Thesis (Ph.D. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.

The objective of this work was the investigation of nanofiltration as a potential avenue to fractionate protein hydrolysates and produce protein hydrolysate fractions with stimulating bioactivity for the development of a supplement for a serum-free media. Mammalian cell culture is widely used for the production of therapeutic proteins such as antibodies, interleukins, and vaccines because of the ability of mammalian cells to glycosylate proteins. A complex media with the addition of serum is often required to meet the requirements of the cells. Although serum is a supplement that provides different proteins such as growth factors and hormones, serum has several disadvantages such as high cost, difficulty of downstream processing due to its high protein content and the possibility of microbiological contamination. Protein hydrolysates from plant, animal, or yeast cells contain a complex mixture of peptides and amino acids and have been shown to enhance growth of certain mammalian cell lines cultured in serum-free media. To fractionate peptide mixtures, nanofiltration was investigated in this study. Nanofiltration is a pressure driven membrane separation process based on size and charge. The investigation of pH and NaCl on the filtration performance for two different nanofiltration membranes (HL membrane and G-10 membrane) was achieved using a 24 factorial design. The total peptide concentration, the antioxidant activity, and organic and inorganic content were analyzed in the permeate and retentate fraction. The fractions were also tested for their enhanced growth ability and the specific -interferon productivity with CHO cells. Furthermore the retentate and permeate fractions were analyzed by reversed phase-HPLC to characterize the peptide and free amino acid distribution profile. Through the factorial design, the membrane type was shown to have a significant effect on the filtration performance for both yeast extract and Primatone. A significant difference, but similar for both feed sources, was observed for the total peptide transmission with around 10% for the HL membrane and around 30% for the G-10 membrane. The average permeate flux was significantly lower for the G-10 membrane although the G-10 membrane is a loose nanofiltration membrane with a reported 2500 Da MWCO compared to the HL membrane with a reported 300-500 Da MWCO. The total peptide transmission, organic and inorganic content of the fractions for the two feed sources and membrane type were affected differently according to pH and NaCl addition. These results indicate that the two feed sources are of different composition and that nanofiltration is a possible method to fractionate peptides. The bioactivity of the nanofiltration fractions was tested as a nutrient additive to a serum-free media in CHO cells. It was shown that the productivity is not always related to the cell density, as the highest overall specific interferon productivity was achieved for low cell density similar to the hydrolysate free negative control. Furthermore, the retentate fraction of yeast extract separated with the G-10 membrane at a pH of 8 resulted in the highest cell density. According to these results, nanofiltration is a promising method for the enrichment of protein hydrolysates as a supplement for serum in cell culture.

The objective of this work was the investigation of nanofiltration as a potential avenue to fractionate protein hydrolysates and produce protein hydrolysate fractions with stimulating bioactivity for the development of a supplement for a serum-free media. Mammalian cell culture is widely used for the production of therapeutic proteins such as antibodies, interleukins, and vaccines because of the ability of mammalian cells to glycosylate proteins. A complex media with the addition of serum is often required to meet the requirements of the cells. Although serum is a supplement that provides different proteins such as growth factors and hormones, serum has several disadvantages such as high cost, difficulty of downstream processing due to its high protein content and the possibility of microbiological contamination. Protein hydrolysates from plant, animal, or yeast cells contain a complex mixture of peptides and amino acids and have been shown to enhance growth of certain mammalian cell lines cultured in serum-free media. To fractionate peptide mixtures, nanofiltration was investigated in this study. Nanofiltration is a pressure driven membrane separation process based on size and charge. The investigation of pH and NaCl on the filtration performance for two different nanofiltration membranes (HL membrane and G-10 membrane) was achieved using a 24 factorial design. The total peptide concentration, the antioxidant activity, and organic and inorganic content were analyzed in the permeate and retentate fraction. The fractions were also tested for their enhanced growth ability and the specific -interferon productivity with CHO cells. Furthermore the retentate and permeate fractions were analyzed by reversed phase-HPLC to characterize the peptide and free amino acid distribution profile. Through the factorial design, the membrane type was shown to have a significant effect on the filtration performance for both yeast extract and Primatone. A significant difference, but similar for both feed sources, was observed for the total peptide transmission with around 10% for the HL membrane and around 30% for the G-10 membrane. The average permeate flux was significantly lower for the G-10 membrane although the G-10 membrane is a loose nanofiltration membrane with a reported 2500 Da MWCO compared to the HL membrane with a reported 300-500 Da MWCO. The total peptide transmission, organic and inorganic content of the fractions for the two feed sources and membrane type were affected differently according to pH and NaCl addition. These results indicate that the two feed sources are of different composition and that nanofiltration is a possible method to fractionate peptides. The bioactivity of the nanofiltration fractions was tested as a nutrient additive to a serum-free media in CHO cells. It was shown that the productivity is not always related to the cell density, as the highest overall specific interferon productivity was achieved for low cell density similar to the hydrolysate free negative control. Furthermore, the retentate fraction of yeast extract separated with the G-10 membrane at a pH of 8 resulted in the highest cell density. According to these results, nanofiltration is a promising method for the enrichment of protein hydrolysates as a supplement for serum in cell culture.

