Applicability of phytoremediation methods to treat chromium contaminated waters

Abstract

Chromium is a hazardous metal available in both Trivalent (Cr +3)and Hexavalent (Cr+6) forms. Cr+6 is evidently toxic whereas Cr+3 is relatively less hazardous than Cr+6. Cr+6 and Cr+3are extensively used in many industrial processcs and causes industrial heavy metal pollution of surface and ground water. There are iiany already practiced methods to remove Chromium such as Chemical Precipitation and Ion Exchange etc. Very little research has been done.on Phyto- remediation of Cr+6 and Cr +3 Currently there is a growing interest on research on 11 'L' capacity of Ferns to extract heavy metals. The amazing uptake rate of Pteris vitata (Br. 'dk fern) gave the initial 'impetus to this study. Nephrolepis exaltata or Common Sword Fern is a commonly found hardy invasive fern. It is recorded to be hardy plant with hign moisture and acidity In this study N. exaltata was comparatively assed with few other species for the capability of chromium extraction. N. exaltata showed a good uptake rate. Ability of Nephrolepis exaltata to extract Cr+3 from an artificial solution was studied in detail separately under 'Hydroponic and Soil water systems. All the experi ments were done in a controlled laboratory environment N. Exaltata showed very high removal rates (about ';1)%) in a Hydroponic medium upto 50 ppmcontamination of T-Cr. The mass balance she-ws that most of the Cr taken up by the plant is retained in the roots (about 75 % or 35uO mg/kg). Little is translocated to above-ground tissues (4% or 120 mg/kg). Therefore \he mechanism of removal is mainly Rizofiltration. The mechanism of uptake may be Bio-sorption or Active uptake by root cells. N. Exaltata hardly shows any symptoms of Ph .to-toxic affects upto 50 ppm of Cr +3,and 15 ppm er Cr+6. But in a Soil water system mass balances show that 1110stof water soluble Cr+3 is sorbed to soil (about 90%). N. exaltata is poor- in de-mineral izing, mobilizing and uptake of soil bound Cr +3.Sand has a remarkable capacity to immobilize Cr+3 in water. More research should be done to identify the capacity of sand and gravel to bind chromium.