Grantee Research Project Results
Final Report: Energy Crops for Reducing Areawide Lead Soil Contamination
EPA Contract Number: EPD07049Title: Energy Crops for Reducing Areawide Lead Soil Contamination
Investigators: Elless, Mark P.
Small Business: Edenspace Systems Corporation
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2007 through August 31, 2007
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2007) RFA Text | Recipients Lists
Research Category: SBIR - Mining , Small Business Innovation Research (SBIR)
Description:
In 1991, the secretary of the U.S. Department of Health and Human Services called lead “the number one environmental threat to the health of children in the United States.” Lead exposure can cause premature birth and impair a child’s mental and physical development, and in adults can cause kidney damage, high blood pressure, and other problems. The U.S. Environmental Protection Agency (EPA) estimates that 12,000,000 homes exceed the new 400 ppm standard for soil lead in play areas. Soil lead at small arms firing ranges, manufacturing plants, and other government and industrial sites poses similar challenges.
While lead can occur in localized areas such as in residential yards, large geographical areas of lead soil contamination also can occur because of past air emissions from nearby smelters, the use of lead arsenate pesticides, and combustion of leaded gasoline. In Washington state alone, nearly 500,000 acres of land surrounding smelters and nearly 200,000 acres of former orchards have been documented as having been affected by lead smelting activities and lead-based pesticide use (http://www.ecy.wa.gov/programs/tcp/area_wide/AW/toolbox_chap1.html Exit ; verified on May 16, 2006). Similarly the Doe Run Herculaneum smelter, the largest primary lead smelter in the United States, has released tons of lead from its location south of Saint Louis since beginning operation in 1892, yielding lead concentrations in residential yards surrounding the smelter as high as 33,000 mg/kg and ambient air lead concentrations of 85 μg/m3 ( EPA, 2002; MDNR, 2001). These two examples demonstrate that area-wide lead soil contamination is a significant and widespread health concern in the many regions of the country that have a legacy of smelting and agriculture. The problem also accompanies past lead-based mining, transportation, and industrial activity.
A promising alternative to excavation and replacement of lead-contaminated soil is phytoextraction, whereby living plants remove hazardous metals from contaminated soils. Lead phytoextraction relies on crop species and chelating agents that facilitate accumulation of lead in the above ground biomass.
This Phase I study sought to demonstrate the dual use of switchgrass (Panicum virgatum) and elephant grass (Miscanthus x giganteus), two crop species commonly cited for their potential use as feedstocks for cellulosic ethanol, for lead phytoextraction. Instead of disposing of the harvested biomass in a hazardous waste landfill, this biomass could serve as a feedstock for cellulosic ethanol production, thereby offsetting the costs associated with the lead remediation. While switchgrass and elephant grass are used as barrier crops to prevent erosion and fertilizer runoff, this appears to be the first application of these crops for phytoextraction and remediation of a heavy metal.
In Phase I, Edenspace Systems Corporation (Edenspace) conducted growth chamber studies in lead-contaminated soils collected from areas near the Herculaneum, Missouri, and Tacoma, Washington, smelters to compare the potential of these two plant species for lead phytoextraction, and to determine whether the accumulated lead would affect each plant’s potential to serve as an energy crop. Phase I results demonstrate that these crops are capable of accumulating lead in significant amounts without affecting their potential to serve as celluosic ethanol feedstocks.
In Phase II, the ability of both energy crops to remove lead from soil affected by smelters will be demonstrated at two field locations, with the harvested biomass then tested in a pilot-scale biorefinery for measurement of ethanol production. Applying dual use energy/environmental crops to the problem of area-wide soil lead contamination should reduce the net costs associated with the cleanup of these problem soils. Attainment of the project’s goals may help to eliminate this public health hazard over large areas that in the past have been prohibitively expensive to clean up.
Summary/Accomplishments (Outputs/Outcomes):
Two smelter soils, one collected near the Herculaneum smelter and the other near the Tacoma smelter, were collected to investigate the use of two potential energy crops, elephant grass and switchgrass. These grasses were compared to a common turfgrass variety (tall fescue) for lead phytoextraction to determine whether the accumulated lead deleteriously affects their subsequent use as feedstocks for the production of cellulosic ethanol. The soils were examined in a combination laboratory/growth chamber study to determine the conditions needed to trigger lead accumulation in these crops, assess the bioavailability of the lead before and after lead phytoextraction, assess methods for recycling or recovering the accumulated lead, and determine the effect of lead on fermentable sugar production.
Specifically, the following observations may be made about the data obtained in this study:
- Both energy crop species grew well in the smelter soils. No phytotoxic conditions were evident in any of the soils.
- The chelant screening identified several biodegradable chelants that were capable of extracting smelter-derived lead from the two smelter soils. These chelants were tested in the growth chamber to assess their ability to trigger lead accumulation into the grass species.
- Because of their larger biomass, the energy crops removed more total lead than the turfgrass despite having a lower concentration of lead in plant tissue. The time during the energy crop growth cycle when the soil was treated was found to be important to lead uptake performance.
- While some chelants caused an increase in levels of lead available for plant uptake, overall bioavailability was largely unchanged due to the addition of chelant to the soil compared to the control soil. Phase II will confirm the expected post-treatment decrease in bioavailability over time as treatment agents are biodegraded in the soil.
- Ashing and grinding of the biomass were successful in recovering the lead from the biomass, thereby allowing significant reductions in disposal of biomass.
- Enzymatic hydrolysis of the biomass showed minimal reductions in glucose and cellobiose levels produced in the energy crops containing lead, supporting the potential dual use of these crops for cellulosic ethanol production as well as for environmental remediation.
Conclusions:
The energy crops switchgrass and elephant grass were effective in removing lead from contaminated soils without adversely affecting their ability to serve as feedstocks for cellulosic ethanol production. These successful findings form the basis for expanded study in Phase II. Subsequent work will explore the appropriate point and method to remove lead from biomass to be processed for ethanol and will grow sufficient quantities of both energy crops in field demonstrations to allow testing in a pilot-scale biorefinery for measurement of ethanol production. Phase II objectives also include examining the effect of the lead-contaminated biomass on co-firing with coal.
Supplemental Keywords:
small business, SBIR, phytoextraction, lead, energy crops, switchgrass, elephant grass,, Scientific Discipline, Waste, Bioremediation, Agricultural Engineering, contaminated sediments, plant-based remediation, biodegradation, lead, bioremediation of soils, switchgrass, phytoremediationThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.