Effect of immobilization on growth of microalgae and removal of nitrogen from urine

Two species of microalgae, Scenedesmus obliqnus and Chlorella vulgaris, were cultivated as free and immobilized cells in synthesized urine to compare algal growth and nitrogen removal. Four levels of initial ammonia concentration were employed, from 25 to 100 mgN/L. No significant differences of growth rates were observed between free and immobilized algae. As to the uptake of nitrogen per cell, immobilization increased that of S. obliqnus by 9.6-53.2%, but decreased that of C. vulgaris by 14.0-28.1%. Results showed that immobilization improved the tolerance of algal cells against high concentration of ammonia. As initial ammonia level increased from 25 to 100 mgN/L, the uptake of nitrogen per cell dropped 34% and 36% for S. obliqnus and C. vulgaris in free cultures, and only 16% and 20% in immobilized cultures.