The document discusses enhanced biological phosphorus removal (EBPR) in wastewater treatment. It summarizes that EBPR increases the amounts of volatile suspended solids and total suspended solids in raw and settled wastewater compared to a system without EBPR. It also decreases the carbonaceous oxygen demand. The document further summarizes that phosphorus removal is influenced by the anaerobic sludge mass fraction, sludge age, total influent chemical oxygen demand, and recycling of nitrates or oxygen to the anaerobic reactor, with higher values generally increasing phosphorus removal except for recycling. Temperature also affects EBPR kinetics and ecology.

1. Biological Wastewaster Treatment, CE-573
Enhanced Biological Phosphorus Removal M.M.Binte, March 26, 2009.

2. Contents
Note: VSS: Volatile Suspended Solid, TSS: Total Suspended Solid ,ODc:
Carbonaceous Oxygen Demand, RBCOD: Readily Biodegradable COD 2
Part-1
Part-2

3. Anaerobic Tank
PolyP Energy+ P release
VFAs + Energy PHA
Aerobic Tank
Consumption of PHA as energy
source
P + Energy Poly P (P uptake)
EBPR- A Review
3
Metabolism of PAOs in anaerobic and aerobic conditions,
Smolders et al.

4. Influence of EBPR on The System
Factors that can be influenced by EBPR
VSS
TSS
ODc
P/VSS
Operating Conditions used for analysis of
VSS,TSS and ODc
Two anaerobic reactors in series
Total anaerobic mass fraction , fAN = 15%
No nitrate recycle to the anaerobic reactor
Operating temp 20 deg C
Based on sludge age
4
Part-1

5. Influence on VSS,TSS and ODc by EBPR
Figure1: VSS,TSS and Odc vs Sludge age. MXv=masses of volatile solids,MXT=Total
Solids,MOc= Carbonaceous Oxygen Demand, FA=Fully aerobic
5

6. Comparison between with EBPR and
without EBPR
Characteristics VSS TSS OD
Raw wastewater
5~12% higher
with EBPR
20~25% higher
with EBPR
5~6% lower with
EBPR
Settled wastewater
15~25% higher
with EBPR
45~55% higher
with EMPR
8~9% lower with
EBPR
Causes
Lower
endogenous
death rate of
PAOs than OHOs
High inorganic
content of PAO
biomass
Amount of VSS mass
is higher with EBPR
Note: PAOs: Phosphorus Accumulating Organisms, OHO: Ordinary Heterotrophic Organism
The increase in TSS with EBPR needs to be taken into account in the design
of the bioreactor volume and daily sludge volume.
6

7. Important parameter to evaluate the
performance of EBPR
Operating Conditions used for analysis of
P/VSS ratio
Two anaerobic reactors in series.
Zero discharge of nitrate to the anaerobic reactor.
Various anaerobic mass factors (fAN).
Based on sludge age.
Figure2: P/VSS and P/TSS vs sludge age
7

8. Observations from Graph (P/VSS vs Sludge age)
Therefore, Fundamental design parameters are Sludge age and fAN .Not P/VSS
ration. 8

9. Summery of Part-1
9
Influence of EBPR on the system
Amount of VSS and TSS increase.
ODc deacreases.
P/VSS ratio can not be a fundamental
parameter for design.

10. Influencing Factors on EBPR
Anaerobic sludge mass fraction
(fAN)
Sludge age (SRT)
Total influent COD
(CODi)
No of anaerobic reactors (n)
Influent RBCOD fraction
Raw/Settled sewage
EBPR
Zero discharge of nitrate and oxygen to anaerobic reactor.Assumptions
10
Part-2

11. Influence on SRT,fAN and CODi
Operating Conditions used for analysis
the influence on sludge age and fAN,
One anaerobic reactor.
Zero discharge of nitrate and oxygen to
anaerobic reactor.
Various anaerobic mass factors (fAN).
Based on sludge age.
11

12. Influence on Sludge Age
12
Figure3: P removal vs sludge age.
At day 3, highest P removal
occurred.

13. Observations from Graph (SRT)
Case I: SRT < 3daysCase II: SRT >3days
13

14. Influence on fAN and CODi
14
Figure: P removal and P removal/CODi vs sludge age.

15. Observations from Graph (fAN)
Anaerobic zone subdivided into two equal reactors improve P removal .
15

16. Settled and Unsettled Influent
Figure 4: P removal vs Sludge Age. Unsettled (left) and settled (right) wastewater.
16

