REDUCTION IN POLLUTION LOAD BY USING MODERN BLEACHING PRACTICES

Abstract

In the last 2-3 decades, environmental issues have been the dominant driving force for development of both pulping and bleaching processes. The bleach plant effluents have traditionally been the major contributors to polluting discharge. Proposed regulations of adsorbable organic halide (AOX) and the consumer's desire to buy environmentally friendly products have led pulp mills to implement AOX reduction strategies. The level of AOX can be decreased by extended delignification, oxygen delignification, substitution of Chlorine dioxide for chlorine, ECF Bleaching and TCF bleaching. The present paper highlights the effects of chlorine dioxide (CO2) substitution in sequence C/DEOpD1D2 applied to Kraft pulp of mixture of hardwoods and bamboo. Based on lab study, process scale trial up to 40% substitution was conducted. BOD, COD, AOX and color were monitored for the effluent generated from bleach plant besides the regular parameters like brightness, reverted brightness and CED viscosity. Chlorine dioxide substitution reduced load of BOD, COD and Color with large reduction in AOX with substantial increase in 0.5% CED viscosity and reduction in P.0 No. of pulp. 40% substitution in plant has resulted approx. 37% reduction in AOX in mill effluent.