The effects of the modification of flat-sheet membranes with bisbal regarding the performance and antibiofouling characteristics of the polymeric membranes

In recent studies regarding fouling in MBR (Membrane bioreactor) have been shown that causes of the fouling in MBR have mostly been SMP (Soluble Microbial Product) and EPS (Extracellular Polymeric Substances), which are produced by bacteria. Most of the research using a different kind of materials have been performed to reduce the fouling problems and to enhance the features of membranes (hydrophilicity, surface roughness, surface load etc.). Nanoparticles and antibiotics can be given as examples to eradicate those problems. Beyond chemical treatments, some modification methods of membranes have gained importance. In this study, aiming to enhance the features of membranes, some modifications have been applied on EPS (Extracellular Polymeric Substances, produced by bacteria) by using an antibiotic called BisBAL (Bizmuth 2-3-Dimercapto-1-Propanol) known as an inhibitor on the production of protein and polysaccharide by the bacteria. Three different modification methods entitling Dip Coating (DC), Spin Coating (SC) and low pressure-treated coating (LPtC) have been used by the way of physical adsorption of BisBAL on the membrane surfaces. The membranes selected by the immersion method were immersed in the modification solution in the container for a certain period of time. As a result of immersion, the expectation was that BisBAL physically bonds with the membrane by means of Van der Waals force. For this method, the duration of awaiting the membrane in the solution was considered. The membranes selected by the rotation method have been modified with the Spin Coating Device. In this operation, it was necessary to pay attention to some parameters to get the best results. Some of those were; solution volume, rotation speed and rotation time. The method of the low pressure-treated coating was based on Van der Waals strength expected to be made with the polymeric layer in the active part of the membrane of BisBAL as in other methods. Modification of membrane was implemented both as a modification of the membranes produced and as a modification of the commercial membranes purchased. In this regard, being in the scope of TUBITAK (The Scientific and Technological Research Council of Turkey) project, the production of the PES membrane, which has been optimized for modification processes based on the results obtained from the results of membrane production in the previous work packages, has been produced. In addition to this membrane, the modified PES (Poli Eter Sülfon) and PVDf (Polyvinylidene Difluoride) commercial membranes were modified and necessary comparisons were performed. Accordingly, various characterization methods have been used to obtain performance information of the modified membranes. These methods included analysis of permeability-blocking, contact angle, Bi oscillation, total organic carbon (TOC), membrane surface load, scanning electron microscopy (SEM) analyzes. The membranes produced by me after the Activated Sludge and Xanthan Gum filtration studies showed better results than commercial membranes. The reason of this might be due to the additional modification layer in commercial membranes. The result of the water filtration after activated sludge filtration, an average of 80 % permeability loss was observed, whilst permeability losses were seen less in the modified membranes. Permeability losses were obtained as 66%, 52%, and 15%, respectively regarding dip coating, spin coating, low pressure treated coating. Membrane modifications and permeability gains were calculated as 14%, 36%, and 81%, respectively. In terms of biofouling, the most successful modification method was found to be BisBAL adhesion on the surface with LPtC. In studies with commercial PVDf, modification of BisBAL with a different polymer and hydrophilic membrane was carried out. According to the contact angles for the PES and PVDf membranes, there has been some reduction in angle values with contamination. Depending on the method variability, no obvious change in contact angle has occurred. Furthermore, the contact angels of the clean membranes were found more than dirty membranes. The reason of this finding is that the accumulation of the organic particules on the membrane surface and adsorbing water within their hydrophilic feature. The decrease of the contact angles are thought to be due to their hydrophilic structure. Although, the BisBAL is produced by lipophilic thiols, it is also easily soluble in the water. Hence, the reaction between bizmuth and lipophilic thiols to produce BisBAL chelate has a hydrophilic feature at the end, and the decrease of contact angles might be because of the BisBAL`s structure. The surface loads of the membranes generally showed the results of acidic conditions that converge negatively to basic conditions and the highest negative level in neutral conditions. Considering the negative charges of organic substances, the negative surface charge on the membranes gives an advantage in terms of antimicrobial activity. Scanning Electron Microscopy (SEM) images were taken after hydraulic washing. Comparisons were made for modification studies of surface contamination of membranes containing pure membrane and BisBAL. SEM images can be used to comment on whether the modification work visually increases the recyclable stagnation on the surface. The post-modification surfaces of commercial PVDF membranes modified by the immersion coating method were different. There are small quantities of organic particles in the images taken after hydraulic washing performed after activated sludge and Xanthan Gum filtration. In the results, generally less adhesion was observed on the surface of the modified membranes. In terms of TOC removal efficiency, TOC removal efficiencies were found to be not affected or better recovery efficiencies were achieved in dip, spin and low pressure treated coating methods for both PES and PVDf membranes. When the Bi results are examined, no Bi release is observed in the immersion method in PES-containing membranes and bismuth concentrations in the effluent waters are measured to a minimum. Very low concentrations of bismuth were observed in the spin coating method. The bismuth concentration in the filtrate water of commercial PVDF membranes modified by immersion, spin and adsorption method was measured at the minimum level. Finally, for all types of membranes within surface modification applications, modification of membranes can bring novel alternatives for energy savings regarding MBR processes in the future due to the reduction on pore blocking and irreversible fouling. In addion to this, the modification studies based on chemical reactions would bring more insights on applicability of the membrane modifications with BisBAL regarding the future real-world applications.