Protein quality and physico-functionality of Australian sweet lupin (Lupinus angustifolius cv. Gungurru) protein concentrates prepared by isoelectric precipitation or ultrafiltration

The protein quality and physico-functional properties of Australian sweet lupin protein concentrates, prepared by isoelectric precipitation or ultrafiltration, were assessed. The ultrafiltration process resulted in a higher yield of protein than did the isoelectric precipitation process. The lupin kernel and the two lupin protein concentrates had similar essential amino acid compositions that were inferior to ideal human requirements. True digestibilities of the isoelectrically precipitated (ISO) and the ultrafiltered (UF) lupin protein concentrates were similar but significantly higher (P<0.05) than that of casein. Net protein utilisations (NPU) of the ISO and UF protein concentrates were similar but significantly lower (P<0.05) than that of casein. The UF protein concentrate had higher protein solubility than did the ISO protein concentrate (P<0.05). Low foaming capacity, low viscosity, but high emulsification capacity (particularly at low pH) were observed for lupin protein concentrates.

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.

The application of ultrasound to dairy ultrafiltration : the influence of operating conditions

Work previously presented has shown that ultrasound can be effective in enhancing both the production and cleaning cycles of dairy membrane  processes. In this present work we extend these previous results to consider the effect of ultrasonic frequency and the use of intermittent ultrasound. These results show that the use of continuous low frequency (50 kHz) ultrasound is most effective in both the fouling and cleaning cycles. The application of intermittent high frequency (1 MHz) ultrasound is less effective. At higher transmembrane pressure, high frequency pulsed sonication can indeed lead to a reduction in steady state membrane flux. The benefits of ultrasound arise from a reduction in both concentration polarization and in the resistance provided by the more labile protein deposits that are removed during a water wash. Conversely, the loss of membrane flux when high frequency pulsed sonication is used arises from a significant increase in the more tenacious ‘irreversible’ fouling deposit.

The optimisation of ultrasonic cleaning procedures for dairy fouled ultrafiltration membranes

Ultrafiltration (UF) of whey is a major membrane based process in the dairy industry. However, commercialization of this application has been limited by membrane fouling, which has a detrimental influence on the permeation rate. There are a number of different chemical and physical cleaning methods currently used for cleaning a fouled membrane. It has been suggested that the cleaning frequency and the severity of such cleaning procedures control the membrane lifetime. The development of an optimal cleaning strategy should therefore have a direct implication on the process economics. Recently, the use of ultrasound has attracted considerable interest as an alternative approach to the conventional methods. In the present study, we have studied the ultrasonic cleaning of polysulfone ultrafiltration membranes fouled with dairy whey solutions. The effects of a number of cleaning process parameters have been examined in the presence of ultrasound and results compared with the conventional operation. Experiments were conducted using a small single sheet membrane unit that was immersed totally within an ultrasonic bath. Results show that ultrasonic cleaning improves the cleaning efficiency under all experimental conditions. The ultrasonic effect is more significant in the absence of surfactant, but is less influenced by temperature and transmembrane pressure. Our results suggest that the ultrasonic energy acts primarily by increasing the turbulence within the cleaning solution.

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.

The use of ultrasonic cleaning for ultrafiltration membranes in the dairy industry

The ultrafiltration of whey solutions is a common feature of dairy processes. However, the frequent fouling of ultrafiltration membranes and the subsequent cleaning cycle significantly affect the economics of such a process. In this work, we investigated the effect of ultrasonics on the cleaning of whey-fouled membranes and examined the variables that influence this effect. Experiments were conducted using a small single sheet membrane unit that was immersed totally within an ultrasonic bath.

Results show that the use of ultrasonics enhances the flux recovery following fouling. The extent of flux recovery is independent of the length of sonication time and increases with ultrasonic power. The use of surfactants in combination with ultrasonic irradiation shows a synergistic effect, providing a better efficiency than either cleaning process alone. Repetitive use of ultrasonic cleaning over a 1 month period does not result in any significant change in the permeate flux of a cleaned membrane, indicating that the ultrasonic treatment does not appear to damage the membrane structure itself.

