Quorum quenchıng membran biyoreaktörlerde kullanılan immobilizasyon medyalarında malzeme tercihinin etkisinin incelenmesi
Investigation of the effect of material preference on immobilization media used in Quorum quenching membrane bioreactors
Yazar: SEMANUR SOYLU
Danışman: DOÇ. DR. BÖRTE KÖSE MUTLU
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Çevre Mühendisliği Ana Bilim Dalı / Çevre Bilimleri, Mühendisliği ve Yönetimi Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Çevre Mühendisliği = Environmental Engineering

Özet:
Geleneksel aktif çamur sistemleri uzun yıllar kullanılarak günümüze kadar ulaşmıştır. Geleneksel aktif çamur sistemlerini kullanan arıtma tesisleri artan nüfus yoğunluğu, alan ihtiyacı gibi nedenlerden dolayı gelişmeye ve farklılaşmaya açık hale gelmiştir. Günümüzde en çok kullanılan yenilikçi atık su arıtma sistemleri arasında membran biyoreaktörler (MBR'ler) yer almaktadır. MBR sistemleri geleneksel aktif çamur sistemlerine kıyasla daha az alanda, yüksek çıkış su kalitesi sunmaktadır.
MBR'lerin kullanımın yaygınlaşması çeşitli konfigürasyonları da beraberinde getirmiştir. Bu konfigürasyonların meydana gelmesinde en önemli etkenlerden biri membranların tıkanma problemidir. Membranlarda biyotıkanma membran ömrünü azaltarak maliyeti artıran bir etkendir. Biyotıkanma problemi ele alınarak tasarlanan Quorum Quenching MBR, klasik MBR modeline kıyasla daha avantajlı işletme süreci sağlamaktadır.
Bakteri hücreleri, popülasyon arttıkça çevrelerinde biriken, genellikle yayılabilen, düşük moleküler ağırlıklı sinyal molekülleri üretir. Molekül konsantrasyonu bir eşik değerini aştığında, sinyal yolları aktive olur ve bakteriler, popülasyon boyunca uyumlu bir şekilde gen ekspresyonunu değiştirerek ve fizyolojik süreçleri modüle ederek yanıt verir. Bu tür hücreler arası iletişimin iyi karakterize edilme durumuna "Yetersayı Etkisi/Quorum Sensing (QS)" denir.
Yenilikçi bir yaklaşım olan "Yetersayı Etkisinin Azaltılması/Quorum Quenching (QQ)" yaklaşımı ile membran biyotıkanmasını geciktirmenin mümkün olduğu görülmüştür. Yetersayı etkisi adı verilen bakteriler arasındaki iletişimi sağlayan mekanizmayı bozmaya yönelik çalışan QQ mekanizması ile bakterilerin membran üzerinde birikmesi ve kek tabakasını oluşturması önlenir. QQ mekanizması 3 yol ile sağlanır. Bunlar; sinyal moleküllerinin sentezlenmesinin engellenmesi, sinyal moleküllerinin algılanmasının engellenmesi, ortamdaki sinyal moleküllerinin degredasyonudur. Tez kapsamında sinyal moleküllerinin degredasyonu sağlanarak QQ mekanizması gerçekleştirilmiştir. QQ mekanizmasını sağlayan bakterileri atık su bulunan ortamına ilave edebilmek için koruma sağlayan bir immobilizasyon medyasının kullanılmasının uygun olduğu literatürde yapılan çalışmalar neticesinde görülmüştür.
Tez çalışması kapsamında QQ aktivitesine sahip bir bakteri türü olan Rhodococcus sp. BH4 kullanılmıştır. Bakteri çoğaltılarak farklı medyalara immobilize edilmiştir. Üretilen medya çeşitleri optimize edildikten sonra çeşitli analizlerden geçirilmiştir. Bu analizler ile medyanın dayanımı, fiziksel yapısı, kimyasal yapısı gibi konular ön plana çıkarılmıştır. Tez kapsamında yapılan çalışmalar neticesinde avantaj sağlayan immobilizasyon medyasının bulunması ilerleyen çalışmalar açısından önem taşımaktadır.

Abstract:
Water released after water use and endangering the environment and living health due to its content is called wastewater. Wastewater is defined as wastewater generated in homes, workplaces, industry and other areas of life and commercial activity. The usage area of water is also very important in wastewater characterization. Depending on the source discharged, it is called domestic and industrial wastewater. Efficient treatment of wastewater can be considered as a direct preventive measure against the pollution of drinking water.
Wastewater treatment has been of great importance in every period. With the increase in population, the amount of wastewater generated has also increased. Discharging wastewater into aquatic ecosystems without treatment endangers the environment and indirectly many areas and living communities. For this reason, various wastewater treatment systems have been developed over the years. Traditional activated sludge systems, one of these wastewater treatment systems, have been used for many years and have survived to the present day. Although traditional activated sludge systems are known and easily operated, they have various disadvantages. In traditional activated sludge systems, the space requirement is quite high depending on the water flow rate to be treated. Considering the increase in population density, there is a need for a system that can purify water at a higher flow rate in less space.
Membrane bioreactors (MBRs) are among the most used innovative wastewater treatment systems today. MBR systems emerge as a combination of membrane and traditional activated sludge system. The membrane is defined as a selectively permeable barrier between two homogeneous phases. It is an important separation material due to its selectivity and barrier to various pollutants due to its properties. MBR systems offer high outlet water quality in less space compared to traditional activated sludge systems. Operating costs of MBR systems are higher than traditional activated sludge systems. One of the main reasons for the high costs in the business is the membrane.
