Combined effects of pH (i.e., 7.5, 8.5, and 9.5) and bicarbonate (i.e., 0, 80 and 160 mM NaHCO3) on lipid accumulation and on biological contaminant viability in a protozoa-contaminated culture of the freshwater microalga Neochloris oleoabundans were studied. Cultures grown in the media containing 160 mM NaHCO3 at pH 9.5 obtained the highest biomass concentration (DCWmax = 1.32 g/L), lipid content (LC = 327 mg/g), which corresponded to a lipid productivity of 56 mg/(L.d), and the culture was protozoa free one day after inoculation. Other cultures, 160 mM NaHCO3 at pH 8.5 (DCWmax = 1.32 g/L, LC = 223 mg/g), and 80 mM NaHCO3 at pH 9.5 (DCWmax = 1.25 g/L, LC = 264 mg/g) could delay protozoan growth, but not inhibit it completely. These results suggest 160 mM NaHCO3 or slightly above at pH levels of 8.5-9.5 may be used in outdoor cultivation processes of freshwater N. oleoabundans to control protozoa contamination while maintain a high lipid content. (C) 2015 Elsevier Ltd. All rights reserved.