Institute for Sanitary Engineering, Water Quality and Solid Waste ...

Waste Water Technology AWT
Research for further P-elimination in Stuttgart’s
wastewater treatment plants in the Neckar
catchment area in the context of implementing
the WFD
As part of the EU Water Framework Directive (WFD)
implementation in the Neckar catchment area, a study
was based and prepared at the Institute for Sanitary
Engineering, Water Quality and Solid Waste Management
(ISWA), covering the major wastewater treatment
plants in the Neckar catchment area and dealing
with more stringent requirements for the discharged
phosphorus load.
Therefore, on behalf of the Stuttgart city drainage company
(SES), it was investigated which total phosphorus
(Ptot) monitoring values at the wastewater treatment
plants outside Stuttgart can be met without introducing
any additional procedural steps for phosphorus
removal. For the group of wastewater treatment plants
WWTP Ditzingen and WWTP Plieningen detailed studies
are conducted, whose results are transferred to
the sewage treatment plant Möhringen.
As a first step, the daily operation records of the treatment
plant from years 2007 and 2008 were reviewed.
It was found that, for both particulate and dissolved
organic phosphorus compounds at the outflow of the
treatment plants, no additional action was needed because
the measured concentrations were in the expected
range. Accordingly, the existing scope for action
was primarily in a reduction of the o-phosphate
concentration in the effluent of the wastewater treatment
plants.
For rapid and systematic implementation of the studies,
a statistical method was developed at ISWA for
the analysis of routinely collected data and, therefore,
improvement of the available phosphorus data, which
provides reliable and comparable results to evaluate
the achievable Ptot concentrations.
Key point of the evaluation is the verifiable statistical
independence of the o-phosphate concentrations
of the remaining phosphate fractions, i.e. essentially
the particulate and dissolved organic phosphate compounds.
The coupling of high-resolution data on the
o-phosphate concentrations in the effluent of the activated
sludge process with a probability distribution
of these remaining phosphate fractions, taken from
the operation diaries of 2007 and 2008, lead to highresolution
probability values for P tot concentrations in
the effluent. As agreed with SES, the goal was to reach
a 90% probability of compliance with the monitoring
values in the qualified sample. In the analysis of the
data, the proportion of the collected high-resolution
data points, which do not meet this requirement, was
increased. This parameter is used as a comparison
between the various stages of investigation and allows
making conclusions on compliance with various assumed
surveillance values.
Prerequisite for the application of the developed evaluation
method is, firstly, the likelihood of giving accurate
high-resolution o-phosphate values. The data
will be collected online for the wastewater treatment
plants outside Stuttgart at the outflow of the activated
sludge tanks. The quality of the data for the group
of wastewater treatment plants Ditzingen and WWTP
Plieningen has been considered sufficient. In the case
of WWTP Ditzingen, however, the o-phosphate concentration
values after the secondary sedimentation
increased, which was considered with an impact factor.
The second prerequisite for the application of the method
lies in the comparability of the probability distribution
of the remaining phosphate fractions between
measurements campaign and the operation diaries
2007-2008. These are the adequate measures taken
for the wastewater treatment plants.
With the help of the developed statistical methods, it
was shown that, in the case of the group of wastewater
treatment plants Ditzingen, compliance with the stringent
monitoring values is possible with a very high
probability, without any additional procedural steps,
only by an appropriate dosage of a precipitation agent.
Regarding the WWTP Plieningen, it can be concluded
that a significant increase of the phosphorus monitoring
value can be accomplished without a problem.
Funding:
Eigenbetrieb Stadtentwässerung Stuttgart
Funding Duration:
01/2009 - 12/2009
Project Manager:
Prof. Dr.-Ing. H. Steinmetz
Project Coordinator:
Dipl.-Ing. RBM C. Meyer
Contact Person:
Dipl.-Ing. Andreas Neft, Dipl.-Ing. Sabine Schmidt
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