Total Nitrogen Removal in the Hybrid Membrane-Biofilm Process

Total Nitrogen Removal in the Hybrid Membrane-Biofilm Process

Robert NerenbergDepartment of Civil Engineering and Geosciences

University of Notre Dame

Metropolitan Water Reclamation District of Greater ChicagoAugust 22, 2008

2

Acknowledgements

Leon Downing Kyle BibbyCollaborators: K. Esposito, B. Bodniewicz, T. Fascianella (Metcalf & Eddy)

Funding:

http://ciceet.unh.edu/

Introduction

4

Problem: eutrophication

5

“Classic” Eutrophication Examples

http://www.longislandsoundstudy.net/pubs/reports/sh03_p1.pdf

Long Island Sound

http://www.cbf.org/site/PageServer?pagename=resources_facts_deadzone

Chesapeake Bay

http://www.ncat.org/nutrients/hypoxia/hypoxia.html

Gulf of Mexico

6

1990 2000 2010

NH3 -N,TN,

mg/L

Year

2

4

6

8

10

0

Nitrogen Standards for Wastewater

Source: Art Umble, Ph.D., Greeley and Hansen

TN = total nitrogen

= NH4+ + NO3

- + NO2- + org N

7

Biological Nitrogen Removal

1) Nitrification

Ammonia oxidizing bacteria (AOB) (Nitrosomonas)

NH4+ + O2 NO2

-

Nitrite oxidizing bacteria (NOB) (Nitrobacter, Nitrospira)

NO2- + O2 NO3

-

8


2) Denitrification

Heterotrophic denitrifying bacteria (DB)

BOD + NO3- (NO2

- ) N2

9

Conventional N removal


NO2- NO3

-AOB NOB

NH4+

6e- 2e-

Nitrification

N2 3e- 2e-

DB DBNO2

-

Denitrification

10

N2 3e- 2e-

DB DBNO2

-

Shortcut Nitrogen Removal

NO2- NO3

-AOB NOB

Conventional N removal

Shortcut N removal

NH4+

6e- 2e-X

X

X

25% reduction in oxygen40% reduction in BOD Low DO favors AOB over NOB

11

Wastewater Treatment

BOD, NH4

+

O2

Settling

tank

Aeration

basin

Anoxic

basin

NO3-

NH4+

Need high SRT!

Aerobic nitrification (AOB/NOB)

Anoxic denitrification

NO3- NO3

-

12

Many older plants cannot achieve nitrification

• Short SRTs

• Landlocked

Upgrades: • Space• Capital costs• Energy

13

Biofilms can retain nitrifiers

IFAS, MBBRLimited denitrification

http://www.brentwoodhttp://www.brentwood--ind.com/water/ifas_main.htmlind.com/water/ifas_main.html

14

New approach

Use air-filled hollow-fiber membranesSuppress bulk aeration

15

Hollow-Fiber Membranes for Gas Transfer

1 mm

1 mm 2 μm

16

Membrane-Biofilm Reactors

281 μm

1 μm

Water

O2

O2

NH4+

Hydrophobic polymers

High specific surface area

Variable driving force J=K(CL-C)

Low energy consumption

17

Hollow-Fiber Membrane Biofilm Process (HMBP)

Return Activated Sludge

Settler Influent (BOD, NH4 +)

Hollow Fiber Membranes

Compressed air to membranes

• Nitrification with short SRTs

• Hybrid thinner biofilms

• Denitrification in bulk

• Passive aeration save up to 70% on energy

18

HMBP Conceptual Model

BODNH4

+

NH4+

O2

Hollow-fiber membrane

Biofilm

Bulk liquid

BOD

Heterotrophs

Settler

NO3-

NO2-

Dep

th

Concentration

AOB, NOB

NO2-

NO3-

DONO2

-

NO3-

NH4+

BOD

• Nitrifiers in biofilm (AOB/NOB)

• Heterotrophs in bulk

• Maximal use of influent BOD for denitrification

(Anoxic)

S is insensitive to BOD loading)1(

1

max xx

x

bqb

kSθθ

θ+−Υ

+=

)1()(

x

ox

a bSSXθθ

θ+−

Υ=

19

Research Objectives

1. Test HMBP concept2. Explore effects of membrane DO and

bulk BOD on nitrification rates3. Can the HMBP be scaled up?

Results

1. Test HMBP ConceptPerformance of a bench-scale HMBP

22

Bench Scale HMBP





23

Performance Tests

Test HMBP for a variety of NH4+ and

BOD loadings

Determine location and activity of AOB, NOB, and Heterotrophs

24

BOD=0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

2.2 (4.0) 4.0 (6.0) 5.0 (12.0) 7.5 (17.0) 12.5 (17.0)

BOD:N (BOD Loading g m-2 day-1)

Nitr

ifica

tion

Rate

(gN

m-2

day

-1)

Vary Influent BOD Concentration

Downing and Nerenberg (in press) Water Research

Nitrification rates are is insensitive to influent BOD concentrations

Nitr

ifica

tion

rate

(gN

/m2 -

d)

