Application of Maize Silage as a Biosorbent for the Removal of Dyes from Aqueous Solutions

The aim of this study was to determine the effectiveness of synthetic dyes removal from aqueous solutions with the use of silage from common maize Zea mays L. as a biosorbent. Two dyes were used as adsorbates: cationic Basic Violet 10 (BV10) and anionic Reactive Black 5 (RB5). The silage from common maize Zea mays L. originated from the Del:aliment of Agrotechnology and Plant Production Management, University of Warmia and Mazury in Olsztyn. Before experiments, the silage was dried at a temp. of 60 degrees C for 12 h and then sieved through a sieve with mesh diameter of 0.25 mm. The scope of analyses included determinations of: the effect of biosorbent dose on the course of adsorption process, optimal time of dyes adsorption, and correlation between type of dye and effectiveness of the adsorption process. The effectiveness of RB5 and BV10 adsorption from aqueous solutions onto silage was analyzed based on a correlation between the quantity of adsorbed dye Q (mg/g d.m.), and its equilibrium concentration C (mg/dm(3)). Results obtained were analyzed with the use of four sorption isotherms: Freundlich, Langmuir, double Langmuir, and Redlich-Peterson. Poorer fit of experimental results to the model was achieved only in the case of Freundlich isotherm. The remaining three models were very well describing the results. Owing to the presence of negative functional groups like e.g. -COOH and -OH in silage, it has a negative charge in aqueous solutions. This has a beneficial impact on the effectiveness of sorption of positively-charged cationic dyes. In turn, electrostatic repulsion of a negatively-charged surface of a biosorbent and anionic dyes exerts a negative effect on sorption effectiveness. The maximum sorption capacity of silage determined for the cationic dye BV10 was ca. 180 mg/g d.m. and was significantly higher than the sorption capacity assayed for the anionic dye RB5 - ca. 80 mg/g d.m. In comparing the achieved results for the sorption of the analyzed dyes RB5 and BV10 onto maize silage with the effectiveness of dyes sorption on other biosorbents, it may be concluded that the waste maize silage displays very good sorption properties and may be successively applied for dye removal.