Investigation of the effects of some signal molecules on biogranulation

Due to the rapidly increasing human population, residential areas and industrialization of the world, clean water resources are rapidly depleting. For this reason, it is very important to treat the wastewater before discharging to the ecosystem. Depending on the wastewater contents, it may be preferable to consecutively use one or all of the physical, chemical, biological and advanced treatment methods. Activated sludge systems commonly used in biological treatment have some drawbacks, such as the need for large plant area and the production of excess waste sludge. For this reason, granular activated sludge systems, which are formed by the flocculent activated sludge becoming compact and stable, are now being developed rapidly. Many physical and chemical factors affect the granulation process. The main disadvantage of this system is that the spontaneously formation of granular sludge requires a long process time. In this doctoral thesis, accelerating the aerobic granulation process was aimed by using appropriate reactor design, operational process control, adding some chemicals (boric acid and cationic polymer chitosan) and signal molecules (C4-HSL / N-butyryl-L-Homoserine lactone, C6-HSL / N-Hexanoyl-L-Homoserine Lactone, C8-HSL/ N-Octanoyl-Homoserine lactone) involved with quorum sensing mechanism. Protein analyses of extracellular polymeric substances, physical properties of granules and molecular studies of the microbial changes of the formed granules were also investigated. For this purpose, a total of 12 bioreactors were set up in 4 different trial sets and the specified chemistry was tested. Microbial structure of the granules was determined by Denaturing gradient gel electrophoresis (DGGE) and Quantitative PCR (Q-PCR) methods. In all the experiments, the granulation process was successfully done and the granules with sizes varying between 0.5 - 1.5 mm were obtained. This process, which takes place in 2-4 months according to the literature, has been reduced to 5 days with the chemicals and signal molecules used in doctoral studies. According to the DNA sequence analysis of the bands obtained from DGGE analyses; Bacteriodetes and Firmicutes group organisms were dominant in the experiments in which boric acid and chitosan chemicals added, and Proteobacteria group organisms in the experiments in which the signal molecules were used. Quantitative analysis by real-time PCR showed that the microbial load in the granules remained constant at about 106-108 copies DNA / ml.