4 6 12 17 17BOD Loading (g/m2-d)

25

Biofilm Activity: Microsensors

200μm microsensor

HFMbiofilm Measure gradients

through the biofilmDO, NH4

+, NO3-,

NO2-,

Determine fluxes into or out of the biofilm

26

0

2

4

6

8

10

12

14

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Relative Thickness of Biofilm [-]

Con

cent

ratio

n (m

g/L)

Biofilm Gradients

NH4+-N

NO3--N

NO2--N

O2

Biofilm Bulk

Nitr

ifica

tion

flux

(gN

/m2 -

d)

27

Nitrite and Nitrate Production in Biofilm

Downing and Nerenberg (in press) Water ResearchMainly nitrite production (shortcut)

0

0.5

1

1.5

2

2.5

5 (12) 7.5 (17) 12.5 (17)BOD:N (Organic Loading Rate [g m-2 day-1])

Flux

(gN

m-2

day

-1)

Ammonia RemovalNitrite ProductionNitrate Production

28

Biofilm Structure: FISH

AOBNitrobacterNitrospira

Membrane

Biofilm Surface

AOB+NOBAOBAOB+Het.

29

Biofilm Microbial Structure

Downing and Nerenberg (in press) Water Research

0

2

4

6

8

10

12

14

16

0-30 30-60 60-90 90-120

Distance from Membrane (mm)

Den

sity

(107 c

ells

cm

-3)

AOBNitrobacterNitrospiraOther

Influent BOD:N=7.5

AOB throughout, Nitrobacter near membraneDistance from membrane (µm)

2. Effects of DO and BODHow does the membrane DO affect performance?How much bulk BOD can be tolerated?

31

Experimental System

Recirculation flow

Air into fiber supply

Influent

2 mL/min

Single hollow-fiber membrane

N2 Sparging

Air out of fiber (periodic venting)

Microsensor access ports

Waste

Stir bar

32

Experimental System

33

Vary membrane pressure (DO)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 2 3 4

Experiment

Flux

(gN

m-2

day

-1)

Ammonium fluxNitrite fluxNitrate flux

Downing and Nerenberg (in press) Biotechnology and Bioengineering

Tradeoff: high shortcut vs. high nitrification rates

2.2 mg/L 3.5mg/L 5.5 mg/L 5.5 mg/L, aerobic bulk

DO at membrane surface

34

Variable DO - modeling


Tradeoff exists, but still some shortcut at high DO

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 1 2 3 4 5 6 7 8 9

Oxygen Concentration (mg/L)

Nitr

ogen

Flu

x (g

N m

-2 d

ay-1

)

NitriteNitrateAmmonia

35

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 3 10

Bulk Liquid BOD Concentrations (g m-3)

Rat

e (g

N m

-2 d

ay-1

)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% D

enitr

ifica

tion

NitrificationN0x ProductionBiofilm Denitrification% denit

Impact of BOD

Downing and Nerenberg (accepted) Applied Microbiology and Biotechnology

BOD slows nitrification, but increases denitrification

1 mg/L 3 mg/L 10 mg/L

36

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 2 4 6 8 10 12

BOD Concentration (g m-3)

Rat

e (g

N m

-2 d

ay-1

)CB NitrificationCB DenitrificationMAB NitrificationMAB Denitrification

Conventional vs membrane biofilm (Model)

CB-Conventional BiofilmMAB-Membrane Aerated Biofilm


Membrane-aerated biofilm much less sensitive to BOD

3. Pilot-Scale Tests

Performance of a larger system with real wastewater

38

Pilot scale testing in NYC with Metcalf & Eddy (26th Ward Treatment Plant, PO-55a)Determine the HMBP performance with real wastewater

Pilot Scale Testing

39

Images from NYC (PO-55a)

40

Reactor System10 hour HRT120 L active volume2.5 day bulk SRT0.2 m2 membrane surface area





Infl. ammonia: 15-20 mgN/LInfl. BOD: 40-150 mg/L

41

Pilot Scale Testing

0

5

10

15

20

25

30

35

1 28 56 82 100 114 126 139 152 167 181 201 215 232

Day

Con

cent

ratio

n (m

gN/L

)NOx Effluent Ammonia Nitrogen Removed

A DCB

42

0

2

4

6

8

10

12

14

16

18

20

6 12 17 21

Con

cent

ratio

n (m

gN/L

)

HRT

Influent TNEffluent NH3Effluent NOx

Pilot Scale Testing

(hours)

Significant levels of TN removal at higher HRTs

Avg. nitrification rate: 0.35 gN/m2-d

43

Issues for scaleup

Membrane materialsMembrane packing densityMixingBiofilm managementCost analysis

44

CONCLUSIONS• The HMBP is effective for TN removal

• Retrofit

• Short bulk SRTs

• Minimal Donor

• Save energy

• Nitrification insensitive to influent BOD, but sensitive to bulk BOD

• Tradeoff exists between nitrification rates and extent of shortcut

• Promising results, further research needed for scaleup

Thank you!

Total Nitrogen Removal in the Hybrid Membrane-Biofilm Process

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