Influence of heavy metals from flue gas integration with algal production on biodiesel production

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Large-scale microalgae production is expected to be integrated with point source carbon dioxide sources such as coal-fired power plants for carbon supply and environmental benefits. Although industrial flue-gasses pass through purification systems, submicron-size particles enriched with heavy metals are emitted to the atmosphere and eventually reach the ground resulting in increased health issues. Algae production integrated with flue-gas will ultimately have heavy metals introduced into the growth media which can be absorbed by the microalgae and potentially degrade growth and contaminate the biomass. This study experimentally evaluates the distribution and impact of heavy metals present in flue-gas on microalgae production systems. Two different microalgae species were evaluated, Scenedesmus and Nannochloropsis, cultivated in batch reactors with media containing at a minimum of ten heavy metals (Cu, Co, Zn, Pb, As, Se, Cr, Hg, Ni and Cd) at concentration representative of flue-gas integration. Heavy metal impact was quantified through biomass growth, lipid content, and heavy metal analysis through inductively coupled plasma mass spectrometry and atomic absorption spectrometry. The results show that heavy metals positively impacted Scenedesmus grown at the reference concentration while negatively impacted Nannochloropsis growth. Further study focused on Scenedesmus showed that heavy metals accumulated mainly in biomass and very low concentrations were measured in the media. Environmental impact assessments show most heavy metals in the effluent water complied with the recommendations for irrigation water and drinking water standards established by the Food and Agricultural Organization of the United Nations and the U.S. Environmental Protection Agency respectively showing microalgae were effective in removing metals from the growth media. This research shows that bioremediation of carbon dioxide and heavy metals in combination with energy production can be integrated and beneficial. Further work is dedicated towards understanding the end fate of heavy metals in terms of end products such as biofuel and algae meal.

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