Adsorption of dyes from water by Prunella vulgaris stem and subsequent fungal decolorization

The residue of herbaceous Prunella vulgaris stem (PVS) was evaluated as a potential adsorbent for dye removal, followed by fungal cultivation to achieve dye degradation on solid waste. PVS was analyzed in terms of nutritional composition such as fiber, ash, protein, and fat, which not only played a role in dye adsorption but also provided solid matrix for fungal growth. Five dyes, namely, crystal violet (CV), methylene blue (MB), reactive black 5 (RB), indigo carmine (IC), and direct red 80 (DR), were tested as adsorbates but only CV and MB were effectively adsorbed. Effect of sorbent dose, contact time, dye concentration, and NaCl on adsorption was investigated individually. Langmuir model was suitable for fitting MB adsorption, while adsorption of CV adopted the Freundlich model. The adsorption capacity was calculated to be 625 mg/g for CV and 303 mg/g for MB, respectively. The adsorption process of both dyes was spontaneous and endothermic, and the adsorption followed pseudo 2^nd order kinetic model and film diffusion model. The dyed PVS was finally cultivated with fungus Pycnoporus sp., wherein efficient dye decolorization was attained under solid state fermentation. As such, PVS coupled with subsequent fungal degradation might serve as novel alternative for dye effluent treatment.