This thesis presents a study to enhance and improve a zero liquid discharge (ZLD) reverse osmosis process that uses seed crystals to promote crystallization of the dissolved salts in the residual brine while it is being treated by identifying those membrane materials that are most suitable for the process. In the study, a one plate SEPA Cell module by GE Osmonics was used to determine which membranes were most susceptible to fouling and/or membrane hydrolysis. A cellulose acetate (CA), polyamide (PA) low MWCO, and PA high MWCO membrane were tested under reverse osmosis conditions. The CA and thin film (TF) membranes were also tested for nanofiltration. The cell was operated under conditions that were determined to be optimum for each membrane by the manufacturer, GE Osmonics. A high pressure, low flow, positive displacement diaphragm pump circulated the saturated calcium sulfate solution with 2 % suspended solids through the cell while the reject and permeate were recycled back to the feed, thereby preserving a saturated solution to promote crystal growth and simulate the seeded reverse osmosis process. The temperature was maintained constant by adding an ice pack to the feed vessel when necessary. The transmembrane pressure differential was maintained constant by adjusting a back pressure valve on the concentrate outlet. The results illustrate that if potable drinking water is the intended use, then the nanofiltration cellulose acetate membrane should be used. If irrigation is the desired use, then the nanofiltration thin film membrane should be used. Overall, the reverse osmosis cellulose acetate membrane was observed to outperform all membranes when all performance parameters were normalized. However, this membrane was observed to be prone to degradation in a seeded slurry and therefore its lifetime should be analyzed further. The polyamide membrane initially had a high water transport coefficient, but fouling led to its rapid decline which was attributed to the membrane’s rough and protrusive surface. A lifetime test on the thin film and cellulose acetate revealed that when operated at their maximum pressure specified by GE Osmonics for a duration of 8 hours that no decrease in rejection occurred.

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.

Membrane fouling is a chronic problem for many nanofiltration (NF) membrane plants. Foulant material can range from colloidal, particulate, inorganic minerals and natural organic matter (NOM) (Schäfer et al., 2006). This research project worked with a small community integrated membrane facility (low-pressure membrane followed by high-pressure) in Nova Scotia with membrane fouling concerns associated with dissolved NOM as the primary foulant. Membrane autopsies conducted in our laboratory have demonstrated that NOM deposits on the NF membrane decreased pore space on the membrane (Lamsal et al., 2012). The membrane fouling resulted in a requirement for increased pressure to produce a constant permeate flow. By adding in-line coagulation prior to low-pressure filtration in an integrated membrane system, the goal was to remove more organic material by MF thereby improving the quality of the feed-water entering the NF membranes. Previous work has shown that for some IMS installations there is a need to reduce the amount of dissolved organic matter prior to NF (Cho et al., 2000; Lamsal et al., 2012; Nilson and DiGiano, 1996; Schäfer et al., 2001). An improved membrane feed-water quality reduces fouling on the membrane and membrane operating cost, and increases productivity and lifespan of the membrane (Choi, 2008). A negative aspect to adding in-line coagulation is it adds another step to the treatment process and sludge removal is required. This study examined the use of in-line coagulation using coagulants aluminum sulphate, ferric chloride and polyaluminum chloride to improve membrane feed-water quality. The addition of in-line coagulation prior to microfiltration will remove NOM with the MF producing improved feed water quality for NF. After determining the optimal dose of each coagulant, 20 L of post-coagulation MF permeate was batched and run through the bench-scale NF membrane for 200 hours. The water quality of the feed tank, concentrate and permeate were monitored constantly as well as the operational properties of pressure and flow. To simulate a full-scale plant the operating conditions of Collins Park water treatment plant on Fletchers Lake were used in the bench-scale set-up. After the 200h NF run time the membranes were analyzed to assess the fouling on the membrane and the performance of each coagulant. Coagulation was found to reduce NF pressure fouling by reduction of NOM in the NF feed-water. Ferric chloride was found to perform best of the three coagulants at a low dose of 0.5mg/L of Fe at a pH of 5.0. / n/a

