Author: Leila Safazadeh Haghighi

Publisher:

Published: 2011

Total Pages: 130

ISBN-13:

The use of Membrane technology is extensively increasing in water and wastewater treatment, food processing, chemical, biotechnological, and pharmaceutical industries because of their versatility, effectiveness, high removal capacity and ability to meet multiple treatment objectives. A common problem with using membranes is fouling, which results in increasing operating costs due to higher operating pressure losses, membrane downtime needed for cleaning, with associated production loss and manpower costs. In the literature, four different mechanisms for membrane fouling have been studied, which are complete pore blocking, internal pore blinding, partial pore bridging and cake filtration. Mathematical models have been developed for each of these fouling mechanisms. The objective of this thesis was to investigate the membrane fouling mechanisms for one porous and one dense membrane, during ultrafiltration of an emulsified industrial oily wastewater. An experimental system was designed, assembled and operated at the Ford Transmission Plant in Sharonville, Ohio, wherein ultrasonic baths were used for cleaning transmission parts before assembly. The oil wastewater, containing emulsified oils and cleaning chemicals was collected in a batch vessel and then pumped through a porous polyethersulfone, monolithic membrane, and through a dense cuproammonium cellulose membrane unit. For the porous membrane, use of a Dupont's flurosurfactant (FS 63) and backwashing with permeate and for the dense membrane the use of both the flurorosurfactant and sparged air were investigated to reduce membrane fouling. For the porous membrane study, it was observed that the permeate flux was strongly dependent on the transmembrane pressure difference, and addition of the flurosurfactant significantly improved the performance of the membrane. The backwashing cleaning efficiency was found to depend on the duration of backwashing and its frequency. An integrated fouling model was developed by combining the individual models for each fouling mechanism, originally published by Hermia [18], and analysis of the experimental data for ultrafiltration of oily emulsion revealed that the primary mechanism for fouling of the porous membrane was cake filtration. With increasing transmembrane pressure, the role of other mechanisms, such as pore blocking and partial pore bridging, increases, although the effect of cake filtration dominates. Hence, for oily emulsions, methods to disrupt the formation of a cake layer at the membrane surface would have the most impact in increasing the water permeation rates through the membrane. For the dense membrane study, permeate flux also increased with increasing transmembrane pressure difference, as in the porous membrane, and the major mechanisms for fouling were found to be concentration polarization gel layer formation on the membrane surface. In this case, the use of both sparged air and fluorosurfactant, increased the water permeation rates, but the permeation rate improvement with sparged air alone was significantly higher than with fluorosurfactant only. A mathematical model was developed to derive the mass transfer coefficients under the various operation conditions. Future studies will concentrate on improving membrane performance by reducing the impact of the dominant fouling mechanisms, found in this study, for both porous and dense membranes.