biofilm in the water environment field · 2014-09-11 · •biofilms are unique microbial systems...

Biofilm in the Water Environment FieldFUNDAMENTALS, APPLICATION, AND FUTURE NEEDS

Leon Downing, Ph.D.

Freese and Nichols, Inc.

September 23, 2009

Outline

• What is a biofilm?

• Past applications

• Current applications

• Future needs

What is a biofilm?

• “cells immobilized at a substratum and frequently embedded in an organic polymer matrix [EPS] of microbial origin” - Characklis and Marshall 1990

What is a biofilm?

• Why is this important?

What is a biofilm?

• Cell residence time independent of hydraulic residence time

• Increased volumetric activity

• Increased operational stability

• Inherent ease in biomass:fluid separation

• Increased resistance to toxic/inhibitory shock loads

• Different bioconversion processes in the same reactor

What is a biofilm?

• Redox conditions

– Different environmental conditions for different metabolisms

– Ecological redox sequence

ORP (mV)

Electron Acceptor Condition

+300

+200

+100

0

-100

-200

-300

-400

Aerobic

Anoxic

FermentiveAnaerobic

O2

NO3-

SO42-

Carbon -Organics

What is a biofilm?

• Nitrogen removal

• Nitrification

• Denitrification

NH4+

N2

+2e-

DB

NO2-

NO2-

NO3-

ORP (mV)

Electron Acceptor Condition

+300

+200

+100

0

-100

-200

-300

-400

Aerobic

Anoxic

FermentiveAnaerobic

O2

NO3-

SO42-

Carbon -Organics

Simplified Nitrogen Cycle

What is a biofilm?

• Suspended growth

– Homogeneous conditions

• Biofilms

– Diffusion

– Different environments in same reactor

– Stratification of ecology• Heterotrophs (carbon oxidizers)

• Nitrifiers (ammonia oxidizers)

S

NH4+

Bulk Liquid Biofilm

NO3-

DO

BOD

Sub

stra

tum

Het

ero

tro

ph

s

Nit

rifi

ers

Het

ero

tro

ph

s

Past Applications

• Oldest applications in wastewater treatment

– Trickling filter (1890s)

– Attachment to walls observed to increase removal in activated sludge (1960s)

• Aerobic processes

• Low-tech, easy to operate

Current Applications

• Focus on design to take advantage of biofilm properties

• Main focus on nutrients

– Nitrogen

• Multiple commercial biofilm technologies

• Water environment field

– Wastewater treatment• IFAS, floc dynamics

– Headwater streams• Dentrification


• Integrated Fixed Film Activated Sludge (IFAS)– Hybrid treatment system that combines fixed film technology

with conventional activated sludge


• IFAS

– First application – 1943

– Gained momentum in late 1990s

– Main driver: increased nitrification in same tank volume


• IFAS

– Twist on impact of diffusion

– BOD is consumed in liquid

– Nitrifying biofilm

– Greatly increases nitrification per volume

DO

NH4+

Bulk Liquid Biofilm

NO3-

BOD

Sub

stra

tum


The Colony, Texas

0

5

10

15

20

25

30

35

40

Jan-0

5

Apr-

05

Jul-

05

Oct

-05

Jan-0

6

Apr-

06

Jul-

06

Oct

-06

Jan-0

7

Apr-

07

Jul-

07

Oct

-07

Jan-0

8

Apr-

08

Jul-

08

Oct

-08

Jan-0

9

Month

EF

FL

UE

NT

(m

gN

/L)

7 per. Mov. Avg. (Effluent)


Contact Stabilization Shut down IFAS Online

Downing et al. (2009) WEFTEC


Sludge

Holding Tank

Anoxic/Anaerobic

Zone

Anaerobic

Zone

Aerobic Zone

-25

-20

-15

-10

-5

0

Ch

ang

e in

Nit

rog

en (

mg

N/L

)

Anaerobic-1-B Anaerobic-2-B Aerobic-B

Downing et al. (2009) WEFTEC


• Diffusion in biofilm

– Aerobic and anoxic conditions

• The Colony

– Approx. 30% of denitrification in aerobic sections

– IFAS units

– 1-2 mm biofilms

DO

NH4+

Bulk Liquid Biofilm

NO3-

BOD

Sub

stra

tum


• What about a floc/granule?

– Floc-aggregate of bacteria

– Granule-big floc

– Are they biofilms??Diffusion gradients

EPS matrix

Immobilized cells

Substratum???

