Membrane fouling caused by extracellular polymeric substances during microfiltration processes | |
| Author | Chackrit Nuengjamnong |
| Call Number | AIT Diss. no.EV-04-06 |
| Subject(s) | Membrane reactors Bioreactors Membranes (Technology) |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. EV-04-06 |
| Abstract | Application of membrane bioreactor (MBR) in wastewater treatment has been a promising technology with considerable advantages over conventional methods. However, membrane fouling is a crucial impediment of the MBR system. One of the major causes of membrane fouling in activated sludge comes from extracellular polymeric substances (EPS). Therefore, this study investigated the effects both of extractable (bound) extracellular polymeric substances (EPS) and the supernatant of sludge floes (i.e., designated as soluble EPS) on the membrane fouling in submerged membrane bioreactors (SMBRs). Three lab-scale SMBRs were operated at a constant permeate flux (12.5 L/m2.h) with a flat sheet micro-filtration membrane (hydrophilic polyolefin, pore size of 0.25 μm) at different solids retention times (8, 20 and 80 days, respectively). The concentrations of extractable EPS (i.e., extracted by cation exchange resin method) and dissolved organic carbon (DOC) in the supernatant at the steady-state period were compared. The results showed that as SRT increased, the organic carbon content in extractable EPS decreased, whereas soluble EPS tended to be independent of SRT. Batch filtration tests were conducted to determine the specific cake resistances of the fouling layer using both of the raw sludge (i.e., composed of soluble and bound EPS) and the twice-washed sludge with buffer solution (i.e., composed of only bound EPS). The specific cake resistance of soluble EPS contributed approximately 50% to the total specific cake resistance. The organic carbon and protein content in the extractable EPS decreased with increasing SR T and protein content in the soluble EPS also had the same tendency. Therefore, the soluble EPS also played a relatively significant role in membrane fouling. The soluble EPS in membrane fouling was confirmed using membrane pore cut-offs i.e., the particle size distribution of biofilm and mixed liquor taken from SMBR. This research also evaluated the influence of EPS concentration on membrane cleaning efficiency for the SMBR system. Two lab-scale flat SMBRs with SR Ts of 25 and 250 days were operated. The experimental set-up was the same as the former experiment. The extractable EPS and protein concentrations were relatively low at the prolonged SRT, leading to easily removable cake layers using the physical cleaning or the de-ionized (DI) water backwashing and the chemical cleaning, i.e. sodium hypochlorite (NaOCl), methods. The extent of flux recoveries (both in SMBRs and batch filtration tests) and macroscopic as well as microscopic images (using scanning electron microscopy, SEM) indicated that the chemical cleaning could enhance the effectiveness of membrane cleaning. The combined method (DI water backwashing followed by chemical cleaning) could be the most effective than only the single cleaning method. Moreover, the mechanisms of membrane fouling and cleaning were also discussed. |
| Year | 2004 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. EV-04-06 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Environmental Engineering (EV) |
| Chairperson(s) | Chongrak Polprasert; Ahn, Kyu-Hong ; |
| Examination Committee(s) | Visvanathan, Chettiyappan; Athapol Noomhorm; Lee, Seung-Hwan; Kweon, Ji-Hyang;Clark, Mark M. ; |
| Scholarship Donor(s) | Royal Thai Government (RTG); Korea Institute of Science and Technology (KIST); |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2004 |