Effect of coagulants on the fouling and performance of ultrafiltration (UF) membranes

The combined coagulation and ultrafiltration (UF) system (C-UF system) is an advanced technology to treat natural organic matter (NOM) present in water. Traditional coagulants — prehydrolyzed inorganic coagulants, organic coagulants and composite coagulants were chosen to treat synthetic water containing humic acid (HA) in order to find an efficient coagulant that could remove NOM from the water effectively. The fouling, removal efficiency of UF and the chlorine decay in the permeate were used to evaluate the effectiveness of the coagulants. The initial UV254 absorption of the tested water samples were from 0.208 to 0.234, and the UV254 after coagulation was from 0.05 to 0.184. The UV254 did not increase after coagulation. Since the humic acid used was soluble, the initial turbidity of the tested water samples were very close to zero. The turbidity increased after coagulation, as the coagulants react with humic acid to form micro-flocs, which cannot be removed fully by sedimentation. The results showed that polyferric chloride could not remove humic acid efficiently during coagulation process, but removed the humic acid well when used in the C-UF system. Moreover, for polyferric chloride and UF system, the concentration of organic compounds in permeates were minimal indicating very low levels of disinfection by-product formation, if chlorinated.

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.

Enhancement of the antifouling properties and filtration performance of poly(ethersulfone) ultrafiltration membranes by incorporation of nanoporous titania nanoparticles

Nanoporous titania nanoparticles (NTNs) were synthesized and used as an additive at a low concentration of 0.1-1 wt % in the fabrication of poly(ethersulfone) (PES) ultrafiltration membranes via non-solvent-induced phase separation. The structure and properties of nanoparticles were characterized using nitrogen sorption, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The NTNs have a size distribution with a particle size of mainly <100 nm and have a Brunauer, Emmett, and Teller surface area of ∼100 m2 g-1. The modified membranes were fabricated and investigated in terms of their pure water flux, solute rejection, and fouling resistance. The water permeability and molecular weight cutoffs (MWCOs) of membranes were determined under constant-pressure filtration in dead-end mode at 100 kPa. The membrane fouling resistance was characterized under constant flux operation using bovine serum albumin as a model foulant. The membranes were characterized in terms of morphology, porosity, pore size distribution, energy-dispersive X-ray spectroscopy, contact angle goniometry, surface free energy, and viscosity of the dope solution. Overall, the modified membrane showed increased wettability and reduced surface free energy and pore size. The modified UF membrane with 0.5 wt % NTN loading exhibited improved fouling resistance (fouling rate of 0.58 kPa/min compared to a rate of 0.70 kPa/min for the control membrane) with ∼80% water flux recovery. The same membrane showed an ∼20% increase in water flux, an improvement in MWCO, and a narrower pore size distribution.

Characterization of haemolytic phospholipase A2 activity in clinical isolates of Campylobacter concisus

A membrane-bound, haemolytic phospholipase A2 (PLA2) activity was detected in clinical strains of Campylobacter concisus isolated from children with gastroenteritis. The clinical strains were assigned into two molecular groups (genomospecies) based on PCR amplification of their 23S rDNA. This calcium-dependent, heat-stable, haemolytic PLA2 activity was detected in strains from both genomospecies. A crude haemolysin extract (CHE) was initially prepared from cellular outer-membrane proteins of these isolates and was further fractionated by ultrafiltration. The haemolytic activity of the extracted fraction (R30) was retained by ultrafiltration using a 30 kDa molecular mass cut-off filter, and was designated haemolysin extract (HE). Both CHE and HE had PLA2 activity and caused stable vacuolating and cytolytic effects on Chinese hamster ovary cells in tissue culture. Primers for the conserved region of pldA gene (phospholipase A gene) from Campylobacter coli amplified a gene region of 460 bp in all tested isolates, confirming the presence of a homologous PLA gene sequence in C. concisus. The detection of haemolytic PLA₂ activity in C. concisus indicates the presence of a potential virulence factor in this species and supports the hypothesis that C. concisus is a possible opportunistic pathogen.

Reverse osmosis membrane fouling and its control

Reverse osmosis (RO) membranes can be used to treat ground water, surface water and wastewater, but a major problem in RO membrane applications is fouling. Many studies have investigated the mechanisms of fouling in RO membranes and suggested various methods to control the membrane fouling. This paper reviews several aspects of RO membranes, such as the types of membrane fouling, their effects on RO membrane processes and fouling control technologies, focussed on the appropriate feed pretreatment technologies and cleaning methods, especially on the membrane filtration pretreatment processes, including microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF), which are the new trends in designing a pretreatment system in the application of RO.