Study on the phycoremediation of aqueous chromium (VI) ion by Haematococcus pluvialis through FTIR spectroscopy

Bioremediation of industrial heavy metal ions from wastewaters by microalgae has been becoming a major approach for their environmentally friendly and highly efficient abilities. While the removal efficiency and mechanism vary significantly among various microalgal species. Herein, the batch experiments for the biosorption and bioreduction of low-concentration chromium (VI) by three cellular stages of Haematococcus pluvialis were performed to investigate the underlying parameters for heavy metals removal. The results demonstrated that the tolerance threshold of chromium (VI) for green vegetative cells and yellow intermediate cells was 3 mg/L, which was lower than the value of 4 mg/L observed for red encysted cells. Accordingly, the cellular physiological status, including growth rates, pigment contents, and cellular morphology, was thoroughly evaluated via biochemical assays. All these distinct cellular characteristics were found to be closely associated with chromium (VI) tolerance. Additionally, Fourier transform infrared (FTIR) approach combined principal component analysis was further employed to comprehensively assess the vital changes of algal cellular components such as astaxanthin and β-carotene which contributed to the variations in biosorption and bioreduction of aqueous chromium (VI) ions. Consequently, it demonstrates that FTIR spectroscopy is a highly effective and reliable tool for elucidating the underlying mechanisms of heavy metal ions removal by evaluating the cellular physiological characteristics based on chemometrics, and it even presents a novel and practical strategy to rapidly identify the potential algal candidates for the phycoremediation of industrial wastewater contaminated by heavy metal ions.