Investigation of membrane pollution in the anaerobic membrane reactor under haloalkaline conditions

In this thesis, membrane fouling during simultaneous sulphate and organic matter removal in a submerged anaerobic membrane bioreactor under haloalkaline conditions was investigated. For this purpose, the enrichment process of microorganisms that survived under salty and alkaline conditions in the sludge taken from Lake Van was carried out. The effect of different chemical oxygen demand/sulfate (COD/SO42-) ratios, hydraulic retention times (HBS), organic loading ratio (OLR) and sulfate loading ratio (SLR), electron donors and salinity on flux, transmembrane pressure, membrane resistance, SMP and EPS concentration in the reactor inoculated by microorganisms in liquid medium were investigated. The reactor was operated for approximately 409 days with 12 periods depending on the operating conditions. Different COD/SO42- ratios ranging from 1-12, HRT values of 7, 10 and 15 days; OLR values in the range of 0.01-0,0417 g/Lday, SLR values in the range of 0.001-0.01 g/Lday and NaCl concentrations of 10-20 g/L to the system during operation were applied. Observing that the membrane was fouled, a new membrane module was used, hence a total of 8 membrane modules were used during the reactor operation. Samples were taken from the reactor and membrane module at each membrane change, SEM, EDX, FTIR, PBD and bacterial analysis were performed and the results were evaluated in terms of the effect of operating conditions on membrane fouling. Throughout the study, membrane fouling was caused by cake formation rather than pore blocking. The cake resistances were calculated to be approximately 4.2 to 242 times the resistances caused by pore blocking. Cake formation occurred mostly in the 7th period (P7) (COD:6000 mg/L; SO42-:1000 mg/L; COD/SO42-:6; NaCl:10 g/L; SLR: 0.006 g/L) due to high concentrations of SMP and EPS as a result of high OLR (0.04 g/Lday) and low HRT (7 days) and the usage of ethanol as a carbon source. When two electron donors are used together, membrane fouling is increased and membrane fouling caused by pore blockage is decreased. Membrane pores showed mostly organic origin fouling. The highest concentrations of SMP and EPS were found in 8th period (P8) (COD:3000 mg/L; SO42-: 3000 mg/L; COD/SO42-:1; HRT: 10 days; NaCl: 10 g/L; OLR: 0.01 g/Lday; SLR: 0.013 g/L) one of the periods with the highest fouling. According to SEM and EDX results, membrane pores were exposed to organic contamination and FTIR spectra showed that hydroxyl functional groups, amide I group, EPS related groups were present on membrane surfaces. Molecules having a larger PBD in the range of 100-1000 μm were observed with the use of the dual organic carbon source, while the particle size distribution of the cake layer was in the range of 10-100 μm. According to the results of microbial analysis, it was observed that the microbial diversity was less when acetate was used as electron donor. Decreasing the COD/SO42- ratio to 1 resulted in a decrease in the number of dominant species. The bacteria belonging to the g-proteobacteria group were determined to be the predominant species (50%) in the reactor during the 6-12th operating periods. Key Words: Membrane Fouling, Transmembrane Pressure, Membrane Flux, Soluble Microbial Product, Extracellular Polymeric Substances, Submerged Anaerobic Membrane Bioreactor