Membran biyoreaktörlerde titreşim ile tıkanma kontrolü
Fouling control of membrane bioreactors by vibration
Yazar: RECEP KAYA
Danışman: PROF. DR. İSMAİL KOYUNCU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Doktora, 2018
Konu: Çevre Mühendisliği = Environmental Engineering
Dizin: Membran filtrasyon tekniği = Membrane filtration technique ; Membran sistemler = Membrane systems ; Membran teknolojileri = Membrane technologies

Özet:
Membran Biyoreaktörlerde (MBR) tıkanmanın geciktirilmesi çeşitli hidrolik yöntemlerle gerçekleştirilmektedir. Bu yöntemler, hava ile sıyırma ve periyordik geri yıkama ve periyodik bekletme olarak sıklıkla kullanılmaktadır. Hava ile sıyırma membran yüzeyindeki kayma gerilmesini bir miktar arttırarak gözenekleri tıkayıcı paritüllerin membrandan uzak durmasını sağlamaktadır. Bunun dışında geliştirilmekte olan bir diğer teknolojisi titreşim ile membranların tıkanmasının geciktirilmesidir. Titreşim sayesinde direk membran yüzeyinin kendisini titreşmesi sağlanarak çok yüksek kayma gerilimi oluşturulmakta ve böylece membran tıkayıcı partiküllerin membran yüzeine çarparak uzaklaştırılması hedeflenmektedir.
Bu tez çalışmasında öncelikle konu ile ilgili litertür taraması yapılmış ve literatürdeki başarılı örnekler incelenmiştir. Literatürdeki sistemlerin çoğunluğu laboratuvar ölçeğinde uygulanabilir sistemler olup gerçek ölçekli ve pilot uygulamaya uygun değildir. Bunun yanı sıra organik ve inorganik olmak üzere laboratuvar ortamında hazırlanmış süspansiyonlar kullanılarak batık MBR sistemi modellenmeye çalışılmıştır. Literatürde kullanılan sistemler mekanik olarak, membranların itme çekme hareketiyle çeşitli yönlerde hareket ettirilmesine dayanmakta olup bir kaç tanesi manyetik transduser yardımıyla yüksek frekans düşük genlik kullanılarak gerçekleştirilen deneylerden ibarettir.
Bu çalışmada öncelikle hem pilot olarak hem de laboratuvar ölçeğinde kullanılacak modüller 3 Boyutlu olarak SOLIDWORKS programı ile tasarlanmış ve labortuavar ölçekli modül ise Computational Fluid Dynamics (CFD) yöntemiyle ANSYS FLUENT programı kullanılarak modellenip simülasyonu yapılmıştır. Bu simülasyonlarda çeşitli frekans değerleri ve genlikleri modele girilerek, membran yüzeyinde oluşturacağı kayma gerilimleri karşılaştırılmıştır. Daha sonra polyetersülfon (PES) ve poliakrilonitril (PAN) bazlı ince boşluklu membranlar üretilmiş fakat bunların titreşimli batık MBR modülü için dayanıksız olacağı yapılan deneylerle görülmüştür. Bunun üzerine güçlendirilmiş ince boşluklu PVDF (polivinil floriden) bazlı membranlar sipariş edilmiş ve bu ticari membranlar kullanılarak titreşimli membran modülleri üretilmiştir. Membran modüllerinin yerleştirileceği titreşim sistemleri ise manyetik ve mekanik sistemler olarak tasarlanmış, sanayide üretimi gerçekleştirilmiş ve üretim aşamaları açıklanmıştır.
Modül ve titreşim sistemlerinin üretimi tamamlandıktan sonra mekanik ve manyetik tahrikli titreşimlerin batık MBR modülleri üzerindeki etikisinin incelenmesi amacıyla laboratuva ve pilot ölçekli uzun dönemli deneyler gerçekleştirilmiştir. Laboratuvar ölçekli deneylerde hem kısa süreli kritik akının belirlenmesi deneyleri hem de uzun dönemli filtrasyon deneyleri sentetik atıksu beslemesi ile gerçekleştirilmiştir. Titreşimsiz kontrol modülü, mekanik titreşimli modül ve manyetik titreşimli modül laboratuvar ölçekli MBR sisteminde paralel olarak işletilmiş ve arıtma ve filtrasyon performansları takip edilmiştir. Elde edilen sonuçlara göre, manyetik titreşimli modülün tıknmayı en iyi geciktirdiği, mekanik titreşimli modülün ise titreşimsiz modüle göre daha erken tıkandığı gözlemlenmiştir. Laboratuvar öleçeğinde en iyi sonucu veren titreşim sistemi ise pilot ölçekli deneyler için seçilmiş ve uzun dönemli deney pilot ölçekli olarak gerçek atıksu ile gerçekleştirilmiştir.
