Comparison in growth, lipid accumulation, and nutrient removal capacities of Chlorella sp. in secondary effluents under sterile and non-sterile conditions

The growth, lipid accumulation and nutrient removal characteristics of an oleaginous microalga Chlorella sp. HQ in two types of secondary effluents (named as X and Q) before/after sterilization were evaluated. The results show that the algal growth rates under sterilization were higher than those under non-sterilization. However, sterilization caused a significant decrease in algal lipid and triacylglycerol (TAG) contents in both X and Q. And the lipid and TAG yields in non-sterile X were as much as 2.7 and 7.7 times higher than those in sterile X, reaching up to 51.3 and 16.1 mg L⁻¹, respectively. However, the sterilization caused algal biomass increase in sample Q. Sterilization or not had almost no effect on the total phosphorus (TP) removal ability of Chlorella sp. HQ and it was found to have similar abilities to remove almost 100.0% TP from samples X and Q. While the total nitrogen (TN) removal efficiencies were promoted slightly under non-sterilization, increasing from 88.5 to 89.7% in X and from 13.3 to 17.2% in Q. Hence, non-sterile circumstances are basically beneficial for Chlorella sp. HQ to accumulate its lipid (TAGs) and remove nutrients from wastewater.