The choice is yours
Graham Sprigg looks at the growing number of technologies available for in-situ and ex-situ remediation.An increasing need to release brownfield sites for redevelopment, coupled with the general trend towards more effective methods of clean up for contaminated land, is leading to the use of a growing number of clean up technologies. Several contractors who have previously been involved primarily in dig and dump solutions, where contaminated soil is merely transported to a suitable landfill location, are now turning to science and technology for more sustainable solutions to the problem of clean up.
At the forefront of this trend are technologies such as Churngold Remediation’s White Karbon, a filtration medium designed for the treatment of contaminated groundwater, which is just one example of a host of biological, physical and thermal remediation technologies now being used in the UK. Part of the reason for this increasing choice of treatment technology is the complexity of problems that now face land owners, developers and environmental consultants, as Duncan Sanders, business development manager of Churngold Remediation explains:
"There is seldom a single approach or remediation technology that can be used to clean up an entire site, unless the problem itself is relatively straightforward." As the number of options continues to grow, the decision regarding which combination will provide the most suitable solution also becomes more complex. "It’s no good applying science for the sake of it", says Mr Sanders. "Another problem is knowing when to adopt what might be a relatively new technology. While developments continue apace, one should always rely on technology which has been proven in the field."
The range of remediation technologies offered by companies like Churngold Remediation can be split into four broad categories: physical, biological, chemical and thermal treatments. Physical processes probably represent around two thirds of the current remediation activity in the UK. Generally they are cost-effective, robust and reliable. However, some (including dig and dump) do not actually reduce levels of contamination, they rely either on physically removing the material to another site (i.e. landfill) or containing the existing contamination within a pre-determined area (for example using barriers, capping or stabilisation).
Conventional treatment using filtration media, such as Granular Activated Carbon for the removal of petroleum hydrocarbons, is now being enhanced by more advanced and effective materials such as the White Karbon mentioned earlier. In addition to petroleum compounds, a wide range of hydrocarbons and other contaminants can be removed from groundwater including; metals, cyanides and pesticides. New technologies enable a diverse mixture of these contaminants to be removed in a single process.
A further physical process, soil washing is now being considered for some projects here in the UK. Already established in parts of Europe, where the necessary supplies of uniform sandy materials are more readily available, soil washing enables contaminated fines to be segregated from mixed soils for subsequent treatment or disposal.Chemical oxidation
With time being such an important priority in many contaminated land projects, in-situ chemical oxidation can be an extremely useful means of ensuring the rapid degradation of suitable contaminants. Strong oxidising chemicals such as Fenton’s Reagent or potassium permanganate are injected into an aquifer as an aqueous solution and break down organic compounds to water and carbon dioxide on contact. The process is hydraulically controlled to maximise the radius of influence and contain the area of treatment.
Significant progress is also being made in the field of bioremediation, which is particularly favoured because it works to enhance the degradation properties of the naturally occurring bacteria. Oxygen and Hydrogen Release Compounds (ORC and HRC) are examples of two reagents which can be injected into the ground for accelerating aerobic and anaerobic biodegradation respectively. Two technologies developed in the USA and currently available from Churngold Remediation; Iso-Gen and ISOC, provide powerful alternatives to the more established techniques of stimulating naturally occurring microbes using oxygen, such as air sparging and soil venting. These new technologies are significantly more effective at delivering dissolved oxygen into the groundwater which is often the critical parameter for effective breakdown of petroleum hydrocarbons. Unlike conventional air sparging, which typically transfers oxygen at concentrations of 5-6ppm, Iso-Gen produces microbubbles of oxygen which diffuse into the groundwater releasing between 50 and 60ppm. This results in reduced treatment times and a much improved reduction in contaminant levels.
Although new to the UK, steam injection has been used successfully in Germany and other European countries for some time. Churngold’s managing director, Craig Sillars is convinced that steam injection offers great potential in the UK and his company has already undertaken some remediation projects with it. Particularly effective for the removal of volatile contaminants, the technology was originally perfected by the oil industry as an aid to enhancing the yield from wells. It was subsequently adapted for remediation in the USA. Used to increase the recovery of hydrocarbons from impacted aquifers and accelerate remediation. A recent Churngold project, believed to be the first application of the technology in the UK, was undertaken to remove heavy viscous oils in chalk and achieved extraction levels of 100 litres/day, compared with 6 litres/day using conventional vapour extraction alone.
As clean up projects increase in complexity, the need for correct selection of a suitable remediation strategy becomes more important. Remediation companies who provide their clients with a competitive advantage will increasingly provide licensed technologies, many of which will have originally been developed for other purposes. White Karbon and steam injection, both originating from the oil industry, are two such examples. The differentiation between remediation specialists will be manifested in the way in which they combine different technologies, to provide a robust and cost-efficient solution to each individual contamination problem.