Comparison of growth characteristics and nitrogen removal capacity of five species of green algae

Abstract

Five common used green algae species, Chlorella vulgaris, Chlorococcum sp. GD, Parachlorella kessleri TY, Scenedesmus obliquus, and Scenedesmus quadricauda, were evaluated for their growth and nitrogen removal properties when being cultivated in synthetic wastewater with ammonium and nitrate as nitrogen sources. The five microalgae could adapt wastewater with different kinds of nitrogen sources, but the growth potential and nitrogen removal ability were species-dependent. Parachlorella kessleri TY cultivated in wastewater with ammonium and nitrate had higher biomass concentration of 2750 and 2765 mg L−1, respectively, compared to C. vulgaris, S. obliquus, and S. quadricauda. Chlorococcum sp. GD in wastewater with nitrate had the highest biomass concentration of 3095 mg L−1. Although all microalgae showed a good removal efficiency of nitrogen (ammonium: 85.30–97.03%; nitrate: 100%) after 7 days of cultivation, Chlorococcum sp. GD and P. kessleri TY removed 85–90.24% of ammonium and 100% of nitrate within 2–3 days, which was faster than the other three microalgae. It was also found that the growth and pollutant removal of microalgae in wastewater with nitrate was superior to those of microalgae in wastewater with ammonium. This was caused by the inhibitory effect of the low pH when microalgae were cultivated in wastewater with ammonium as the nitrogen source. Based on the results above, the growth and nitrogen removal was closely related to the microalgal species and the pH of the wastewater.