Decontaminating contaminated soil is a difficult process that often requires digging up the soil and transporting it to an offsite remediation facility. But now, scientists have developed an environmentally friendly way to treat soil on the spot - shocking it with electricity. The technology, called a high-temperature electrothermal (HET) process, was developed by scientists at Rice University in Houston and the U.S. Army's Engineer Research and Development Center (ERDC), led by Rice professor James Tull.

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First, carbon-rich conductive materials such as biochar are mixed into contaminated soil on-site. Biochar is a nontoxic charcoal-like substance produced through a process called pyrolysis, in which heat is used to break down organic matter in the absence of oxygen.

Next, using a procedure called flash Joule heating developed by Rice, an electric current is passed quickly through the soil/biochar mixture, heating it to temperatures of 1,000 to 3,000ºC (1,832 to 5,432ºF).

High temperatures convert organic contaminants, such as pesticides and crude oil, into non-toxic minerals such as graphite. At the same time, it can also convert various heavy metals (such as lead, arsenic and mercury) into steam and collect it through the extraction pipeline. This versatility is an important consideration because most existing repair techniques can only target one or two metals at a time.

While high temperatures may initially kill some beneficial microorganisms, tests have shown that plants actually increased germination rates by 20 to 30 percent in HET-treated soil. This improvement may be due to the production of growth-promoting minerals during the remediation process, as well as increased water infiltration due to the addition of biochar.

The researchers hope that if the technology is further developed and scaled up for use in the field, the HET device could be pulled by a tractor through large areas of contaminated soil.

"This method is very fast, does not require water, and can treat a wide range of contaminants in soil," said ERDC research chemist Mine Ucak-Astarlioglu. "Flash Joule heating is a very promising technology for recovering critical metals from waste and removing heavy metals for remediation."

A paper on the research was recently published in the journal Nature Communications.