Thesis (Ph.D. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.

Thesis (Ph.D. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2009.

Membrane technology is a potential method for upgrading gasoline quality, with respect to its tendency to promote fouling of engine inlet-systems. This thesis investigates the transport and separation mechanisms of dense polydimethylsiloxane (PDMS) membranes in nanofiltration applications relating to the filtration of gasoline fuels. Simulated fuels were created which comprised representative organic solvents with organometallic and poly-nuclear aromatic solutes. The flux and separation behaviour of the solvent-solute systems were studied using several apparatus and a range of operating regimes. Tests were performed with real fuels and refinery components to verify the mechanisms observed with the model solvent-solute systems, and several strategies were developed by which the process could be optimised or improved. Parallel to this work, a project was undertaken to assess the suitability of the technology on an industrial scale and to identify any scale-up issues. The key factors influencing flux were found to be the viscosity and swelling-effect of the solvent or solvent mixture. The dense membrane was shown to exhibit many characteristics of a porous structure when swollen with solvents, with the separation of low-polarity solutes governed principally by size-exclusion. It is postulated that swelling causes expansion of the polymer network such that convective and diffusive flow can take place between polymer chains. In general terms, a higher degree of swelling resulted in a higher flux and lower solute rejection. The separation potential of the membrane could be partly controlled by changing the swelling-effect of the solvent and the degree of membrane crosslinking. The transport of polar/non-polar solvent mixtures through PDMS was influenced by swelling equilibria, with separations occurring upon swelling the membrane. Separation of the more polar solvent occurred in this manner, and the solute rejection in multicomponent polar/non-polar mixtures deviated significantly from the behaviour in binary mixtures. The results obtained from a pilot-plant scale apparatus were largely consistent with those from laboratory-scale equipment, and engine tests showed that fuel filtration with PDMS is a technically-viable means of upgrading gasoline quality.

Membrane processes are increasingly used in water treatment. Experiments were performed using stirred cell equipment, polymeric membranes and synthetic surface water containing natural organics, inorganic colloids and their aggregates, and cations. All processes could remove a significant amount of natural organics. Pretreatment with ferric chloride was required to achieve significant organic removal with MF and high MWCO UF. Additionally, fouling mechanisms for the three processes were investigated. Crucial parameters were aggregate characteristics (fractal structure, stability, organic-colloid interactions), solubility of organics and calcium, and hydrodynamics. In MF, fouling by pore plugging was most severe. Variations in solution chemistry changed the aggregation state of the colloids and/or natural organic matter and dramatically affected rejection and fouling behaviour. UF membrane fouling was mainly influenced by pore adsorption and could improve natural organics rejection significantly. Coagulant addition shifted fouling mechanism from pore adsorption to cake formation. Aggregate structure was most significant for flux decline. In NF, rejection of natural organics involved both size and charge exclusion. Fouling was caused by precipitation of a calcium-organic complex. Fouling could be avoided by pretreatment with metal salt coagulants. Thorough chemical characterisation of the organics used demonstrated that only size and aromaticity can be related to fouling. The study is concluded with a process comparison based on a water quality parameter and a cost comparison. Treatment cost of microfiltration with chemical pretreatment was similar to that of nanofiltration at a comparable natural organics rejection.