SOIL, SEDIMENT AND SLUDGE: EX-SITU BIOLOGICAL TREATMENT
Landfarming
Typical Landfarming Treatment Unit
Contaminated soil, sediment, or sludge is excavated, placed over an impermeable lined bed, and periodically turned over or tilled to aerate the waste.
Soil conditions are controlled to optimise the rate of contaminant degradation, e.g.:
- Moisture content (usually by irrigation or spraying).
- Aeration (by tilling the soil with a predetermined frequency, the soil is mixed and aerated).
- pH (buffered near neutral pH by adding crushed limestone or agricultural lime).
- Other amendments (e.g., Soil bulking agents, nutrients, etc.).
The waste, soil, climate, and biological activity interact dynamically as a system to degrade, transform, and immobilise waste constitutes.
A Land Treatment site must be managed & monitored properly to prevent both on-site and off-site problems with ground water, surface water, air, or food chain contamination.
Typically a medium- to long-term technology.
Uses:
- Most successful in treating petroleum hydrocarbons
- Above-ground bioremediation is usually limited to heavier hydrocarbons, as the lighter, more volatile contaminants tend to be treated more easily by in situ technologies.
- As a rule of thumb, the higher the molecular weight (and the more rings with a PAH), the slower the degradation rate. Also, the more chlorinated or nitrated the compound, the more difficult it is to degrade.
- Can be used to treat diesel fuel, No. 2 and No. 6 fuel oils, JP-5, oily sludge, wood-preserving wastes (PCP and creosote), coke wastes, and certain pesticides.
Limitations:
- A large amount of space is required.
- Conditions affecting biological degradation of contaminants (e.g., temperature, rain fall) are largely uncontrolled, which increases the length of time to complete remediation.
- Inorganic contaminants will not be biodegraded.
- Volatile contaminants (e.g. solvents) must be pretreated because they would volatilise into the atmosphere (air pollution).
- Must control dust given off.
- Runoff collection facilities must be constructed and monitored.
- Topography, erosion, climate, soil stratigraphy, and permeability of the soil at the site must be evaluated to determine the optimum design of facility.
Cost:
Costs prior to treatment - Approx. $35,000 for laboratory studies, less than $100,000 for pilot tests & the cost of prepared bed during treatment is typically under $100 per cubic meter.