Phosphate removal from wastewaters using a weak anion exchanger prepared from a lignocellulosic residue

Surface modifications of lignocellulosic residues has become increasingly important for improving their applications as adsorbents. In this study a new adsorbent system (BS-DMAHP) containing dimethylaminohydroxypropyl (DMAHP) weak base groups was prepared by the reaction of banana stem (BS), a lignocellulosic residue with epichlorohydrin and dimethylamine followed by treatment of hydrochloric acid. The original BS and BS-DMAHP were characterized with the help of surface area analyzer, infrared spectroscopy (IR) and scanning electron microscopy (SEM). Surface charge density of the samples as a function of pH was investigated using potentiometric titrations. Adsorbent exhibits very high adsorption potential for phosphate and more than 99.0% removal was achieved in the pH range of 5.0-7.0. Adsorption has been found to be concentration dependent and endothermic and follows a reversible second-order kinetics. The Langmuir and Freundlich isotherm models were applied to describe the equilibrium data. Equilibrium data agreed very well with the Langmuir model. Adsorption experiments were conducted using a commercial chloride form Duolite A-7, a weak base anion exchanger. The removal efficiency was tested using fertilizer industry wastewater. Adsorbed phosphate on BS-DMAHP can be recovered by treating with 0.1 M NaOH solution. A stability test operated for four cycles indicate a capacity loss of < 12.0%.