Nanofiltration membrane cleaning characterization

Abstract

In membrane process industries, membrane cleaning is one of the most important concerns from both economical and scientific points of view. Though cleaning is important to recover membrane performance, an inappropriate selection of cleaning agent may result into unsatisfactory cleaning or irreparable membrane. In this study, the cleaning performance has been studied with measurements of membrane contact angle values, surface roughness, zeta potential and pore size by positron annihilation spectroscopy, and salt rejection as well as flux measurement. Thin-film nanofiltration membranes such as DK, provided by GE-Osmonics are used in this study. Tests were carried out with virgin DK. Several cleaning agents were investigated, some of them were of analytical grade such as HCl, NaOH, and others such as SDS mix agents were commercial grade agents that are already in use in commercial plants. Contact angle values, surface roughness, zeta potential and pore size, and salt rejection as well as flux of virgin membranes before and after chemical cleaning were measured and compared. The membrane contact angle values, surface roughness, zeta potential, and pore size measurements with and without chemical cleaning of virgin membranes were measured and revealed very interesting results which may be used to characterize the membrane surface cleanliness. The membrane contact angle values, surface roughness, zeta potential, and pore size results revealed that the cleaning agents are found to modify membrane surface properties. The details of these results were investigated and are reported in the paper. The salt rejection levels of divalent ions before and after cleaning by high- and low-pH cleaning agents were looked into it.