Removal of high concentration of nitrate and phosphate from aqueous mixotrophic solution by Chlorella vulgaris

Abstract

Microalgae exhibit large potential as an alternative to advanced biological nutrient removal in wastewater or simulated wastewater at laboratory conditions. Therefore, it is necessary to determine the optimum conditions for nutrient removal. This study investigated the total carbohydrate, chlorophyll-a, -b, carotenoid and lipid production and nutrient removal of mixotrophic microalgae ( C. vulgaris ) cultured in different nitrate/phosphate rich modified BG-11 medium (0-200 mg L -1 ) at longer growth periods (10 days). The mean removal efficiency of NO 3 -N (in nitrate source), and PO 4 -P (in phosphate source) (88.29 ±0.12 and 31.06 ±0.22%, respectively) was reached in the mixotrophic culture. Under the optimum conditions (200 µmol photon m⁻ 2 s⁻ 1 16 h photoperiod and 28% inoculum size), 63.61-99.05% of NO 3 - and 13.97-63.77% of PO₄ 3 ⁻were successfully removed. The lipid and carbohydrate productivities were 27.95 and 29.53 g L −1 d −1 , 0.2869 and 0.2435 g L -1 d -1 respectively, which were approximately 9-12 times higher than those in photoautotrophic condition. The BG-11 growth media containing 10 g L −1 glucose and excessive amount of nutrient effect results indicate that the Chl-a, -b and carotenoid contents of C. vulgaris is higher at 100 mg L -1 N and 50 mg L -1 P growth media composition compared to 100% growth media composition. Thereby, the findings of this study provided an insight into the role of algal uptake of nutrients under the nutrient rich mixotrophic medium for the future algae-based treatment application.