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Monday, September 30, 2013
Old Concrete Can Protect Nature
This is simple easily managed protocol that allows
for successful phosphorus management at least.
What it also does is make crushed concrete a desirable feedstock to
collect against usage. A simple crusher
will also reduce the material well enough to be acceptable. Powder like seems a bit over the top when
what is wanted is a charge able to absorb a lot of water for a slow trickle through
A simple lined pond with an outlet siphon would
possibly work well.
Now we must develop the will to implement such a
scheme as cheaply as possible. I think that it will be found highly attractive for agricultural application were a lined pond is oftem useful.
Lakes and streams are
often receiving so much phosphorous that it could pose a threat to the local
aquatic environment. Now, research from the University of Southern Denmark
shows that there is an easy and inexpensive way to prevent phosphorus from
being discharged to aquatic environments. The solution is crushed concrete from
Usually we think of
demolished concrete walls and floors as environmental contaminants, but in fact
this material may turn out to be a valuable resource in nature protection work.
This is the conclusion from researchers from University of Southern Denmark
after studying the ability of crushed concrete to bind phosphorus.
"We have shown that
crushed concrete can bind up to 90 per cent of phosphorus, "says PhD
student and environmental engineer, Melanie Sonderup, Department of Biology at
the University of Southern Denmark.
Contributors to the
research are also postdoc, PhD, Sara Egemose and associate professor Mogens
Flindt from the same place. Since March 2013 the researchers have tested the
technique in a full-scale experiment, which will run until March 2014. But
already now they find that the technique is very effective.
Large amounts of
phosphorus can be washed out into lakes and streams when it rains. Rainwater
that runs off from catchments, especially those fertilized with phosphorus,
carries the phosphor with it. This phosphorus rich rainwater is then often
collected in rainwater ponds, which discharges into lakes and streams.
"The water in these
rainwater ponds can be very rich in phosphorus, and if it is discharged into a
lake, it can lead to an increase in algae growth. This can lead to oxygen
depletion and a reduction in the number of species that can live in the
water," explains Melanie Sonderup and continues:
"By letting the
pond water pass through a filter of crushed concrete, we can remove up to 90
per cent of the phosphorus".
Phosphorus binds so well
to the concrete because it contains cement. Cement is rich in calcium and also
contains aluminum and iron. All three can bind phosphorus. Preliminary results
show that the size of concrete grains is of importance. The smaller the grains
the better they bind phosphorous. Fine concrete powder is thus more effective
than millimeter sized concrete bits.
"It is also important
that we do not use concrete that has been exposed to wind and rain for a long
time, as this washes out the cement, which holds the essential calcium,"
explains Melanie Sonderup.
As the experiments have
only run for six months, the scientists do not yet know the durability of
crushed concrete, but they believe that a filter of crushed concrete can last
for a long time, probably several years.
"Only when the
concrete cannot bind more phosphorous, it will be time to switch to a new layer
of crushed concrete - and then the disposed layer can be recycled as road
fill", says Melanie Sonderup. In its first months the filter of crushed
concrete needs some assistance:
"In the first app.
six months, the water flowing through the filter has a high pH value. This is
because the cement in concrete is alkaline, and therefore, the water that comes
in contact with the cement, is also alkaline. This can be compared to the water
that bricklayers often work with when they mix cement or limewash.
to a lake or stream must not be this alkaline. In order to reduce its pH value,
we add a little acid before we discharge it into the receiving water body.
After running our full-scale experiment for approx. six months, enough cement
has been washed out of the crushed concrete so that we no longer need to reduce
the water's pH value, and then I believe that the system can take care of
itself", says Melanie Sonderup.