This study develops and demonstrates a microfluidic module for investigating the mechanism of inorganic fouling caused by the precipitation of calcium sulfate (CaSO4) on nanofiltration membranes. The developed microfluidic module enables sensitive system responses, rapid detection and real time observation of inorganic fouling commonly encountered in water treatment industries. For this development, CaSO4 is selected as the model salt due to its unique fouling characteristics. The effect of the operating conditions, such as pressure and permeate flux, was on the fouling behavior is investigated. A plate-frame type microfluidic chip was fabricated and employed in a dead-end filtration mode for constant-flux fouling experiments. The nanofiltration chip module has a dimension of 50 mm ¡Ñ 25 mm ¡Ñ 12 mm. It is consisted of a polymeric nanofilter, a pressure acquisition unit, a C.C.D., and micro electrodes on the nanofilter for investigating the relationships among trans-membrane pressure, conductivity on membrane surface and permeate fluxes. With the microfluidic system, real-time concentration polarization, bulk nucleation of CaSO4 and surface crystal accumulation were observed in terms of the variations of pressure and conductivity on membrane surface, which were verified with scanning electron micrographs to confirm the corresponding fouling stage. It is found that membrane surface conductivity increases with trans-membrane pressure before bulk crystallization of CaSO4, then slightly decreases after the formation of bulk nuclei due to the removal of solute in the aqueous phase. The conductivity remains relatively constant during cake formation stage while trans-membrane pressure steadily increases. This study successfully integrates microfluidic technology with pressure and electrical measurements for detecting the dynamic transition during CaSO4 fouling, and reports for the first time the experimental measurement of the initiation of inorganic cake formation.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0818106-154622 |
| Date | 18 August 2006 |
| Creators | Hsu, Chih-peng |
| Contributors | Che-Hsin Lin, Long-ming Fu, Che-Jen Lin, none |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0818106-154622 |
| Rights | off_campus_withheld, Copyright information available at source archive |
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