SOIL, SEDIMENT AND SLUDGE: EX-SITU BIOLOGICAL TREATMENT
Composting
Typical Windrow Composting
Contaminated soil is excavated and mixed with bulking agents and organic amendments such as wood chips, hay, manure, and vegetative (e.g., potato) wastes.
Proper amendment selection ensures adequate porosity (for the oxygen, moisture & nutrient supply) and provides a balance of carbon and nitrogen (apt nutrients) to promote optimum microbial activity.
Uses:
Limitations:
Cost:
Proper amendment selection ensures adequate porosity (for the oxygen, moisture & nutrient supply) and provides a balance of carbon and nitrogen (apt nutrients) to promote optimum microbial activity.
- Composting is a controlled biological process by which organic contaminants (e.g., PAHs) are converted by microorganisms (under aerobic and anaerobic conditions) to innocuous, stabilised byproducts.
- Typically, temperatures of 54 to 65 °C must be maintained - to properly compost soil contaminated with hazardous organic contaminants. The increased temperatures result from heat produced by microorganisms as they biodegrade the organic matter in the waste.
- Usually uses indigenous (native/existing) microorganisms.
- Soils are excavated and mixed with bulking agents and organic amendments (e.g. wood chips, animal, and vegetative wastes) - to enhance the soils porosity.
- Maximum degradation efficiency is achieved through maintaining oxygenation (e.g., daily windrow turning), irrigation as necessary, and closely monitoring moisture content, and temperature.
- The two most common process of composting are aerated static pile composting (compost is formed into piles and aerated with blowers or vacuum pumps) and windrow composting (compost is placed in long piles (windrows) and periodically mixed with mobile equipment).
- Windrow composting is usually considered to be the most cost-effective composting process but it may also have the highest fugitive emissions.
- If VOC or SVOC contaminants are present in soils, off-gas control may be required.
Uses:
- Commonly applied to soils and lagoon sediments when contaminated with biodegradable organic compounds.
- Aerobic composting (with temp~50degrees C) is able to reduce the concentration & toxicity of explosives (TNT, RDX, and HMX) and PAH-contaminants to acceptable levels.
Limitations:
- Large space requirement.
- Excavation of contaminated soils is required
- If volatile organic, requires collection/control of off-gas.
- The addition of bulk materials (e.g. wood chips) increases soil volume.
- Not applicable if high concentrations of heavy metals present (toxic to MOs).
Cost:
- Highly variable - dependent on the soil volume requiring treatment, contaminant type and concentration, the soil density and the availability of the nutrients & bulk materials required.