Multitasking Grasses: Phytoremediation Coupled with Biofuel Production

This project aims to remediate heavy metal contamination in marginal land (from mineral mining processes) via phytoremediation (uptake of the heavy metals by plant mechanisms), while making use of the heavy metal contaminated biomass to produce an added product, ethanol, for an alternative fuel source. At this point in the project, we have evaluated two different plant species for their ability to take-up metals from contaminated soil. Both species are able to survive in and remediate the toxic heavy metal soil environment. The levels of metals within the plant tissue following uptake are actually within ranges that increase ethanol production, via yeast fermentation, by providing the yeast with necessary co-factors for metabolism (in the same way that humans require vitamins and minerals)! We have also evaluated the effects of heavy metals on the lignin and sugar composition of the plants and have found that the metals did not impact or reduce the fermentability of the grasses. This means that plant growth in the presence of toxic levels of metals does not reduce the sugars that can be converted to ethanol. At this point, we are using Response Surface Methodology (RSM- a statistical optimization method) to design studies for optimizing the amount of sugars released from the plant matter and to minimize the amount of fermentation inhibitor compounds from the plant matter for the production of ethanol. By maximizing the release of sugars by methods called dilute acid pretreatment or enzymatic saccharficiation and minimizing inhibitors in solution, we can optimize the yield of ethanol from the heavy metal contaminated biomass during fermentation. We are at the point of optimizing the actual fermentation by investigating factors such as yeast species, time, temperature, pH, and innoculation rate.