Soil washing treatment process

Figure 14.5. Soil washing treatment process. (From Mann, 1999.)...

Polyaromatic hydrocarbons absorb strongly to humus and other soil components, rendering these contaminants difficult to remove by thermal, physical, or chemical means, and unavailable for biodegradation. To desorb polyaromatic hydrocarbons from soil, surfactant flooding processes and soil-washing processes or treatments to enhance the biodegradation of polyaromatic hydrocarbons have been considered. 

Several unit processes can be used in the washing process. The soil is mixed with washing agents and extraction agents that remove the contaminants from the soil and transfer them to the extraction fluid. The soil and washwater are then separated. The soil can be further rinsed with clean water. The soil is removed as clean product, ready to put back into the original excavation, and the washwater is ready to be treated by conventional wastewater treatment processes as addressed in the next subsection. 

Many conventional soil vashing processes are based on the principle that pollutants adsorb onto very small particles fine fractions of the soil such as silt, clay and humic matter ivhich tend to be attached to coarser sand and gravel particles. These larger particles make up the majority of the soil content. A primary aim in soil washing is therefore to dislodge and separate these fine components from the bulk soil. If the pollutant materials can be detached from the bulk, possibly together with some other surface contamination, a concentrated volume of polluted soil can be produced. This can then be treated or disposed of and a large volume of residual soil which requires relatively little treatment and can be returned to the site as back fill. 

T0465 Klohn-Crippen Consultants, Ltd., ChemTech Soil Treatment Process T0480 Linatex, Inc., Soil/Sediment Washing Technology T0510 Metals Recovery, Inc., Metals Leaching... 

T0709 Sevenson Environmental Services, Inc., MAECHTE Chemical Treatment Process T0719 Soil/Sediment Washing—General... 

The SW-400 soil washing unit is an ex situ, treatment technology that removes contaminants from soil using biodegradable chemical surfactants and/or coUoidals. The water-based, soil washing process mechanically and chemically scrubs excavated soUs. Contaminants are removed from soils by suspension or dissolution within the wash solution. The SW-400 is mobile and transportable and can operate either as a stand-alone technology or in combination with others. The SW-400 system is currently commercially available. 

In general, soil washing technologies produce a small volume of contaminated soil and/or wash water that requires further treatment. Soil washing is generally not cost effective for soils with more than 30 to 50% silt or clay. The treatment process can be complicated by variable, infiuent... 

BioTrol soil washing system costs for the MacGilhs and Gibbs Superfund site in New Brighton, Minnesota, were examined on both an integrated and a unit process basis. Costs for the demonstration study were extrapolated to full-scale treatment of the wood preserving site. The extrapolation included both operating costs and capital costs amortized over an assumed 10-year equipment life span. Costs were estimated in 1991 dollars. 

ENSR International Group soil cleaning process is an ex situ treatment for soils contaminated with petroleum hydrocarbons. The process uses a combination of soil washing and solvent extraction. Soil washing removes heavy metals and hydrocarbons from coarse soil particles, resulting in a reduced volume of material to be treated by solvent extraction. Solvent extraction uses a chemical additive that enhances the extraction of hydrocarbons from soil particles in an aqueous slurry. 

The vendor states the cost of full-scale MERS treatment depends on soil characteristics, the concentration and chemical state of the targeted metal contaminants, the concentration of unregulated metals, and the cleanup objectives. The vendor claims the cost of MERS processing is competitive with the cost of landfill disposal, soil stabilization, and soil washing (D124538,... 

Stockpiling, transporting, and depositing clean, washed soil product fraction temporarily Dirty washwater treatment process (usually a treatment train including clarifiers, chemical reactors, filter, carbon contractors, dewatering presses, tanks, etc.)... 

The Snrbec-ART Environmental, L.L.C. (Snrbec), soil washing technology is a process based on mining and mineral processing principles that incorporates physical and chemical separation techniqnes (D12463A, p. 3). The technology separates and treats oversized fractions and sand fractions so that they can be placed back on the site as clean backfill. Contaminants are concentrated in the fines, and this fraction can be managed separately for further treatment or disposal. 

The overall cost of operation of a 6.6-ton/hr soil wash, metals removal, and bioslurry treatment train is estimated at 219 (1993 U.S. dollars) per ton. The individual process costs that make up this estimate are as follows ... 

WaterSmart Environmental, Inc. (WaterSmart), has developed the Express process technology for simultaneous treatment of contaminated soil and groundwater. Express, a combination of soil washing/leaching and in situ biological treatment, is an acronym for EXPedited REmediation Site Strategy. 

The WRS soil washing process (WSWP) is a commercially available, ex situ technology for the treatment of soils and sludges contaminated with organics, heavy metals, radionuclides, and combinations of contaminants. 

After soil washing wash water could be reintroduced into the CHEMFIX process later for hydration purposes thus eliminating the need for any post-washing water treatment. 

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