Treatment of a wastewater resulting from dyes manufacturing with ozone and chemical coagulation

The degradation of the compounds present in a previously chlorinated wastewater resulting from the production of azoic dyes has been studied in this project. Towards this end, the first step developed was the characterization of the spillage water by GC/MS and GC/FID. Secondly, a combined ozone + Ca(OH)(2) treatment was carried out, determining its efficiency on this wastewater. The majority of compounds found in the wastewater are aniline derivatives and azo compounds. Also, as a result of the chlorination treatment which is carried out by the factory, some organochloride compounds were identified, being the most important those which are subjected to legislative control, namely: chloroanilines, chloronitrobenzenes and chlorophenols. After ozonation, the concentration of the compounds present is reduced to good percentages. The by-products formed after this first treatment were, mainly, nitrobenzene derivatives and organic acid compounds. The following treatment with Ca(OH)2 leads to almost total elimination of the remaining compounds in the ozone treatment. However, aniline and chloroanilines are formed after chemical coagulation due to the strong basic medium at which the sample in this process is set. C.O.D. is reduced 25% after ozonation, while it decreased 50% after the complete treatment. T.O.C. remained constant during ozonation, but a 42% reduction was obtained after chemical coagulation. Color decreased gradually during ozonation reaction, and after the final treatment the reduction was 62%. The complete process of ozonation and chemical coagulation with Ca(OH)2 is, in general, very effective to treat this kind of wastewaters. (C) 1998 Elsevier Science Ltd. All rights reserved.