Chemical Technology July 2015

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Pesticides,drugsan
elements contaminate our wastewater. Removing
these micro pollutants requires new methods and
Endress+Hauser has been part of this development
right from the start.
Ordinary sewage treatment plants remove
solids mechanically with rakes and sedimen-
tation tanks. Microorganisms in the biological
treatment stage help to eliminate nitrogen
charges. Most plants eliminate the remaining
phosphate chemically by precipitation, with
an increasing number of facilities also using
biological methods at this stage. Micro pol-
lutants are only partially retained. “These can
be the active ingredients of drugs, biocides
fromagricultural and construction chemicals,
or ingredients of body care products and
cleaning agents,” explains Stefan Vogel,
Product Manager Water and Environmental
at Endress+Hauser Switzerland.
Some trace elements interfere in nature’s
cycles in minute concentrations. Hormones
and hormone-active substances, for example,
compromise the growth and fertility of fish,
crustaceans and amphibians; biocides im-
pair the photosynthesis of algae and aquatic
plants. Higher concentrations of micro pol-
lutants are mainly found at places where
sewage plants discharge into smaller rivers.
How is all this regulated by law?
Currently there are almost no limits set for the
intrusion of trace elements. Legal limits are
only defined for heavy metals and biocides.
Many regulatory authorities in Europe have
identified the problem. “In Switzerland, over
100 sewage treatment plants are to be refit-
ted with an additional cleaning stage which
will eliminate most micro pollutants,” says
Stefan Vogel. After mechanical, biological,
and chemical cleaning, this involves a fourth
treatment in most cases.
Concerns regarding trace elements have
been raised at various conferences in South
Africa. Currently no legislation has been imple-
mented but various institutes are researching
this important issue.
What can be done to get rid of micro
pollutants?
The Swiss government-fundedwater research
institute Eawag has looked into various large-
scale technical methods, with two methods
appearing to be the most suitable for use in
communal sewage treatment plants: in ozoni-
sation, the ozone blown into the water reacts
with the trace elements and the cracked com-
pounds are biologically degraded in a sand
filter. In the treatment with powder-activated
carbon, the molecules settle on the surface
of the carbon and are incinerated together
with the dried sewage sludge.
Both the ozonisation and the powder-ac-
tivated carbon treatment eliminate between
80 and 90 percent of the micro pollutants in
wastewater, which means they are highly ef-
fective. The installation of a powder-activated
carbon treatment needs more space. Ozoni-
sation is linked with higher energy needs,
while powder-activated carbon requires
material consumption.
What’s the importance of measurement
technology?
Measurement technology is needed both for
controlling ozonisation and for the treatment
with powder-activated carbon. Beside flow,
temperature and pressure sensors, liquid
analysis is also used. The spectral absorption
coefficient appears to be the most promising
candidate as the key value; measuring the
reduction/oxidation potential seems to be
best suited to identify increased ozone
For more information contact
Hennie Pretorius on tel: +27 11 262 8000
or email z
Upgrading sewage plants using Endress+Hauser's technologies