücüye verilmesi yerine mutfak öğütücülerinin yaygınlaştırılması ile mutfak atıklarının kanalizasyon sistemi vasıtasıyla AAT'lere iletimi sağlanabilir. Bu yolla atıksu arıtma aşamasında giderilen organik maddenin çamura geçmesi ve oluşan yüksek organik madde içerikli fazla çamurun çürütülmesiye hem atık toplama maliyetleri azalacak hem de üretilen enerji miktarını artış gösterecektir.

Abstract:
Sludge management and disposal after wastewater treatment is a very important issue in environmental engineering. Although the generatedsludge characterization can be changed in a wide range, the treatment and disposal of the treatment sludges in wastewater treatment plants is considerably higher in terms of investment and operating costs. Anaerobic digestion of municipal and industrial wastewater sludges have been applied for a long time and it is known as a reliable sludge  stabilization method. The energy content of the excess sludge can be recovered by anaerobic digestion. Produced biogas through anaerobic digestion can compensate energy expenditures, which have the biggest share among the operating expenses of the wastewater treatment plants (WWTPs).
Anaerobic treatment is essentially the conversion of organic matter into end products such as CH4, CO2, NH3 and H2S in absence of oxygen environment via complex biological processes. It has been known for centuries that methane has formed as a result of this process, which is also referred to as the refinement of organic matter. It has been understood that various microorganisms have been involved in the process. Microbiological and biochemical investigations have also increased on this subject and anaerobic digesiton has become a common application. This method, which has been applied for many years in disposal of sewage sludge, has recently been applied in the treatment of industrial and urban wastewater and in the management of organic solid wastes. There are three basic steps in the anaerobic oxidation of organic wastes; hydrolysis, acid production (fermentation) and methane production.
Reducing energy consumption through anaerobic digestion with energy recovery is also an important element for energy management in wastewater treatment plants. Intensive aeration in the conventional activated sludge processes cause high energy consumption in WWTPs. High-rate activated sludge systems can be used to avoid this application. These systems are known as having  quite low hydraulic retention times and low oxygen consumption. In particular, the high loaded stage (A-stage), which is the adsorption phase of the two-stage system AB processes, can capture the organic matter very efficiently and the organic matter can be converted to biogas in anaerobic digesters.
Looking at solid waste management practices, it is seen that the collection of waste at the source and recovery are not at the desired levels yet. As a common method, mixed solid wastes are disposed in landfills. This situation causes two important problems. Reuse of waste, recycling, becoming a useful final product and recovery of energy content, etc., are hampering the reduction of the environmental impacts that will arise in the provision of raw materials. Storage of organic solid wastes also causes limited capacities of landfill areas to fill up earlier. At present, national and international regulations and arrangements to reduce the amount of organic waste coming to the landfill areas are stated. Taking all these into consideration, it will be a more efficient and effective solution to evaluate organic wastes, which are the biggest components of domestic solid wastes, with separate collecting and recycling processes (compost, anaerobic digestion etc.).
It is beneficial to collect the municipal organic solid wastes separately and treatment them together with treatment sludge for energy recovery. It is very convenient to treat these two waste species according to the principles of treatment together (co-treatment). However, the high efficiency of transporting municipal organic solid wastes to the waste treatment plants without being collected at the source and contaminated with other types of waste depends on too many variables and control is also very difficult. Moreover, even if these wastes are collected with a high efficiency and transported to the plants, this application will result in a significant operational cost. Given these circumstances, a waste management scenario in which kitchen grinders are used is seemed a much more efficient solution. The grinders placed in the kitchens, organic wastes are directly included in the sewage system and sent to the WWTPs without any transportation cost and the extra organic matter load can be recovered via the valorization of the excess sludge. With this method, significant amount of money can be saved, and higher energy recovery can bepossible by the valorization of the treatment sludge.
Physically treated wastewater discharged from the Baltalimanı Wastewater Treatment Plant (WWTP) discharge was treated in a pilot scale high rate activated sludge system in order to increase the energy recovery of organic wastes as well as the treatment of the excess sludges. The Electrolab brand FerMac 320 model bioreactor fermentor was operated to digest the sludge. While the reactor is mixed with the aid of a rotating rotor connected directly to a motor, it is provided with jacket type resistance heater wound around the outside reactor for heating and hot water circulated in the closed system in the reactor. It is also possible to observe the % O2 and% CO2 values of the biogas formed from the control panel while measuring on-line pH, temperature and redox parameters with probes. At the beginning of the operation, the reactor was filled up with 6 L of seed sludge. The reactor was operated with a sludge age of 20 days by feeding 300 mL of sludge per day. In addition, the reactor was operated under mesophilic conditions (37 °C).
The resulting excess sludge was digested in the laboratory environment during two operational periods (90-day). In addition, in order to observe the effects on excess sludge of a system treating kitchen wastes, organic solid wastes from the ITU refectory were grinded and included in the pilot plant treatment system during the second operating period. Thanks to the sludge generated by increasing the organic load entering the system was compared to the previous situation under the same operating conditions of the biomethane potential. Biogas generation,  methane content of the biogas and  the removal efficiencies of volatile solids (VS) and chemical oxygen demand (COD) were investigated.
As a result of the study, when the pH changes were examined, it was observed that it was fluctuated between 7.2 and 7.9 for the first period. In the second operating period, it was more stable. The pH value ranged from 7.2 to 7.4. Also redox potentials ranged from -430 to -480 mV. Organic loading rate (OLR) ranged from 2.5 to 2.9 kg COD/m3.day.
Total Solids (TS) removal efficiency were 56 % in the first period and 40 % in the second period, respectively. VS removal efficiency was around 58 % during first operating period and 59 % during second operating period, respectively. It was seen that during the operating periods of the removal efficiency of COD wer 62 % at first period and 63 % at second period, respectively. Soluable COD values varied between 700 - 2000 mg/L in the reactor. The methane content of the biogas was 67 % during the first operating period andit increased to 73 % in the second operating period. The average methane yield for the first period was 282 L CH4/kg VSremoval. During the digestion of excess sludge after the addition of organic waste to the treatment system, the methane yield increased to 373 L CH4/kg VSremoval. The amount of COD converted to methane was calculated as 0,60 gCODmethane/gCODfeed. Zeta potential and particle size distributions (PSD) were also investigated. No significant change was observed during the first operating period. In the second operating period, there was a decrease in PSD after the digestion. The concentration of ammonium ranged from 1000 to 1300 mg/L during the first operating period and from 600 to 730 mg/L during the second period. 
In the high rate activated sludge systems, by means of low O2 consumption and low retention times energy consumption of the WWTPs can be lower than conventional systems. In addition, biogas produced in anaerobic digestion of the A-stage excess sludge is an important source of energy. This potential can be increased by the addition of organic wastes to the A-stage excess sludge, which has a high energy potential. Instead of direct disposal of organic waste, the spread of kitchen grinders can be transmitted to the WWTPs through the sewage system of kitchen waste. In this way, the organic matter removed during the wastewater treatment phase will be reduced to the wastewater, and the amount of energy generated will increase.