PERFORMANCE RESTORATION, AUTOPSY AND ANALYSES OF FIVE DIFFERENT COMMERCIAL SWRO MEMBRANES1

The study describes the experience encountered during performance restoration, autopsy and foulant analyses of five different commercial SWRO membranes of both spiral wound and hollow fine fiber configurations of minimodule size. Feed to the membrane consisted of nonchlorinated seawater from an open intake which received regular coagulation- filtration pretreatment. The coagulant used was ferric chloride at 1 ppm as Fe3+, while filtration consisted of a dual media filter followed by a fine sand filter. The filtrate with SDI less than 3 was sent to the membranes after adjusting the pH to 6.8 by dosing sulfuric acid. A decline in membrane performance was observed after more than 2 ¢ years of operation, i.e., membranes had low permeate flux and low salt rejection. Various chemical cleaning procedures were tried to restore the performance of membranes and one of the methods was effective in improving the membrane performance considerably, especially the permeate flux. Depending on the membrane system, the increase in flux due to cleaning ranged between 30 % up to 100%. The reduction in permeate conductivity ranged from 35 % to 45%. Also, autopsy an