Influence of hydrodynamic and physico-chemical approaches on fouling mitigation in a membrane bioreactor | |
| Author | Khan, Sher Jamal |
| Call Number | AIT Diss. no.EV-08-03 |
| Subject(s) | Bioreactors Membrane reactors |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Membrane bioreactor (MBR), a combination of biological degradation by activated sludge and direct solid liquid separation by membrane filtration, is an attractive alternative to conventional activated sludge process (CASP) for the treatment and reuse of industrial and municipal wastewaters. Due to the higher operating costs involved in side-stream MBRs, submerged MBRs have become the preferred choice in MBR plant installations from the mid 1990s. However, the wide spread application of the submerged MBR process is constrained by membrane fouling and it is considered as the most serious problem affecting system performance. Therefore, most MBR researches aim to identify, investigate, control and model membrane fouling. The aim of this research was to investigate hydrodynamic and physico-chemical approaches on fouling mitigation in a submerged MBR using hollow fiber membranes. Moreover, sludge characteristics and their contribution to membrane fouling under each set of mitigation approaches were examined. The thesis was structured in two parts, of which the first part focused on hydrodynamic approach and the second part on physico-chemical approach. In the first part, the influence of shear intensity induced by mechanical mixing on activated sludge characteristics as well as membrane fouling propensity in MBRs was investigated. Four laboratory-scale MBRs were operated at different mechanical mixing conditions. The control reactor (MBR₀) was operated with aeration only supplemented by mechanical stirring at 150, 300 and 450 rpm in MBR₁₅₀, MBR₃₀₀ and MBR₄₅₀, respectively. It was found that the MBR₃₀₀ demonstrated prolong filtration cycle and low rate of membrane fouling. The fouling potential of the MBR₃₀₀ mixed liquor was also low characterized by the specific cake resistance (a) and the normalized-capillary suction time (CSTN) depicting MBR₃₀₀ condition as the optimum. Moreover, it was found that the mean particle size reduced with increase in the shear intensity. The bio-particles under high shear intensity were observed having low activity in terms of specific oxygen uptake rate (SOUR). Furthermore, the low SOUR of microbes demonstrated low biopolymer release during the biofilm simulation test due to the slow cell death rate. These results reveal that membrane fouling can be significantly mitigated by appropriate shear intensity induced by mechanical mixing condition in a MBR. In the second part, the influence of hybrid MBRs with addition of Kaolin clay, NALCO cationic polymer (MPE50) and powdered activated carbon (PAC) on the fouling propensity was investigated. Optimum initial dosages of clay, polymer and PAC to the MBRclay, MBRpotymer and MBRPAC, respectively were determined using jar tests. The filtration performances and the biomass characteristics in the hybrid MBRs were compared to that in the conventional MBR (MBRcontrol) from the first phase of the study. It was found that the MBRPAC exhibited low fouling tendency and prolonged filtration as compared to that in the others MBRs. Improved filtration performance in MBRPAC was attributed to the flocculation and adsorption phenomena. The effective flocculation of biomass by PAC was verified by the increase in mean particle size and narrow particle size distribution and the more or less rounded and firm flocs revealed by microscopic investigation. Moreover, the SOUR of microorganisms in the MBRPAC was found to be lower than that in the other MBRs. The large bio-flocs with low SOUR due to PAC addition could have been the basis of improved filtration performance in the MBRPAC. |
| Year | 2008 |
| 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) | Vigneswaran, S.;Preeda Parkpian;Shipin, Oleg V.;Babel, Mukand S.; |
| Scholarship Donor(s) | Higher Education Commission (HEC), Pakistan;Asian Institute of Technology Fellowship; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2008 |