Comparison of the effects of nitrogen concentration on nutrient removal, growth and physiological characteristics of immobilized and free Chlorella Vulgaris: I. growth and nutrient removal

Abstract

The effects of nitrogen concentration on nutrient removal and the growth of immobilized and free Chlorella vulgaris were compared through laboratory ‐ scale batch experiment. The nitrogen concentration had much less influence on immobilized algae than free algae. During the 6 days experimental period, at nitrogen concentrations of 10, 20, 40 and 80 mg.l−1, immobilized algae achieved the growth rates of 0.168, 0.242, 0.137 and 0.093 day−1, and removed 62.0%, 78.0%, 91.2% and 97.1% total ‐ N, respectively, and 85–90% NH4 +‐N as well as more than 90% PO4 3−P. However, free algae obtained the growth rates of 0.071, 0.090, 0.059 and ‐0.021 day−1, and removed 36. 8%, 61.8%, 70.1%, and 45.9% total ‐ N, respectively. Especially at nitrogen concentration of 80 mg.l−1, its removal efficiency of NH4 +‐ N was only 22.2%, and at nitrogen concentration of 10 mg.l−1 that of PO4 3−‐P was only 38.7%. It shows that the immobilization of algae may protect cells against the inhibition of high nitrogen concentration and low N:P ratio. The nutrient removal of immobilized algae increased as nitrogen concentrations increased, but was not much correlated with the increase of cells number. This result suggests that nutrient removal of immobilized algae may be more dependent on the physiological activities of algae entrapped in Ca ‐ alginate, which makes its removal processes of nutrient different from free algae. The present study shows that immobilized Chlorella vulgaris has great potentialities for removing nutrient from wastewater with high nitrogen concentration loading or with a wide range of nitrogen/phosphorus.