The high chemical oxygen demand (COD) and the dark brown colour of the distillery spentwash even after anaerobic treatment indicates that conventional treatment methods are far from optimal in attaining the safe limits of disposal. The application of two bacterial strains, Pseudomonas putida U and Aeromonas strain Ema, in a two-stage column bioreactor to reduce COD and the colour of the anaerobically treated spentwash under aerobic conditions was studied. In the first stage, P. putida reduced the COD and colour by 44.4 and 60%. The Aeromonas strain Ema, in the second stage, reduced the COD by about 44.4%. Algal bioassay was used to evaluate the quality of spentwash before and after treatment by the two bacterial strains. The spentwash was eutrophic before experimental treatment, but, after treatment, distillery spentwash showed poor growth of the test alga even at higher spentwash concentrations. (C) 2002 Elsevier Science B.V. All rights reserved.