Adsorption of toxic metals from greywater using low-cost spent green tea as a novel adsorbent

Abstract

Adsorption has been shown to be the most efficient, easy to use, less costly, and most importantly, environmentally friendly method of removing toxic metals from aqueous environments. The study attempted to use spent green tea to remove mercury (Hg2+), lead (Pb2+) and cadmium (Cd2+) from greywater. The study was conducted in a mono-system at an adsorbent dosage with corresponding 100 mL of different initial metal concentration of the greywater and a constant rotatory speed of 14.6 U/min, and a contact time of 60 min. The adsorption efficiency at different concentrations in mono systems by the adsorbent from tea waste ranged from 99.99% to 100% for mercury and lead, and from 11.11% to 18.28% for cadmium. The maximum adsorption capacity for the three metals in the experiment ranged from 10 to 100 mg g–1 for Hg2+, 10 to 100 mg g–1 for Pb2+ and 9.60 to 90.50 mg g–1 for Cd2+. Pb2+ had a greater affinity to the binding or active sites of the tea waste adsorbent than Hg2+ and Cd2+. Langmuir adsorption isotherm model was the best fit for the adsorption of toxic metals by impra ginseng-flavoured green tea. The pH at which the experiments were conducted showed very high removal efficiency for almost all the toxic metals studied, except for cadmium, which showed slightly lower removal efficiency. Spent green tea can be used as an effective and cheap adsorbent for toxic metals removal in greywater and wastewater. Spent green tea has a large surface area with a considerable number of active sites. Based on the findings, a further similar adsorptive experiment should be conducted at varying contact time, varying temperature and elevated metal concentrations.