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Micro-Media Filtration: Superior Pre-Filtration For Desalination Systems

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White Paper: Micro-Media Filtration: Superior Pre-Filtration For Desalination Systems

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.

The level of suspended solids removal ahead of a reverse osmosis system depends on the concentration and nature of the contaminants as well as how the system is to be operated. Higher concentrations of suspended solids will obviously necessitate more frequent membrane cleanings.

The concentration of un dissolved material in water can be measured and expressed in several ways. For relatively high concentrations, a gravimetric procedure is normally used to determine the total suspended solids (TSS). However, TSS measurements are not accurate for the low solids levels found in filtered water. Turbidity measurements, expressed in nephelometric turbidity units (NTU), provide quick and easy measurements. This method is only semi-quantitative though, and does not have a direct relationship to TSS. In addition, turbidity measurements are not valid at extremely low solids concentrations.

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White Paper: Micro-Media Filtration: Superior Pre-Filtration For Desalination Systems