Performance tests of hybrid membrane bioreactor (IFAS MBR) system in different sludge and hydraulic retention time

Abstract

In recent years, research has intensified on new treatment processes that occupy less space, are cost-effective, and provide highly efficient treated effluent quality due to the increasing volumes of water requiring treatment. Membrane technologies are at the forefront of these technologies. Particularly, Membrane Bioreactor (MBR) systems, which can be used as alternatives to conventional treatment systems in domestic wastewater treatment plants, have created a wide range of research opportunities due to their economic and easy operability. Membrane Bioreactor (MBR) systems are widely used in the treatment of domestic and industrial wastewaters. They are combined treatment systems where biological treatment using activated sludge is integrated with membrane filtration for solid-liquid separation. The MBR process primarily relies on the physical separation of treated water and activated sludge by membranes. Due to its high separation efficiencies, it involves the incorporation of a membrane module providing physical separation instead of the final sedimentation tank found in conventional domestic wastewater treatment plants, either submerged or externally integrated into the process. According to research, wastewater discharge from the Marmara Basin is approximately 5 million m3. According to data from the Ministry of Environment and Forestry, approximately 1.5 million m3 of this wastewater is discharged directly after preliminary treatment. With rapid population growth and industrialization, it is anticipated that this wastewater discharge will increase further in the coming years. In Istanbul specifically, due to spatial constraints, wastewater is only subjected to preliminary treatment before being discharged into the Sea of Marmara through deep-sea outfalls. Additionally, industries such as textiles, which generate a significant amount of wastewater, contribute to point source pollution in the Sea of Marmara. While the recent emergence of mucilage is believed to be nitrogen and phosphorus-related, efforts are needed to reduce the nutrient load entering the Marmara Sea. Action is required to address both water scarcity issues and promote resource recovery, as well as to upgrade existing systems to advanced biological treatment. In this context, the thesis in question has implications for reducing wastewater discharge and preventing marine pollution. At the current stage, it is imperative to upgrade conventional wastewater treatment plants to ensure the removal of nitrogen and phosphorus and to achieve treatment efficiencies sufficient for wastewater recovery in water intensive industries. In this regard, new technologies should be employed, and whenever possible, facility designs and equipment selections should leverage local resources. This approach aims to eliminate dependence on foreign sources in the environmental sector. Integrated Fixed-film Activated Sludge (IFAS) is a relatively new wastewater treatment technology that offers various advantages over traditional activated sludge technologies. It involves the addition of a growth media to the activated sludge tank to facilitate biomass growth and enhance the treatment process. The added media can be fixed or free-floating. The technology is relatively new and can be installed as an upgrade to an existing facility or built anew. The IFAS treatment process combines traditional activated sludge and biofilm technologies in a single reactor. It offers a performance increase of up to about 40% without the need to add new aeration tanks to existing systems. IFAS adds a high surface area to the activated sludge tank, providing additional biomass and increasing the rate of microbial growth.This not only increases the sludge age but also ensures high-performance wastewater treatment. Within the scope of the thesis, the combination of MBR (Membrane Bioreactor) and IFAS (Integrated Fixed-film Activated Sludge) systems within a single system is planned to enhance the efficiency of the membrane system. In this regard, utilizing the film attachment feature offered by IFAS, low F/M (Food to Microorganism) ratio filtration is conducted in the membrane tank, thereby increasing flux rates and reducing transmembrane pressure. Additionally, due to the high microbial attachment, high-efficiency wastewater treatment can be achieved in small footprint areas hydraulically. This situation will provide numerous advantages, especially in areas with spatial constraints, during the revision of conventional wastewater treatment plants to advanced biological wastewater treatment plants and in capacity expansions, enabling much more wastewater treatment in the same volume. Within the scope of the thesis, a 500 L/day capacity IFAS MBR system was designed and constructed. The designs of the systems were created using a 3D drawing program. Wastewater feed to the IFAS MBR system was introduced from beneath the fixation materials placed within the biological pool, ensuring homogeneous distribution. The system was fed with real wastewater, with hydraulic feed gradually increased. In this way, organic and hydraulic loading rates were determined for each system, identifying the maximum wastewater quantities that could be treated. Additionally, within the thesis scope, the IFAS MBR system was operated at different sludge ages. It was observed that even at low sludge ages, as low as 5 days, the nitrification rate was high in the IFAS MBR system operated at different sludge ages. Another promising feature of the IFAS MBR system is its ability to achieve high nitrification rates and total nitrogen removal even at low sludge ages. Since the majority of discharges into the Sea of Marmara consist of domestic wastewater, the IFAS MBR system will be utilized for domestic wastewater treatment within the ITU Ayazaga Campus. Subsequently, this system can be adapted for the treatment of various types of industrial wastewater as well. Within the project scope, the efficiency of the membrane system was enhanced by combining the MBR system with the IFAS system within a single system. In this regard, low F/M ratio filtration was achieved in the membrane tank using the film attachment feature offered by IFAS, thereby increasing flux rates. The integrated use of the IFAS system with the MBR system is not widely documented in the literature, thus contributing valuable information to the field. Operating the hybrid IFAS MBR system within the project will reduce the footprint of wastewater treatment facilities, facilitating the revision of existing systems. This means that advanced biological treatment can be achieved at much higher capacities using existing conventional systems.