Effekt af tilsætning af Petrotech til dieselolieforurenet jord

Summary and conclusions

Petrotech

Petrotech is a very efficient fire extinguisher that is more environmentally friendly since it does not contain any poisoning or ozone layer degrading compounds. However, it is more expensive than other fire extinguishers. Petrotech has been shown to enhance the biodegradation of oil. In order to examine whether it can be applied to enhance the biodegradation of oil at on site treatment of soil, a field experiment was carried out to study the on site treatment of diesel contaminated soil in piles.

Contents of the report

This report contains the results of pre-experiments to examine the effect of Petrotech addition to a diesel contaminated soil on the analyses itself and on the leaching and the evaporation of hydrocarbons from the soil and a on site field experiment to examine the effect of Petrotech on the biodegradation of diesel in the soil. The monitoring of the field experiment included:

• Total hydrocarbons
• Oxygen
• pH
• Water content
• Respiration tests (oxygen consumption)
• Mineralisation tests (mineralising of hexadecane)
• Total number of bacteria at 21°C
• Number of hexadecane degrading bacteria in soil.

The soil

The diesel contaminated soil was excavated at Høvelte Military Base and transported to Sandholm Military Base for use at the field experiment. The 20 tons of contaminated soil were manually mixed with 5 tons of sand to improve the permeability of the soil, since the soil was more clayish than expected. The mixed soil was distributed in two piles with a height of 20-40 cm. Petrotech was added to one of the two piles.

The results of the pre-experiments

The results of the pre-experiments showed that Petrotech does not interfere with the analyses of hydrocarbons or results in enhanced evaporation or leaching of hydrocarbons from the contaminated soil. Thus, the field experiment can be carried out without taking precautions regarding evaporation and leaching.

The on site field experiment

The on site field experiment showed that the addition Petrotech did not result in an enhanced biodegradation of diesel during the experimental period of 90 days with this specific soil based on the measurements of hydrocarbons in the soil.

The operation

The operation of the field experiment was successful because it was possible to avoid any limitation of e.g. oxygen. In addition the homogenisation of 20 tons of soil seemed to be satisfactory.

An experiment without limitation for 125 days

The respiration test initiated at day 0 in the laboratory continued for 125 days indicating that the microbiological activity in the soil was maintained without limitation of nutrients.

Monitoring parameters

In the following a few examples of the connection between some of the monitoring parameters are given:

• During most of the experimental period, an oxygen consumption of 5-10 ml oxygen/(day kg dry weight) was measured that corresponds to a biodegradation of 4.2-8.3 mg hydrocarbons/(day kg dry weight) assuming that the oxygen is only used for biodegradation of the hydrocarbons and that 50% of the carbon is build into the bacteria. At those assumptions 370-750 mg hydrocarbons/kg dry weight should have been degraded which may correspond to the observed biodegradation (depending on the interpretation of the measured concentrations of hydrocarbons).

• Due to the biodegradation of Petrotech there was a difference between the oxygen consumption from day 0 to day 10 in the soil with Petrotech and the soil without. There was not a difference between the mineralisation rate at day 0 in the two soils, which was as expected, because the number of hexadecane degrading bacteria at day 0 was the same in the two piles. The initial biodegradation of Petrotech the first 10 days resulted in a higher mineralisation rate at day 13 in the soil with Petrotech than in the soil without indicating a higher number of hexadecane degrading bacteria. The mineralisation rate remained higher at day 42 and 90 in the soil with Petrotech than without. The mineralisation tests seem to show that the addition of Petrotech had a positive effect on the biodegradation of diesel in soil. However, this effect is not reflected in the removal of diesel based on the analyse of hydrocarbons. One reason may be that the soils content of oil is not bio-available to the same degree as the hexadecane added to the mineralisation tests.