Piggery wastewater that is used for microalgae cultivation has usually been treated by secondary treatment processes. The present study investigates mixotrophic cultivation of the green microalgae Chlorella pyrenoidosa with primary piggery wastewater that has merely been diluted before use. The biomass productivity of the microalgae exhibited a positive linear correlation with the initial COD values, which ranged from 250 to 1000 mg/L Nutrients in the piggery wastewater were removed efficiently; for example, the removal rate of ammonium was over 90% in all diluted samples. Profiles of fatty acids in the algal lipids were different after cultivation in piggery wastewater medium compared to Bristol's solution. The maximum lipid productivity of 6.3 mg L-1 day(-1), which was achieved when the initial COD was 1000 mg/L, is not superior to other reports, but it suggests a convenient way to reduce the high organic content of piggery waste with the production of algal lipids. (C) 2011 Elsevier Ltd. All rights reserved.