ESTIMATION OF CHLOROPHENOLS IN EFFLUENT FORMED UNDER DIFFERENT CONDITIONS OF BLEACHING

Abstract

The use of chlorine and chlorine containing bleaching agents in the production of bleached chemical pulp leads to the formation of a variety of chlorinated organic compounds that are discharged in bleach-plant waste waters. Hence bleach Plant effluents aie known to be the main contributors of toxicity, colour and BOD in bleached kraft mill effluent. The chlorinated organic compounds formed during bleaching of pulp have proved to be highly toxic to aquatic organisms and adversely affecting on human health as well. These are quite persistent in the environment and readily accumulate in organisms. In addition, they can be responsible for the deterioration of flavour of sea food. They, therefore, are of great environmental concern. The end of pipe treatment methods employed by Indian paper mills consist of primary and secondary treatment plants which reduce the suspended solids and BOD significantly, with small reduction in COD, AOX and colour loads. The aim of the present investigation is to identify a set of pulp chlorination conditions in which the production of chlorinated phenolics would be minimal without any adverse impact on pulp quality. Most of these studies have been carried out on softwood and hardwood pulps. A very little information is available on non-woods and agro-residue pulps, which are important in Indian context due to decreasing wood resources. In view of the above, following objectives were formulated for this study: I. To identify and quantify various chlorophenols formed during •different stages of pulp bleaching. II. To study the impact of change in chlorination condition on the production of toxic chlorinated phenolics in C, E and H stages. III. To study the integration of Oxygen deliginification stage with conventional CEH bleaching sequence and its impact on the generation of chlorophenolics. IV. To study the impact of partial or complete replacement of chlorine by chlorine dioxide on the generation of chlorophenolic compounds.