Biomedical Engineering Reference
In-Depth Information
Anaerobic Phase 0th min.
Anaerobic Phase 120th min.
Anoxic Phase 0th min.
Anoxic Phase 120th min.
20.0
120
18.0
100
16.0
14.0
80
12.0
10.0
60
8.0
40
6.0
4.0
20
2.0
0.0
0
C/N=12
C/N=6
C/N=3
Figure 5. TP removals of anaerobic-anoxic SBR reactors after PAO rejuvenation.
Obvious phosphorus release was observed in all the three SBR reactors; and phosphorus
removal efficiencies of the SBR reactors were more than 85%. The lower DOC concentration
at the beginning of anoxic stages and NO
3
-
-N concentration at the beginning of anaerobic
stages, the better phosphorus removal efficiency the process achieved (figure 6).
3.3. Factors Influencing PAO Activity
Influent wastewater characters, SRT, HRT, internal/external return ratios, temperature, pH are
the main factors that influence PAO activity in any EBPR process (Csiti 1991; Hu et al., 2003).
Temperature accounted for part of PAO deactivation in the parallel AN/AO process since
it happened during winter time; but as stated above it was not the main factor and its effects
are very complicated since lower temperature can also help PAO out competing non-PAO in
the process (Cech and Hartman, 1993; Ahn et al., 2002; Raymond et al., 2003). Considering
operation temperature was even lower in the PAO rejuvenation run than that in the PAO
deactivation run, temperature was not the main factor that deactivated PAO in the parallel
AN/AO process. No temperature effect should be considered in the anaerobic-anoxic SBR
reactors as they were operated in temperature controlled room.
Influent pH for the parallel AN/AO process was 6.5-8.5; Influent pH of synthetic
wastewater for the anaerobic-anoxic reactors was around 7.2. When phosphorus release and
uptake functioned normally, pH in anaerobic tanks and/or anaerobic stages were higher than
those in anoxic/aerobic tanks and/or anoxic stages (data not shown); less pH difference between
anaerobic stages and anoxic/aerobic stages was observed when PAO deactivation accrued. pH
control can help improve phosphorus removal efficiency, which was not studied in this study
but was done in other researches (Carsson et al., 1997; Kuba et al., 1997; Ochmen et al., 2005).
It was found in anaerobic-anoxic and anaerobic-aerobic SBR reactors that ready
biodegradable organic at the beginning of anoxic stages and NO
3
-
-N at the beginning of
anaerobic stages were main factors that influence PAO activity; DOC at the beginning of
anoxic stages and NO
3
-
-N at the beginning of anaerobic stages as low as 3 mgL-1 and 2.3
