Biomass production and nutrient removal by Chlorella vulgaris as monoculture and in a consortium from centrate wastewater: optimization through acclimation
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Microalgae-based wastewater treatment has shown promise in the removal of contaminants such as nutrients and heavy metals. Municipal wastewaters could be used as low-cost cultivation media as they provide the necessary nutrients for microalgal growth. This technology could represent a viable and sustainable option to implement as part of biological wastewater treatment. However, microalgal culturing requirements and conditions must be more clearly understood. At a number of wastewater treatment facilities, centrate (CW) is produced from the dewatering process of biosolids following anaerobic digestion. CW exhibits high nutrient concentrations, generally much higher than the initial influent wastewater. Therefore, CW represents a potential nutrient-rich cultivation medium for microalgal growth, but it can also be toxic for their metabolism. This study evaluated the acclimation of microalgae culture to CW diluted with secondary wastewater (SW) as a growth media following a 16-week acclimation period. Monoculture C. vulgaris and a native consortium sampled from Amhertsview water pollution facility were used. This consortium was maintained in two conditions –Bold´s Basal Medium (BBMC); and 50% CW (CWC). The initial ammonia (NH4-N) and phosphate (PO43--P) concentrations were 451.67 ± 7.82 mg/L and 22.33± 0.69 mg/L for CW, and 0.65 ± 0.10 mg/L and 1.38 ± 0.04 mg/L for SW, respectively. Results showed that the acclimation process of microalgal cultures increased their tolerance by the fifth cycle, after 75 days of cultivation. Afterward, acclimated and non-acclimated cultures were cultivated in 30%, 50% and 100% dilution of CW to compare and evaluate nutrient removal and biomass production in CW. In terms of biomass productivity, 30% CW resulted in low values, while in 100%, nutrient toxicity leads to physiological stress on cellular metabolism, increasing lag phases. The 50% CW had the highest biomass production with continuous growth. Moreover, nutrients removal was dependant on the dilution of CW used, resulting in a significant removal (> 80%) for ammonium and phosphate when microalgae were cultivated in 50%CW. These results demonstrate the feasibility of microalgae to acclimatize, adapt, and grow under high nutrient loadings while providing efficient constituent removals.