Pilot ölçeğinde manyetik titreşimli modül ve titreşimsiz kontrol modülü sırayla çalıştırılmış ve elde edilen arıtma ve filtrasyon performansı verileri karşılaştırılmıştır. Manyetik titreşimli sistem 150 Hz frekans ile en iyi filtrasyon performasını sağlamıştır. Arıtma performansı olarak incelendiğinde ise hem titreşimli hem de titreşimsiz modüller birbirinin aynı sonuçları göstermiştir.

Abstract:
Fouling control on Membrane Bioreactors (MBR) can be done by various hydraulic methods. These methods are generally air scouring, periodic backwashing and periodic retention. Air scouring increases the shear stress on the membrane surface, thereby ensuring that the pores are secured from the plugging particles. Another technology that has been developed apart from these is the retardation of membrane fouling by vibratory shear stress. High and equally distrubuted shear stress is created by moving the membrane walls directly, thus aiming the membrane blocking particles off the membrane surface.
In this research thesis, a broad literature research from Comptutational Fluid Dynamics (CFD) apllications to vibratory membrane processes was completed. Most of the systems in the literature are applicable on laboratory scale and are not real scale and not suitable for pilot application. In addition, the submerged MBR system was modeled using suspensions prepared in the laboratory environment which are organic and inorganic suspensions. Most of the systems used in the literature are mechanical vibration systems based on moving the membranes in various directions by push-pull movements, and some of them are magnetically induced systems using high frequency low amplitude oscillation with the help of a magnetic transducer.
Before the experiments, the modules to be used both as pilot and laboratory scale were designed with 3D software  program called SOLIDWORKS and laboratory scale module was modeled and simulated with Computational Fluid Dynamics (CFD) method using ANSYS FLUENT program. In these simulations, various frequency values and amplitudes are modeled and the shear stresses which are to be formed on the membrane surface are compared. Later, thin-film membranes based on polyethersulphone (PES) and polyacrylonitrile (PAN) have been produced but have been shown to be non-usable for submerged vibratory MBR modules. On this, reinforced PVDF (polyvinyl fluoride) based hollow fiber  membranes were ordered and vibrating membrane modules were produced using these commercial membranes. The vibration systems in which the membrane modules are to be placed are designed as magnetic and mechanical systems, the production steps are planned and completed in the industry.
In the ANSYS FLUENT simulations, 5-10-15-30-40-50-60 Hz frequencies and 1-5-10 mm amplitudes were modeled. Based on the results, increase of frequency values are more effective than the amplitude increments on the shear stress profile of the membrane surface. 
For laboratory scale experiments, a mechanical vibratory system and a magnetically induced vibration system were designed and built. Machanical vibration system consists two industrial vibration motors with frequency inverter and magnetically induced system consists two I beam magnetic transducer with a stereo amplifier. Mechanical vibration system  is limited to 30 Hz frequency while the magnetic system can produce as high as 150 Hz vibration fequency. The amplitude values for the mechanical and magnetic vibration systems are 0.5-5 mm and 0.01-1 mm, respectively. Special oscillation springs used in both vibration systems which can oscillate membrane modules up 20 kg. The control module was non-vibrated module which has isolation springs from the ground and vibration systems did not affect the control module during the experiments. 
Laboratory scale MBR with three parallel vacuum pump is used to compare all three modules simultaneously. The laboratory scale MBR plant was fed with sythetic domestic wastewater. Seed sludge was taken from a real scale wastewater plant and vacinated to activated sludge tank. Vacuum pumps and all other equimpents was connected to a SCADA which controls the valves, pumps and filtration-backwashing sequence.  SCADA computer were recorded trans-membrane pressures, membrane fluxes, dissolved oxygen, oxygen reduction potential, pH and temperature values of the system. 
Long-term laboratory experiments were completed in three stages. Before every stage new modules were produced and modules which are having similar permeabilities were used. Critical fluxes were determined and 26 l/m2.h were chosen as operation flux during the stages. In the first stage, machanical vibration system was set to the 5 Hz and magnetic vibration system was set to 30 Hz. In the second and third stage magnetic vibration system set again to 30 Hz but mechanical vibration system set to 30 and 20 Hz, respectively. The mechanically vibrated module, magnetically vibrated module and non vibrated module operated under these conditions in the same reactor. All TMP datas were recorded and compared. Chemical oxygen demand (COD), turbidity, total khjeldal nitrogen (TKN), NO3-N and NO2-N analysis of the influent and effluent waters were done. Mixed liquior suspended solids (MLSS) and mixed liquor volatile suspended solids (MLVSS) analysis were also done in the MBR reactor, weekly. All the data obtained from the MBR system were evaluated and performances of three modules based on treatment and filtration were compared.
