Quantification of effects of flue gas derived inorganic contaminants on microalgae growth system and end fate of contaminants

Abstract

Increasing demand for renewable fuels has researchers investigating the feasibility of alternative feedstocks, including microalgae. Inherent advantages of microalgae include high potential yield, use of non-arable land, and integration with waste streams. Large-scale production of biodiesel from microalgae will require the integration of growth platforms with point source carbon dioxide such as coal derived flue gas. The introduction of this waste stream into the growth system will inevitably introduce trace inorganic contaminants which have a high affinity to bind to microalgal cells, could be toxic to the cells, and if transferred to the microalgae could impact the end use of the derived products. Inorganic contaminants As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Se, Sn, V and Zn were added to microalgal growth medium at a base concentration estimated to be representative of concentrations expected from 7day growth periods where coal derived flue gas is used as the carbon source. Nannochloropsis salina was cultivated in photobioreactors at outdoor light levels, 984μmolm−2s−1, with results for biomass, lipid yield, and fatty acid profiles evaluated. Results show trace inorganic contaminants negatively impacted growth and lipid yields with the average biomass productivity dropping from 1.13gL−1d−1±0.12 (control) to 0.37gL−1d−1±0.18, corresponding to a 67.5% decrease in biomass yield and a lipid decrease from 43.8±1.6 (control) to 29.8±5.7 (% dry biomass). Inorganic contaminant analysis performed using inductively coupled plasma mass spectrometry shows significant biomass sorption of the majority of the inorganic contaminants, which impacts the potential end uses of the biomass.