Evaluation of ligninolytic microorganisms for efficient decolorization of a small pulp and paper mill effluent

Several ligninolytic microorganisms isolated from the environment of a small pulp and paper mill were evaluated for their ability to decolorize dark brown colored effluents of an agriresidue-based pulp and paper mill and their decolorization efficiency was compared with two known lignin degrading organisms, Phanerochaete chrysosporium and Trametes versicolor. Two isolates, identified as Aspergillus fumigatus and Aspergillus flavus produced higher degrees of color reduction. A. fumigatus showed highest efficiency for effluent decolorization and was capable of producing extracellular laccase, manganese peroxidase and xylanase. This culture was capable of decolorizing effluents over pH range 6.0-9.0, the optimum being pH 8.0 and hence no adjustment of effluent pH for decolorization was necessary. Cellulose, sucrose, glucose and xylose could be used as co-substrate and no additional nitrogen source was necessary for effluent decolorization. Studies on molecular size distribution of untreated effluent and effluent decolorized by A. fumigatus showed that the high- and medium-molecular weight colored compounds are biochemically degraded and depolymerized.