Biofilm2009_JoshuaBoltz.pdf

1WWWEST 2009 Lyngby, Denmark5/6/2009

Application of biofilm models in engineering design: a critical analysis of uncertainty

Presented by:Joshua P. Boltz

Seminar:Model Based Optimization of Biofilm Systems in Wastewater Treatment

Organized by:MOSTforWATER

in collaboration with theDanish Hydraulic Institute, DHITechnical University of Denmark, DTU

Ph.D. P.E., Biofilm Technologies Community of Practice Leader, CH2M HILL, 4350 W. Cypress Street, Suite 600, Tampa, FL, USA


A more fundamental approach to describing biofilm reactors driving factors

Existing biofilm models Using biofilm models to describe biofilm-reactors Biofilm-reactor modules in WWTP models Introducing the concept of uncertainty to biofilm-

reactor models Discussing biofilm-reactor modeling uncertainty Conclusions Questions

Presentation Outline


Models are commonly used in practice wastewater master planning WWTP design WWTP optimization Biological process pilot testing (and more)

Consultants and clients generally have confidence in the value added by WWTP simulation efforts

Benefits to biofilm reactors are attractive reliable robust easy to operate compact

Biofilm modelling has matured: deductive approach supports use in practice



Model Compartments and Biofilm Processes Considered

Compartments: Completely-mixed bulk phase

Water Suspended biomass

Mass-transfer boundary layer (LL) Biofilm (LF) Biofilm carrier (a [=] m2 m-3)

Major Biofilm Processes: Flux of soluble substrate i

Ji [=] g m-2 d-1 External mass transfer Internal mass transfer & reaction Electron donor vs. acceptor limitations

TSS detachment/attachment

=

=

n

kkFF XX

1,

LF LL Bulk-phase

Si

z

JJ = SB,i

SLF,iSF,i

a


Existing biofilm modelsSpatial complexity

1980 1985 1990 1995

M

o

d

e

l

D

e

s

c

r

i

p

t

i

o

n

R

e

n

d

e

r

i

n

g

1975

Steady-state Pseudo-

Analytical 1 Analytical 2 Numerical 3

1-D heterogeneous

3-Dflow

2000 2005

S

zz

S

Dynamic Numerical 4,5, 6

Dynamic Numerical 7,8

Year

C

o

m

p

u

t

a

t

i

o

n

I

n

t

e

n

s

i

t

y

a

n

d

C

a

l

c

u

l

a

t

i

o

n

T

i

m

e

1-D homogeneous

2-Dno flow

SBSLF

SBSLF

LFLF LL LL

1 Williamson and McCarty (1976)2 Harremos (1978)

3 Harris and Hansford (1978)4 Kissel et al. (1984)

5 Wanner and Gujer (1986)6 Wanner and Reichert (1996)

7 Picioreanu et al. (1998)8 Picioreanu et al. (2003)

*www.biofilms.bt.tudelft.nl/material.html

* *


Complex model structure Biofilm development/experiment1 day 3 day

MODEL OBJECTIVE

The type of biofilm model used is objective specific.No consensus biofilm model exists as for activated sludge

Biofilm reactor design Simple model

z

z

S

SBSLF

LF LL

S

z z

R1 R2 RnL


The "best" model for a particular application is the simplest model that will answer the question

MODEL OBJECTIVE

The type of biofilm model used is objective specific.No consensus biofilm model exists as for activated sludge

Biofilm reactor design Simple model

z

z

S

SBSLF

LF LL

S

z z

R1 R2 RnL


Description of biofilm reactor models used in engineering practice

Table: Boltz, J.P., Morgenroth, E., Sen, D. (2009). Mathematical modelling of biofilms and biofilm reactors for engineering design. Wat. Sci. Tech. submitted.


Description of biofilm reactor models used in engineering practice



Not all biofilm reactors were created equalRBC (top) and TF (bottom) MBBR and IFAS BAF (top) and MBfR (bottom)

Photos courtesy: Envirex, WesTech, Veolia, Severn Trent, and Applied Process Technology


Not all biofilm reactors were created equal

Typical Biofilm Thicknesses for a Variety of Biofilm Reactors

Typical biofilm thicknss (m) Type of Biofilm Reactor

Lower Estimate Upper Estimate

Moving Bed Biofilm Reactor 50 400

Biologically Active Filters 20 300

Fluidized Bed Biofilm Reactors 50 400

Rotating Biological Contactors 200 2,000

Trickling Filters 200 2,000

Membrane Biofilm Reactors 50 500


Modeling Nitrifying Trickling Filters

Figure. Actual and Predicted Effluent form a NTF (Parker et al., 1995). Predicted Effluent was Calculated Using the Modified Gujer and Boller Model.

