LEE- Çevre Bilimleri Mühendisliği ve Yönetimi-Doktora
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ÖgeDynamic membranes in aerobic membrane bioreactor systems for municipal wastewater treatment(Graduate School, 2021-06-08) Işık, Onur ; Demir, İbrahim ; Özgün, Hale ; 501142704 ; Environmental Sciences Engineering and Management ; Çevre Bilimleri Mühendisliği ve YönetimiThe amount of municipal wastewater produced around the world is expected to increase parallel to the increase in population. Therefore, the treatment of municipal wastewater is very crucial for public health. Conventional activated sludge systems have been used for the treatment of municipal wastewater for a long time. Due to limited area availability and stringent discharge standards in most cases, compact treatment systems enabling high effluent quality have become attractive recently. Membrane bioreactor (MBR) technology is a good alternative to conventional activated sludge systems. There are several advantages of MBR technology over conventional biological treatment systems. Low footprint and high permeate quality can be considered as the most distinguishing features of the MBRs. Due to the retention of high suspended solids concentration in the bioreactor, smaller reactor volume and low sludge production can be achieved by the MBR process. However, some constraints have been observed during the operation of MBRs including membrane fouling and membrane costs. Dynamic membrane (DM) technology is a promising solution for problems encountered during the operation of MBRs for wastewater treatment. Membranes can be substituted with coarse-pore filters made of low-cost materials such as meshes or fabrics in dynamic membrane applications for cake (DM) layer formation. DM is a secondary layer formed on a low-coast porous support material. DM layer acts like a Microfiltration (MF) or Ultrafiltration (UF) membrane and keeps the sludge particles inside the bioreactor providing high permeate quality. Besides, physical cleaning, without using chemical reagents, may be enough for cleaning in dynamic membrane bioreactors (DMBRs), thus, the operational costs can be reduced. Flat sheet submerged module configurations were mostly used for aerobic DMBR studies for municipal wastewater treatment in the literature. Also, few studies used tubular modules in DMBRs. However, no studies reported using hollow fiber modules in the literature. The main aim of this thesis was to investigate the applicability of hollow fiber DM for municipal wastewater treatment in an aerobic DMBR. This thesis was conducted in 6 Stages. In stage 1, a hollow fiber polyester fabric support material was used for DM formation and compared with a commercial hollow fiber UF membrane. The system was fed with medium strength synthetic municipal wastewater to keep the characteristics of the wastewater same, and to evaluate the treatment and filtration performances of both membranes clearly. Morphological analyses were also carried out for DM and UF surfaces. The system was operated continuously at a flux of 5 L/m2·h for 85 days. High chemical oxygen demand (COD) removal efficiency and total suspended solids (TSS) rejection were achieved by the DM. Transmembrane pressure (TMP) of the DM was higher in comparison to the UF membrane, which was related to the formation of the cake layer in DM. In Stage 2, impact of support material type on DMBR performance was investigated for municipal wastewater treatment. A hollow fiber polyester support material was compared with a glass fiber support material in terms of treatment and filtration performances. Medium strength synthetic municipal wastewater was used for a stable feed characteristics. Similar treatment performances were obtained with each membrane achieving high removal efficiencies for COD(>97%) and TSS (>99%) parameters. Higher TMP was observed for glass fiber material in comparison to polyester material. Based on morphological analyses, dynamic layers formed on both support materials had similar compositions, organic and inorganic materials. A homogeneous layer was formed on a polyester support material, while fine particles were deposited between the filaments of glass fiber support material, which caused clogging. In Stage 3, a hollow fiber polyester fabric support material was used for DM formation for raw municipal wastewater treatment. The wastewater had average COD concentration of 413 mg/L, sCOD concentration of 208 mg/L and TSS concentration of 259 mg/L. Treatment and filtration performances were evaluated. High treatment performance was obtained in the permeate achieving over 93% of COD removal efficiency and low TSS concentration (<10 mg/L) in the permeate. The average TMP value was observed as around 598 mbar after the system reached stable conditions. In Stage 4, effect of different TSS concentrations on the DM layer was evaluated in terms of biological treatment and filtration performances. Hollow fiber polyester support material was used for DM layer formation. Treatment and filtration performances of the DMBR were investigated at two different TSS concentrations (5 g/L; 10 g/L). The DMBR was operated at a flux of 18 L/m2·h at each condition. High treatment performance and permeate quality were achieved at each sludge concentration. However, a shift to a relatively higher range in particle size distribution of permeate was observed at high sludge concentration. Furthermore, higher TMP was observed at the sludge concentration of 10 g/L, resulting in a rapid clogging. Overall, results indicated that selection of the optimum sludge concentration played a significant role in achieving homogeneous and stable DM layer in DMBRs. In stage 5, hollow fiber polyester support material was used for DM formation and compared with a commercial UF membrane in terms of micropollutant and heavy metal treatment performance from raw municipal wastewater, also biological treatment and filtration performances were evaluated. The removal of different micropollutants; sulfamethoxazole, ciprofloxacin, trimethoprim, caffeine and acetaminophen, was assessed for both membranes. The membranes were operated at a flux of 10 L/m2·h. High TSS (>99%) and COD (> 91%) removal efficiencies were achieved with both membranes. Similar high removal efficiencies of micropollutants (>68.3->99.7%) were achieved with both membranes. DM was operated at higher TMP compared to UF membrane, since DM layer was formed on the support material. Morphological analyses were conducted for both membranes to get insight to the DM layers which accumulated on the membranes. In Stage 6, effect of using different inoculum on DMBRs performance was investigated. Excess sludge from HRAS and conventional activated sludge system retuned activated sludge were used as inoculums. Conventional UF membrane was used in parallel with a dynamic membrane (DM) in the same reactor to be operated at the same conditions. Both sludges were characterized to understand the changes during the operational period. Biological treatment and filtration performances of both membranes were investigated. High TSS (>99%) and COD (> 86%) removal efficiencies were achieved with both membranes for both inoculum sludge. Because of the inoculum sludge characteristics, lower TMP values were observed for DM at Phase-2. Morphological analys (ESEM measurement) was conducted to understand the effect of different inoculum on the sludge cake on the surface of the membranes.