The effects of phosphorus concentration on the cell growth, nutrient assimilation, photosynthetic parameters, and biomass recovery of Ettlia sp. were evaluated with batch experiments using groundwater, 50 mg/L of N-NO3-, and different concentrations of P-PO43-: 0.5, 2.5, 5, and 10 mg/L. The maximum biomass productivity and phosphorus removal rate were 0.2 g/L/d and 5.95 mg/L/d, respectively, with the highest phosphorus concentration of 10 mg/L. However, a phosphorus concentration of 5 mg/L (N: P = 10) was sufficient to ensure an effective nitrogen removal rate of 11 mg/L/d, maximum growth rate of 0.88/d, and biomass recovery of 0.72. The appropriate hydraulic retention time was considered as 4 days on a large scale to meet the effluent limitation demands of water. While nitrogen depletion had a significant effect on the photosynthetic parameters and ratio of chlorophyll a to dry cell weight during the stationary phase, the effect of phosphorus was negligible during the cultivation.