Adsorption and decolorization of dyes using solid residues from Pleurotus ostreatus mushroom production

We investigated the use of solid residues from Pleurotus ostreatus mushroom production in adsorbing and decolorizing different dyes. The solid residue used in this study was composed of hemicellulose and cellulose (52.81 %), acid-insoluble lignin (25.42%), chitin (6.5%), and water extractives (14.82%). After incubating 14% (wt/vol) solid residue in distilled water for 4 h, laccase and manganese peroxidase (MnP) activities were 0.5 U/g and 12 mU/g, respectively. Enzymatic decolorization percentages were up to 100 for azure B (heterocyclic dye) and indigo carmine (indigoid dye), 74.5 for malachite green (MG) (triphenylmethane dye), and zero for xylidine (azoic dye). The optimum temperature for decolorization was in the range of 26 ∼ 36°C for all dyes. Data obtained on adsorption (enzymatic decolorization was prevented with sodium azide) at different dye concentrations and in a pH range of 3 ∼ 7 were used to plot Freundlich isotherms. The spent fungal substrate (SFS) displayed large differences in adsorption capacity, depending on the dye tested. The highest adsorption capacity was observed at pH 3 for MG, while xylidine was slightly adsorbed at pH 3 and 4 and not adsorbed at higher pH values. Laccase and MnP production were affected by the presence of the dyes. The highest enzyme levels were observed in the presence of MG, when laccase and MnP increased 1.39- and 2.13-fold, respectively. Decolorization and adsorption to SFS are both important processes in removing dyes from aqueous solutions. The application of this spent substrate for wastewater treatment will be able to take advantage of both of these dye removal processes. An important problem in bioremediation processes involving microorganisms is the amount of time required for their growth. In this report, we used the spent substrates from mushroom cultivation in wastewater treatment, thus solving the problem of waiting for microorganisms to grow.