Membran biyoreaktörlerde membran biyotıkanmasını engellemek amacıyla Rhodococcus sp. BH4 ile bakteriyel quorum quenching uygulamaları

The increasing world population and development of industry have resulted in environmental problems like climate change and water scarcity. The membrane bioreactor (MBR) can be used to treat wastewater and provide a source of irrigation water. As such, it represents an innovative and sustainable solution that can be employed to alleviate existing water scarcity problems. While MBRs have a lot of advantages, they also have a distinct disadvantage: the fouling that results from the attachment of biomass to the membrane surface. Scientists have only recently discovered that microorganisms can communicate with one another and show group behaviors in their environments. The creation of biofilm represents one example of the primary group behavior of microorganisms, which use "Quorum Sensing" (QS) to increase the effectiveness with which they can protect themselves against external factors and to prolong their life cycles more easily. Species that can produce signal molecules and species that can use signal molecules as carbon sources live together in the same ecological environments. Species that use signal molecules as a substrate may interfere with intraspecies and between species communications because they use signal molecules for their own lifecycles. The use of these species to degrade signal molecules in order to interrupt communication between microorganisms is referred to as quorum quenching (QQ). In this study, a QQ mechanism was adapted to an MBR and an innovative approach to prevent and control biofilm formation during MBR operation was suggested and researched by experimenting with different QQ bacteria immobilization configurations. The scope of this PhD thesis was as follows. First, the QS mechanism was proven through an experiment in an activated sludge system. The QQ microorganisms were then isolated from the activated sludge mixed liquor and their QQ activities were determined. These QQ bacteria were examined for their QQ applicability during MBR operation by using different immobilization media. Microbial vessel and cell entrapping beads (CEBs) were preferred as immobilization media because they are the only two unique QQ MBR application media examples described in the literature. In addition to these two media, a new medium was also trialed. The main aim of these studies was to identify transmembrane pressure (TMP) profile differences between the control MBR and the QQ MBR, which were a conventional MBR and an MBR that incorporated QQ media respectively. The expectation was that the use of QQ products in the QQ MBR would result in a reduction in TMP values. In this thesis, two different QQ bacteria were supplied from the WEMT laboratory: Rhodococcus sp. BH4 and Pseudomonas sp. 1A1. Since the QQ activity of Rhodococcus sp. BH4 was determined to be higher than the QQ activity of Pseudomonas sp. 1A1, Rhodococcus sp. BH4 was preferred and used as the QQ bacteria of choice to immobilize the media in this study. Microbial vessel studies were carried out using two different QQ bacteria amounts. Microbial vessels were manufactured from microfiltration hollow fiber membranes, and QQ bacteria were immobilized in the fibers. After the manufacture and QQ activity determination, the microbial vessel was located in the reactor in a stable position. Microbial vessel applications could, on average, result in 44% TMP reduction during MBR operations. The microbial vessel application had a medium level QQ effect. In addition to this, there was an approximately 32% difference in QQ effect between the batch QQ activity determination bioassay result and the reduction in TMP during MBR application. This difference resulted from the immobility of a microbial vessel in the reactor, which resulted in low food/mass (F:M) ratios in the microbial vessels and low lactonase (QQ enzyme) dispersion in the reactor. Following the microbial vessel studies, six QQ bead studies were conducted under different operation conditions. QQ beads were manufactured using alginate or polymer as the base immobilization material. QQ bacteria immobilization was carried out by adding QQ bacteria to the alginate or polymer dope solution. After manufacturing, the QQ beads were added to the reactor and moved dispersedly throughout the reactor during the operation. A reduction in TMP in the QQ MBR with the addition of QQ beads was observed, and the average reduction in TMP across the six studies was 90%. Also, the addition of the QQ beads to the QQ MBR resulted in a 70% and 38% reduction in the concentrations of the protein and carbohydrate content of extracellular polymeric substances (EPSp and EPSc) respectively. As such, the results indicated that the application of QQ beads to the QQ MBR successfully decreased TMP in the MBR. Scientists have recently discovered that the center of QQ beads can be anoxic. In this regard, a one-step MBR study was carried out with polymeric beads in which immobilized nitrification/denitrification bacteria from the anoxic tank of a real MBR plant were utilized. The aim of this study was to eliminate the anoxic tank, mission of which is to remove nitrogen forms, from the flowchart and an adjustable nitrogen removal capacity by