STUDIES ON THE GENERATION OF CHLOROPHENOLICS FORMED DURING BLEACHING OF CHEMICAL PULPS

Abstract

During the production of bleached chemical pulp, chlorine and chlorine containing bleaching agents are used, that form the chlorinated organic compounds. The bleach plants effluents are known to be the main contributor to the effluent toxicity, color and BOD. The chlorinated organic compounds formed during bleaching of pulp have proved to be highly toxic to aquatic organism that affects unfavorably human health as well. These compounds are quite continual in the environment and readily accumulate in organisms. These compounds are also responsible for the deterioration of flavour of sea food. So these compounds are of great environmental concern. The end of the pipe treatment methods employed by Indian paper mills consist of primary treatment (clarification) and secondary treatment plants (mostly aerobic).These methods while being effective in reducing suspended solids and BOD significantly, with small reduction in COD, AOX and color loads. Thus the treated wastewater discharged from Indian paper mills is expected to contain chlorinated organic compounds. The bleach plant effluents contribute about 65% of total BOD and 90% of total color load discharged from a paper mill. Chlorination (C) and extraction (E) stages often account for the largest toxicity. The aim of present investigation is to identify a set of pulp chlorination conditions in which the production of chlorinated phenolic compounds would be minimal without any adverse impact on pulp quality. Such studies have mostly carried out on soft wood and some hard wood pulps. A very little information is available on non-wood and agro-residue pulps, which are important in Indian context, as wood resources are continuously decreasing. In view of above the following objectives were formulated for this study: I. To identify and quantify various chlorophenolic 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.