Membrane biofouling is defined as the adherence and growth of algae and bacteria on a membrane surface. The process of biofouling will affect the performance of a membrane system. First by the attachment and growth of microorganisms and algae on the feed spacer which will lead to an increased resistance over the feed channel. Second, by covering the membrane surface with a layer of biomass and blocking the feed water from the area where ROor nanofiltration can take place. As consequence, more feed pressure (i.e more energy ) is needed for the same mass flow of produced water.