To ensure trouble free-operation of seawater desalination systems, membrane manufacturers recommend removal of suspended solids to negligible levels, as even small amounts of solids adhering to the surface of the membrane elements may adversely foul the membranes, deteriorate permeate quality and reduce membrane life. The past two decades have seen a dramatic increase in the use of reverse osmosis desalination systems. RO systems are less forgiving in terms of pre-treatment than evaporation systems. The close spacing of spiral wound membranes results in trapping of suspended solids inside the modules. This is exacerbated by the fact that, RO membranes bear a surface charge which may cause fine solids to be attracted to the membrane surface. Once fouling begins, cleaning of the membranes becomes very difficult and the system may not return to original performance levels once fouling has occurred.
According to one manufacturer, “membrane fouling in RO systems is as all-pervasive and inevitable as the common cold”.1 In fact, many of the failures experienced by these systems can be traced back to inadequate pre-filtration.