membrane aerated biofilms - freese and nichols, inc.membrane aerated biofilms: who is there, what...

Membrane Aerated Biofilms:Who is There, What are They Doing, and Why

are They Beneficial

Leon Downing, Ph.D.

University of Notre Dame

Freese and Nichols, Inc.

Outline

Nitrogen removal in wastewater

What is a membrane aerated biofilm (MAB)?

Past application research

Fundamental research needs

Impact of oxygen gradients

Impact of BOD concentrations

Results

Discussion and conclusions

Nitrogen Removal in Wastewater

AOB - ammonia oxidizing bacteria

NOB - nitrite oxidizing bacteria

DB - denitrifying bacteria

Conventional N removal

Nitritation

a.k.a Shortcut N removal

NH4+

N2 3e-

DB

2e-

DB

NO2-

NO2-

AOB

6e- NO3-

NOB

2e-X

X

X

Nitrogen Removal in Wastewater

Why?

Nutrient permits to

protect water quality

Energy reduction through

reduced oxygen demand

Phosphorus removal

-120

-80

-40

0

40

80

120

mgO

D/L

BOD

Ammonium

Nitrate

Membrane aerated biofilms (MABs)

Air

Membrane Aeration MBR

Water

Nitrifying Bacteria

Heterotrophic Bacteria

DO

Membrane Aerated Biofilms (MABs)

MAB

Water

Nitrifying Bacteria

DO

Heterotrophic Bacteria

Air

Advantages

Concurrent

nitrification and

denitrification

Biofilm process –

reduced bulk SRT

for nitrifiers

Nitrite

accumulation?

Past Application Research

Membrane aerated biofilm reactors (MABR)

Biofilm based process in columns

High levels of TN and BOD removal at low loading rates (Semmens et al., Water Research, 2003)

Shortcut TN removal suggested (Hibiya et al., Journal of Biotechnology, 2003; Schramm et al., AEM, 2000)

Increased BOD loading leads to decreased nitrification (Walter et al., Water Research, 2005)


Hybrid Membrane Biofilm Process (HMBP) Relies on attached nitrifiers and

suspended heterotrophs (similar to IFAS)

Achieves TN removal with a

low bulk liquid SRT and limited

heterotrophic biofilm (Downing and Nerenberg (2007) WS&T)

Less susceptible to BOD loadings;

BOD concentration controls nitrification

and impacts heterotrophic content of

biofilm (Downing and Nerenberg (2008) Water Research)

Pilot scale testing indicated low

level TN removal (effluent <6 mgN/L)

was possible with a real wastewater(Downing et al. (accepted) WER)

Research Needs

Impact of constituent gradients on MABs

Oxygen gradients and BOD gradients

Who is there

What are they doing

How does this impact the beneficial aspects of

MAB systems

Methods

Column reactors with a

single membrane

Two sets of experiments,

with a new membrane for

each condition

Varied intra-membrane

pressure, constant

ammonium and no BOD

Varied BOD, constant intra-

membrane pressure and

ammonium

Microsensor Studies

200μmmicrosensor

HFM

biofilm Measure

gradients through

the biofilm

Small spatial

resolution

Determine flux

into or out of the

biofilm

Net production of

nitrite and nitrate

Methods

Fluorescence in situ

hybridization (FISH)

DNA “tagging” technique

Identify:

Nitrosomonas spp. (AOB)

Nitrobacter spp. (NOB)

Nitrospira spp. (NOB)

heterotrophs

Methods

*Note: From Schramm, 1996

Results – Impact of Oxygen Gradients Who’s There?

Lower DO – Fewer NOB; Nitrospira spp. more prevalent

Higher DO – Nitrobacter spp. more prevalent

0-3030-60

60-9090-120

0

5

10

15

20

25

30

35

Den

sity

(1

09 c

ells

cm

-3)

Distance from Membrane ( m)

14 kPa

35 kPa

70 kPa

70 kPa, Aerobic bulk

0-3030-60

60-9090-120

0

5

10

15

20

25

30

35

Den

sity

(109

cel

ls c

m-3

)


14 kPa

35 kPa

70 kPa

70 kPa, Aerobic bulk

Nitrobacter spp. Nitrospira spp.

