Decolorization of pulp-paper mill effluents by white-rot fungi

Phenolic effluents are waste products of pulp and paper, coal conversion, dying, textile, and olive oil industries. Such effluents impose coloration and toxicity problems in the receiving waters, causing serious environmental hazards. The pulp and paper mill effluent is highly colored, imparting black/brown color to the water body. The color is mainly due to lignin and its derivatives released during various stages in the paper-making process. The complex nature of such lignin compounds and their phenolic nature make them extremely resistant to microbial degradation. Conventional treatment methods such as aerated lagoons and activated sludge process are ineffective in removing color. However, physical and chemical treatment methods, including ultrafiltration, ion-exchange, and lime precipitation, are expensive and less efficient. Therefore, alternate low-cost biotreatment processes are now being considered, most of which are based on lignin-degrading fungi. Depending on the treatment process, the fungal inoculum for decolorization could be used in the form of mycelium, pellets, or in the immobilized state. The decomposition of lignin is an enzymatic process employing various ligninases being produced by the fungal species. Soluble and immobilized ligninolytic enzymes have also been employed for effluent decolorization. Therefore, the present review is an attempt to compile the scattered information on pulp-paper mill effluent decolorization employing microbes. The structure, distribution, physiology, and enzymology of lignin degradation is also briefly discussed.