A bioremediation technique capable of restoring oil-contaminated soil to a state suitable for plant growth has been developed by Lithuanian company Biocentras.

The method involves washing soil using a water solution of biosurfactant to separate the oil from the sludge, and renders both the soil and the collected oil ready for re-use. Biocentras claims to have already cleaned over 22,000 tons of soil so far, without the need for chemicals or genetically modified technologies.

Oil refining can create high levels of contaminated soil for a number of reasons. On the one hand, there are vast quantities of oil sludge that exist in raw oil that are pumped from oil fields, needing to be removed during the refinement process. On the other hand, the oil itself can often spill during exploration, refining, transport across the network of pipes, railroads and tanker trucks, and even during consumption and usage. This can pose a different set of environmental problems to a spill at sea. ‘Oil can leak down to deep soil layers and it can be difficult to access the area where oil is spilled, such as in mountains.’ says Monika Kavaliauske, Manager at Biocentras.

Washed out

The first stage of the process involves separating the oil from the sludge then removing it to a field with an isolated coating. ‘The biosurfactant solution is a product of microbe fermentation, and is biodegradable therefore not harmful to the environment,’ says Kavaliauske. ‘The same process happens in nature. By optimising biodegradation conditions, we just intensify this process and achieve a very effective (phytoremediation) process.’

The biosurfactant water solution is then used to wash part of the oil out. As oil is not soluble in the water, it can be separated by decantation or centrifugation.

‘The oil is treated with microorganisms and fertilisers, which contain nitrogen and phosphorous, and reduce the contamination of the soil from 30% down to 2-3%,’ says Kavaliauske. ‘Then this soil is moved to another field with a loam bottom [layer] where the treatment process is finished with phytoremediation.’

Any oil that is still bound in the soil is treated by the micro-organisms that lower the contamination concentration to a point when phytoremediation can start. The team then tested the levels of oil hydrocarbons in the soil to confirm that it is ready to be used for growing plants.

Natural method

Kavaliauske adds that the use of natural microorganisms means that there is no need for harmful chemicals or genetically modified technologies.

‘Our technology can reduce contamination levels from up to 30% down to allowed contamination levels (according the environmental standards) over a period of up to 18 months,’ says Kavaliauske.

She adds that the biosurfactant solution used in the washing process can be applied up to ten times, and claims that the team have verified this according to the ratio of biological oxygen demand and chemical oxygen demand.

Though the technology is only used in Lithuania, Biocentras are looking to develop the technology for other countries.