U.S. Environmental Protection Agency
Toms River, New Jersey
The Following is information supplied by the EPA at the April Meeting on the Ciba-Geigy Superfund Site.
In Situ and Ex Situ
Jerome J. Kukor
Biotechnology Center for Agriculture and the Environment &
Department of Environmental Sciences Rutgers University
What is Bioremediation?
Using microorganisms to destroy environmental contaminants
Chlorobenzene + oxygen ---------->carbon dioxide + water + chloride
State of the Science
What are in situ and ex situ treatment?
In situ treatment-- "in place"
Can include addition of amendments to stimulate bacteria
Usually applied to contaminants in saturated zone
Ex situ contaminated material is treated elsewhere
Contaminated soil excavated and treated in a treatment unit
Usually applied to contaminants in unsaturated zone
What is required for bioremediation?
A biodegradable contaminant
Competent microorganisms capable of carrying out the transformation
Environmental conditions (pH, inhibitory materials, contaminant concentration)
Adequate supply of nutrients (nitrogen, phosphorus, trace elements)
Respiration (oxygen, nitrate, sulfate, iron)
Not all contaminants inherently biodegradable
"Rules of thumb" for biodegradability
Importance of treatability tests
100,000 - 10 billion cells/gm soil
90 - 99% of cells attached to soil
Adaptability (microbes at Ciba site exposed to contaminants for 40 years)
Natural occurrence of chlorinated compounds
pH (acidity/alkalinity): usually 5.5-8.5 (typically seen in nature)
Heavy metals: Pb, Cr, Hg, Cd inhibitory (natural mechanisms in bacteria to deal with many heavy metals)
Carbon sources used preferentially
Salinity (% level inhibitory)
For growth bacteria need N,P,K,S,Ca,Fe,Mg,trace metals, but usually only N and P need to be supplied
Chlorobenzene + oxygen----------> carbon dioxide + water + chloride
Oxygen usually must be added (poor solubility; used for many metabolic reactions)
Oxic, hypoxic and anoxic conditions in subsurface
Bacteria metabolically versatile with respect to respiration
What are the "limits" to bioremediation?
Highly hydrophobic contaminants in organic-rich soils
Very high contaminant concentrations (free product)
Inhibitory materials present
What are the advantages of bioremediation?
Process takes advantage of natural metabolic diversity of bacteria
Potential for complete destruction of some contaminants to innocuous end- products
>> Chlorobenzene + oxygen ----------> carbon dioxide + water + chloride
Disadvantages/challenges for bioremediation
Process can be slower than physical/chemical treatment
Challenge of getting the bacteria + nutrients + contaminants all together in the same place for in situ remediation
Might not be able to achieve "target" levels for all contaminants
How to tell whether the process is working
Contaminant disappearance is necessary but not sufficient
Need for mass balance determination
Production of "indicator" metabolites
Essential to have abiotic controls
Change in microbial community development