Potential of Water Hyacinth (Eichhornia crassipes (Mart.) Solms) for the Removal of Chromium from Tannery Effluent in Constructed Pond System

Abstract

The objective of the present study was to evaluate the potential use of water hyacinth for the removal of chromium (Cr) from tannery wastewater. This experiment was performed using healthy, young and acclimatized water hyacinth collected from unpolluted Awash River. Cr concentrations of 3, 5, 7, 10 and 20 mg/L were added to five different polyethylene tanks, containing 40 litre tap water cultured with Hoagland’s solution. A sixth tank containing Cr-free water was used as a control group. Six plants of equal wet mass (each 12.5 ± 2 g), shoot length (11 ± 2 cm) and root length (6 ± 2 cm) were transferred into each tank and allowed to grow in a greenhouse for 42 days. From each tank plants were harvested randomly every week. Bioaccumulation factor, translocation factor, shoot and root length; wet biomass and dry weight of the shoot and root were measured, and relative growth rate, tolerance index of the root and tolerance index of wet mass were analyzed. The maximum accumulation of 2.52 X 10³ µg/g of water hyacinth was achieved in the plants exposed to 20 mg/L Cr solution. The root part of the plant accumulated 2.42 to 3.82 times higher than the shoot part. An overall Cr removal efficiency of up to 91% was achieved in this study, but the efficiency decreased as the concentration of Cr in water increased. The growth of the plant was inhibited at high concentration due to Cr toxicity. Therefore, the application of water hyacinth for Cr removal will be sustainable, if the concentration of Cr in wastewater does not exceed about 10 mg/L. The relative growth rate (RGR) of the plant decreased with increasing Cr concentration and the growth was inhibited above 15.3 mg/L Cr in water. Based on the above data, it could be concluded that water hyacinth can potentially be used for the removal of Cr from tannery effluents which is a major environmental problem in Ethiopia. However, further investigation is needed to ascertain the optimum conditions for maximum removal.