SOIL, SEDIMENT AND SLUDGE: EX-SITU BIOLOGICAL TREATMENT
Slurry Phase Bio-reactor
Slurry Phase Bioreactor
Process:
- The excavated soil is physically pre-treated to separate stones and rubble. In some cases, it is also pre-washed to concentrate the contaminants into a smaller volume of soil.
- An aqueous slurry is created by combining the contaminated soil, sediment, or sludge with water and nutrients - amount depends altering the concentration for an apt rate of bio-degradation to occur. (Typically, the slurry contains from 10 to 30% solids by weight).
- This is then placed into a bio-reactor as shown above.
- The slurry is mixed to keep solids suspended and microorganisms in contact with the soil contaminants.
- Upon completion of the process, the slurry is dewatered and the treated soil can be replaced to it's position. Only the contaminated fines & collected wastewater require further treatment.
- If necessary, an acid or alkali may be added to control pH.
- Microorganisms also may be added if a suitable population is not present.
- Dewatering devices that may be used include clarifiers, pressure filters, vacuum filters, sand drying beds, or centrifuges.
- Slurry-phase bioreactors may be classified as short- to medium-term technologies.
Uses:
- Treats solid phases contaminated by non-halogenated SVOCs and VOCs, explosives, petroleum hydrocarbons, petrochemicals, solvents, some pesticides, wood preservatives & other organic chemicals.
- The ability to add specially adapted microorganisms & cometabolites allow treatment of halogenated VOCs and SVOCs, pesticides, and PCBs. (e.g. otherwise more persistent compounds).
- Ex-situ bioreactors are favoured over in situ systems for either heterogenous or low permeability soils because the mixing ensures even treatment and faster treatment times.
Limitations/Disadvantages:
- Must excavate & transport the contaminated media (unless lagoon implementation).
- Bio-reactor design can be difficult and expensive.
- Nonhomogeneous or clayey soils can create serious material handling problems.
- Dewatering soil fines after treatment can be expensive.
- An acceptable method for disposing/further treating waste-water is required.
- A preliminary treatability study should be conducted.
Treatment costs using slurry reactors range from $130 to $200 per cubic metre, slightly greater if VOCs present because the off-gas would also require further treatment.