High-rate activated sludge for carbon management and energy productionMark W. Miller, Pusker Regmi, Jose Jimenez, Charles B. BottNovember 15 | 2016
96th NC AWWA-WEA Annual Conference
2
Conventional Activated Sludge
ProcessSRT SLR MLSS HRT BOD5 Removal
(days) (kgBOD5/kgMLSS·day) (g/L) (hours) (%)
CAS 3-15 0.2-0.4 2-4 4-9 > 95
RAS
WAS
PS
< 0.1 mg/L TAN< 30 mg/L TSS< 30 mg/L BOD5
3
High-Rate Activated Sludge
ProcessSRT SLR MLSS HRT BOD5 Removal
(days) (kgBOD5/kgMLSS·day) (g/L) (hours) (%)
CAS 3-15 0.2-0.4 2-4 4-9 > 95
HRAS 1-4 1.5-2.0 3-5 1-3 > 85
RAS
WAS
PS
< 30 mg/L TSS< 30 mg/L BOD5
4
Multi-stage BNR
RAS
WAS
Carbon< 0.1 mg/L TAN< 3 mg/L TN
RAS
WAS
PS
< 30 mg/L TSS< 30 mg/L BOD5
HRAS BNR
ProcessSRT SLR MLSS HRT BOD5 Removal
(days) (kgBOD5/kgMLSS·day) (g/L) (hours) (%)
CAS 3-15 0.2-0.4 2-4 4-9 > 95
HRAS 1-4 1.5-2.0 3-5 1-3 > 85
5
A/B Process
ProcessSRT SLR MLSS HRT BOD5 Removal
(days) (kgBOD5/kgMLSS·day) (g/L) (hours) (%)
CAS 3-15 0.2-0.4 2-4 4-9 > 95
HRAS 1-4 1.5-2.0 3-5 1-3 > 85
A-stage 0.1-1 2.0-10 1-5 0.5 30-70
RAS
WASWAS
RAS
< 0.1 mg/L TAN< 30 mg/L TSS< 30 mg/L BOD5
A-stageB-stage
Nitrifying Activated Sludge
6
Single-sludge BNR: 5-Stage Bardenpho
MLR
RAS
WAS
PS
Carbon< 0.1 mg/L TAN< 3 mg/L TN
ProcessSRT SLR MLSS HRT BOD5 Removal
(days) (kgBOD5/kgMLSS·day) (g/L) (hours) (%)
CAS 3-15 0.2-0.4 2-4 4-9 > 95
HRAS 1-4 1.5-2.0 3-5 1-3 > 85
A-stage 0.1-1 2.0-10 1-5 0.5 30-70
Primary Clarifier
- - - 1.5-2.5 25-40
MLR
RAS
WASWAS
RAS
Shortcut N RemovalNitrite Shunt
SNDDeammonification
< 1 mg/L TAN< 5 mg/L TN
A-stage B-stage
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Shortcut Nitrogen Removal
Controlled C/N required to reduce heterotrophic competition with anammox
Intensification of treatment to reduce footprint, energy, and chemical usage
Energy neutrality possible by capturing carbon and redirecting to anaerobic digestion for biogas production
Carbon Capture
Controlled C/N
1. Limited nitrogen removal in the B-stage when using conventional BNR processes
2. Biological phosphorus removal not possible (chemical P removal can be achieved in A-stage)
3. More complex process operation4. Produces ~10% more sludge than comparable single-
stage BNR process
Why not to use the A-stage process?
8
1. Overall tankage volume reduction when compared to single-stage process with primary sedimentation
2. Energy efficiency and energy recovery through carbon capture
3. Produces less biosolids after anaerobic digestion than single-stage BNR process
4. Removes soluble COD unlike physical unit processes5. Couple with shortcut BNR process to obtain energy
neutral operation while meeting nitrogen removal requirements (C/N control)
Why use the A-stage process?
