Phytoremediation

Term project by Matthew Dempsey, December, 1997

Decades of industrial growth have left an international legacy of soil and water contamination of toxic and potentially carcinogenic organic compounds and heavy metals. With the remediation market of the United States and European Union expected to exceed $20 billion annually, combined with many abandoned sites, the demand for cost-effective cleanup solutions has soared. Present technology has presented plants as a potential for environmental cleanup, "phytoremediation". US government agencies and private corporations have responded by increasing research support in this area.

One company that has taken advantage of this new market is Living Technologies. Their phytoremediation process of is referred to as the "Living Machine". Dr. John Todd, world renownd for his contributions to biology, has pioneered the development of Living Machines. Living Machines purify water by accelerating natures process. Using a diversity of organisms including bacteria, plants, snails and fish, break down and digestion of organic pollutants occurs with the help of sunlight and a managed environment. Using greenhouses to enhance the growth of many beneficial organisms, sewage flows through a series of clear-sided tanks, engineered streams, and constructed marshes where contaminants are metabolized or bound up. The sewage treatment process occurs in three stages and typically is completed in 2.5 days. The system is designed for 4.5 days' retention time for peak loads. A schematic of a Living Machine is shown below:

Flow diagram of Phytoremediation process



  • Solubilization and Metabolism of Complex Organics
    Through aeration and bio-augmentation, complex organic compounds (such as fats, proteins, and starches) and certain inorganic ones are transformed into simple soluble compounds, biomass, carbon dioxide, and water. By-products of these processes provide food for higher organisms downstream.
  • Nitrification and Nutrient Reduction
    Nitrifying bacteria, algae, and other plants metabolize nutrients in the waste stream. Ammonia is oxidized into nitrate, some of which is directly metabolized by green algae and higher plants. Snails and zooplankton graze upon solids within the system.

  • Denitrification and Pathogen Reduction
    The waste stream flows through a sand media followed by marshes where remaining solids are filtered out. The solids are removed to a reed bed and decomposed over a long period of time. Nitrates not used by plants are reduced microbially to nitrogen gas. Pathogens are ingested by higher organisms or killed by antibiotic releases from plant roots. The effluent is suitable for groundwater recharge, irrigation, fish farming, or recreational ponds.

  • Siting Requirements
    The greenhouse portion of the system requires approximately .15 square feet per gallon per day of treatment; thus, a 100,000 gpd system (waste from approximately 1,500 people) would take 1/3 of an acre. The site should not be shady - a protected, sunny site is preferred. If one-site composting (sludge and vegetation) is required, approximately 50 square feet per 1000 gpd of treatment would be needed.

    Soil Treatment



    Water Treatment




    Some history of phytoremediation:


    In the early 1980's, researchers began to scrutinize the work of other pioneering phytoremediation technology. After the nuclear accident at Chernobyl, Ukraine, in 1986 Phytotech began using plants to decontaminate water and soil. This was to be the proving ground for the new technology. Iowa City used tree farms to clean landfills in 1989, after results of the Phytotech experiments were published. In 1990 phytoremediation was adopted as the method of choice to control Nitrogen contaminated aquifers in New Jersey. The first Living Machine was designed and constructed in Europe during 1995, which lead to researching genetic engineering applications. Research proved that specific plants were capable of removing toxins of certain metals. The Department of Defense and EPA joined forces to develop plant-based cleanup approaches to large scale cleanup projects.


    Plants and their Functions

    Alfalfa

  • symbolic with hydrocarbon-degrading bacteria

    Arabidopsis

  • carries a bacterial gene that transforms mercury into a gaseous state

    Bladder campion

  • accumulates zinc and copper

    Brassica juncea (Indian mustard)

  • accumulates selenium, sulfur, lead, chromium, cadmium, nickle, zinc, and copper

    Buxaceae (boxwood) and Euphorbiaceae

  • accumulates nickel

    Compositae family

  • symbolic with Arthrobacteria, accumulates cesium and strontium

    Ordinary Tomato

  • accumulates lead, zinc, and copper