Use of hyperaccumulator plants in conjunction with plasma-arc torch technology to

bioremediate heavy metal contaminated soils.

Rodney Farris

Plasma Arc Torch- developed by NASA during the 1960's

- able to generate heat that is hotter than the surface of the sun

- can produce temperatures from 5000 to 21,000 oC

Plasma Arc Torch

Plasma Arc Torch- The destructive and removal process efficiency is approximately 90-99.99% with residence times of waste in a 150 kW unit of approximately 20-50 milliseconds. The system can be built as a stationary unit or as a mobile unit which can be placed at a site of contamination.

Plasma Arc Torch- Waste (solid, liquid, or gas) is introduced into the furnace area by either continuous or batch feeding and is melted (vitrified) by the extreme heat.

- by-products that are generated from the plasma arc torch have less volume that the original waste material

- has implications for increasing the life of landfills by five times by the melting of current waste.

Plasma Arc Torch- the torch has even been effectively used to vitrify high-level radioactive waste in storage by DOE at the Hansford Reservation in Washington State as well as asbestos and asbestos containing materials

The processing destruction of substances leaves behind a non-leachable substance that can be placed into any landfill. Contaminated soil can also be processed with the glass-rock like material being produced; which is 5-10 times stronger than reinforced concrete.

Plasma Arc Torch- dissociates organic and inorganic substances into their elemental constituents and vitrifies them into a secondary useable product or a clean fuel gas (hydrogen, carbon dioxide, and water vapor)

- The gases (also known as syngas) can be sold as a usable gas product

- The product gases that leave the reactor of the torch can be used to generate electricity

- metals (in gas form) can be recovered from the off-gas by passed them through a condensor

- a glass-like slag product can be sold and used for gravel, bricks, construction tiles, glass-ceramic stones, concrete aggregate, sand-blasting media, or other products. The glass like material or slag has properties that are similar to marble or granite

Hyperaccumulator Plants UsedThere are approximately 400 taxa of hyperaccumulator plant species identified (<0.2% of flowering plants ), with about 300 of them being Ni accumulators

Plants used for experimentation include: Alyssum lesbiacum

Scirpus lacustris Phragmites karka, Bacopa mon-nieri Brassica napus Hibiscus cannabinus

Festuca arundinacea Pteris spp. Salix spp. Arabidopsis spp.Populus spp..

Others include members of the Composite, Solanum, Euphorbia, and Legume Families

Hyperaccumulator Plants Used

Bladder CampionSilene vulgaris (Silene cucubalus) Medicago

truncatula

Hyperaccumulator Plants UsedFigure 1 Top, Phyllanthus “palawanensis” (Euphorbiaceae), a shrub in open areas of stunted forest at approximately 170 m on Mount Bloomfiels, Palawan, Republic of the Philippines; left, cut stem is pictured exuding a jade-green liquid which contained 88,580 µg Ni g-1 dry weight; middle, leaves containing 16,230 and stems 5,440 µg Ni g-1 dry weight; right, leaves crushed onto dimethylglyoxime soaked paper, showing the vivid purple color of the dimethylglyoxime-Ni complex. Middle left, Euphorbia helenae, found in Cuba contains 3160-4430 µg Ni g-1 dry shoot biomass; right, Sebertia acuminate, a tree endemic to serpentine soils of New Caledonia, showing the cut stem exuding latex which contains 25.74% Ni on a dry weight basis. Leaves of this species also contained 11,700 µg Ni g-1 dry weight. Bottom left, Thlaspi goesingense, found in Redschlag, Austria contains up to 9,490 µg Ni g-1 dry weight; right, Thlaspi caerulescens, growing on an abandoned Pb mine in Bradford Dale, Derbyshire, England contains up to 29,465 µg Zn g-1 dry weight. (Photographs courtesy of Alan Baker and Walter Wenzel.)

Hyperaccumulator Plants Used

Salix fragilis Crack WillowThlapsi caerulescens

Hyperaccumulator Plants Used

Cottonwood Populus deltoides

Hyperaccumulator Plants Used

Brassica juncea Brown mustard, Chinese mustard, Indian mustard

Hyperaccumulator Plants Used

Alpine pennycress

Hyperaccumulation of Metals

Heavy Metal Threshold Value for Hyperaccumulation

Mn or Zn = 10,000 g/g

Ni, Cu, or Se = 1000 g/g

Cd, Cr, Pb, or Co = 100 g/g

Al and As = 1000 g/g

Phytoremediation

Problems with Current Research

- conducted in laboratory or greenhouse

- experiments are non-reproducible in field situation

- only a few plants that show promise for in-field situation

- does not account for heterogeneous spatial nature of metals in soil

- does not account for environmental, biotic, or chemically driven interactions

- phytoextracted or accumulated metals left in plant or pulled to soil surface

Proposed Research

1. Field screening of various plants with comparison of the plants ability for heavy metal(s) uptake and hyperaccumulation of the heavy metal(s) on both contaminated and non-contaminated field sites

2. Evaluate the use of a plasma arc torch’s ability to completely vitrify plant and accumulated heavy metal(s) material as a means for phytoremediation/heavy metal waste removal from a contaminated field site; with determination of the torch process’s ability to produce secondary useful products from the vitrified plant and metal material.