17. Observations from Graphs
Settling reduces the P removal by the system.
Settling causes less biodegradable COD in the
influent.
Lower mass of OHOs.
Lower fermentable COD conversion.
But P removal per influent COD is higher for
the settled than for the unsettled wastewater.
The ratio of readily biodegradable COD conc to the
influent biodegradable COD conc (fss=Ss,i/CODi)) is
higher for settled wastewater.
For unsettled wastewater, fss= 0.25 and for settled
wastewater, fss=0.38 17

18. Minimum Aerobic SRT for EBPR-1
Why need minimum SRT?
PHA formed in anaerobic must be consumed
during the aerobic phase.
If not, the PHA level in the cells will increase
untill a maximum level is reached.
After reaching max level, no substrate uptake
will occur under anaerobic conditions leading
to deterioration of EBPR.
18
Reminder: PHA: Poly-β-hydroxyalkanoates ,In anaerobic tank,VFAs+energy=PHA and
In aerobic tank, PHA is used as energy source)

19. Minimum Aerobic SRT for EBPR-2
Why need minimum Aerobic SRT?
Total SRTmin = Anaerobic SRTmin+ Aerobic SRTmin.
Time required for PHA consumption
Under aerobic/anoxic conditions
Time needed for anaerobic
RBCOD conversion to PHA
Biomass specific substrate
Loading rate
The operation of the system
Temperature
Cell maximum PHA content
Total
SRTmin
In activated sludge system design,
SRT are directly linked to the growth rate of the
microorganisms.
Minimally required SRT are corresponds to the
maximal growth rate.(SRTmin=1/µmin)
Since growth only occurs under aerobic conditions,
only aerobic SRTmin can be considered.
19

20. Model for prediction of SRTmin
Figure 5: Aerobic SRTmin vs Temperature
How to use this graph?
Known parameter is
maximal PHA storage
capacity of enriched culture
(gCOD PHA/gCOD-active
mass)
Example: For known value
0.4, the operational aspects
of EBPR in a SBR system
can be aerobic SRTmin=
5days and Temperature 11
deg C (approximated) or
10days and 6 deg C.
20

21. Influent RBCOD Fraction(fss)
Figure 6: P removal vs RBCOD fraction (fss=Ss,i/CODb,i)
For a selected fAN,
As fss increases ,P
removal also increases.
How to increase fss?
By supplementation of
influent RBCOD.
Example: Acid
fermentation of primary
sludge.
21

22. Recycling Effect of Nitrate and Oxygen
Figure 7: P removal vs NO3 concentration in recycle(mgN/l)
22

23. Observations from Graph-1
Before 11 mgN/l,
As Oxygen/Nitrate is recycled to the anaerobic
reactor increases, the P removal decreases also.
OHOs utilize nitrate or oxygen as an external
electron acceptor.
OHOs can not transform fermentable COD to
VFAs due to recycling.
Recycling reduces the mass of VFAs available
to the PAOs for storage.
Consequently it reduces the P release, P uptake
and P removal.
23

24. Observations from Graph-2
After 11mgN/l,
P removal remains constant at about 3 mgP/l
All the influent RBCOD is denitrified by OHOs.
No VFAs, consequently no COD is available
for PAOs.
P removal occurs only by normal metabolic P
content.
24

25. Temperature Effect on EBPR-1
25
A stoichiometric study by Brdjanovic et at.(1997,1998c)
Investigations on
Short-term (hours) temperature changes on the
physiology of the EBPR system.
Long-term (weeks) temperature changes on the
ecology of the EBPR system.

26. Physiological Effects on EBPR
Stoichiometry of anaerobic and aerobic
processes was not strongly effected by
temperature.
Kinetics of the both processes were strongly
effected by temperature.
The anaerobic P release rate was maximum at 20ºC
and the temperature co-efficient,θ= 1.028 (5 ºC≤ T ≤
20ºC )
The aerobic P uptake rate was continuous in the
interval of 5-30 ºC and θ= 1.057 (5 ºC≤ T ≤ 30ºC )
26

27. Temperature Effects on EBPR-2
Temperature effects on the ecology of the EBPR
Both long and short-term have the same effect in
anaerobic metabolic processes.
Temperature has a moderate impact on the aerobic P-
uptake during long-term tests.
But strong effect on PHA consumption, Oxygen uptake
and growth for both long and shor-term tests.
It is not wise to take a decision only considering an
easily observable parameters ( P uptake).
27

28. Summery of Part-2
28
Zero discharge of nitrate and oxygen to anaerobic
reactor .
Higher amount of fAN and CODi can remove larger
amount of P.
Unsettled sewage can remove larger amount of P than
settled sewage.
Only minimum aerobic SRT can be considered as
minimum SRT for the whole system.
Recycling of nitrate and oxygen to anaerobic reactor
adversely effect P removal efficiency of EBPR.
Temperature has strong effect on the aerobic metabolic
processes compare to anaerobic metabolic process.

29. 29