The long-term experiments were comleted in three stages during 130 days. In all stages machanically vibrated module average vacuum pressure was 188,2±113,6 mbar, magnetically vibrated module average vacuum pressure was 66,8±27,6 mbar and non-vibrated control module average vacuum pressure was 80,1±43,5 mbar. After the stages, addtional expreiments were done with 150 Hz magnetic vibration and 30 Hz mechanical vibrations. These tests were completed in 20 days. Mechanically vibrated module vacuum pressure was 41,6±18,9 mbar, and magnetically vibrated module vacuum pressure was 11,1±4,9 mbar during these tests. The lowest TMP profile achieved with the magnetically vibrated module in all stages and additional experiments. Magnetically vibrated module with 150 Hz frequency get the best TMP results when compared to 30 Hz frequency tests. 
Mechanically vibrated module TMP profile was even higher than the non-vibrated control module during 3 stage tests. In mechanical vibration system, amplitude values were in between 1 – 5 mm, thus the system created very high shear stress near the membrane wall and this caused destructive force for the big flocs near the membrane wall, which was protecting the membrane pores from smaller particles. When compared to magnetic vibration system, amplitude values of magnetically vibrated module were much lower than the mechnically vibrated module, which is approximately 0,01 mm.
After long term experiments comleted, resistance analysis for all three module in three stages were completed. Based on the results, mechanicallyvibrated module has the lowest cake resistance and highest irrecoverable resistance which caused by pore plugging. Magnetically vibrated module has the highest cake resistance and lowest irrecoverable membrane resistance compared the mechanically vibrated module and non-vibrated control module. This results explains why the mechanically vibrated module gets highest TMP profile during the long term experiments. This also explains why the magnetically vibrated module get the best TMP performance when compared the other two modules. Magnetic vibration with high frequency (30-150 Hz) and low amplitude (0,01 mm) were kick-backed the small pore plugging particles near the membrane wall, while weren't damaging the big flocs around the hollow fiber membrane surfaces.
MLSS and MLVSS values were measured between 6027-10061 mg/L and 3885-6288 mg/L during the long term experiments. COD removal rates were in between 96-98% for all three module permeates. Turbidity values for non-vibrated, mechanically vibrated and magnetically vibrated modules were between 0.27-0.56 , 0.48-0.71 and 0.28-0.53 NTU, respectively. In other words, there were no significant differenc between all three modules based on treatment performance datas.
For pilot scale experiments, bigger module then laboratory scale membrane module produced which has 200 pieces of 50cm long hollow fiber PVDF membranes with 0.40 m2 total surface area. Magnetic vibration system was chosen as vibraion source for pilot scale tests, based on the lab-scale experiment results. Two I beam magnetic transducer with stereo amplifier were used as vibration equipment. 
Pilot scale experiments were completed in three stages, first 30 Hz magnetic vibration were tested, second non-vibrated module tested and third 150 Hz magnetic vibration were tested under same condition with real domestic wastwater feed. Pilot MBR module was operated during 24 days in every stage total of 72 days.
Critical flux test were done with pilot scale module and 26 L/m2.h were chosen as operational flux. Pilot MBR module TMP profile and water quality analysis were recorded during the experiments. Magnetically vibrated module at 30 Hz were reached 161 mbar, non-vibrated module were reached 228 mbar and magnetically vibrated module at 150 Hz were reached 69 mbar maximum during the experiments. 
Laboratory scale and pilot scale experiments with different type of vibration systems with different vibration frequency were proved that, mechanical vibration created very high shear stress near membrane wall which could be destructive for the cake layer. Thus, pore plugging particles may easily penetrate inside the membrane pores without blocked by big flocs and cake layer. Magnetically induced membrane vibration has very low amplitude (0,01 mm) values when compared to mechanical vibration (1-5 mm). Magnetically induced membrane vibration system can also produce frequency values as high as 150 Hz which is impossible by the mechanical vibration system. From this perspective, frequency and amplitude values affects membrane fouling differently. With high frequency and low amplitude smaller particles which plugs the memrbrane pores can be blocked, while maintaning loose cake layer near the membrane wall.