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

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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?

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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?

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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)

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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

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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?