Problematik vid höga flöden - Gästrike Vatten AB

primary sludge hydrolysis. For the same reasons the maximum influx-flow was also lowered
from 3000 m 3 /h to 2500 m 3 /h to both the primary sludge hydrolysis and the biological stage.
During both december 2007 and 2008, the WWTP experienced exceptional high-flow
conditions with a slightly higher mean influx flow during 2008 compared to 2007. In figure 7
the effluent phosphorus load and the usage of precipitation chemicals for the two periods are
plotted, as well as three months afterwards, when the operation conditions had returned to
normal. At december 2008, the bypass point had been changed, and this year less than half the
amount of phosphorus was discharged and less than one third of precipitation chemicals were
used compared to the year before. After the high-flow event 2007 the EBPR process was
deteriorated for about three months. 2008 the process recovered much faster, which led to a
lower effluent phosphorus load with only one fifth of precipitation chemicals.
P (kg)
1600
1200
800
400
0
(a) Effluent phosphorus load
December January-March
Bypass at 3000 m3/h, 2007 Bypass at 2500 m3/h, 2008
Figure 7. (a) Effluent phosphorus load and (b) usage of precipitation chemicals before and after optimization
changes in the process. During (December) and after (January to March) high-flow conditions in 2007 and 2008.
The overall results from the changes implemented were: a more stable process, smaller
effluent peaks, a minimal usage of precipitation chemicals, avoiding need for external carbon
source and less energy consumption. In figure 8, a plot of the usage of precipitation chemicals
and the effluent phosphorus load during the years 2006 to 2009 is presented. In 2009 the
effluent phosphorus load and the usage of precipitation chemicals were the lowest since the
WWTP was rebuilt for EBPR, and this makes the prospects for managing the stringed
demands 2012 optimistic.
Effluent P (tonne)
8
6
4
2
0
Figure 8. Overall effluent phosphorus load and total usage of precipitation chemicals from the year 2006 to 2009.
61
FeCl 3 (tonne)
60
40
20
0
(b) Chemical precipitation
December January-March
chemical
300
200
Precipitation
100
0
2006 2007 2008 2009
Year
Effluent P Precipitation chemical
(tonne)