IWA Specialist Group Directory - Nieuwe Sanitatie - Stowa

at their extremely low environmental quality standards.
Although GC/MS is restricted to non-polar and semi-polar
contaminants, liquid chromatography (LC)–MS/MS has
allowed the determination of much more polar substances
(pharmaceuticals, illicit drugs, estrogenic hormones …) at
levels of parts per trillion. Once restricted to target compound
analysis, with the advent of very high resolution
instruments, LC tandem MS and LC-Orbitrap MS now
offer the possibility of identifying and quantifying unknown
polar compounds in all kinds of environmental matrices, a
feature that will contribute to the discovery of an increasing
number of emerging contaminants and hopefully their
transformation and degradation by-products. Another
trend lies in the miniaturisation of laboratory-scale instruments
such as GC/MS, which will likely allow on-line monitoring
in the future. A miniature GC/MS with a submersible
purge-and-trap probe is already commercially available
with potential application for on-line monitoring of volatile
organic compounds.
On the other hand, with the exception of fullerene nanoparticles
that can be determined by LC–MS, there are no
adequate methods to determine other organic nanoparticles
such as carbon nanotubes at environmental levels.
Bioanalytical methods, common in the pharmaceutical
industry, are growing in popularity for water quality and
treatment effi cacy monitoring. These in vitro bioassay
tools can provide an integrative measure of mixture toxicity.
Although several practical questions remain to be
answered, in particular their exact role in regulation (if
any), bioanalytical tools are a promising development in
water quality testing.
Treatment methods
The removal performances of existing treatment processes
are currently well known for an increasing number
of substances (Poseidon 2004; Snyder et al. 2007; Joss
et al. 2008; Choubert et al. 2011).
• Coagulation and settling can be effi cient for very
adsorbable substances (e.g. polychlorinated biphenyls),
but few emerging compounds are retained.
• Biological processes like activated sludge or fi xedfi
lm processes can achieve a signifi cant reduction of
micropollutant loads in wastewater treatment plants.
Removal mechanisms like biotransformation, stripping
and adsorption on sludge are involved. Parameters like
sludge age and nitrifying capacity appear to be critical
to maximise removal effi ciencies. Membrane separation
of sludge seems to bring additional retention performance
towards several emerging compounds. However,
substances are generally not really removed in biological
treatments: about two-thirds of the regulated substances
are mainly transferred to sludge, whereas many polar
emerging compounds are partly biodegraded with formation
of by-products. Thus, complementary advanced
tertiary processes are generally required to guarantee
an effi cient removal.
• Oxidation with ozone appears an effi cient advanced treatment,
with more than 80% removal, for most emerging
substances so long as their molecular structure presents
accessible electrons. However, the fate and toxicity of
by-products still remains an issue to be investigated.
Optimisation of ozone dose depending on water quality
IWA Specialist Groups
and combination with ultraviolet light and hydrogen peroxide
through advanced oxidation processes are still
being studied, especially for wastewater applications.
Other oxidants (chlorine, chlorine dioxide, permanganate,
ultraviolet light alone) are generally not effi cient
for micropollutant removal, and may present the risk of
generating more harmful by-products.
• Activated carbon adsorption (granular or powder)
appears as well as an interesting treatment for micropollutants.
Again, more than 80% removal for
most substances is achievable. Substance properties
(log Kow , pKa ) and operating conditions (dose, contact
time) will determine the actual effi ciency of retention.
Only a few molecules like iodinated contrast media or
some antibiotics present limited affi nity for activated
carbon. In the fi eld of wastewater treatment, more returns
of experience in terms of life duration in fi lters or
achievable polyaluminium chloride recovery rates are
still needed. The fate of used activated carbon, either in
sludge or in fi lters, may also be an issue.
• Membrane retention processes like reverse osmosis and
nanofi ltration allow the most effi cient retention of a wide
range of substances, but they need an extensive pretreatment
and they are the most energy intensive. Additionally,
the fate of the concentrate should be mastered
to get a completely sustainable process. Their high cost
makes their application to wastewater treatment very
limited, except in conditions of high water stress. In large
potable water treatment plants, the combination of different
advanced processes in a multi-barrier approach
is already applied to ensure a maximum removal.
The best solution remains the reduction at the source to
avoid the introduction of emerging contaminants in the
water cycle.
Regulation trends
In general, the standard setting is either based on the
precautionary principle, on risk assessment or on technical
feasibility. The precautionary principle has the big
advantage that it allows legal action without the comprehensive
knowledge on the fate and effects of the respective
substance as required for risk assessment. In the risk
assessment approach, for the identifi cation of hazardous
substances we distinguish between substances with and
substances without threshold, e.g. the cancerogenic,
mutagenic and substances toxic for reproduction. These
different assumptions are made as well in human risk
assessment (WHO 2006, 2008) as also in environmental
risk assessment (TGD 2003; ECHA 2010). For some
substances there are already suffi cient signifi cant ecotoxicological
data to suggest that the compound can cause
adverse effects on wildlife, or that there is a signifi cant
risk to human health. For example, in the European Union
those compounds are listed under the EC Water Framework
Directive 2006/60/EC (EC 2006) as priority substances or
priority hazardous substances as they are bioaccumulative,
persistent and toxic. Also the UNEP compiled a list of
persistent organic pollutants that fulfi l the defi ned criteria
for persistence, bioaccumulation and long-range transport.
Both lists have international reporting and minimisation/phase
out requirements and are under rolling revision.
Pharmaceuticals and polar personal care products are not
subject to any regulation yet and have not been monitored
within the European Water Frame Work Directive (Directive
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