Membran biyoreaktör ile evsel nitelikli atıksuların arıtılması ve geri kazanılması
Treatment and reclamation of domestic wastewater with membrane bioreactor
Yazar: SAİME YILMAZ
Danışman: PROF. DR. MUSTAFA TURAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri ve Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
Artan su ihtiyacı, tükenen ve kirlenen su kaynakları nedeniyle mevcut su kaynaklarının akıllıca kullanılması, kirlenmelerinin önlenmesi gerekmektedir. Ayrıca atıksuların klasik sistemlerle arıtılıp su kaynaklarına deşarj edilmesi yerine membran biyoreaktör gibi ileri atıksu arıtma teknolojileri ile arıtılıp geri kazanılarak tekrar kullanılmaları su kaynaklarının geleceği bakımından çok önemlidir. 
İ.T.Ü. Çevre Mühendisliği Laboratuvarı'nda pilot ölçekli batık membran biyoreaktör sistemi kurulmuştur. Hans Huber AG firmasından alınan MembraneClearBox® (MCB) adlı membran biyoreaktör sistemi, aktif çamur prosesi ve daldırılmış ultrafiltrasyon (UF) membranları vasıtasıyla arıtılmış suyun ayrılması işleminin birleşimi olan bir arıtma sistemidir. Membran modülü plaka-çerçeve tipli olup ultrafiltrasyon membranıdır, por büyüklüğü 38 nm olup 9 adet membran plakası bulunmaktadır ve toplam yüzey alanı 3.5 m2'dir.
Membran biyoreaktör sistemi kompakt bir sistem olup üzerinde bulunan ekipmanlar hava bloweri, scouring (sıyırma) bloweri, debi ölçer, numune alma vanası, basınç ölçer ve kontrol ekranıdır. Sistem ayarlamaları kontrol ekranı vasıtası ile yapılmaktadır. Sistemde normal işletme modu, ekonomi modu ve yüksek yük modu olmak üzere üç adet işletme modu bulunmaktadır. Sistem normal şartlarda normal modda işletilir, membran biyoreaktöre atıksu girişi olmadığı zamanlarda ise (tatil zamanları) mikroorganizmaların ölmemeleri için gereken minimum oksijen sağlanmaktadır. Yüksek yük modu ise sisteme aşırı yük geldiği durumlarda kullanılmaktadır. 
Orta karakterli evsel atıksu niteliğinde sentetik atıksu ile çalışmalar yürütülmüştür. Ham atıksu giriş değerleri KOİ, BOİ, Toplam Azot (TN) ve Toplam Fosfor (TP) için sırasıyla 500 mg/L, 400 mg/L, 40 mg/L ve 8 mg/L'dir. Ham atıksuyun C:N:P oranı 100:8:1.6'dır ve bu değer ideal değer olan 100:5:1 değerine oldukça yakındır. Daha gerçekçi olması bakımından sentetik atıksu ideal değerlere uyacak şekilde hazırlanmamıştır. 
Önce anaerobik besleme tankına (fosfor giderimi için gereklidir) gelen atıksu peristaltik pompa vasıtasıyla reaktöre girer. MBR içerisinde kesikli havalandırma sayesinde karbon giderimi, nitrifikasyon ve denitrifikasyon işlemleri gerçekleşmektedir. 
MBR sistemi geri devirli ve geri devirsiz olmak üzere iki farklı tipte işletilmiştir. Geri devirsiz işletme süresince elde edilen giderme verimleri sırasıyla AKM, KOİ, BOİ, TN, TP, Ca+2, Mg+2, Na+, CI- ve toplam koliform parametreleri için  % 99.97, % 98, % 98, % 60, % 40, % 2.4, % 3.4, % 0.55, % 67 ve % 100'dür. Geri devirsiz arıtma için ise AKM, KOİ, BOİ, TN ve TP giderme verimleri sırasıyla % 99.98, % 99.28, % 98.3, % 66 ve % 60'dır. Elde edilen sonuçlara göre geri devirli arıtma verimleri kısmen daha iyidir. MBR sistemindeki MLSS konsantrasyonu işletme süresince 7356 mg/L'ye kadar yükselmiştir. Reaktördeki ortalama iletkenlik, MLSS, sıcaklık, pH ve çözünmüş oksijen değerler sırasıyla 7121 µS/cm, 4935 mg/L, 20.63 ºC, 5.64, 1.07 mg/L'dir. 
