Removing color while lowering toxicity: the case for decolorization of textile dyes and simulated effluents with yeasts

The textile industry produces high amounts of effluents containing synthetic dyes that are recalcitrant and potentially hazardous to the environment, being azo dyes one of the most commonly used classes. Biological methods for dye degradation are promising, but knowledge of the toxicity of the resulting products is key for assessing their safety discharge on the environment. The present study investigated the potential toxicity of simulated effluents with dyes commonly used in the textile industry (reactive, direct, and basic groups). These effluents were treated by yeasts Candida parapsilosis (HOMOGS20B), Candida pseudoglaebosa (LIIIS36B), and Yarrowia lipolytica (HOMOGST27AB) after which their toxicity was assessed using three different assays in order to represent different trophic levels. Mutagenicity was also evaluated. C. pseudoglaebosa (LIIIS36B) was the most effective, completely decolorizing four of the five simulated effluents. Degradation products resulting from the yeast treatment were detected in the supernatant of the treated effluents and could be aromatic amines. Although the toxicity of the original simulated effluents was high, treated effluents demonstrated a decrease in toxicity and none exhibit mutagenicity. This work shows that the three selected yeasts could have a high potential for dye removal from textile wastewaters without generating toxic end-products, thus being an environmentally safe biological method.