Integrity and perfomance evaluation of new generation desalting membranes
Various RO membrane integrity monitoring methods are currently being evaluated during pilot testing at the North City Water Reclamation Plant (NCWRP) located in San Diego, CA. The main purpose of the testing is to assess both direct and indirect monitoring techniques currently available to measure the integrity and reliability of RO membranes during water reclamation. Specific methods being evaluated include vacuum hold testing, conductivity probing, online conductivity/sulfate monitoring and soluble dye testing. In addition, the testing program is designed to assess the integrity of new generation RO membranes being offered for water reuse applications. The specific membrane suppliers participating in this study include Koch, Woongjin Chemical, Hydranautics and Toray. Field evaluations are being conducted in three distinct phases. Phase I testing was conducted between August – April 2005. During this time period, the integrity of RO membranes from each of the participating suppliers was assessed using the various test methods during operation on tertiary wastewater from the NCWRP. Phase I pilot testing was performed using single stage RO systems operating at feed water recovery of 50%. Results from Phase I showed each of the methods tested correlated well to virus rejection but varied in sensitivity and ease of implementation. In addition, the degree of virus rejection observed from the membranes varied among suppliers. The purpose of Phase II testing, currently underway, is to assess the impact of staging on the sensitivity of each of the integrity monitoring techniques tested during Phase I. Accordingly, the RO membrane, which showed the highest level of rejection during Phase I testing, is currently being operated in a two-stage system at feed water recovery of 75%. Lastly during Phase III, the sensitivity of selected monitoring techniques to purposeful breaches in integrity will be evaluated.