Effects of chromium on the removal of nitrogen and phosphorus in domestic wastewater and the content of nitrogen and phosphorus in plants

In order to study the effects of chromium on the removal of nitrogen and phosphorus in domestic wastewater and the content of nitrogen and phosphorus in plants,Cyperus alternifolius and Coix aquatica Roxb were cultured in domestic wastewater with four Cr6+ concentrations(0,1,10,20 mg·L-1).The results were as follow:(1) the removal of total nitrogen was promoted at 1 mg·L-1 Cr6+ concentration,but inhibitted at 20 mg·L-1,and it was different with different treating time,the removal rate of 17 days was significantly higher than that of 7 days at 0 and 1 mg·L-1 Cr6+concentrations,but lower at 20 mg·L-1;the removal rate of Coix aquatica Roxb was significantly higher than that of Cyperus alternifolius at all Cr6+ concentrations except 20 mg·L-1.(2) The removal rates of Cyperus alternifolius and Coix aquatica Roxb on total phosphorus decreased with the prolonging of treating time,the removal rates of 10 and 20 mg·L-1 treatment were significantly lower after 17 days than that after 7 days;the removal rate of 20 mg·L-1 treatment was significantly lower than that of control;the removal rate of Cyperus alternifolius on total phosphorus was significantly higher than that of Coix aquatica Roxb at 10 and 20 mg·L-1.(3) The changes of nitrogen and phosphorus content in Cyperus alternifolius and Coix aquatica Roxb were different with different Cr6+ concentrations,nitrogen and phosphorus contents of 20 mg·L-1 treatment were significantly lower than that of the control in the stems of Cyperus alternifolius and the roots,stems and leaves of Coix aquatica Roxb.