Two modified membranes are used for the treatment of industrial effluent by electrodialysis. This surface modification of membrane using both immersion and electrodeposition method improves the selectivity for monovalent ions against to divalent. In this work both neutralisation of the effluent and acid enrichment are achieved. The immersion method appears more efficient when not more than two compounds are inside the solution. On the other hand, electrodeposition technique should be used allowing to attain 2.8 N acid concentration. It was noticed that polyethyleneimine plays two different roles according to the modification method. The multilayer was formed by adsorption using immersion method though electrodeposition technique permits PEI to penetrate into the pores and play a role of an effective carrier for proton. (C) 2002 Elsevier Science B.V. All rights reserved.