Removal of Heavy Metals in Vegetative Graywater Biofiltration Columns

Abstract

This study investigates the performance of laboratory-scale vegetative biofiltration systems in reducing five heavy metals [cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn)] from synthetic graywater. Thirty-six biofiltration columns of the same design were constructed, and twelve species of ornamental plants were planted, with three specimens from each species being planted in a single column. The study was conducted for six months in an arid climate. The overall removal efficiency for Zn and Cu was found to be about 98% and 75%, respectively. It was observed that soil Zn and Cu concentrations increased from 11.24 to 26.13 mg/L and from 11.9 to 12.12 mg/L, respectively, after irrigation with graywater. Zn and Cu were mainly removed by soil accumulation and plant uptake, respectively. Both Pb and Cr increased in effluent (about 29% and 6.5%, respectively) and in soil (about 12% and 63%, respectively) after irrigation with graywater, whereas Cd increased in effluent (about 7.6%) but decreased in soil (about 46%). Finally, the plants were ranked and recommended for application based on their performance consistency and effectiveness. The species Alternanthera ficondea topped the ranking, followed by the species Ixora coccinaea, Vitex agnus, Rhoeo discolor, and Jasmine sambac.