Treatment of synthetic acid mine drainage (AMD) by photoautotrophic and mixotrophic cultivation of Galdieria sulphuraria.

Acid heavy metal wastewater is primarily originated from mining, electroplating, metallurgical, and chemical industries, such as acid mine drainage (AMD). AMD is harmful to the environment owing to its strong acidity and high concentrations of heavy metal ions. In the present study, an environmentally friendly phycoremediation approach was used to purify synthetic AMD. The results suggested that Galdieria sulphuraria grew well in synthetic AMD without the requirement of pH regulation. In addition, the additional supplementation of nitrogen (N) and phosphorus (P) alone did not result in significant differences in cell growth, phycocyanin content, and heavy metal removal efficiency. In contrast, exogenous supplementation of organic carbon sources (glycerol and glucose) combined with the addition of N/P in synthetic AMD significantly increased the microalgal concentration by 240.3% and 298.4%, respectively. However, adding only the carbon source did not lead to a statistically significant improvement in microalgae growth because of the low N/P concentrations in AMD. Moreover, the removal efficiencies of heavy metals (Cu, Fe, Al, and Zn) significantly improved when glucose was supplemented in conjunction with N/P sources. Overall, this study proved that AMD can be ecologically treated by Galdieria sulphuraria integrated with algal biomass production, which provides a foundation for acid-heavy metal wastewater valorization and resource recycling.