D10: Impact of Contaminants - Hydromod

Integrated Water Resource Management for Important Deep European Lakes and their Catchment Areas
EUROLAKES
D10: Impact of Contaminants
FP5_Contract No.: EVK1-CT1999-00004
Version: 4.0
Date: 25/07/01
File: D10-vers.4.0.doc
Page 114 of 136
of ions is restricted as the anions cannot pass through the negative membranes an the
cation cannot pass through the positive membranes. (supposed they are arranged alternately).
Compared to reverse osmosis the percentage of wastewater produce is only
10%. A disadvantage is that all dissolved salts are retained what requires additional
treatment of the produced water to make it suitable for drinking. With special membranes
it is possible to retain only defined ions, like Nitrates, therefore it is used to remove
nitrates from groundwater [DEGREMONT Water Treatment Handbook, 1991].
With this process it is possible to demineralise water. However, the non ionised molecules
in particular organic compounds remain behind in the treated water. Therefore
electrodialysis can never remove all endocrine substances.
Adsorption to activated carbon
Another promising process to eliminate endocrine substances is adsorption to activated
carbon as it is used to eliminate pesticides. The main features of the process are described
above.
The problem with regards to endocrine substance is the fact that these substances are
found in raw water in very low concentrations. That means the adsorbent is likely to be
saturated with other pollutants. Another problem is that more easily absorbable substances
can re-mobilise already adsorbed substances. In any case the water treated
with activated carbon must be properly pre treated with other processes prior to go for
particular substances which are contained in the water in very low concentrations. A
promising approach would be a two step process with PAC followed by a GAC process.
Activated carbon and membrane processes are also applied for “tertiary treatment” of
wastewater treatment plants effluent. Both processes can retain dissolved organic
compounds which have resisted upstream biological treatment. So also endocrine substances
contained in wastewater can theoretically be retained from the effluent. In other
words also for wastewater “technically everything is possible”, its just a question of
costs.
Biological processes
According to what is known about Alkylphenolpolyethoxylates and steroid hormones,
aerobe biological processes seem to contribute to a shortening of NPnEO chains and to
a degradation of steroid hormones. So one can assume that also aerobe biological processes
as used in drinking water treatment will have an effect on these substances.
However the role of biological processes in drinking water treatment is not comparable
to wastewater treatment. Raw water of drinking water contains only very little nutrients
which mostly have to be added to the process.
Nevertheless, bio-films can be found on slow sand filters which are nowadays only used
in small water works. According to Degrémont the biological action of slow sand filters
is not effective when it comes to removing all micropollutants (phenoles, detergents,
pesticides). For instance, they can only remove about 50 % of organo chlorinated pesticides.