Su, Xu (2018-11). Concentration Polarization and Colloidal Fouling in the Vibration Enhanced Reverse Osmosis Membrane Desalination System. Doctoral Dissertation.
Thesis
The focus of this study was on concentration polarization (CP) and colloidal fouling control in the vibration enhanced reverse osmosis desalination system and the fundamentals of centrifugal reverse osmosis (CRO). A two-dimensional numerical model simulating colloidal particle fouling was proposed aiming at visualizing the process of colloidal fouling accumulation and leading a better understanding of the mechanism of colloidal fouling in a spacer-filled membrane channel. This model predicts the porous cake layer thickness distribution among membrane surface and its effect on the cake enhanced osmotic pressure (CEOP) phenomenon. Results show that colloidal fouling has a huge influence on the membrane performance with up to 47% of the permeate flux decline and 1.77 of the NaCl CP modulus within 12 hours. A novel vibration enhanced reverse osmosis technique was employed to control the concentration polarization phenomenon and colloidal fouling by silica colloids during the reverse osmosis membrane desalination process. Both simulations and experimental results show that membrane performance can be improved by vibration enhanced reverse osmosis technique for all 7 systems investigated in this study. Membrane NaCl CP modulus decreases and the permeate flux increases as the vibration frequency increases up to 60 Hz, with a constant vibration amplitude. A maximum 60% improvement of the normalized permeate flux and 25% reduction of the NaCl accumulation after 12 hours was found. In addition, a new CRO concept was proposed to reduce the energy consumption and device size. Results show that the energy cost of the new CRO concept is competitive compared with current medium and large size SWRO systems, while the capital cost is only 0.1% of them. The operation cost is 30% lower compared with the convectional membrane desalination plant. Return on Investment (ROI) study also shows that a total profit over 60k USD and 87% of the ROI can be achieved within 30 years operation of the new CRO system. The outcomes of this study may lead to a better understanding of the vibration enhanced reverse osmosis desalination process, membrane colloidal fouling simulation and control, and the CRO desalination process.