Elde edilen çıkış suyu sulama suyu olarak (tarımsal, yeşil alan, peyzaj, golf sahası) kullanılabilir. Ayrıca yangın söndürme, araç yıkama ve sifon suyu olarak da kullanılabilmektedir. Sulama suyu olarak kullanımda sulanacak bitki türü ve toprak yapısı oldukça önemlidir ve dikkatle seçilmelidir.

Abstract:
There is an increasing water demand in the world and water supplies keep getting polluted, so it is necessary to prevent further contamination and planned usage of available clean water resources. In addition, instead of classic wastewater treatment systems we should use advanced wastewater treatment systems like membrane bioreactor and reuse the treated wastewater. 
Pilot scale submerged membrane bioreactor system (SMBR) was set up in the I.T.U. Environmental Engineering Department Laboratory. MembraneClearBox® (MCB) MBR system was bought from Hans Huber AG firm and it is a hybrid system combined with classical activated sludge proses and submerged UF membrane module. Type of the membrane module is plate-frame and pore size of the membrane is 0.38 nm (UF membrane). There are 9 plates and total membrane area is 3.5 m2. Volume of the feed tank was 200 L. Volume of the membrane bioreactor always was kept fixed at 500 L while operation time. 
Experiments were conducted with synthetic wastewater which prepared as medium strength domestic wastewater. It assumed that the source of untreated wastewater was only domestic and there was no industrial discharge to that water, so it was not contain any toxic chemicals and heavy metals. COD, BOD, TN and TP values of the influent synthetic water was 500 mg/L, 400 mg/L, 40 mg/L and 8 mg/L respectively. C:N:P ratio of the wastewater was 100:8:1.6, that ratio was very close to the ideal C:N:P ratio of 100:5:1. The synthetic wastewater could be prepared like ideal ratios but that was not done because of being more realistic. 
Operation of the system was all automatic and it could be customized by electrical control monitoring unit. In the operation system there were an air blower, scouring blower, flow meter, permeate pump, sampling valve, pressure meter. System worked with negative transmembrane pressure and the pressure value could be seen all the time while operating. 
Scouring blower supplied air for preventing membrane fouling, scouring blower time could also be changed on the control unit. When permeate flow is too low (when fouling increased) the scouring blower started running automatically. If fouling is too much scouring blower could not be efficient sometimes. If the scouring blower worked 5 times in 1 minute, system stopped filtering the water. When that happened, the membrane needed chemical cleaning. Since it was a plat-frame membrane module, chemical backwash could not be done automatically. Chemical cleaning was done manually by giving the solution through permeate pipe backward. Sodium hydroxide (NaOH) and citric acid solutions were used as chemical cleaning agents. When permeate flow was too low, system stopped and chemical washing was done manually and after sometime system started to work again. When chemical washing was done wastewater did not filtered and enter into the membrane bioreactor system. 
There were 3 mode option in the operation system. Economy mode, normal mode and high load mode. Economy mode especially could be used for the vacation times when there was no wastewater entrance in the membrane bioreactor, minimum oxygen demand was supplied, so microorganism did not die. Normal mode was used when there was entrance and effluence of the wastewater to the membrane bioreactor and it could be used for normal operation times. High load mode could be used when there was more wastewater entrance of the wastewater than usual. 
MLSS concentration in the membrane bioreactor was very low initially, so experiments was not started until higher MLSS values. In treatment process, wastewater enters the anaerobic feed tan first (which required for the biological phosphorus removal) and pumped to the membrane bioreactor via peristaltic pump, feed tank also worked as a sedimentation tank and solid particles can settle in the bottom of the tank. Blower of the reactor turns on and off automatically so there can be carbon removal, nitrification and denitrification processes. On and off time, system modes could customized. Oxygen was not given continuously because denitrification process was necessary for the nitrogen removal, all processes happened in one tank (membrane bioreactor).  
