Evaluation of biofilm performance of different structures with integrated fixed activated sludge and membrane bioreactor

Abstract

Water is an indispensable resource for living things to continue their vital activities although natural resources are limited. The intensification of water use with the rapid population growth and the rise of industrialization stands out as the main reason for the concept of global water scarcity. While the intensification of water use will increase the demand for water and the pressure on water resources, it will also cause the current water scarcity to turn into a "water crisis" in the coming years. Unless a precaution is taken, it is inevitable that this problem will reach an even more critical level as time goes on. In order to prevent this problem, wastewater should be well treated and reused. It is necessary to determine a good treatment technology within the scope of reuse of waste water. For a good treatment technology, it is necessary to focus not only on high removal efficiencies, but also on the feasibility of the technology. In this context, in big cities where space is an important issue, the small space requirement of treatment technology is a priority. In the scope of the thesis, considering this subject, the integration of the membrane bioreactor (MBR) systems, which take up little space and provide high removal efficiencies, and the biofilm system for the treatment of wastewater is examined. Compact biofilm systems have become highly preferred today due to their low energy requirements and low labor requirement. Biofilm systems, which have become especially popular in organic matter removal, are used in villages, hotels, sites and similar low-population areas. In these low-population areas, compact biofilm systems are also more affordable than the design and implementation of a large-scale treatment plant. The performance of the biofilm system is greatly affected by the loading conditions. High and very low loadings deteriorate the quality of the effluent. Optimum loading values in air biological treatment systems differ according to the type of reactor used. The effect of different operating parameters and active features on the behavior of IFAS-MBR systems was reviewed with the pilot scale system. Based on the main experimental findings, the following conclusions can be drawn: •COD removal was generally satisfactory for most of the experiments. However, a sudden decrease in the incoming C/N ratio or a shock in the inlet salinity of the persistent pollutant can affect the behavior of the bacterial consortium in the IFAS-MBR that treats industrial wastewater. •Thanks to the biofilm expertise, good nitrification ability of the system was achieved throughout the experiments. The long retention time of the biofilm enhanced the growth of nitrifications, thus promoting nitrification even for the lowest mixed liquor SRT values; The biofilm effectively contributes to the removal of more stubborn pollutants such as hydrocarbons, even in hostile environments (high salinity). •Respirometric batch tests highlight the greater ability of suspended biomass to remove COD, while biofilm often contributes to nitrification or removal of specific persistent contaminants. •Biofilm separation strongly influences membrane fouling. Biofilm separation can create a beneficial "seeding" effect on suspended biomass (nitrification, removal of hydrocarbons) and also provide the correct compactness to the cake layer. Within the scope of the thesis, the effect of the media type on the removal efficiency was examined by using two different media types and studies were carried out on the optimum amount of use. With the MBR system, which is integrated with the biofilm system, high removal efficiencies have emerged, and it has been concluded that it is a technology that should be highlighted due to its low space requirement. The results and comments of the analyzes made during all these examinations are also detailed in the "Conclusions and Discussion" section. In addition, with the biofilm system in front of the MBR system, the load on the membrane is reduced, and the possibility of clogging of the membrane and the use of chemicals for backwashing are reduced. In this case, it has allowed the membrane to prolong its useful life and be more cost-effective than the systems using only MBR.