Effective scale control for seawater RO operating with high feed water pH and temperature

An effective scale control program for seawater RO is widely recognized as an important factor in ensuring trouble free and cost effective operation. This is especially important under the high feed water pH and temperature conditions found in Southern Europe and Middle East.In addition, regulatory issues concerning maximum acceptable boron levels in drinking and irrigation water necessitate the growing need to operate plants at higher feed water pH. Operating at increased pH increases boron rejection but also increases the scaling tendencies of the water. This can lead to calcium carbonate and magnesium hydroxide precipitation in the membranes.A complete scale control program needs to control calcite and brucite saturation at the maximum operating reject pH and temperature. Antiscalant chemistry, optimum dose rate as well as accurate monitoring and control of the scale inhibitor are key factors in long-term cost effective “scale free” operation.This paper details the operating strategies and scale control issues related to both single and two pass seawater RO plants operating at elevated feed water pH and temperature.