Many different methods for solving the problems associated with water quality, water scarcity and the resulting environmental pollutions are already established. Energy efficient pressure driven membrane separation processes such as ultrafiltration, reverse osmosis or microfiltration have gradually become feasible treatment alternatives in many drinking water facilities and wastewater reclamation centers. However, this technology has the major problem of flux decline due to concentration polarization and membrane fouling. In this thesis first the mere ultrafiltration was characterized using a latex suspension and the results were compared with the previous work of (Duwadi, 2009). Then the effect of an external dc electric field to reduce the problems with fouling and concentration polarization during crossflow ultrafiltration beside the effects of other experimental parameters such as transmembrane pressure, crossflow velocity, pH and feed concentration was studied. Hereby, a model colloidal alumina suspension was used to represent the characteristics of positively charged pollutants in wastewater during electro ultrafiltration. Finally a statistical analysis of the importance of different experimental factors and their possible interactions was done.
During the UF of the latex suspension, it was noticed that in addition to concentration polarization, adsorption or other kinds of membrane fouling also played a significant role in the flux decline during the filtration process. The experimental study was also conducted under crossflow velocities of 5cm/s, 26cm/s and 37cm/s. Filtration resistance appreciably decreased with a fivefold increase in crossflow velocity especially at higher TMP. In examining the effect of water chemistry, for a pH change from 4.5 to 10.5, the flux was observed to increase from 129L/m2/h to 200L/m2/h. Independent experiments undertaken at 50 and 75mg/L latex suspension to examine the effect of the feed concentration gave virtually identical fluxes owing to the increased crossflow velocity relative to the previous study by (Duwadi, 2009).
The EUF experiments were preceded by characterizing the characteristics of the alumina particles. Overall, a weak pressure dependence was observed in the experimental results especially at higher pressure ranges. A clear enhancement of flux was achieved by superimposing an electric field on the TMP across the membrane. The enhancement was substantial for higher TMP and higher feed concentration values. By superimposing 10 and 20V/cm electric field strength to 50kPa TMP, the increase in flux was found to be as high as 30% and 35%, respectively.

Besides, the flux declines in raising the feed concentrations from 100 to 500mg/L. The pH of the feed suspension was also found to be a major factor in determining the efficiency of EUF through alteration of the surface charge of the alumina particles. As the pH increased from the lower range to the vicinity of the zero point of charge (pH 4 to pH 8 with the corresponding change in zeta potential of +46mV to +17mV), the permeate flux was observed to decrease by 6% on average under all the TMP examined. Moreover, the membrane fouling becomes more severe as the initial ionic strength of the feed solution increases. In 80% of the cases the calculated retention values were found to be more than 97%. Remarkable pH alterations were noted in the feed, concentrate and permeate with a more aggravation at higher ionic strengths. The conductivities of the permeates also exhibited a logarithmic increase with increase in salt concentration whilst more or less similar conductivities were recorded for both feed and concentrate. Finally, a statistical analysis was undertaken to identify the importance and the interaction of operating parameters. Based on the results, feed concentration and then the electric field strength were found to be the most significant parameters affecting the filtration, while the electrolyte concentration was less significant. The only interaction which was important within a smaller significance level was the one between the electric field strength and electrolyte concentration and all the others were found to be negligible.
To conclude, the EUF process was found to be promising even for higher order feed concentrations, at low ionic strength.

Faculty of Bioscience Engineering - Center for Environmental Sanitation
Academic year 2009-2010

Promotor: Prof. Dr. ir. Paul Van der Meeren
Dr. ir Hans Saveyn
Department of applied analytical and physical chemistry Particle Interfacial and Technology Group

Tutor: Mrs. Maryam Hakimhashemi
Master’s dissertation submitted in partial fulfillment of the requirements for the degree of Master in Environmental Sanitation