Stephen Young outlines an innovate new technology for in-situ decontamination of metals and hydrocarbons in contaminated soils and sediments. ViroSoil™ technology, incorporating a unique reagent suite together with project know-how, equipment and techniques, offers a cost effective complete solution alternative to expensive conventional decontamination methods.
Brownfield redevelopment, particularly for new housing, is viewed by authorities and the electorate as preferable to building on greenbelt or floodplains. However, in many cases, brownfield sites have suffered from historical contamination by metals, acidity and/or hydrocarbons. Conventional approaches to remediation, including soil washing and excavation, often make remediation options financially prohibitive. Under the New Regime, identified land contamination needs to be treated such that potential migration of contaminants to human receptors is reduced to an acceptable risk level. Conventionally a variety of stabilisation techniques are used to retain contaminants, notably metals, in place. These include treatment with lime, pulverised fuel ash (PFA) or other materials, many of which are harmful to handle, transient in their treatment effectiveness, or are themselves detrimental to the ecological recovery of the treated area.
Virotec’s ViroSoil Technology is a modern alternative remediation technology for the in-situ treatment of contaminated soils and sediments. It is safe to use, ecologically benign and cost effective, and has a proven track record of success internationally for the stabilisation of a wide range of metals and hydrocarbons, and treatment also neutralises acidity. ViroSoil Technology offers tailored complete treatment solutions to each contamination situation.
Central to the technology is a suite of ViroBind™ reagent formulations. These formulations are safe to handle and are manufactured from sustainable sources. ViroBind reagent has excellent metal binding and acid neutralising characteristics. Metals (including arsenic) are removed from soil leachate, soil moisture and from soil surfaces, and are bound directly to (and retained on) the reagent surface where they are no longer bioavailable. Binding (≥1500 meq/kg) is permanent and rapid, reducing leachate contamination within hours ultimately to low part per billion (µg/l) concentrations.
The reagents are themselves highly insoluble (<0.1 mg/kg solubility), even under strongly reducing/acidic conditions, and will not migrate from the treated zone. Treated soils will be classified as inert or non-hazardous waste should disposal prove necessary. Complementary treatment methodologies (Rapid Sequestro-Degradation, RSD), can be incorporated to ensure hydrocarbons are also effectively treated. ViroBind reagent also has both short-term (total actual acidity) and long-term (total potential acidity) excellent acid neutralising properties. Neutralisation takes place directly in the area of application and in a significant area underneath this zone, significantly promoting vegetation recovery potential.
The application of ViroSoil Technology is logistically and operationally simple and versatile; being effective when intimately mixed with the contaminated soil (Figure 1), or applied using spray irrigation where ground conditions dictate. Alternative formulations, including pelletised media and blocks, are available to ensure the most appropriate application method is used for each specific situation, including the treatment of landfill leachate or contaminated groundwater.
Figure 1
Operationally simple treatment through intimate mixing of dry ViroBind reagent (red powder) with contaminated soil, one of several treatment formulation options.
ViroSoil Technology offers several advantages over conventional approaches for the stabilisation of metals and other contaminants in contaminated soils. In contrast to some alternatives, treatment is effective across a wide range of soil types. Being inorganic, ViroBind reagents are not adversely impacted by soil conditions, nor is contaminant sequestration impacted by aluminium or iron salts in the soils. Soil hydration is not necessary. Metal immobilisation is highly effective (Table 1), outperforming lime treatment (which only treats acidity) and many other conventional techniques, whilst the benign nature of the reagents to humans, flora and fauna offer distinct safety advantages over use of thermoplastic, PFA or granulated blast furnace slag media. Toxicological studies shown no identified adverse impacts on flora or fauna, including even highly sensitive species such as shrimp, worms and minnows using ViroSoil Technology. This is supported by our project experience that has shown that vegetation can rapidly recover on treated soils.
Table 1
Effective metal treatment using ViroSoil Technology. Data are from a project to treat 4,000 m3 soil from an abandoned industrial site in Australia. Metal leachability concentrations are quoted in mg/l (TCLP).
|
Parameter |
Regulatory limit |
Untreated soil |
After ViroSoil |
|
pH |
6.0-10.0 |
5.9 |
9.0 |
|
Copper |
100 |
0.24 |
0.01 |
|
Lead |
5.0 |
10 |
0.04 |
|
Zinc |
500 |
18 |
0.02 |
ViroSoil Technology remediation solutions can incorporate Rapid Sequestro-Degradation (RSD) for the decontamination of light and heavy hydrocarbons. Metal and acidity treatment remains effective. Decontamination of organics in soils is difficult, though commonly required, using conventional technologies. These often involve expensive thermal sterilisation/soil washing and subsequent soil excavation/disposal. RSD operates by adsorbing hydrocarbons onto specially formulated reagent fibres where hydrocarbons are microbially broken down, ultimately to carbon dioxide and water, by an enriched population of indigenous microbes, enzymes and other additives incorporated into ViroBind reagents (Table 2).
Table 2
Hydrocarbon treatment with ViroSoil Technology incorporating RSD. Data are from a project to treat 150,000m3 soil contaminated with hydraulic sump oil from a derelict industrial site. Contamination concentrations are quoted in mg/kg.
|
Parameter |
Untreated Soil |
After ViroSoil |
Treatment Targets |
|
C6-C9 |
7,600 |
20 |
100 |
|
C10-C14 |
12,500 |
55 |
100 |
|
C15-C28 |
52,000 |
780 |
1,000 |
|
C29-C36 |
35,000 |
560 |
1,000 |
|
Total petroleum hydrocarbons |
107,100 |
1,415 |
|
ViroSoil Technology offers a viable and cost effective alternative approach for the in-situ remediation of metals, hydrocarbons and acid neutralisation in soils that outperforms conventional technologies. Versatile formulations ensure that each contamination situation is optimally addressed.
Useful Links
Virotec website: www.virotec.com.
About the Author
Dr Stephen Young is managing director at Virotec Europe Limited.
Contact by phone on +44 1865 304060 or email via the Virotec website above.