Miljøprojekt, 1060; Teknologiudviklingsprogrammet for jord- og grundvandsforurening – BioGel til rensning af olieforurenet jord

BioGel til rensning af olieforurenet jord

Summary and conclusions

Purpose and strategy

The purpose of this project is to investigate the technical potential of the BioGel technology for aerobic degradation of heating and diesel oil in the vadoze/unsaturated zone of soils. The overall strategy has been to perform a series of laboratory experiments under optimal conditions, and to compare information obtained in a number of in-situ projects carried out in Denmark.

Laboratory experiment

Based on the laboratory experiment it is concluded that a significant increase in the degradation of heating oil can be accomplished simply by stimulating the naturally occurring microorganisms. A significant additional effect was accomplished by adding BioGel, while no extra effect was accomplished by stimulating with a culture of oil-degrading microorganisms without gel. It is estimated that the clean-up time can be reduced by up to a 25 – 30 % by stimulating with BioGel, as compared to stimulating the naturally occurring microorganisms only. However, this estimate is associated with considerable uncertainties. Also, the test soil was selected so that it presumably had a low microbial activity level.

Biodegradation has potential – but it takes time

Based on the results of the laboratory experiment it is concluded that there is little doubt that stimulated biological degradation, both with and without BioGel, offers a technical potential. However, it is stressed that a realistic expectation level regarding the clean-up time should be assumed. Based on the results, it is estimated that this type of clean-up takes on the order of 1.5 to 3 years - as an absolute minimum - unless the biological treatment is supplemented with physical removal mechanisms.

Field experience

Experience from 15 cases was collected, where BioGel or closely related technologies were used for in-situ clean-up of heating oil or diesel-polluted soil in the unsaturated zone.

Good results – although not in clay

On the basis of the available case material, the field experience with the BioGel technology and/or closely related technologies has apparently been good – although not in clay soils. For seven of 12 closed cases, there is information that the case in part or as a whole was closed to the satisfaction of the environmental authorities. For six cases the active efforts were concluded within a period of six months.

Documentation in general very poor

The apparently good results are compromised by the fact that, in general, although not for all cases, the documentation of the clean-up is considered very poor.

Overall recommendations

Overall recommendations for the use of biological remediation have been presented, and among these, recommendations for site closure and end documentation, as well as a more thorough documentation of the biological mechanisms and activity levels for external microorganisms; recommendations that might increase belief in the effect of biologically based clean-ups. Note, however, that several of these recommendations also apply for other types of remediation.