Engineers
and environmental scientists at the University of Leeds are developing methods
of helping contaminated water to clean itself by adding simple organic
chemicals such as vinegar.
The harmful
chromium compounds found in the ground water at sites receiving waste from former
textiles factories, smelters and tanneries have been linked to cancer, and
excessive exposure can lead to problems with the kidneys, liver, lungs and
skin.
The
research team, led by Dr. Doug Stewart from the School of Civil Engineering and
Dr. Ian Burke from the School of Earth and Environment, has discovered that
adding dilute acetic acid (vinegar) to the affected site stimulates the growth
of naturally occurring bacteria by providing an attractive food source. In
turn, these bacteria then cleanse the affected area by altering the chemical
make-up of the chromium compounds to make them harmless.
“The
original industrial processes changed these chemicals to become soluble, which
means they can easily leach into the ground water and make it unsafe,” says Dr.
Burke. “Our treatment method reconverts the oxidized chromate to a non-soluble
state, which means it can be left safely in the ground without risk to the
environment. As it is no longer ‘bio-available,’ it doesn’t present any risk to
the surrounding ecosystem.”
Chromate
chemicals previously have been successfully treated in-situ in neutral pH
conditions, but this study is unique in that it concentrates on extremely
alkaline conditions, which potentially are much more difficult to treat.
The current,
favored method of dealing with such ground water contaminants is to remove the
soil to landfill, which can be costly, both financially and in terms of energy
usage. The Leeds methods being developed will allow treatment to take place on
site.
Dr. Stewart
notes, “Highly alkaline chromium-related contaminants were placed in
inadequate landfill sites in the UK right up until production stopped in the
1970s – and in some countries, production of large quantities of these
chemicals still continues today. The soluble and toxic by-products from this
waste can spread into ground water, and ultimately into local rivers, and
therefore will remain a risk to the environment as long as they are untreated.”
Current
environmental regulations mean that before the team can test out its research
findings in the field, they need water-tight proof that their methods can work,
as it is illegal to introduce any substance into ground water – even where it
is contaminated – unless it has been shown to be beneficial.
“From
the results we have so far, I am certain that we can develop a viable treatment
for former industrial sites where chromate compounds are a problem,” says Dr.
Stewart. “Our next step is to further our understanding of the range of
alkalinity over which our system can operate. As society becomes more
environmentally aware, new regulations demand that past mistakes are rectified
and carbon footprints are reduced. By designing a clean-up method that promotes
the growth of naturally occurring bacteria without introducing or engineering
new bacteria, we are effectively hitting every environmental target possible.”
