Nutrient removal capacity of <i>Chlorella vulgaris</i> , <i>Chlorella sorokiniana</i> and <i>Haematococcus pluvialis</i> from wastewater at high temperature, and changes in biochemical composition of algal biomass

This research focused on applying three microalgae <i>Chlorella vulgaris, Chlorella sorokiniana</i>, and local strain <i>Haematococcus pluvialis</i> for wastewater remediation at high temperature, assessing their efficiency in reducing nitrogen (NH₄⁺ and NO₃^-), phosphorus (PO₄^-3) and soluble chemical oxygen demand (COD). The growth rates, proximate and fatty acid (FA) compositions of microalgae were also investigated. Initially, microalgae were cultured in BG-11 medium in 250-mL Erlenmeyer's for 10 days, then scaled up to 1-L Erlenmeyer's for another 10 days, and finally to 5-L plastic vessels for another 15 days. For wastewater treatment (WWT), microalgae were cultivated in rectangular, bench-scale plastic containers (15 L) for 14 days at 35 °C. Growth performance did not change for the first 10 days; however, <i>C. vulgaris</i> and <i>H. pluvialis</i> showed significantly higher growth, compared to <i>C. sorokiniana</i> at the end of the experiment in BG-11 medium. Regarding WWT, <i>C. vulgaris</i> and <i>H. pluvialis</i> showed significantly higher growth performance than <i>C. sorokiniana</i> at the end of the14-day experiment. <i>H. pluvialis</i> showed the highest PO₄^-3 removal rate (96.53%). However, no significant difference was observed in NH₄⁺ removal, which was over 90% for all species. On the other hand, <i>C. vulgaris</i> and <i>H. pluvialis</i> showed significantly higher removal for NO₃^- (92.07% and 92.17%) and for COD (88.44 and 87.55%), respectively, compared to <i>C. sorokiniana</i>. Regarding FA composition of microalgae before WWT, <i>C. sorokiniana</i> and <i>H. pluvialis</i> were dominated by saturated fatty acids (SFA) (39.4 and 50.1%, respectively), while monounsaturated fatty acids (MUFA) were the most abundant ones in <i>C. vulgaris</i> (35.1%). After WWT, SFAs significantly increased in <i>C. vulgaris</i> (95.5%-increment) while they were significantly decreased (17.9%-decrement) in <i>H. pluvialis</i>, and did not change in <i>C. sorokiniana</i>. The findings suggest that all strains, specially <i>C. vulgaris</i> and <i>H. pluvialis</i>, have remarkable capabilities for nutrient absorption at high temperatures, which makes these strains suitable for arid regions.