Pulp and paper industries are one of the most polluting industries and is highly water intensive. Pulp and paper industry is the third largest water consuming industry in India. Fresh water consumptions in wood-based and agro-based paper mills are 125-200 and 125-225 m~3 per tonne of paper production respectively. The color of effluent discharged from pulp and paper industries into streams and rivers have been a serious environmental problem; The color of the effluent is due to the presence of lignin and its derivative which impart dark brown color to the black liquor and waste water. The color persists for a long distance because lignin and its derivatives present in the effluent are not easily biodegraded. The black liquor and effluents are conventionally treated by biological methods—which reduce COD and BOD but cannot reduce color. Color removal of pulp and paper mills have been studied using waste sludge and fungi. In earlier publication, bamboo black liquor and agro-based paper mills black liquor were treated using coal fly ash by the author. In the present investigation, coal fly ash an industrial solid waste has been used as an adsorbent for decolorization of mixed hardwood black liquor of pulp and paper mills. Comparative studies were performed with silica gel for decolorization of mixed hardwood black liquor.
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