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Ex-situ Bioremediation

Various ex-situ bioremediation techniques can be applied in order to reduce contaminant concentrations from excavated soil.

cardiff1Various ex-situ bioremediation techniques can be applied in order to reduce contaminant concentrations from excavated soil. The determination of the most appropriate ex-situ method is dependent on a number of site-specific factors, including soil type, contaminant type, space available and environmental setting. The key to successful bioremediation is the improvement of soil characteristics to enable uniform oxygenation, optimal moisture control and nutrients distribution.

For VOC contaminated soils or where space is limited it may be preferable to use Biopiling. This method uses engineered systems to inject and/or extract air (to oxygenate the soil), irrigation/drainage systems to inject and re-circulate nutrient laden water (to control moisture and nutrient loadings) and cover systems to prevent heat loss. Soil may also require re-engineering to improve the performance of the above systems, maximising the number of biological reaction sites within the soil. Churngold can offer an innovative, low cost solution of maintaining heat within biopiles, making it a viable option during the colder months.

The main disadvantage of biopiling is its complexity and the need to build, install and operate systems to regulate aeration and moisture control. A simpler method of ex-situ bioremediation is Windrowing or Land Farming, which uses mechanical plant to agitate and oxygenate soil. During the agitation period nutrients and water can be added to improve conditions. The continual working of soil offers the benefit of reducing the risk of dead spots and continual reworking of soil to maintain a good structure. This can be further improved by applying a comprehensive monitoring strategy that can identify soil that needs additional targeting. Windrowing however requires more space, has the potential to generate more emissions and is prone to heat loss meaning that in a UK context it is most commonly applied in the warmer months.

Ex-situ bioremediation of soil is cost effective and proven for most TPH range contaminants. More recalcitrant compounds, such as PAH's can be treated using ex-situ bioremediation, but additional amendments may also be required when contaminant concentrations are elevated, where NAPL may be present or where soil is likely to inhibit oxygen transfer and moisture regulation.