Problematik vid höga flöden - Gästrike Vatten AB

The results presented in this paper are based on observations in full-scale at the WWTP, and
the experimental work was carried out between the years 2006 to 2009. During this period,
the process has been followed by collecting data from an on-line phosphate analyzer with
continuous samplings of the effluent, as well as laboratory analyses of flow-proportional
samples taken on daily bases in the influent and effluent from the WWTP.
Different tools were used to evaluate the performance of the EBPR-process and to identify
crucial key-factors of significance for the process failure. A hypothesis was adopted based on
recent research, see figure 2. The hypothesis was then used to identify the critical key factors
for the EBPR-process during high-flow conditions. The conclusions from this identification
were finally used to develop different control strategies that were then implemented and
evaluated in full-scale.
To evaluate the EBPR-activity of the activated sludge, anaerobic phosphorus release batch
tests were performed according to Tykesson et al. 2005. The variation of phosphate release
and uptake performance in full scale were monitored by constructing phosphate-profiles along
the anaerobic and aerobic phases which were based on samples taken on a daily basis. The
performance of the primary sludge hydrolysis was followed by taking samples at the outlets
of the primary sedimentation tanks and these were analyzed for phosphate and VFA using a
5-point titration method. The nutrient compounds as well as COD, TOC and VSS were
measured by standard laboratory methods.
Inhibition of primary
sludge hydrolysis
Decreased anaerobic
retention time
Aerobic conditions and
reduced amount of
substrate in the sewer
system
Influence of oxidative
compounds in the
anaerobic reactor
Endogenous starvation
(lack of PHA)
Lack of VFA
Reduced phosphate
release in the
anaerobic reactor
Reduced phosphate
uptake in the aerobic
reactor
High effluent
phosphate loadings
Figure 2. Factors with a possible inhibiting effect on the EBPR process during high-flow conditions.
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Excessive aeration and
high levels of oxygen
Endogenous starvation
(lack of PHA)
Microbial competition
and changes in bacterial
community structures
Occurrence of
precipitation chemicals
in the activated sludge