The paper presents the results of experimental investigations of treatment of concentrated wastes by electrocoagulation using sacrificial aluminium (Al) anodes. Tests were carried out batchwise in an electrochemical cell with recirculation for various wastes of industrial significance: the technique was shown to allow efficient abatement of the suspensions with concentrations of dissolved Al ranging from 150 to 500 mgl(-1). Hydrogen evolution and Al dissolution occurred with current yields over unity. Besides, the time variation of the COD largely depended on the nature of the waste treated: whereas the treatment proceeds regularly for latex suspensions, the COD abatement with oil and silica suspensions starts only after sufficient accumulation of Al (111) species in the media. We proposed a phenomenological model for prediction of the waste abatement in term of COD by complexation of the matter suspended by Al (III), and taking into account the "latency" period observed experimentally. The values of the parameters involved are discussed in relation to the suspension treated. (c) 2006 Published by Elsevier Ltd.