Decolorization Treatments of Paper Industry Effluents

Pulp and paper mills emit effluents that are often tainted with color substances. Most often, lignin fragments form chromophores that impart a yellow-brown color to the effluent; making colored paper also causes residual dyestuffs to infuse the effluent with colors. Despite otherwise adequate effluent parameters, the color in effluents evokes a perception of uncleanness and often leads to environmental confrontations; thus this issue needs to be resolved. In this study, we explored several means of color removal from effluents. The results indicated that the colored substances in effluent were often difficult to agglomerate due to their small particle sizes, but adsorption using activated carbon and more cheaply, fly ash, could achieve good removal. Membrane treatment using ultrafiltration (UF) films with a molecular weight cut-off of 5000 Da could effectively remove colors from pulp mill and OCC mill effluents. Certain colored paper effluents could also be treated with good effect as well. The advanced oxidation processes (AOPs) applied to various effluents achieved mixed results, with red-dyed paper effluent showing strong resistance. Reductive treatments were effective against ligneous chromophores, but this was often not so for chemical dyestuffs. Most treatments entail high costs or residual environmental concerns. Electrochemical means including dipole induction and flocculation were found to be able to decolorize dye-stained white water, but was less effective toward the decolorization of bleaching effluent.