Bioremediation injects speed into decontamination

New environmental protection legislation, restrictions on land fill capacity and increases in waste disposal costs have reduced the viability of traditional methods of dealing with contaminated soils. Professionals are therefore looking increasingly at the possibilities offered by in-situ bioremediation. Simon Martin, Director of Response Bioremediation, discusses the principles of bioremediation and the benefits for users.

Over the next five years, the contaminated land assessment and treatment market is expected to grow by some 30%, fuelled by increased house-building and construction activity, the Government's commitment to bring brownfield land back into use, greenfield land protection and an increased awareness of environmental responsibilities.

Although excavation and disposal remain the most popular methods of contaminated land remediation, new environmental protection legislation, decreasing landfill capacity and rising disposal costs have reduced the viability of these traditional methods of dealing with the problems of contaminated soil.

This, combined with new HM Treasury incentives for investing in sustainable methods of treating contaminated land, means that more and more local authorities, property owners and developers are turning to in-situ bioremediation, which will increasingly become the preferred and most cost-effective technique, as more widespread use increases confidence.

Bioremediation process

Bioremediation is the process of biologically enhancing the degradation of organic contaminants in both soils and groundwater. Given time, indigenous bacteria in the soil will destroy localised hydrocarbons and other complex organic compounds. They simply digest the pollutants, reducing them to carbon dioxide and water. This can, however, take decades, so to speed up this process a remediation material such as Response's Bio-Gel™ is injected though wells or hand-held lances directly into the contaminated areas.

A non-toxic, organic food grade substance, Bio-Gel™ is used as a carrier, an insulator and as an initial source of nourishment for the bacteria used in the bioremediation of soils and water containing elevated concentrations of hydrocarbon contamination.

Site-Specific Response Bio-Gel™ contains the optimum composite of non-pathogenic bacteria, found naturally within soils, nutrients and dissolved oxygen to maximise the interface of bacteria and contaminant. This promotes the colonisation of biomass and assists the bioremediation process. As part of the colonisation process, the Bio-Gel™ is consumed and converted into carbon dioxide and water, along with the contaminants.

Amongst the contaminants that can be treated are polyaromatic hydrocarbons, chlorinated hydrocarbons, aromatic hydrocarbons, aliphatic hydrocarbons and synthetic mineral oils.

Bioremediation provides a cost-effective method of completely neutralising contamination in land and water, creating commercial opportunities for brownfield land development and a sustainable environment for future generations. As there is no need for material to be cleared or taken off site for disposal, there is negligible disruption on site. At half the cost of traditional "dig and dump" methods it is a cost-effective, value added sustainable solution. Each project can be carefully assessed in advance and a site-specific risk based strategy prepared. As the process takes place entirely underground, there is minimal disruption and, accordingly, following completion of the injection works, the site can be made available to the developer. It is non-pathogenic and conforms to all environmental regulations.

Case study: Hinckley, Leicestershire

Response Bioremediation was requested by David Wilson Homes to undertake the treatment of 3,575 m3 of contaminated soil. The site, a former bus depot and engineering works, was to be redeveloped for housing. Investigations had revealed two areas of Total Petroleum Hydrocarbon (TPH) and Polycyclic Aromatic Hydrocarbon (PAH) contamination within the soil matrix to a depth of 2.5 metres.

In developing a bioremediation strategy for the site, Response Bioremediation worked closely with the regulatory authorities regarding the content of their Site-Specific Mobile Plant Licence Working Plan. This document was subsequently approved by the Environment Agency prior to work commencing. Response Bioremediation prepared a site-specific, risk-based strategy utilising Precision Injection Technology incorporating Response Bio-Gel™.

In this instance Response Bio-Gel™ was injected manually under positive pressure into the two target areas of contamination using lances. Due to careful planning and communication between all parties involved, construction work commenced immediately following injection.

In accordance with the Site-Specific Working Plan, project monitoring and validation work was undertaken, soil samples were retrieved at weeks 2, 4, 6, 10, 14 and 18 after completion of the injection programme, with all samples analysed by a NAMAS/UKAS accredited laboratory.

All the chemical analysis results confirmed that the remediation target values within the soils had been achieved. The bioremediation process had effectively reduced the elevated concentrations of TPH and PAH contamination in the soils to acceptable levels.

Case study: grid substation

When oil was spotted in the River Linnet near Bury St Edmunds, the Environment Agency traced an oil leak back to an electrical substation. A number of sources were identified; there was an old oil tank on site, oil was seen to be leaking from transformers and there was evidence of general oil spillages on the ground.

EDF Energy, the company responsible for distributing power throughout the east of England, swiftly appointed Response Bioremediation to undertake a thorough site investigation to determine the extent of the impacted ground and make recommendations to remedy the situation as quickly as possible. After analysing soil samples most of the Total Petroleum Hydrocarbon (TPH) contamination was found at 0.5 metres below ground level. A maximum TPH concentration of 5,965mg/kg was recorded in the soil samples. The site was criss-crossed with live cables so excavating the contamination was not an option.

In-situ bioremediation was therefore chosen for remediating the contaminated soil. The process used was a patented Response Novacell System, an automated treatment system, which introduces a Biological Solution into the identified contaminated ground. Once the Response Novacell has been calibrated no further inputs are required, other than for monitoring and maintenance checks.

After 22 weeks remediation of 395m3 was deemed to be complete. All samples achieved TPH levels of <5mg/kg which were well below the target levels of 1,000mg/kg. The old tank was removed and the transformers were fully bunded as part of the annual pollution prevention works programme undertaken by EDF Energy.

Conclusion Since its inception in 1994, Response Bioremediation has successfully treated, in-situ, in excess of 135,000m3 metres of contaminated soil, material which would otherwise have been disposed of to landfill.



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