adding these special beads to the MBR tank without pausing the aeration. A very high QQ effect (94%) coupled with a 7% and 21% increase in COD and TN removal efficiencies respectively was observed. As such, the results indicated that a one-step MBR operation may represent an effective alternative to advanced wastewater treatment. Long-term studies of the QQ beads revealed that they are effective as an immobilization medium because they have a high QQ effect, but are also ineffective as an immobilization medium because they have low mechanical durability. QQ beads can easily destroy themselves and mix into the activated sludge. These destroyed QQ bead particles and leaked QQ bacteria result in excess sludge and modify the structure of the activated sludge. However, it is the high F:M ratio and the additional physical cleaning effect on the membrane surface via mobility that allows the QQ bead to achieve such high levels of biofouling prevention. In the light of the advantages and disadvantages of the microbial vessel and QQ bead applications, an innovative, more effective, and practically feasible application media was designed and manufactured. This new media was referred to as the rotating microbial carrier frame (RMCF). The RMCF incorporates a carrier frame that is manufactured from an inert material and several cubbyholes covered with a microfiltration membrane. After QQ bacteria immobilization in these cubbyholes, RMCF is located under the membrane module and rotated during the operation of the MBR. While the inert material incorporated in the RMCF can eliminate the disadvantages of QQ beads in terms of mechanical durability, rotational motion can eliminate the low F:M ratio disadvantage of the microbial vessel application. RMCF was examined comprehensively for its QQ and physical cleaning effects during short- and long-term MBR operations. Short- and long-term QQ MBR operations with an RMCF were tested. The results indicated that the use of an RMCF in the QQ MBR could result in a 65% reduction in TMP and a reduction in biofilm formation. Moreover, the RMCF decreased concentrations of EPSp and EPSc by 54% and 29%, respectively. The RMCF could be used over the course of 30 days without any external addition or intervention. In addition, 20% of the biofilm prevention effect of the RMCF resulted from the physical cleaning effect. The results indicated that a small increase in the amount of immobilized QQ bacteria could easily increase the percentage by which TMP decreased within RMCF applications. According to the MBR plant scale and the target QQ effect level, the number of RMCFs and cubbyholes of the RMCF can be increased and adjusted. Furthermore, the design of the RMCF can allow immobilized bacteria to be emptied and refilled. In this regard, the growth kinetic of Rhodococcus sp. BH4 was determined under the MBR operation conditions. The sludge retention time of Rhodococcus sp. BH4 was calculated and it was found that the number of immobilized QQ bacteria can be kept at the same level, and immobilized QQ bacteria can be kept alive in their exponential growth phase during operation by removing about 8% of immobilized QQ bacteria daily. In real-scale plants, the daily removal of immobilized QQ bacteria can be carried out using special lines. QQ bacteria can affect microbial communities by degrading signal molecules and decreasing the concentration of EPS; these two factors are indissociable. The microbial community in the activated sludge was monitored throughout all these QQ application studies to check the possible effect of the QQ mechanism on the bacterial species. While short-term QQ applications had no significant effect on the microbial community, there was a significant increase in the number of bacteria species following long-term QQ applications. This change can be evaluated as follows: the degradation of signal molecules by QQ bacteria prevented some common species from being dominant in population equilibrium, and provided other rare bacteria species with the opportunity to gather and grow without any social stress. Quorum quenching bio-product usage results in TMP decreasing and energy saving QQ bio-product usage results in a reduction in TMP and enhanced energy saving during MBR operations. Within the scope of this PhD thesis, a cost analysis was conducted to identify the energy savings percentages and QQ product manufacturing costs of three different QQ media. If manufacturing costs were not taken into consideration, cost savings were 12%, 24% and 23% for the microbial vessel, QQ bead, and RMCF applications respectively. On the other hand, if manufacturing costs were taken into consideration, cost savings were 6%, 15% and 21% for the microbial vessel, QQ bead, and RMCF applications respectively. These differences can be attributed to the fact that the manufacturing cost of the RMCF was the lowest due to design factors like inert material and bacteria regeneration line. To summarize, the feasibility of a QQ MBR was examined from several different perspectives. The QQ MBR, which has very limited application examples and research results in the literature, was successfully used for advanced wastewater treatment at a lower unit cost than a conventional MBR. Keywords: Membrane Processes, MBR, Biofouling, Quorum Quenching, Energy Saving