(53b) Effects of Heavy Metals From Flue Gas on Algal Growth and Lipid Production and Their Distribution In the System

Flue gas from coal fired plants is a major source of carbon and heavy metal emission. Broadly, CO₂, SO_X, NO_X and trace metals are the constituents of flue gas which are of environmental concern. Capturing these airborne constituents using algae cultivation would allow initiation of a beneficial use program for flue gas and provide an environmentally sustainable alternative for coal fired plants. Biosorption properties, high growth rates, production on nonagricultural land, high lipid productivity of algae offer an encouraging alternative for heavy metal capture. Several studies have indicated the influence of heavy metals on algae. This study attempts to address the distribution and impact of heavy metals present in flue gas on microalgae production.  Ten heavy metals namely, As, Cd, Cr, Co, Cu, Pb, Ni, Hg, Se, and Zn are being considered for this study. To understand the effects, algae strain (Scenedesmus sp.) is being grown in batch reactors using APS media with individual addition of the heavy metal at concentration likely to be present in the culture after permeate recycling. Total Suspended Solids and optical density are used as indicators for growth monitoring. Metal distribution and uptake are analyzed using ICP-MS. Lipid accumulation inside the algal cell is analyzed using gas chromatography.

Co, Pb and Zn at a concentration of 0.32, 1.09 and 8.8 mg/L were evaluated. The metal concentration in the permeate was close to zero after 18 days for Pb, whereas, Zn and Co were present in the permeate.  Pb, Co, and Zn were found in the harvested algal biomass, mostly distributed in the intracellular portion than the extracellular portion of the cell. Pb, Co and Zn had been observed to adsorb to cell wall and reached a plateau within few days. Progressively these metals accumulated inside the cell. Pb, a not-essential nutrient, took longer to accumulate inside the cell wall, while Co and Zn, micronutrients, where uptaken since the beginning of the experiments. After 18 days of growth, around 25% of the Zn and Pb evaluated had accumulated mostly inside the cell while the Pb adsorbed to the cell wall was close to zero. Around 20% of the Co evaluated entered the cell while the Co adsorbed on the cell wall reduced slower probably due to dynamic equilibration with the Co available in the medium. Adsorption in the reactor walls was also observed. The growth and lipid production where practically not affected during the period of evaluation.