Electrodialysis as an alternative for reverse osmosis in an integrated membrane system

Amsterdam Water Supply investigated the possibilities of increasing the capacity of the production plant "Leiduin" from 70 to 83 million m(3)/y. Three different integrated membrane systems (IMS) are evaluated for the extension of 13 million m(3)/y. In IMS 1 pretreated Rhine River water (C/S/F) is treated sequentially by ozonation, biologically activated carbon filtration, slow sand filtration and reverse osmosis (RO). In IMS 2 pretreated Rhine River water is treated sequentially by ozonation, biologically activated carbon filtration, slow sand filtration and electrodialysis reversal (EDR). In IMS 3 pretreated Rhine River water is treated sequentially by EDR, ozonation, biologically activated carbon filtration and slow sand filtration. The IMSs were compared for temperature dependency, scaling and fouling, disinfection strategy and bromate control, dual-barrier concept, and energy and chemical consumption. All IMSs performed well with respect to scaling and fouling. The IMSs using EDR were much more affected by temperature as compared with IMS 1 using RO. IMS 2, in which EDR was used as the final process unit, cannot comply with the bromate standard of 5 mu g/l in the finished water. Hence, the choice is between IMS 1 and IMS 3. IMS 1 using RO has the advantage that a dual barrier is present for disinfection and removal of organics (a.o. pesticides). IMS 3 using EDR is characterized by a lower energy consumption (factor 2) and lower chemical consumption (factor 3). The final selection of the optimum process scheme depends on the criteria mentioned above and on investment costs and environmental impact.