Investigations with Electrodialysis Reversal for the Treatment of Surface Water to Make-Up Water

Abstract

In the Dutch power stations, boiler make-up water is nowadays prepared by treating drinking water with ion exchangers. A problem, however, is that drinking water is expensive in certain areas of the Netherlands. Therefore it seems to be attractive to prepare make-up water out of surface water with aid of electrodialysis reversal (EDR). The experiments with an EDR installation were carried out with different types of surface water.

The process consists of three main stages:

• pretreatment of the surface water to meet the requirements set for feed water for the EDR unit

• desalination in the EDR unit

• post-treatment of product water (with ion exchangers) from the EDR unit to comply with the guidelines for make-up water.

From experiments on pilot plant scale it could be concluded that a simple filtration step to remove suspended matter was sufficient to comply with the requirements set for feed water for the EDR unit. Further it was possible to desalt the surface water to a large extend (about 90% or more) at a low energy consumption. By means of ion exchangers installed downstream the EDR unit water could be produced that met all the guidelines for make-up water. Finally it was noted that during all experiments with different types of surface water no membrane fouling did occur. From an economical evaluation it appeared that the pay out time for a commercial EDR installation, including a pretreatment step, with a production capacity of 20 m³/h amounted to about 6.5 years.