Implications of sludge liquor addition for wastewater-based open pond cultivation of microalgae for biofuel generation and pollutant remediation.

The growth improvement of microalgal strains in municipal secondary-treated wastewater by addition of nutrient-rich activated sludge centrate liquor was examined. Two strains (Chlorella luteoviridis and Parachlorella hussii) were tolerant to liquor, with addition of 25% liquor providing the best growth, biomass productivity and nutrient removal values. The capability of C. luteoviridis and P. hussii for full seasonal cultivation in a 150 L open pond in a temperate climate was studied, using the optimised secondary wastewater +25% liquor medium. Each strain was capable of growth all year including in autumn and winter but with strongest growth, productivity and remediation characteristics in the summer and spring. Both strains could maintain monoculture growth with no significant contamination or culture crash, demonstrating the robustness of these strains for wastewater cultivation in a northern European climate. Each strain could also be efficiently cultivated in a semi-continuous system for steady production of biomass and nutrient removal.