Biomedical Engineering Reference
In-Depth Information
20.0
18.0
16.0
14.0
Anaerobic Phase 0th min.
Anaerobic Phase 120th min.
Anoxic Phase 0th min.
Anoxic Phase 120th min.
12.0
10.0
8.0
6.0
4.0
2.0
0.0
1
3
5
7
9 11 13 15 17 19 21 23 25 27 29 31
Operation Time（d）
(c) DOC=0.3mgL-1
Figure 6. TP profiles under different DOC concentrations at the beginning of anaerobic stages.
Since seed sludge of anaerobic-anoxic SBR reactors were taken from the parallel AN/AO
process, which was also operated partly in anaerobic-anoxic mode, they should share some
common characters. Operation results showed however, that PAO deactivation was caused by
different factors in two configurations, which indicated the complicated nature of EBPR
systems. NO
3
-
-N concentration at the beginning of anaerobic stages in the anaerobic-anoxic
configuration can be linked to external sludge return ratio in the parallel AN/AO process.
During operation of the parallel AN/AO process, PAO deactivation was not observed when
external sludge return ratio was 50% (mass content of phosphorus in biomass was 4% , at
which time NO
3
-
-N in the anaerobic reactor was 0.1 mgL-1), but occurred when external
sludge return ratio was 100% (mass content of phosphorus in biomass was 2.6%, at which
time NO
3
-
-N in the anaerobic reactor was 0.4 mgL-1). Ready biodegradable organic contents
at the beginning of anoxic stages in the anaerobic-anoxic SBR configuration is related to
internal MLSS return ratio, influent wastewater characters, and performance of the anaerobic
compartments; the latter two are very difficult to be evaluated quantitatively. Internal MLSS
return ratio was controlled as 200% in this study. No PAO deactivation was observed by
varying internal MLSS return ratio from 100% to 300% in the study.
4. Conclusions
PAO deactivation was observed in both the parallel AN/AO process and the anaerobic-
anoxic SBR reactors. Excessive HRT and SRT were main factors that caused PAO
deactivation in the parallel AN/AO process; ready biodegradable organic content at the
beginning of anoxic stages and NO
3
-
-N concentration at the beginning of anaerobic stages
were main factors that influenced PAO activity in anaerobic-anoxic SBR reactors. Ready
biodegradable organic content was probably more essential to PAO activity in anaerobic-
anoxic SBR reactors. Other factors such as pH, temperature, internal MLSS return ratio and
