Comparison of high-pressure and low-pressure fouling detectors at a full-scale seawater reverse osmosis desalination plant

In an attempt to better understand and control seawater reverse osmosis (RO) membrane fouling, low-pressure (LPFD) and high-pressure fouling detectors (HPFD) were employed in an ex situ, side stream configuration at a full-scale seawater desalination plant. These fouling detectors contained flat-sheet membrane and spacer materials extracted from the membrane modules installed at the plant. The high-pressure fouling detectors reasonably replicated full-scale plant permeate quality, permeate flux, and differential pressure, whereas low-pressure fouling detectors could only simulate differential pressure. When evaluating different pre-treatments, it was observed that activated carbon and chlorine dioxide (after chlorination, microfiltration and dechlorination) to be effective at preventing RO membrane fouling, whereas chlorination, microfiltration and dechlorination and the same sequence followed by ultraviolet irradiation were less effective. Accelerated fouling was found when dosing both colloidal and dissolved nutrients, but the colloidal nutrient caused more severe fouling through a combination of colloidal cake layer formation in addition to biofilm formation and growth. In some cases, differential pressure may be an adequate early warning fouling indicator, but in this study, the high-pressure fouling detector more accurately captured plant fouling impacts. Finally, full-scale seawater RO plant fouling impacts were sufficiently captured while monitoring only pressure, flow and electrical conductivity; therefore, the added cost and complexity of employing more sophisticated optical, electrical, ultrasonic or other methods in ex situ, side stream fouling detectors may not be justified.