The growth rate of Chlorella vulgaris was shown in Fig. 1. The lag-phase period for adaptation to the wastewater condition was be found to be 10 d. During the growth phase, the cell density of Chlorella vulgaris dramatically increased until 70 d, indicating activephotosynthetic reaction. The pH of the wastewater continued to increase from the lag phase through the growth phase as shown in Fig. 2. Microalgae are known to produce hydroxyl ions (OH−) when a bicarbonate ion is consumed for photosynthesis within the algal cell by following the reaction: HCO3−→CO2+OH− (Shiraiwa et al., 1993).