Studies on the treatment of kraft bleaching effluents with lignin-degrading fungi

Abstract

Typically, for production of high brightness pulp, the residual lignin in unbleached kraft pulp is commonly removed through a multi-stage bleaching process with the use of chlorine species. The effluent from such a bleaching process is dark brown due to their content of chromophoric and polymeric lignin derivaties. Moreover, the organically bound chlorine [measured as total organically bound chlorine (TOCI) or adsorbable organic halogen (AOX)) is present in a wide range of organic materials which have toxic and mutagenic properties. It has recently been discovered that small quantities of dioxines [polychlorinated dibenzo dioxin (PCDD) and polychlorinated dibenzo furan (PCDF)) can also appear in bleach plant effluents. Consequently, this bleaching effluent is not easily recycled within a mill recovery system because of the potential corrosion problems created by its high chlorine content and finally affects the harmful effects on the environment. The purpose of the present research is to describe the decolorization of the El effluent with white-rot fungi showing the Iigninolytic activity, to accomplish efficient treatment of kraft bleachery efficient with less energy and in relatively short treatment-period. First, it was attempted to design the effective treatment process of the El effluent with the fungus IZU-154 showing ligninolytic activity. It has revealed that the color of the effluent was effectively removed when glucose was added as an additive. Furthermore, the addition of glucono-d-lactone to the El effluent produced a more remarkable degree of decolorization than did that of glucose. All white-rot fungi tested showed high decolorization effect of the El effluent in the presence of glucono-d-lactone. It is suggested that the effect of glucono-d-Iactone on the high decolorization of El effluent are closely associated with the activity of the surfaces of the mycelium due to the change of pH of the effluent during fungal treatment. Moreover, to establish a more practical system for the decolorization of the bleaching effluent, a screening have been performed to find fungi having high decolorization activity of the El effluent without any additional nutrients. The