Sword ferns for phytoremediation of chromium contaminated waters

Abstract

Chromium is a highly soluble transition metal of vital industrial importance. It occurs in both trivalent and hexavalent forms. Due to many well identified adverse impacts of chromium to human health and natural ecosystems, treatment of chromium contaminated waters has become a major concern and challenge for environmental engineers. The currently practiced conventional mechano-chemical treatment systems for remediation of chromium contaminated waters have high operational costs, especially when the concentrations are low. Therefore alternative natural attenuation systems are becoming the focus of modem research. This paper presents a research to asses the applicability of Common Sword Ferns in phytoremediation of water contaminated with low or medium concentration of bot trivalent and hexavalent chromium. Saword ferns (N. Exaltata) showed very high removal rates (about 99%) in a Hydroponic medium upto 50 ppmcontamination of T-Cr. The mass balance shows that most of the Cr taken up by the plant is retained in the roots (about 75 % or 3500 mg/kg). Little is translocated to above-ground tissues (4% or 120 mg/kg). Therefore the mechanism of removal is mainly Rizofiltration. The mechanism of uptake may be Biosorption or Active uptake by root cells. N. Exaltata hardly shows any symptoms ofPhyto-toxic affects upto 50 ppm of Cr +3, and 15 ppm ofCr+6• But in a Soil water system mass balances show that most of water soluble Cr+3 is sorbed to soil (about 90%). N. exaltata is poor in de-mineralizing, mobilizing and uptake of soil bound Cr +3. Sand has a remarkable capacity to immobilize Cr+3 in water.