There were probes for measuring dissolved oxygen, MLSS, pH, electrical conductivity and temperature all the time in the membrane bioreactor. Water level of the reactor had always kept stable. The MBR system was operated in two different modes, one was with no recycle of the sludge and the other one was with recycle of the sludge to the feed tank. Sludge was never discharged from the system. Sludge age was infinity for both operating modes. 
Mixed liquor suspended solids (MLSS) concentration in the membrane bioreactor increased to the level of 7356 mg/L (highest value) and changed between 800 mg/L and 7356 mg/L during the experimental work. Mean values of the conductivity (EC), temperature, pH, dissolved oxygen (DO) and MLSS were 7121 µS/cm, 20.63 ºC, 5.64, 1.07 mg/L and 4935 mg/L respectively in the membrane bioreactor. When sludge was returned from the membrane bioreactor to the feed tank, MLSS concentration started to decrease because biomass was also returning to the feed tank too. Electrical conductivity (EC) value was high and there were some reasons for that. One of the reasons was addition of the sodium hydroxide (NaOH) to the membrane bioreactor for adjusting the pH value, because of the reactions in the membrane bioreactor tank pH value tented to get low and sodium hydroxide (NaOH) was added. The other reason was evaporation of the water from the membrane bioreactor. Diffusor in the membrane bioreactor could also contributed to that evaporation. Air pressure in the membrane bioreactor could also helped the homogeny mixing and there was no additional mixer in the membrane bioreactor tank. 
Removal efficiency of the SS, COD, BOD, TN, TP, Ca+2, Mg+2, Na+, CI- and total coliform were 99.97%, 98%, 98%, 60%, 40%, 2.4%, 3.4%, 0.55%, 67% and 100% respectively for the no sludge returning mode. Removal efficiency of the SS, COD, BOD, TN and TP were 99.98%, 99.28%, 98.3%, 66% and 60% respectively for the sludge returning mode. Calcium (Ca+2), magnesium (Mg+2), sodium (Na+) and chlorine (CI-) concentrations were not measured for the sludge returning mode because removal of them was not related with the operation mode. In addition, removal of them were so low that it could be neglected. According to the results there was better removal efficiency when sludge was returned to the feed tank. When sludge was return to the feed tank, there was better phosphorus and nitrogen removal. There was no oxygen in the feed tank, so anoxic process could be more efficient that way. There was % 100 removal of the total coliform and that meant ultrafiltration membrane removed them very efficiently. Calcium (Ca+2), magnesium (Mg+2), sodium (Na+) and chlorine (CI-) removals were so low that it could be negligible. Ultrafiltration membrane could not remove monovalent and multivalent ions efficiently. They also effected the electrical conductivity value of the effluent water which was important for irrigation water. Turbidity values also measured only in the effluent water for both operating modes. It was 0.66 FAU when sludge was not returned and 0.45 FAU when sludge was returned.
Effluent water from the membrane bioreactor can be used for the purposes of irrigation (parks, gardens, play grounds, golf courses). In addition they can be used for fire water, flushing water, fire reserve storages and car washing. 
Irrigation water must be analysed carefully for the toxic compounds that can be found in the effluent water. Heavy metals and other toxic compounds can be found either in very low concentrations in the domestic wastewater or they can not be found at all. When there is a discharge of the industrial wastewaters to the domestic wastewater systems, toxic compounds can be exist in the wastewater, so if there was a plan to reuse the effluent water industrial wastewaters should not be discharged into the domestic wastewater canals. 
Turkish Wastewater Treatment Plants Technical Aspects Bulletin (2010) has some criteria for wastewater reuse in irrigation. According to the bulletin there are two main class (A and B) for the irrigation. Class A is for landscape and non-commercial plant irrigation. BOD, pH, turbidity, fecal coliform and residual chlorine must be      < 20 mg/L, 6-9, < 2 NTU, 0/100 ml and > 1 mg/L respectively. Class B is irrigation for commercially processed plants, restricted areas and non-eatable plants. Class B criteria were, BOD, pH, SS, fecal coliform and residual chlorine must be < 30 mg/L, 6-9,  < 30 mg/L, < 200/100 ml and > 1 mg/L. Fecal coliform criteria is lower for Class A because in landscapes people can contact with the bacteria and viruses that can be found in domestic wastewater. Most important criteria for reuse of treated domestic wastewater is microbiological criteria.