A study of charge and hydrodynamic effects in protein ultrafiltration

This thesis is concerned with the study of different effects in protein ultrafiltration including device configuration, solution chemistry and membrane charge In the recent and more established literature membrane fouling remains a challenging problem that limits the wider application of ultrafiltration. Thus, investigations which can aid understanding and potentially reduce membrane fouling are of particular interest and in this study the problem has been addressed from several different angles Polyethersulfone membranes were studied at varying pH and two ionic strengths using bovine serum albumm and lysozyme as the model proteins. The study was conducted both in a stirred cell and a crossflow configuration in order to evaluate the influence of different system hydrodynamics on filtration This work was further substantiated through the application of filtration models An attempt was also made to modify the membrane surface by low temperature plasma modification with the intention to preferentially alter the characteristics of the membrane surface Both unmodified and plasma-modified polyethersulfone membranes were characterised using a range of analytical methods including flux data, streaming potential, contact angle and MWCO measurements to aid results interpretation. The research showed that MWCO data quoted by manufacturers is mostly greater than that obtained during laboratory studies The MWCO technique was also used to highlight differences between the unmodified and plasma-modified membranes demonstrating that the modification resulted in a membrane with tighter pores in the lower molecular weight region. Concentration polarisation effects were found to be reduced as a result of the plasmamodification The study of protein filtration at different pH and ionic strengths demonstrated that ionic strength effects were more pronounced than pH effects It was also shown that changes m the ionic strength can be used to alter the degree of protein rejection for the given system concentration polarisation was found to be higher during crossflow filtration compared to stirred cell filtration The thesis adds to existing knowledge in the area of ultrafiltration emphasizing the importance of device configuration, solution chemistry as well as the potential of charged membranes