Analysis of RO elements operated at more than 80 plants in Japan

Abstract

Eighty-two samples of NTR-759HR thin-film composite RO membrane elements were analyzed in order to investigate factors of RO performance decline, including potential factors. For the membranes used in brackish water desalination, 75% of the performance decline factors were some kind of fouling such as bacterial slime, inorganic colloids, silica or coagulants. Many of these performance declines were caused by improper pretreatment or poor services. To control bacterial growth and avoid membrane degradation at the same time, dechlorination with GAC (granulated activated carbon) proved to be effective if combined with periodical disinfection. To insure more stable operation, factors of performance decline should be determined early by the monitoring of routine operations. In pure water treatment, biofouling, similar to that in brackish water treatment, was the important potential factor of RO membrane performance decline. Unique to pure water treatment, there were cases of flux decline caused by the absorbance of trace amounts of organics son the membrane surface. Although detection of those organics is limited at this time due to their minute quantities, analytical techniques to identify these compounds are being developed in order to improve RO operations in any application.