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

This research focused on applying three microalgae Chlorella vulgaris, Chlorella sorokiniana, and local strain Haematococcus pluvialis 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, C. vulgaris and H. pluvialis showed significantly higher growth, compared to C. sorokiniana at the end of the experiment in BG-11 medium. Regarding WWT, C. vulgaris and H. pluvialis showed significantly higher growth performance than C. sorokiniana at the end of the14-day experiment. H. pluvialis 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, C. vulgaris and H. pluvialis showed significantly higher removal for NO3− (92.07% and 92.17%) and for COD (88.44 and 87.55%), respectively, compared to C. sorokiniana. Regarding FA composition of microalgae before WWT, C. sorokiniana and H. pluvialis were dominated by saturated fatty acids (SFA) (39.4 and 50.1%, respectively), while monounsaturated fatty acids (MUFA) were the most abundant ones in C. vulgaris (35.1%). After WWT, SFAs significantly increased in C. vulgaris (95.5%-increment) while they were significantly decreased (17.9%-decrement) in H. pluvialis, and did not change in C. sorokiniana. The findings suggest that all strains, specially C. vulgaris and H. pluvialis, have remarkable capabilities for nutrient absorption at high temperatures, which makes these strains suitable for arid regions.