Effects of metal ions on the cultivation of an oleaginous microalga Chlorella sp

A coupling technique to purify wastewater for lipid production based on microalgae is attractive and promising for its potential to clean water and as biofuel feedstocks. Metal ions from wastewater might be involved in microalgal cultivation. In this study, the effects of metal ions on algal growth, lipid-producing potential, and water purifying capability of Chlorella sp. HQ were investigated. The effects of metal ions (Cr⁶⁺, Cu²⁺, Mn²⁺, Zn²⁺, Fe³⁺, Na⁺, and K⁺) on alga lipid production combined with water purification showed that Chlorella sp. HQ had strong resistance to metal ions and could efficiently remove them (Fe³⁺ 85.40~98.73%, Mn²⁺ 45.63~97.24%, Zn²⁺ 81.93~100.00%, Cu²⁺ 81.71~95.19%, Cr⁶⁺ 20.07~45.60%). Meanwhile, nutrient removal (total nitrogen (TN) 78.15~94.77%, total phosphorus (TP) 80.52~100%) was not inhibited by metal ions. Besides that, the highest algal biomass, lipid yield, and triacylglycerol (TAG) yield peaked at 350.00 ± 31.50, 87.50 ± 3.54, and 33.39 ± 19.42 mg L^-1, respectively, with the addition of Fe³⁺ (6.6 mg L^-1), Na⁺ (101.81 mg L^-1), and K⁺ (31.9 mg L^-1). The lipid/TAG content significantly increased up to 54.17 ± 11.91%/44.92 ± 0.42%, 100%/100%, 32.56 ± 12.40%/37.53 ± 4.58%, and 77.50 ± 1.77%/46.19 ± 1.06%, separately, with the addition of Cr⁶⁺(0.50 mg L^-1), Cu²⁺(5.02 mg L^-1), Zn²⁺(5.05 mg L^-1), and Mn²⁺(50.52 mg L^-1).