Technology : A positive force in cleansing land

Technology 10 August 1996

CONTAMINATED land could be cleaned up more quickly using a technique that
builds on the usual “pump and treat” approach. The new method could also remove
several times more contamination than standard methods, claim its

The standard procedure is to pump polluted water to the surface, clean it,
and reinject it. The problem is that heavy metals and organic chemicals stick to
soil particles, says Paul Bertsch, an environmental chemist at the University of
Georgia, and a researcher at the Savannah River Ecology Laboratory in South
Carolina. So only a small fraction of the contamination can be removed each
time. After the water is pumped back into the ground the soil releases more of
the contaminants, which pollute the water again.

The contaminants tend to cling to iron oxides on the surface of the soil
particles or “matrix”. According to Bertsch, heavy metals form strong bonds with
the oxides’ oxygen atoms. Organic contaminants, many of which are hydrophobic,
also cling to the iron oxides.

Bertsch and his colleague John Seaman developed a method of separating the
iron oxides from the surface of the matrix. “What we do is introduce large
positive organic ions, which are specifically adsorbed by both the oxides and
the matrix,” he says. These cations make the oxides and the matrix repel one
another, driving the oxides into suspension.


The ions are injected into the groundwater, and when the water is pumped to
the surface the contaminants are removed by adjusting the pH until they
precipitate. Bertsch has a patent pending on the process.

He unveiled the idea last month at the Western Pacific Geophysics meeting in
Brisbane, Australia.