The optimization of biomass and lipid yields of Chlorella sorokiniana when using wastewater supplemented with different nitrogen sources

• Growth of Chlorella varies with addition of different nitrogen sources.
• 1.5 g L−1 urea produced 0.218 g L−1 biomass and 61.52% lipid by relative fluorescence.
• Fatty acids produced were predominantly 16 and 18 carbon chains in length.
• Urea is an effective nitrogen supplement for growth of C. sorokiniana in wastewater.

The potential of nitrogen sources supplementing domestic wastewater for the cultivation of microalgae was assessed. Urea, potassium nitrate, sodium nitrate and ammonium nitrate were evaluated for their effect on cultivation and lipid production of Chlorella sorokiniana. Urea showed the highest biomass yield of 0.220 g L−1 and was selected for further experimentation. Urea concentrations (0–10 g L−1) were assessed for their effect on growth and microalgal physiology using pulse amplitude modulated fluorometry. A concentration of 1.5 g L−1 urea produced 0.218 g L−1 biomass and 61.52% lipid by relative fluorescence. Physiological stress was evident by the decrease in relative Electron Transport Rate from 10.45 to 6.77 and quantum efficiency of photosystem II charge separation from 0.665 to 0.131. Gas chromatography analysis revealed that C16:0, C18:0, C18:1, C18:2 and C18:3 were the major fatty acids produced by C. sorokiniana. Urea proved to be an effective nitrogen supplement for cultivation of C. sorokiniana in wastewater.