9
Hampton Roads Sanitation District (HRSD)BNR Pilot Study
10
RAS
Air
RAS WAS
RWI Influent
A-stage HRAS
Air
B-stage AVN Anammox MBBR
IMLR
Inf
WAS
HRSD A-stage Pilot Study
11RAS
To B-stageProcess
WAS
Clarifier
Tank3
RWI
Tank2
Tank1
Air EffluentEQ Tank
DO Controller
MLSS Controller
PLC
DOMLSS
MOV
VFD
FlowMeter
VFD
FlowMeter
FlowMeter
(▬) Process water
(▬) Solids
(▬) Air
(–) Sensor signals
(---) Controller output
Influent COD• Includes plant recycles
• Characterized as septic
A-stage COD Removal
A-stage Effluent COD• 48% pCOD removal
• 35% sCOD removal (includes colloids)
12
Days0 100 200 300 400 500 600 700
CO
D (m
g/L
)
0
100
200
300
400
500
600
700
800Influent pCODInfluent sCOD
(a)
Days0 100 200 300 400 500 600 700
CO
D (m
g/L
)
0
100
200
300
400
500
600
700
800Effluent pCODEffluent sCOD
(b)
A-stage Effluent COD/TAN
• Narrow controllable range
• COD fractions vary with SRT
Impact of COD/TAN on TIN Removal Efficiency
B-stage TIN Removal %
• >10 COD/TAN is excessive
• NOB out-selection impacted13
A-stage SRT (days)
0.0 0.2 0.4 0.6 0.8 1.0
A-s
tage
Effl
uent
CO
D/T
AN
(g/g
)
4
6
8
10
12
14
16 (a)R = -0.51p<0.001
A-stage Effluent COD/TAN (g/g)
4 6 8 10 12 14 16B
-sta
ge T
IN R
emov
al E
ffici
ency
(%)
0
20
40
60
80
100 (b)
R = 0.64p<0.001
Impact of SRT on COD Removal
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SRT (days)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
CO
D R
emov
al E
ffic
ienc
y (%
)
0
20
40
60
80
100
This studyJimenez et al. (2015) Ge et al. (2013)Model
SI
Primary Sludge
Bioflocculation Efficiency
Hydrolysis and Microbial Diversity
Specific Removal Rates
SRT (days)
0.0 0.5 1.0 1.5 2.0
CO
D F
ract
ion
(%)
0
20
40
60
80
100
A-Stage Process
COD Mass Balance
Data adopted from Jimenez et al. (2015) 15
PS
Oxidized
Effluent
WAS
XSP+XI = Particulate and inert
XSC = Colloidal
SSC = Soluble complex
SSV = VFAs
SI = Soluble inert
Average COD Fraction Mass Balance
16
RWI Effluent WAS Oxi/Prod
Frac
tion
of R
WI C
OD
(%)
-20
0
20
40
60
80
100
SI
SSV
SSC
XSC
XSP + XI(a)
Average COD Fraction Distribution
17
RWI Effluent WAS
Frac
tion
of C
OD
(%)
0
20
40
60
80
100(b)
SI
SSV
SSC
XSC
XSP + XI
COD Mass Balance of Pilot Study Processes
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A-stage B-stage MBBR Combined
CO
D F
ract
ion
(%)
0
20
40
60
80
100 Effluent WAS Oxidized
Higher overall sludge production (compared to single-sludge process)
Lower overall aeration energy required for COD removal
45%
47%
70%
30%
0.57±0.18 0.17±0.07YObs (kg-VSS/kg-COD)
A-stage B-stage PS WAS
Vol
atile
Sol
ids R
educ
tion
(%)
0
20
40
60
80
100
Spec
ific
Met
hane
Yie
ld(m
3 met
hane
/kg
VS
adde
d)
0.0
0.2
0.4
0.6
0.8
VSRSMY
Biochemical Methane Potential Tests
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• Better understanding of bioflocculation mechanisms and impact of operational parameters
• Intracellular and extracellular storage mechanisms• Establish design criteria for intermediate settling tanks• Evaluate alternative configurations like contact
stabilization• Development of better mechanistic process models• Whole plant process controllers?
Future Outlook and Research Needs
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Questions?
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