Phytoremediation of chromium from tannery wastewater using local plant species

Phytoremediation, which is an emerging technology for cleaning up contaminated sites, is cost effective and has aesthetic advantages and long term applicability. The technology involves efficient use of plant species to remove, detoxify or immobilize contaminants in a growth matrix (soil, water or sediments) through natural processes. For this study, swamp smartweed (Polygonum coccineum), para grass (Brachiara mutica) and papyrus (Cyprus papyrus) were grown on 20 mm crushed rock filled plastic vessel watered with synthetic chromium containing solution in a greenhouse under ambient conditions. For comparison, the plants were also grown on both synthetic solution and tannery effluent with known concentration of 0.1, 0.5 and 1 mg/L Cr³⁺ at Bahir Dar tannery. Plants were harvested after 72 days of planting period and their roots and above ground parts were cleaned and digested through microwave digester for further analysis. Chromium in roots and shoots was determined by ICP-OES. It was observed that all plant species have the ability to remove both Cr³⁺ and Cr⁶⁺ from the aqueous solution for the specified initial concentration. Interestingly, using single factor analysis of variance, significant differences were also observed in their partitioning. All the three plants exhibited a significant transfer of Cr from wastewater to roots and shoots, but removal efficiency of Cr for swamp Smartweed was relatively low as compared to para grass and papyrus. On average translocation factor and removal efficiency of para grass for synthetic solution at 0.5 mg/L level and papyrus for tannery effluent at 1 mg/L level of chromium were relatively high (1.260, 83.08% and 1.715, 73.77% respectively). This finding indicated that all the tested plants (swamp smartweed, para grass and papyrus) can be used for phytoremediation of Cr³⁺ and Cr⁶⁺ containing wastewater discharged from industries.