Cultivation of selected microalgae in dairy wastewater for the production of natural astaxanthin

Abstract

Freshwater microalgae species, Haematococcus pluvialis and Chlorella zofingiensis accumulate high quantities of natural astaxanthin. Nonetheless, cultivation of these microalgal species requires a large quantity of supplementary nutrients and freshwater to facilitate cell growth, photosynthesis and to overcome evaporative losses. With increasing water scarcity, directing large quantities of freshwater for microalgae cultivation can be controversial. Hence, the cultivation of these species in dairy wastewater could be an alternative for using freshwater. Additionally, wastewater contains nutrients such as nitrogen, phosphorus and organic carbon, which facilitate microalgal growth. In this study, the ability of dairy wastewater to support growth and astaxanthin accumulation of H. pluvialis and C. zofingiensis was assessed, with the aim of reducing the requirement for freshwater and additional nutrients. Both species exhibited considerable growth in synthetic dairy wastewater with final biomass concentration of 0.575±0.007 g/L and 0.595±0.007 g/L for H. pluvialis and C. zofingiensis respectively. Two-tailed t test indicated no significant difference between microalgal growth in dairy wastewater and Bold’s basal medium (control), suggesting it could be used as a substitute for standard growth medium. Astaxanthin concentration in the microalgal culture was measured using spectrophotometry subsequent to solvent extraction. The highest astaxanthin content (w/w) was observed in H. pluvialis grown in dairy wastewater, which was 25.3% higher than that of the control. In comparison, C. zofingiensis cultivated in dairy wastewater indicated a 6.5% increase compared to its control. Thus, results of this study indicate that astaxanthin production from microalgae cultivated in dairy wastewater could provide a sustainable alternative to using freshwater.