Membrane fouling studies in suspended and attached growth membrane bioreactor systems | |
| Author | Kwannate (Manoonpong) Sombatsompop |
| Call Number | AIT Diss. no.EV-07-02 |
| Subject(s) | Membrane reactors Bioreactors Water--Purification--Membrane filtration |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | The use of membranes in attached growth bioreactor has been growing interests for wastewater treatment plants. The membrane bioreactor (MBR) system can be regarded as an alternative way to achieve the design of compact wastewater treatment plants. Membrane fouling is known to be a serious problem in reductions of the membrane performance and the efficiency of the wastewater treatment. The objectives of this work were to examine the test conditions, to select the suitable media type, and to compare the effects of operating conditions, such as HRT and MLSS, on the membrane performance, fouling phenomena, extracellular polymeric substance (EPS) production and sludge properties in the suspended and the attached growth MBR systems. To investigate the effect of hydraulic retention time (HRT) on membrane performance, EPS production and sludge properties, the MBRs were operated at different HRT values of 2, 4, 6 and 8 hrs. The MBRs consisted of three bioreactors which included (i) suspended growth without media, (ii) attached growth with moving media, and (iii) attached growth with fixed media. The cylindrical polypropylene (CP) with 24% reactor volume was used as the moving media, while the fixed media used polyvinylidine chloride fibers. The fixed media had the specific surface area of 7.33 m2 /m, and specific media volume of 0.3 Lim. The amount of the fixed media used in the reactor was 5% of the total reactor volume. The removal efficiency of COD was found to be greater than 90%, even with a short HRT. For nitrogen mass balance of MBRs, the nitrogen removal was accomplished by microorganism assimilation and nitrification reaction in the MBR at all HRT values. The attached growth MBR with the moving media obtained higher capillary suction time (CST) value, indicating a poor sludge dewatering property. The movement of the media in the attached growth MBR was thought to cause the floe breakage which led to the production of the small floe. To examine the fouling mechanism in the attached and the suspended growth MBRs for three different biomass concentrations (6, 10, and 15 g/L of MLSS), two different sets of submerged MBRs: suspended (without media) and attached growth (with moving media) MBRs were used. The media used in the attached growth system was CP rings. Synthetic domestic wastewater was fed to the reactors at 2 h HRT and 500 mg/L COD. The biofouling phenomenon in the reactors was monitored by the changes in transmembrane pressure (TMP) as a function of operating time. It was found that the increase in fouling was associated with increasing MLSS concentration. The attached growth reactor was found to have lower fouling and prolong filtration as compared to the suspended growth reactor due to the difference in particle size distribution of biomass between these two reactors. The bound EPS contents in the suspended growth and attached growth reactors were very similar. The amount of soluble EPS at 15 g/L MLSS was higher than that at 6 and 10 g/L MLSS. In this work, the EPS was not the main factor to cause the fouling while the particle size of the biomass influenced by the movement of the media gave a significant effect on the formation of cake layers on the membrane. |
| Year | 2007 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Visvanathan, C. ; |
| Examination Committee(s) | Annachhatre, Ajit P. ;Rakshit, Sudip K. ;Wu, Jy S. ;Shipin, Oleg V. ;Buckley, Chris A. ; |
| Scholarship Donor(s) | KMIT, North Bangkok, Thailand ;AIT Fellowship ; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2007 |