Dos Santos et al. (1996) Water Research


• Trinity River Authority (TRA) of Texas Central Region Wastewater System (CRWS) Treatment Plant

– 189 MGD plant

– Aerobic treatment

• Nutrient removal study using Biowin


• Nitrogen balance

– Influent TKN: 32 mgN/L

– Effluent NH3 + NO3-: 13 mgN/L

– Change in nitrogen: 19 mgN/L

– Where is the nitrogen going?• Assimilation: 12.5% of biomass (~3 to 5 mgN/L)

• Nitrogen removed: 14 to 15 mgN/L

FlowAeration Basins

Clarifiers


• Simultaneous nitrification and denitrification

– Nitrate reductase activated in sludge blanket

– High mixed liqour suspended solids (MLSS) concentration

– Leads to large flocs

~1mm

DO

NH4+

Bulk Liquid Biofilm

NO3-

BOD

Sub

stra

tum

DO

NH4+

NO3-

BOD

Biofilm Bulk Liquid


• Simultaneous nitrification and denitrification

– SND Switch in Biowin

– Means for accounting for SND• Floc diameter

• Nitrate reductase activity

0

2

4

6

8

10

12

14

16

18

0 0.1 0.2 0.3 0.4 0.5 0.6

SND "Switch" (mgO2/L)

Eff

luen

t N

itra

te (

mgN

/L)


• Headwater streams

– Nitrate from agriculture

– Some denitrification occurs in streams

– Limited by:• Oxygen

• Electron donor availability


• Denitrification with elemental sulfur

– Sulfur can serve as an electron donor for autotrophic denitrification

– Sulfur is solubilized by sulfur oxidizing bacteria in biofilms

– Sulfur diffuses through the biofilm• Used by both aerobic and anoxic metabolisms

DOBulk Liquid

Biofilm/Sediment

NO3-

Sulfur Bed

So SO42-


• Initial results

– Thin biofilms on sulfur particles (10-50 m)

– Denitrification rates 5 to 35 times as high as baseline rates• 0.5 gN/m2-day

– Significant sulfate production

Read-Daily et al. (submitted) Water Research

Future Needs

• New “environments”

• Modeling

• GHG production

Future Needs

• Membrane aerated biofilms (MABs)

– Co-diffusion biofilms• Solid substratum

• All substrate from bulk liquid

– Counter-diffusion biofilms• Porous substratum

• Delivery of oxygen from substratum

• Other substrates from bulk liquid

DO

NH4+

Bulk Liquid Biofilm

NO3-

BOD

Sub

stra

tum

DO

NO3-

Future Needs

• Hybrid Membrane Biofilm Process (HMBP)

– Similar to IFAS

– Attachment in Activated Sludge Process

– Bench-scale tests:• Aerobic biofilm, anoxic bulk liquid resulted in high total nitrogen (TN)

removal (Downing and Nerenberg, 2007)

• Ecology: nitrifiers in attachment, heterotrophs in suspension (Downing and Nerenberg, 2008a, 2008b)

– Pilot-scale testing to determine scale-up

Future Needs

• Hybrid Membrane Biofilm Process (HMBP)

– Pilot testing in conjunction with Metcalf&Eddy/AECOM

– Varied loading over 8 months

Downing et al. (2009) Water Environment Research

0

5

10

15

20

25

30

35

40

45

50

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

Day

Conce

ntr

atio

n (

mgN

/L)

NOx Effluent Ammonia Nitrogen Removed

A DCB

Future Needs

• Similar nitrification rates as IFAS

• High levels of denitrification

0

5

10

15

20

25

30

0.29 0.33 0.5 0.94

Nitrogen Loading (g m-2

day-1

)

Co

nce

ntr

atio

n (

gN

m-3

)

Influent TN

Effluent Ammonia

Effluent TN

Downing et al. (2009) Water Environment Research

Future Needs

• Modeling

– Mass transfer

– Biological consumption

– Biofilm structure

– Microbial competition

– Complexity vs. applicability

Boltz et al. (2009) Water Environment Research

Future Needs

• Greenhouse Gas (GHG) Emissions

– Nitrous oxide emissions during nitrification

– EPA has already set preliminary emissions values for WWTP

– Ratio of / max has been shown to be key to this production (Ahn et al., 2009)

NH4+

N2

+2e-

DB

NO2-

NO2-

NO3-

N2O

Future Needs

• GHG emissions controls

– max is the maximum growth rate for bacterial strain

– is the actual growth rate

Temperature Substrate Acceptor pH

Future Needs

• GHG production during nitrification

DO

NH4+

Bulk Liquid Biofilm

NO3-

BOD

Sub

stra

tum

Future Needs

• GHG production in IFAS units

– Joint project between SMU (Prof. Jim Yu) and FNI

– Compare liquid N2O concentration

– Floating carriers (BioPortz)

– Rope media (BioWeb)

Environmental Microbiology LabSouthern Methodist University

Future Needs

• Fundamental biofilm research

– Nerenberg lab at UND

– Microsensors and FISH

Summary

• Biofilms are unique microbial systems

– Physical, physiologically, and environmentally

• Application of biofilms has been around a long time

– First applications in 1890s

• Biofilms are here to stay

– One of the hottest topics in the water environment field

• Questions still remain…

Questions?


• Clarifiers

– Sludge blanket denitrification

– 4-6 mgN/L removed

biofilm in the water environment field · 2014-09-11 · •biofilms are unique microbial systems...

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