Problematik vid höga flöden - Gästrike Vatten AB

O 2 (mg/l)
5
4
3
2
1
(a) Aerobic reactor 1
0
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Figure 5. DO-concentrations in (a) aerobic reactor 1 and (b) aerobic reactor 2 during a prolonged period of highflow.
During and after prolonged high-flow periods chemical precipitation was sometimes
necessary to ensure acceptable P-removal. Phosphorus release batch tests were performed on
activated sludge both with and without the presence of chemical precipitants. The results from
such tests before and during a prolonged period with high-flow in December 2008 are shown
in table 1. The results indicate that chemical precipitation can have an inhibiting effect on
both the maximum phosphorus release and the maximum release and uptake rate.
Table 1. Phosphorus release batch tests with and without chemical precipitation. Mean value from 4 tests each.
Chemical precipitation Maximum P-release Maximum P-release Maximum P-uptake
(Yes/No)
(mg/g VSS) rate (mg/g VSS·h) rate (mg/g VSS·h)
Yes 11.3 10,1 8.6
No 19.7 12.8 11.0
Operation control strategies
To ensure for an anaerobic phosphorus release during high-flow conditions, the main goal
was to secure the supply of VFA and, at the same time, secure an anaerobic retention time
without occurrence of inhibitive oxidative compounds. If this could be achieved together with
a better control of the aeration-system to avoid oxygen peaks and excessive aeration, the
system should be able to retain an acceptable biological phosphate removal both during and
after high-flow conditions.
The measures taken to achieve this were:
O2 (mg/l)
Optimization of the primary sludge hydrolysis to maximize the production of VFA.
Rebuilding of the inflow to the anaerobic reactor to avoid turbulent flow and, thereby,
to ensure anaerobic conditions.
Development of operating control strategies during and after high-flow conditions to
maintain sufficient EBPR activity and avoid peak effluent concentrations.
Additional substrate for the hydrolysis was created by pumping substrate from both the
primary sludge and the activated sludge clarifier. This was done in pilot scale in one out of six
sedimentation tanks using a pump giving 8 m 3 /h. Samples were also taken directly from the
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4
3
2
1
(b) Aerobic reactor 2
0
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On-line oxygen probe (1)
On-line oxygen probe (2)