Bio-Slurry is the controlled treatment of excavated soil in an enclosed vessel. The bio-slurry process is used for remediation of soil contaminated with explosives such as trinitrotoluene (TNT), Royal Demolition Explosive (RDX), and High Melt Explosive (HMX), and various other contaminants. It is a form of a bioreactor. After removal of stones and rubble, excavated soil is mixed with water and placed in a tank. Typically, the slurry contains from 10% to 30% solids. Nutrients are added to enhance the ability of soil microbes to destroy contaminants. The vessels are designed with various process controls so that temperature, mixing, and nutrient additions can be manipulated to achieve maximum efficiency. After treatment, the soil is dried and tested to ensure that the explosive compounds have been degraded. Then, the soil may be disposed of or put back in its original location. Mobile treatment units are available.
Limitations and Concerns
The excavation of contaminated media is required, and therefore dust and particulate emissions must be controlled.
Any free-phase contaminants must be removed prior to mixing soils into the slurry. Very high contaminant concentrations may be toxic to microorganisms.
Drying the soil after treatment may be expensive. Disposing of wastewater may also present a problem. It should be carefully monitored for residual contaminants.
The biodegradation of specific contaminants in any specific soil/site condition is dependent upon many factors, including soil type, soil chemistry, the mix of contaminants and temperature. To determine whether biodegradation is an appropriate remedy, it is necessary to characterize the contamination, soil, and site, and to evaluate the biodegradation potential of the contaminants. A preliminary treatability study should be conducted.
An acceptable method for disposing non-recycled wastewater is required.
Low ambient temperatures can decrease biodegradation rates. Heavy metals are not treated by this method. They can be toxic to microorganisms.
Slurry bioreactors are used primarily to treat nonhalogenated (halogens are a class of chemicals consisting of bromide, fluorine, iodine and chlorine) semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs), petroleum hydrocarbons, and explosive compounds in soil. Bio-reactors are favored over in-situ (i.e., in-place) biological techniques in situations where underlying ground water may be difficult to capture, or when faster treatment times are required. Slurry-phase bio-reactors containing cometabolites and specially adapted microorganisms are both used to treat halogenated VOCs and SVOCs, pesticides, and polychlorinated biphenyls (PCBs) in excavated soils and dredged sediments.
Technology Development Status
This technology is field-tested. Demonstrations of three different bio-slurry processes are underway. An aerobic (with oxygen) bio-slurry was used to reduce TNT, HMX, and RDX concentrations at the Joliet Army Ammunition Plant, Illinois by 99%. An approach that alternates anaerobic (without oxygen) and aerobic states in the reactor is being tested. An anaerobic process is also being tested.
Other Resources and Demonstrations
See technology description of Bio-reactors.
The U.S. Army Environmental Center (USAEC) soil slurry bioremediation test at Joliet Army Ammunition Plant, Illinois, conducted by Argonne National Laboratory, sought to prove that degradation of explosives-contaminated soil is an affordable alternative to incineration. See http://aec.army.mil/usaec/technology/field.pdf.
USAEC field tested several bioremediation methods, including soil slurry reactor treatment, at the Umatilla Army Depot Activity, Oregon and the Iowa Army Ammunition Plant in Middletown, Iowa.
See http://clu-in.org/characterization/technologies/exp.cfm#86 for a technical description of explosives in different media and the use of some analytical techniques.