The widespread use of MBRs has brought various configurations. One of the most important factors in the formation of these configurations is the fouling problem of the membranes. One of the factors affecting the clogging problem in MBRs is the operating conditions of the MBR. As the flux increases in MBRs, the clogging rate increases. For this reason, it is important to pay attention to some important points such as membrane area when choosing the operating flux. The operating limit at the sustainable membrane permeability level at constant flux and transmembrane pressure (TMP) is defined as the "critical flux". Although MBRs are operated at fluxes lower than the critical flux, TMP increases significantly when operated at a flux value above the critical flux. Therefore, very frequent periodic washing or cleaning is required. In addition, aeration is required for biological treatment, mixing of flocs and removal of impurities from the membrane surface. There are basic methods to prevent fouling. These are classified as pre-treatment of the feed stream, chemical and physical cleaning, reducing the flux, increasing aeration, and chemical or biochemical modification of the mixed liquid.
Fouling in membranes limits membrane permeability. In other words, it causes a decrease in the flux passing through the membrane in response to unit transmembrane pressure, and therefore, a decrease in the production of purified clean water per unit membrane area. Membrane fouling is roughly divided into two mechanically: reversible (removal of the gel and cake layer formed on the surface by aeration or physical backwashing) and irreversible (accumulation of dissolved or colloidal substances in the pore as a result of adsorption and removal of pore fouling by chemical cleaning).
Membrane fouling occurs in different ways. In this thesis, the problem of biofouling in membranes is discussed. Membrane biofouling occurs as a result of the adhesion of sludge flocs and the subsequent growth of microorganisms on the membrane surface. Microbial growth on the membrane surface is the main factor that increases filtration resistance and significantly reduces permeate flux. Bio fouling in membranes is a factor that reduces membrane life and increases costs.
Physical, chemical and biological methods are used to solve the fouling problem in membranes. When physical methods are examined, methods such as ventilation and physically scraping the cake layer attract attention. Backwashing with the addition of chemicals is also one of the steps to prevent fouling. However, chemical addition is not done frequently because it damages the sludge content. In addition, it may cause wear on the membrane surface. Physical methods, on the other hand, have low impact and become unsustainable in the long term. For this reason, biological methods attract attention in the literature. Among the various methods investigated considering bacterial activities, there are some remarkable and highly effective methods.
Bacteria attract attention when examined in terms of life form. Although they are small in size, such as micro and nano, many bacteria have complex life forms. There are hundreds of species that differ in their characteristics, lifestyle, contribution to the environment and many other aspects.
Many bacteria do not live as isolated entities but instead exist as communities. They can communicate by producing and responding to chemical signals. Bacterial cells produce low-molecular-weight signaling molecules, which are often diffusible and accumulate in their environment as the population increases. When the molecule concentration exceeds a threshold value, signaling pathways are activated and bacteria respond by altering gene expression and modulating physiological processes in a concerted manner across the population. This type of intercellular communication is well characterized and is called Quorum Sensing (QS).
Examples of group behavior include virulence, production of secondary metabolites (including antibiotics), sporulation, and biofilm formation. The most studied intercellular signals are Gram-negative and Gram-positive bacteria. Quorum Sensing (QS) is used by both Gram-negative and Gram-positive bacteria to regulate various physiological functions.
Signaling systems can be divided into two paradigmatic classes: LuxI/LuxR-type signal-sensing systems in Gram-negative bacteria and oligopeptide/two-component-type signal-sensing circuits in Gram-positive bacteria. In Gram-negative bacteria, LuxI-like proteins are enzymes responsible for the production of specific acylhomoserine lactone (AHL) autoinducers. Each strain of Gram-negative bacteria produces a unique AHL or a unique combination of AHLs. As a result, only members of the same species recognize and respond to it.
Extracellular polymeric substances (EPS) and soluble microbial products (SMP) produced by QS interaction are considered the main factor causing biofouling. EPS, which are binding materials for the agglomeration of microbial flocs and biofilms, consist of different organic molecules such as polysaccharides, proteins and humic substances. AHLs-based nuclei detected by gram-negative bacteria are responsible for the production of EPS in activated sludge. Furthermore, oligopeptides produced by gram-positive bacteria and some universal autoinducers lead to the development of highly cooperative colonies in the form of biofilms on the membrane surface.
It has been shown that it is possible to delay membrane biofouling with the innovative approach of "Quorum Quenching (QQ)". The QQ mechanism, which works to disrupt the mechanism that enables communication between bacteria, called "Quorum Sensing (QS)", prevents bacteria from accumulating on the membrane and forming the cake layer. The QQ mechanism is provided in 3 ways. These mechanisms; Blocking AHL synthesis in the sender cell, deactivating AHL via enzymatic destruction, interfering with signal receptor in the receiving cell. Within the scope of the thesis, the QQ mechanism was realized by ensuring the degradation of signal molecules.
Rhodococcus sp. BH4, a bacterial species with QQ activity, was used in the thesis study. Although it is known from literature studies that the bacterium has QQ activity, studies were started by making sure of its activity with the QQ activity test. The test results were comparatively examined with a bacterial strain without QQ activity. The bacteria were propagated and immobilized on different media.
Immobilization media in the literature are important for the study. 6 different immobilization media were produced by developing previously tested materials. After the media types produced were optimized, they were subjected to various analyses. With these analyses, issues such as the strength, physical structure and chemical structure of the media were brought to the fore.
As a result of the studies carried out within the scope of the thesis, finding advantageous immobilization media is important for future studies. It is important to reveal advantageous immobilization media in terms of expanding the usage areas of QQ activity, which manages to prevent biological contamination and membrane clogging, and making it usable in large-scale facilities.