Potential uses of ultrasound in the dairy ultrafiltration processes

There has been a growing interest in the industrial application of ultrasound, especially in the food industry. Power ultrasound can have a number of physical effects; it can increase turbulence through both the introduction of vibrational energy and through acoustic streaming, it can cause both particle agglomeration and particle dispersion and clean surfaces with a scouring action. Our work in this area has focused on the use of ultrasound to enhance membrane processing. Low frequency ultrasound has been used to facilitate cross flow ultrafiltration of dairy whey solutions for both during the ultrafiltration production cycle and the cleaning cycle. During the production cycle, the use of ultrasound reduces both pore blockage and the specific resistance of the fouling cake layer. This leads to higher flux rates and the potential for longer production cycles. During the cleaning cycle, ultrasound systematically increases cleaning efficiency, thus has the potential to reduce both total chemical consumption and system downtime. There was no deterioration in cleaning effectiveness or membrane condition which imples that sonication , has not damaged the membrane itself. Similarly, there was no change in the chemical nature of soluble proteins following sonication.

Mechanisms for the ultrasonic enhancement of dairy whey ultrafiltration

Low frequency ultrasound has been used to facilitate cross-flow ultrafiltration of dairy whey solutions. Experimental results show that ultrasonic irradiation at low power levels can significantly enhance the permeate flux with an enhancement factor of between 1.2 and 1.7. The use of turbulence promoters (spacers) in combination with ultrasound can lead to a doubling in the permeate flux. The application of a combined pore blockage/cake resistance model to the observed experimental data suggests that the use of ultrasound acts to lower the compressibility of both the initial protein deposit and the growing cake. Conversely, the pore blockage parameter is not significantly affected. The use of a gel polarization model shows that the ultrasonic irradiation increases the mass transfer coefficient within the concentration polarization layer. Electron microscopy results showed no evidence that the ultrasonic irradiation altered the membrane integrity. HPLC analysis of the whey proteins in the feed solution before and after sonication showed that the concentration profile of the whey proteins was also not affected by the sonication process.

Performance evaluation of different ultrafiltration membranes for the reclamation and reuse of secondary effluent

This study investigates and compares the performance of two different types of ultrafiltration (UF) membranes in the recovery of water from secondary treated wastewater. Filtration experiments were carried out on a pilot scale cross-flow unit using synthetic wastewater similar to the quality of secondary treated wastewater by varying the operating parameters such as transmembrane pressure (TMP), feed composition and membrane configuration. The filtration experiments demonstrated that the flux recovery through spiral polymeric UF membrane was more sensitive to the variation in TMP compared to the tubular ceramic UF membrane over the range of TMP studied. The resistance in series model was used for the evaluation of the resistance to the permeate flux. The fouling resistance, particularly irreversible resistance compared to reversible resistance plays a major role in the total resistance for the tubular ceramic membrane. In contrast clean membrane resistance is the major contributor for the total resistance of the spiral polymeric membrane. Finally, the effectiveness of the filtration treatment was determined by evaluating the rejection coefficients for various pollution indices of the wastewater. Significant differences in the performance of the membrane types were observed which are likely to impact on the selection, operation and maintenance of the membrane system.

Comparison of the performance of ceramic microfiltration and ultrafiltration membranes in the reclamation and reuse of secondary wastewater

Advanced treatment of secondary wastewater generally has been achieved using polymeric microfiltration and ultrafiltration membranes. Newly developed ceramic membranes offer distinctive advantages over the currently employed membranes and were recently introduced for the purpose. This paper presents results of a pilot study designed to investigate the application of ceramic microfiltration (MF) and ultrafiltration (UF) membranes in the recovery of water from secondary wastewater. Synthetic wastewater similar to the quality of secondary treated wastewater was fed to ceramic MF and UF system in a cross-flow mode. The filtration experiments revealed that the flux recovery through tubular ceramic MF membrane was more sensitive to the variation in TMP compared with the tubular ceramic UF membrane over the range of TMP studied. The resistance in series model was used for the evaluation of the resistance to the permeate flux. The results revealed that for ceramic UF membrane, the contribution to the total resistance of fouling was higher than the inherent of the clean membrane resistance. However, both the clean membrane resistance and the fouling resistance contribute equally in the case of MF membrane. Various wastewater indices were measured to evaluate the effectiveness of the filtration treatment. The ceramic UF membrane consistently met water quality in the permeate in terms of colour, turbidity, chemical oxygen demand and absorbance, suggesting that the permeate water could be made to be reused or recycled for suitable purposes. However, MF membrane appeared to be incompetent with respect to the removal of colour. The unified membrane fouling index (UMFI) was used to measure the fouling potential of both the membranes. The result showed that for UF membrane, the value of UMFI is one order of magnitude higher than MF membrane. The overall results suggest that there were significant differences in the performance of both the ceramic UF and MF membranes that are likely to impact on the operation and maintenance of the membrane system.