Enhanced production of astaxanthin and co-bioproducts from microalga Haematococcus sp. integrated with valorization of industrial wastewater under two-stage LED light illumination strategy

Abstract

Microalgal-based biochemicals and biofuels integrated with phycoremediation of industrial wastewater can potentially increase the profitability and sustainability of the food–water–energy–environment nexus. A key challenge in the high-density cultivation of microalgae is to provide light of efficient wavelengths in photobioreactors. In this study, specific narrow bands of light-emitting diodes (LEDs) and their intensities were manipulated to enhance astaxanthin and co-bioproduct production by the microalga Haematococcus sp. Among the strategies tested, the two-stage LED light illumination involving red LED for 5 days and then blue LED for the next 5 days, with a continuous light intensity of 40μmol m−2 s−1, was shown to be the most efficient in improving the performance of Haematococcus sp. These conditions led to the highest astaxanthin production, of 2.55 mg/L, which was 1.22- to 2.07-fold higher than that by one-stage cultivation, with no significant effect on pigments (chlorophylls and carotenoids) and lipid production. Using a two-stage strategy integrated with the valorization of seafood processing effluent, Haematococcus sp. grew well in the secondary effluent from a seafood processing plant, giving 1.33 g/L of biomass, with 3.39 mg/L of astaxanthin, 14.3 mg/L of chlorophylls, 6.22 mg/L of carotenoids, and 0.41 g/L of lipids. The produced astaxanthin can be used as a sustainable source of bioactive ingredients with desirable antioxidative properties, giving ABTS activity of 5.24 mg of TE/g of astaxanthin, DPPH activity of 2.04 mg of GAE/g of astaxanthin, and PFRAP activity of 0.87 mg of GAE/g of astaxanthin. Meanwhile, lipids contain long-chain fatty acids (C16–C18> 96%) and their biodiesel characteristics were also satisfactory when compared to those required by international biodiesel standards, indicating the potential for use as biodiesel feedstock. Our results suggested that the integration process was cost effective and environmentally friendly for microalgal-based wastewater treatment and a microalgal-based multiproduct biorefinery.