Chlorella sp. is often used in the treatment of wastewater to produce lipids, a practice which could go beyond wastewater treatment and be used to generate green energy. Our objectives here are to explore how the ratio of carbon to nitrogen (C/N) affects the removal of carbon and nitrogen in a wastewater treatment system, while simultaneously generating biomass and lipids. In this study, the C/N ratio is adjusted to 0.002, 6, 8, 10, 12 and 32. The results indicate that a C/N of 10 is sufficient to ensure the consumption of carbon and nitrogen, achieving the lowest concentration in the shortest culturing time (32 h). When nitrogen is lacking in the culture, there will be a slight decrease in the rate of carbon consumption which leads to a limitation of nitrogen and an increase in the lipid/cell density even at 96 h of culture time. The highest lipid content (0.57 g/L) and lipid increase rate (0.4 g/L) occurs with a C/N of 32. The greatest amount of biomass, 1.42 g/L is achieved when the C/N is 32. The carbon concentration is the main factor affecting the nitrogen consumption and the increase in the biomass and lipid content.