The biotechnological treatment of alkaline waste waters (AWW) resulting from the production of caprolactam by the SNIA-viscosa process has been studied, The pollutant in the AWW is 80-120 g litre(-1) cyclohexanecarboxysulphonate (CECS) sodium salt with a COD up to 325 000 mg litre(-1), Bacterial strains have been isolated which are able to grow on AWW and to degrade the largest possible range of organic compounds. These strains have been screened for their performance in lowering the COD and degrade the sulphonic bonds. Combinations of strains have also been verified. The strains have been compared in cultures both in shake flasks and in a laboratory scale fermenter. The results showed that: (a) a 1/10 dilution of AWW with water permitted microbial growth coupled with decrease in COD and carboxylic concentration (representative of several organic compounds such as cyclohexanecarboxysulphonate, 2-aminocapronic and epsilon-aminocapronic acids); (b) the polymerised caprolactam molecules are exhaustively degraded; (c) very similar results are found both in shake flask tests and in the lab scale fermenter but with different kinetics; and (d) pretreatment of alkaline waters with CaCl2 and lowering the pH with H3PO4, implement the kinetics and yields of the process in terms of degradation of COD and carboxylic compounds. The experiments gave very preliminary results and led to some suggestions for the development of a chemical and biological process to treat this kind of AWW. (C) 2000 Elsevier Science Ltd. All rights reserved.