Influence of operating pressure on concentration polarization layer resistance in revers osmosis

Abstract

Introduction. The experimental examination of hypothesis about linear dependence of concentration polarization resistance from pressure was carried out and the influence of hydrodynamic condition on this resistance is determined. Materials and methods. The research was carried out with using of commercially available membrane modules TFC-75 type. The measurements of productivity were carried out with using of deionized water (total dissolved solids 5-15 mg/dm 3) and also NaCl solutions. The volumetric technique was used for flux measurements. The concentration was measured by conductometric technique. Results and discussion. The membrane resistance during reverse osmosis of deionized water did not change with applied pressure in experimental conditions and was equal Rm=7,549•10 13 m-1. The concentration polarization layer resistance (Rcp) increased from 0.65-1.29•10 13 m-1 to 1.46-1.83•10 13 m-1 with applied pressure increasing from 0.2 MPa to 0.6 MPa and from 0.65-1.46 m-1 to 1.29-1.83•10 13 m-1 with increasing of feed concentration from 100 mg/dm 3 to 600 mg/dm 3. This increasing of Rcp value with pressure was linear which is in agreement with previously reported data for the ultrafiltration process. Moreover, in considered range of applied pressure, the exponential dependence of index of concentration polarization from applied pressure could be approximated by a linear equation with correlation coefficient 0.93. Therefore, assumption about linear dependence of concentration polarization layer resistance from pressure is reasonable and could be extended to reverse osmosis process for mentioned above conditions. The increasing of concentration polarization layer resistance with increasing of applied pressure is determinated by higher values of transmembrane fluxes and lower values of mass transfer coefficient at higher values of applied pressure in the considered system. These results are in agreement with film theory of concentration polarization. Conclusions. The exanimated hypothesis is validated for reverse osmosis in considered range of applied pressure. The correlation between concentration polarization layer resistance and index of concentration polarization was defined.

The Estimation of Feed Solution Composition Influence on Concentration Polarization Layer Resistance during Reverse Osmosis

“…As it has been done in work [3], the researches were carried out with commercially available membrane modules but anther trademark namely HID TFC 1812-75 GPD (Made in China). As membrane modules, Dow Filmtec TW30-1812-50, which used in work [3] the membrane module under investigation is destined for tap water post-treatment. The membrane modules HID TFC 1812-75 GPD have higher productivity up to 50 % and lower selectivity up to 10 % by comparison with the membrane modules Dow Filmtec TW30-1812-50.…”

“…In work [3], it was mentioned set of works dedicated determination to techniques of determination of fouling layer resistance, i. e. defining of the relation between specific cake layer resistance and applied pressure during dead-end ultrafiltration of carbohydrates solutions in work [5].…”

“…In work [3] it was mentioned out that the most comprehensive study of the concentration polarization layer resistance was carried out by Macedo and al. [12].…”

“…In our previous work [3] it was defined, that assumption about the linear dependence between concentration polarization layer resistance and the applied pressure is reasonable, and it was determined the influence of operating parameters (applied pressure and hydrodynamic conditions in membrane module) on the concentration polarization layer resistance. However, those results do not allow to define the relationship for determination of concentration polarization layer resistance due to the absence of information about the influence of solution composition on the value of mentioned resistance, since the experiments were carried out with using of one solution namely NaCl.…”

“…Current research is the extension of our previous work [3] which was dedicated to the development of the technique for the experimental determination of concentration polarization layer resistance and additionally to defining of influence of working parameters on the value of mentioned resistance. However, in work [3] the experiments were carried out with using sodium chloride with various concentrations as feed solution. This does not allow to define the influence of feed solution composition on the value of concentration polarization layer resistance.…”