Impact of four different operating trials on performance of a seawater reverse osmosis plant on the Red Sea coast

Serious membrane fouling has been experienced in a seawater reverse osmosis (SWRO) plant situated on the Red Sea coast of Saudi Arabia. Four different operation trials were made (in four phases under normal and modified process conditions) to find out the optimum conditions that would minimize membrane fouling. The first trial included normal plant operation, where the coagulant (polyelectrolyte) is dosed upstream and sodium metabisulfite (SBS) downstream the media filter, ahead of the micron cartridge filter (CF). During the second trial the coagulant dosing point was shifted close to the seawater intake pump providing increased residence time for proper coagulation prior to filtration. In the third trial, to avoid any biological growth within CF, the SBS dosing was shifted to the downstream of CF. Chlorine dosing was at the intake chamber during all these trials. In the fourth trial, the plant was operated without chlorination but with the coagulant dosing as in the case of second trial. The first two trials did not improve either the pretreated seawater quality or the membrane flux, but the latter two gave some positive results. A significant decrease in the rate of ∆P build-up across cartridge filter with increased rate of membrane fouling (∆P) was observed during the third trial. Compared to earlier trials, the 4th trial resulted in an increase in the rate of coarse and cartridge filter clogging, a high SDI value, a lower rate of ∆P build up across membranes and, a lower decline in flux rate. However, when this trial wa