MEMBRANE APPLICATIONS IN RAW WATER-TREATMENT WITH AND WITHOUT REVERSE-OSMOSIS DESALINATION

Conventional raw water treatment methods are normally used for pretrea tment in RO plants. The extent of pre-treatment depends on the raw wat er quality. The utilization of ultrafiltration [UF] instead of convent ional pre-treatment stages before reverse osmosis was investigated fro m a technical-economical point of view by Ericsson and Hallmans [1]. D ifferent types of raw water were included in the cost comparison, viz. surface brackish water and seawater with worse quality than normal gr oundwater. Troublesome raw waters may be of particular interest for pr e-treatment with membrane methods [UF, NF and/or MF]. It was concluded from the investigation that the UF-RO concept is applicable on new de salination plants for reliable and stable operation. The aim of this p aper is to investigate further the two alternatives with conventional pre-treatment and the membrane methods, which also are applied in wate r treatment plants without desalination. A literature review clearly i ndicates that membrane plants have advantages compared to conventional water treatment plants, but the costs are higher. On the other hand t he treated water quality is usually much better, which is important if it otherwise is difficult to comply with some stringent quality limit s. As an example it has been reported by Lyonnaise des Eaux [2] experi ences of 6 UF-plants with hollow fiber membranes in France that the ra w water quality is deteriorated considerably with respect to turbidity and organics. It has been shown that the required potable water quali ty could be attained easier with membrane plants compared to conventio nal treatment plants for surface water. The quality of the produced po table water was much better and uniform in membrane plants, but the wa ter cost was doubled approximately. The applications of UF, NF and MF in different raw water treatment stages are discussed and compared wit h alternative treatment methods with respect to efficiency and economy . Recommendations are made concerning the use of these membrane method s under optimum conditions both with and without RO desalination.