Adsorption and biological removal of basic green 4 dye using white-rot fungi immobilized on agave tequilana weber waste

The fungi Trametes versicolor and Pleurotus ostreatus were used to remove the triphenylmethane dye Basic Green 4, which is a toxic compound used in dye industries and in aquaculture as a biocide and fungicide. Agave tequilana Weber was evaluated as a support and biosorbent because it has high quantities of nutrients and good adsorption capabilities, and its leaves are a by-product of the tequila industry. The kinetics of the uptake of Basic Green 4 by agave fiber showed a relatively fast rate of dye adsorption. At 29 ^°C, the dye adsorption properties were described by the Freundlich isotherm model, with a K_f value of 0.5683 (mg g^-1) ((L g^-1) ^1/n)^-1 The fungal culture immobilized on agave fiber and without added glucose was found to provide the best option for pigment removal, obtaining 99.3% discoloration of 200 ppm dye with nonsaturated support and 79 U L^-1 lacease production during 4 days of treatment at 29 ^°C in Erlenmeyer flasks. Toxicity tests revealed that the immobilization of fungi in agave fiber decreases the toxicity compared with immobilization of fungi in agave leaves. Additionally, when the fiber was previously saturated with the dye and then immobilized, an increase in the effectiveness of the system resulted due to the removal of the dye by biological degradation and by adsorption to the support. In a bubble column reactor, under these conditions, the discoloration was 90% of 50 ppm in 9 days, or two removal cycles, and the toxicity of the degradation products decreased.