The removal of nitrite is shown in Fig. 3. During the lag phase, the nitrite removal efficiency varied little from 0.32±0.04 mg/L to 0.30±0.03 mg/L matched with no growth of the Chlorella vulgaris. The nitrite concentration did not decrease during the initial lag phase, but then sharply decreased from 0.32±0.04 mg/L to 0.06±0.01 mg/L during the rapid growth-phase.