Effects of chromium on purification of domestic wastewater and its accumulation in constructed wetlands.

Sand culture experiments were conducted in order to study the effect of different concentrations of chromium(0,10,20,40 mg.L-1) on domestic wastewater purification of Cyperus alternifolius and Coix aquatica Roxb wetlands and chromium accumulation rules.The results were as follow:(1)At the seedling stage,the COD removal rates gradually increased along with the enhancement of chromium concentration,but they were significantly inhibitted under the treatments of 20,40 mg.L-1 in the other stages(except the flowering stage of Cyperus alterni-folius);TN removal rate of Cyperus alternifolius wetland wasn′t significantly affected along with the increase of Cr6+ concentrations,but it was inhibitted as far as Coix aquatica Roxb wetland was concerned(except treatment with Cr6+ 10 mg.L-1 at flowering stage);These two wetlands had good purification effects on domestic wastewater which contained chromium.Chromium was only detected in water that flowed out from the constructed Cyperus alternifolius wetland under 40 mg.L-1 treatment(.2)Treatment with Cr6+ 10 mg.L-1 induced the enhancement of Cyperus alternifolius and Coix aquatica Roxb biomass,but higher concentrations(20 mg.L-1 and 40 mg.L-1)showed inhibition effects on the biomass(.3)Fine sand and plant roots had great capabilities of adsorption and accumulation of Cr6+ in wastewaster.Chromium contents in fine sand and plants significantly increased along with Cr6+ concentration enhancement.The accumulations of chromium in roots of the two plants were significantly higher than those in shoots,proving that roots chromium of the two plants were hardly transfered to the shoots.