Comparative Study on the Effects of Copper,Zinc and Cadmium on Phosphate Removal by Immobilized and Suspended Chlorella pyrenoidosa

The efficiency of phosphate removal by immobilized and suspended Chlorella pyrenoidosa entrapped in cadmium alginate was studied.The experiment was conducted in a laboratory and was based on settled synthetic wastewater with pH ranging from 4 to 8,and copper,zinc,cadmium mass concentrations of 0,0.05,0.5 and 5 mg/L.The results showed that:(1) Compared to the suspended state,the immobilized Chlorella had higher phosphorus removal efficiency due to greater stability of the encapsulation of sodium alginate.(2) The effects of the heavy metals on the phosphorus removal efficiency depended on the heavy metal concentrations.As the heavy metal concentrations increased,the phosphorus removal efficiency decreased and the negative influence was enhanced.(3) Cu2+ exerted bigger negative influence on the phosphorus removal efficiency of the immobilized and suspended Chlorella than Zn2+ and Cd2+.The negative influence on the immobilized and suspended Chlorella caused by Zn2+ and Cd2+ differed somewhat according to heavy metal concentration variation.(4) The effect of pH on the phosphorus removal efficiency was dependent on the heavy metal type,concentration and time.With the existence of Zn2+ and Cd2+,the highest phosphorus removal efficiency of Chlorella was generally present under weak alkaline conditions,especially pH up to 8,while the effect of pH on the phosphorus removal efficiency of Chlorella with the existence of Cu2+ showed a non-significant difference(P0.05).