טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentIris Sutzkover-Gutman
SubjectPerformance Improvement of Polymeric Membranes
DepartmentDepartment of Chemical Engineering
Supervisors Professor Emeritus Semiat Raphael
Professor Emeritus Hasson David
Full Thesis textFull thesis text - English Version


Abstract

The general objective of this thesis was improvement of polymeric membranes performance through better understanding and control of organic fouling propensity, exemplified by humic acid (HA) fouling. Factors affecting HA fouling propensity were investigated in the two commonly applied pretreatment methods - the classical conventional deep-bed filtration and the emerging membrane pretreatment technique.

    The main issues investigated were as follows:
  • A comprehensive critical literature review which served to highlight the major unresolved issues related to the complex phenomena involved in HA fouling.
  • Experimental characterization of HA removal by deep-bed filtration in a system enabling measurements of the clarification profile along the bed.
  • Experimental characterization of HA removal by ultrafiltration in a tubular system enabling well-defined hydrodynamic conditions.
  • Confrontation of the experimental data with available models and development of new approaches.

A dominant issue in assessing the relative effectiveness of a pretreatment technique is how representative are the various parameters commonly used for characterizing the product quality. Meaningful interpretation of conflicting water quality data was obtained by interlinking the TOC and turbidity removal measurements with the particle size distribution of the feed solutions.

    The main results relating to the deep-bed filtration study were as follows.
  • While it is not possible to generalize the effect of each of the numerous parameters involved in the filtration process, the filtrate product quality was found to be substantially constant over a wide range of operating parameters.
  • Deep-bed filtration was found to provide constant filtrate quality (2.5-3.5 PPM TOC) similar to what is claimed to be an important advantage for membrane filtration.
  • An empirical correlation was developed for predicting the breakthrough threshold of humic acid solutions.
  • The blocking laws invoked in membrane fouling analysis were successfully applied for deep-bed filtration.

    The main results relating to the ultrafiltration study were as follows.
  • As in the case of deep-bed filtration, the permeate product quality was found to be substantially constant over a wide range of operating parameters.
  • As anticipated, ultrafiltration also provided constant permeate quality (1.5-3.5 PPM TOC), having a similar order of magnitude as that of deep-bed filtration.
  • Experimental data was well correlated by available models which however lack predictive abilities. A new modeling approach is proposed based on the assumptions involved in the familiar BET model for gas adsorption. Further elaboration of this novel model might provide a predictive tool.
  • Membrane history was found to be one of the governing factors dictating the limiting flux.
  • Experimental evidence from this study and from literature data indicated that the concentration polarization level in UF membranes may very well be much higher than is commonly believed.

It is evident from literature results and from the analyses of this study that currently, it is possible to provide rational explanation for experimental data but reliable predictive design information is not within reach. The need to carry out elaborate pilot tests under real conditions is inescapable.