What is ex-situ bioremediation?
Ex-situ bioremediation refers to treatment of excavated contaminated soil using natural biological processing and can be extremely cost effective compared to alternative soil remediation methods. Excavated soil is placed in a lined above-ground treatment area and aerated following processing to enhance the degradation of organic contaminants by the indigenous microbial population. There are various factors important to the success of ex-situ bioremediation, for example temperature, pH, oxygen, nutrients, contaminant types and concentrations.
A range of soil microorganisms can be encouraged to utilise organic contaminants such as petroleum hydrocarbon mixtures, diesel, kerosene and mineral oils as a source of carbon and energy and degrade them ultimately to carbon dioxide and water.
Hydrocarbon contaminants that are amenable to treatment by ex-situ bioremediation are wide ranging and include, for example:
- Petroleum hydrocarbons
- Lubricating oils
- Polycyclic aromatic hydrocarbons
- Phenols and cresols
Shallow turned treatment beds
Where there is sufficient space available on site, shallow treatment beds are an ideal solution but work best during warmer and drier months. The contaminated soil is excavated, processed and spread out in layers typically up to 0.5m in thickness on a lined treatment area. Bioremediation occurs by optimising moisture and nutrient levels, and by periodic turning of the bed using a rotovator.
The excavated soil is placed into a shaped pile typically up to 2m high and 6m wide in a lined area. The soil bioremediation windrows are aerated by period turning using specialised machinery which can be excavator mounted or self-propelled. Soil amendments and nutrients can be added to the windrows during turning to optimise biological activity and degradation of organic contamination. Between turning of the windrows it is usual to cover the beds with a weatherproof breathable membrane. Turned windrows require less space than shallow treatment beds and so may be more appropriate if space on site is limited.
Actively aerated biopiles
Bioremediation using actively aerated biopiles is an ideal solution where space is limited and is not affected by weather conditions. The excavated soil is processed and placed into a shaped pile up to 3m in high in a previously prepared lined treatment area. The deep bioremediation bed is aerated using a vacuum pump connected to slotted pipework at the base of the biopile. Vapours extracted from the biopile are collected using granular activated carbon (GAC) filters to reduce aerial emissions.
Telluric Land Remediation is one of the most experienced bioremediation contractors in the UK having successfully completed many contracts since the 1990s. We will review the available site investigation data and provide our opinion on the suitability of ex-situ bioremediation to meet the required targets for your site and to give an accurate estimate of timescales and costs involved.