The production of flocs for water treatment by electrodialysis in a diaphragm cell

Abstract

This paper considers a novel system of producing flocs for water treatment as part of a larger process of recycling the floc chemicals rather than dumping the waste at the treatment site. The cell produces high pH conditions in the cathode side of the cell and a porous diaphragm allows the passage of the cations to this side where they are precipitated. In several instances the apparent current efficiency of the process is over 100% owing to a contribution of bulk diffusion of iron from the anode to the cathode chamber. The process has some drawbacks. Firstly an alkali has to be fed into the cathode chamber and secondly bulk transport of water due to electroosmosis forces fluid from the cathode to the anode. This causes membrane fouling in a number of cases. Both aluminium and ferric iron flocs have been studied in this investigation. The process is more suitable for the production of ferric flocs.