Bacteria remove PCBs
Jan Erik Kaarø
To what extent can nature itself help remove the environmental toxin PCB? That is the question being asked by two researchers from SINTEF Oslo in a study they are carrying out in Bergen.
Research Scientist Ove Bergersen took no risks when the field trials with PCB-contaminated soil started outside Bergen at the end of April.
Like stranded frogmen, Tormod Briseid and Ove Bergersen waddle into the bunker in one of The Norwegian Navy's sites near Bergen. They need their gas-masks and protective suits, for the concrete walls hide a 150 cubic metre pile of PCB-contaminated soil, which is believed to be refuse from German Second World War submarines.
Difficult job
The bunker has heating cables, a sprinkler system and systems for controlled air and nitrogen ventilation. Sensors that continuously measure the humidity, temperature and oxygen and CO2 content of the soil have also been rigged up. The aim of the project is to find out whether naturally present microorganisms can be used to treat large quantities of PCB-contaminated soil."We have already worked a great deal on the natural breakdown of oil, creosote and PAHs, but PCBs are much worse to deal with because they are more stable," says senior scientist Tormod Briseid. There are a number of alternatives to biological treatment, such as burning or washing the mass, but such methods are expensive and may be difficult to implement in practice when large areas or amounts of soil are contaminated.
Treated as dangerous material
Polychlorinated biphenyls are synthetic man-made products, of which a total of 209 different compounds are known. PCBs are difficult to break down and they accumulate in the food chain; they have even been found in polar bears in the Arctic. PCBs affect the genes, and when they are burnt can form dioxin. It is for reasons such as these that they are treated as hazardous waste. PCBs used to be widely used as insulants and coolants in transformers and condensers. The State Pollution Control Authority has a stated aim of removing all equipment that contains PCBs from use by the end of 1994 and of having it destroyed in a responsible manner in 1995.Long-term treatment
The disadvantage of biological breakdown is that it takes a long time. Briseid and Bergersen do not expect that the Bergen experiments will have any results for several months.In the first instance, the aim is to find out whether the contaminated soil in the bunker contains bacteria that will "eat up" PCBs. If it does not, such bacteria will have to be added to the soil. The next stage will be to give the bacteria particularly attractive working conditions, for example by irrigating and fertilizing the soil and warming it up to 20 - 30oC. If the PCBs contain high levels of chlorine the first stage of the process must take place without added oxygen.
Researchers in several countries have previously carried out bacteriological PCB purification in the laboratory, but few large-scale work has been done. This project is being carried out in collaboration with the Norwegian Defence Construction Service and the State Pollution Control Authority, which have also joined forces to finance most of the PCB tests in Bergen.