Re-utilization of ash gourd (Benincasa hispida) peel waste for chromium (VI) biosorption: Equilibrium and column studies

Ash gourd (Benincasa hispida) is a commonly consumed vegetable in the Asian subcontinent, known to possess a good medicinal value. It has high waste index, 15% of which comes from peel alone. The present study describes the utilization of ash gourd (defatted) peel in biosorption of chromium (Cr), wherein equilibrium conditions and column operations were investigated and further modeled. Peel powder was studied for particle size (446 μm), BET surface area (0.4854 m2/g), point of zero charge (pHpzc 4.8), SEM-EDAX and zeta potential. In equilibrium studies at pH 1, more than 91% Cr (VI) gets adsorbed on ash gourd peel powder at an adsorbent dosage of 6 g/L for 125 mg/L solution. The quantitative adsorption of Cr (VI) ions was described by Freundlich adsorption isotherm. The sorption capacity of peel for Cr (VI) in batch studies was 18.7 mg/g. FTIR spectroscopy of samples before and after adsorption revealed the presence of carboxyl functional group, which play an important role in adsorption of Cr (VI). The processing of 1000 kg of ash gourd generates peel capable of adsorbing as high as 261.8 g of Cr (VI). Thus this work provides an effective approach for re-utilization of peel waste in removal of Cr (VI) from aqueous system.