Elimination of biological fouling in seawater reverse osmosis desalination plants

The main trouble in the RO method of seawater desalination is biological fouling (bio-fouling) from microorganism growth. In this work, the growth rate of microorganisms in the Red Sea and sterilization by chlorine injection were measured and quantified. Furthermore, actual demonstration of RO pilot tests using cellulose triacetate (CTA) RO membranes with chlorine resistance was performed in RO plants where bio-fouling actually occurred. By carrying out direct chlorine sterilization of the RO membrane with an intermittent chlorine injection method, bio-fouling was eliminated. The combination of the CTA membrane and chlorine injection successfully prevented increases of differential pressure and stabilized product water quantity and quality.

Simulation of the required minimum chlorine concentration and injection time for elimination of bio-fouling was established based on basic experiments of growth rate and sterilization of microorganisms in Middle East seawater. The experiments in pilot plants were conducted based on the result of the simulation. The operational results of pilot tests at actual plants in Bahrain and in Saudi Arabia using Toyobo CTA membranes proved that direct chlorine sterilization to the membrane was the most effective methods to achieve best operating performance of the RO process of desalination.