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

Waste Water Technology AWT
Examinations to improve the hygienic river quality
of the Koersch
The determination of significant anthropogenic pollutions
and the evaluation of their effects on the ecological
current state of the surface water are an important
part of the European Union water framework directive
(2000/60/EG).The causes for poor quality (hygienic)
of river water are mainly anthropogenic loads, first of
all sewage discharges. These degrade the river water
hygienic-biologically as well as optically (e.g. by foam
formation, sanitary products etc.).
The Koersch is a small river south of the Stuttgart
metropolitan area and an important inflow into the
Neckar. It is significantly affected by anthropogenic
sources, 2 wastewater treatment plants and 52 stormwater
overflow tanks (only within the boarders of
Stuttgart City). Under the scope of this research project
microbiological examinations of the river Koersch,
the discharges from certain stormwater overflow
tanks and the two wastewater treatment plants Stuttgart-Moehringen
and Stuttgart-Plieningen were to be
carried out. The main objective of this investigation
was to identify the major sources of pathogen entry
into the river during both dry and rainy weather conditions.
The results were then used to suggest technical
measures to reduce the pathogen entry, as well as
to simulate the polluting load.
After the examination, the impact of the sewage became
obvious during dry weather periods (discharges
from the first wastewater treatment plant), as well as
by rainy weather periods (discharges from the sewage
overflow tanks). The concentrations of the pathogens
in the river were higher at rainy weather than that at
dry weather by 1 to 2 orders of magnitude.
The results show that in addition to the effluents from
wastewater treatment plants and stormwater overflow
tanks, diffuse pollution is also a significant source of
hygienic pollution of surface water. River sections were
heavily burdened even without wastewater entry and
did not meet the requirements of the EU Bathing Water
Directive (2006/7/EC). Additionally, under dry weather
conditions, wastewater treatment plants were responsible
for high pathogen concentrations. Effluents from
wastewater treatment plants with advanced treatment
steps, such as sand filtration, resulted in some dilution
of pathogen concentrations in rivers. However, the
EU Bathing Water Directive criteria were still not met.
During rainy weather conditions, the effluents from
stormwater overflow tanks then produced peaks in the
hygienic load in the rivers. Hence, the efficiency of advanced
wastewater treatment steps is to be critically
evaluated when a simultaneous reduction of diffuse
pollution cannot be achieved.
Figure: Escherichia coli concentrations of the Koersch as well as the confluences Steinbach and Ramsbach and the
discharges of municipal wastewater at dry and rainy weather conditions
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