Engineers Find New Way to Clean Contaminated Soil

Environmental engineering professor Makram Suidan's innovative work on bioremediation frequently brings him invitations to travel around the world to help others find solutions to their pollution problems.

Most recently, Suidan traveled to China to explain a new system for cleaning up contaminated soil and to chair a session at an international environmental symposium in Beijing.

Suidan's paper on "Bioventing of Contaminated Soils" showed that it's possible to remove toxic solvents from soils without digging up tons of dirt in the process. The method was developed in collaboration with U.S. EPA researcher Gregory Sayles, and the two have applied for a joint patent on the process.

The system works when the contaminants are above the water table. A mixture of gases is injected into the soil, allowing natural degradation to occur. "We can achieve complete degradation," said Suidan, referring to work done on PCE (perchloroethylene).

After injecting hydrogen, carbon dioxide, and nitrogen into the soil, naturally occurring microbes were able to break down the PCE present. The method was first tested in Suidan's lab, then field tested by Battelle scientists at a contaminated site in Kansas.

Suidan explained that PCE can't be degraded when oxygen is present in the soil. By injecting a mixture with 99 percent nitrogen, oxygen is prevented from interferring with the degradation process. The first phase of the degradation is therefore anaerobic, but complete degradation also requires aerobic degradation.

Further work is now being done to examine the role of other gases. "We want to look at the effect of carbon dioxide. We must look at how oxygen travels in the soil," said Suidan.

The researchers are also looking at other common soil pollutants, such as the pesticide DDT and DNT, a chemical used in weapons production. Both also require anaerobic processes to be degraded, but they're also much less volatile than PCE. That means they're more likely to stay in one place, rather than dispersing which makes biodegradation easier and more effective.