Downing and Nerenberg (2008) Biotechnology and Bioengineering

Results – Impact of Oxygen Gradients

What are they doing?


0

0.2

0.4

0.6

0.8

1

1.2

1.4

14 35 70 70 (aerobic bulk)

Intra-membrane pressure (kPa)

Flu

x (

gN

m-2

day

-1)

Ammonium flux

Nitrite flux

Nitrate flux



Parameter Value

Nitrobacter spp.

μ 0.33 gN gX-1 day-1

KO2, Nit

0.51 gN m-3

Ks, Nit

0.39 gN m-3

Nitrospira spp.

μ 0.26 gN gX-1 day-1

KO2, Nsr

0.4 gN m-3

Ks, Nsr

0.27 gN m-3


0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 2 4 6 8 10

Oxygen Concentration (g m-3

)

Nit

rogen

Flu

x (

gN

m-2

day

-1)

Nitrite

Nitrate

Ammonia


Why is this beneficial?

Adjust MAB operation to your conditions

Low carbon – more nitrite accumulation

Excess carbon – higher nitrification rates

Kinetics for NOB in biofilm systems

Nitrospira spp. have a higher tolerance to low DO

conditions

Nitrospira spp. have a lower nitrite oxidation and SOUR

that Nitrobacter spp. (Blackburne et al. (2008) Water Research)

Results – Impact of BOD Concentration

Who is there?

0-3030-60

60-9090-120

Nitrobacter spp.

Nitrospira spp.

AOB

Heterotrophs

0

20

40

60

80

100

120

140

160

Cel

l d

ensi

ty (

109

cel

ls c

m-3

)


0-3030-60

60-9090-120

120-150

Nitrobacter spp.

Nitrospira spp.

AOB

Heterotrophs

0

50

100

150

200

250

Cel

l d

ensi

ty (

109

cel

ls c

m-3

)


0-60 60-120 120-

180180-

240240-

300300-

360

Nitrobacter spp.

Nitrospira spp.

AOB

Heterotrophs

0

50

100

150

200

250

Cel

l d

ensi

ty (

109

cel

ls c

m-3

)


Downing and Nerenberg (2008) Applied Microbiology and Biotechnology


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

)

Flu

x (

gN

m-2

day

-1)

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

% D

en

itri

ficati

on

Ammonium Flux

Nitrite Flux

Nitrate Flux

% Denitrification





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 Nitrification

CB Denitrification

MAB Nitrification

MAB Denitrification

CB-Conventional Biofilm



Why is this beneficial?

Bulk liquid BOD concentration controls nitrification

Hybrid system lowers the bulk liquid concentration with

decreased heterotrophic biofilm thickness

Conventional biofilm vs. MAB MAB sustains nitrification at much higher BOD concentrations

than a CB


Conclusions/Discussion

Fundamentals of MABs

Oxygen concentration can be controlled within a

biofilm

The resulting oxygen gradients can be used to

control shortcut nitrification

BOD concentration is the controlling parameter for

nitrification in MABs

Nitrification in MABs is less sensitive to BOD

concentration than nitrification in conventional

biofilms

Conclusions/Discussion

Application of nitrification dynamics

Nitrospira spp. are selected for in low DO

conditions

Nitrospira spp. have lower nitrite oxidation

kinetics, and their presence as the dominant NOB

can lead to more nitrite accumulation

Nitrification in a biofilm is dependent on the bulk

liquid BOD concentration

IFAS and MBBRs

Acknowledgements

Advisor: Rob Nerenberg

Nerenberg Research Group

Funding agencies

CICEET (Cooperative Institute for Coastal and Estuarine Environmental Technology)

NSF GRFP (National Science Foundation Graduate Research Fellowship Program)

Questions?

NBDB

Biofilm


NB

BOD

DO

Biofilm

DB NB

NO3-

BOD

MABR HMBP

BODDO

NO3-

membrane aerated biofilms - freese and nichols, inc.membrane aerated biofilms: who is there, what...

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