( ) ( ) zkNBN

NBON eSK

STJETzJ

+=

,

,

max,23.4,

Modified Gujer and Boller Model (Parker et al. 1995)


Nitrifying Trickling Filters, Complex System Dynamics


Modeling Integrated Fixed-Film Activated Sludge

Pro2D (Boltz et al. 2009a, 2009b)


What are the sources of uncertainty when modelling biofilm reactors in engineering practice?

Are adequate methods and techniques available, quantitative or qualitative, to evaluate model accuracy and sources of uncertainty?

How large is the gap between supporting basic research and existing biofilm models, dynamical and steady state used for engineering practice?

Do transparent and uniform biofilm reactor model calibration methods exist? If so, what is the appropriate level of calibration/validation?

What is the risk, and how does one quantify risk, of existing biofilm-reactor model misapplication?

Belia, E., Amerlinck Y., Benedetti L., Johnson B., Sin G., Vanrolleghem P., Gernaey K., Gillot S., Neumann M., Rieger L., Shaw A., and Villez, K. (2009). Wastewater treatment modelling: dealing with uncertainties. Wat. Sci. Tech. Submitted.

Uncertainty concept in WWTP modelsgeneral description by Belia et al. (2009)


Some sources of uncertainty in biofilm reactor modeling

LF LL Bulk-phase

Si

z

SB,i

SLF,iSF,i

a

Uncertainty Extent of mass transfer

resistance external to the biofilm surface (RL = LL/D; LL = ? m)

Fate of particulate substrate ( ) (hydrolysis, degradation, attachment)

Biofilm distribution in reactor and its impact

Biofilm detachment ( )

attach?

hydrolyze or detach?

hydrolyze or enjoy the ride?




reactor models Discussing biofilm-reactor modeling uncertainty:

the mass transfer boundary layer problem Conclusions Questions



Modeling the Mass Transfer Boundary Layer

Shc

LLL =

nmBA ScReSh +=

1.

2.

4.

cLU =Re ?=U

3.iaqD ,

Sc =

rLC

LC


Why be Concerned with Velocity?Should one not Simply Fit LL?

(1) As reported by manufacturer

12 mm x 12mm660 m2/m3ABC 5Siemens Water Technologies Corp.

15 mm x 22mm450 m2/m3ActiveCell 450Infilco Degremont, Inc.

12 mm x 25 mm500 m2/m3K3

7 mm x 9 mm500 m2/m3K1Kruger Inc.

Carrier Photograph

Nominal CarrierDimensions

(Height x Diameter)

Bulk Specific Area(1)

Carrier NameManufacturer

Comparison of Plastic Biofilm Carriers Potential Project Vendors


Mass transfer boundary layer



0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800

V = 0.17 cm/sV = 0.59 cm/sV = 2.05 cm/s

O

x

y

g

e

n

c

o

n

c

e

n

t

r

a

t

i

o

n

,

S

(

m

g

/

L

)

Distance from the substratum (microns)

SLF1

SLF3

SLF2

LL,3LL,2LL,1

Biofilm thickness, LF Bulk liquid

U1= 147 m hr-1

U2= 510 m hr-1

U3= 1,711 m hr-1

Variation in LL can lead to significant variability in SLF,i(consequently changing JLF,i)

Figure:Boltz, J.P., Morgenroth, E., Sen, D. (2009). Mathematical modelling of biofilms and biofilm reactors for engineering design. Wat. Sci. Tech. submitted.Data: Zhang, T.C., and Bishop, P.L. (1994). Experimental determination of the dissolved oxygen boundary layer and mass transfer resistance near the

fluid-biofilm interface. Wat. Sci. Tech. 30(11). 47-58.


0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800

V = 0.17 cm/sV = 0.59 cm/sV = 2.05 cm/s

O

x

y

g

e

n

c

o

n

c

e

n

t

r

a

t

i

o

n

,

S

(

m

g

/

L

)

Distance from the substratum (microns)

SLF1

SLF3

SLF2

LL,3LL,2LL,1

Biofilm thickness, LF Bulk liquid

U1= 147 m hr-1

U2= 510 m hr-1

U3= 1,711 m hr-1

Variation in LL can lead to significant variability in SB,i (consequently JLF,i)

Figure:Boltz, J.P., Morgenroth, E., Sen, D. (2009). Mathematical modelling of biofilms and biofilm reactors for engineering design. Wat. Sci. Tech. submitted.Data: Zhang, T.C., and Bishop, P.L. (1994). Experimental determination of the dissolved oxygen boundary layer and mass transfer resistance near the

fluid-biofilm interface. Wat. Sci. Tech. 30(11). 47-58.

Cause:Insufficient basic research exists.

Effect:Many uncertainties associated with biofilm-reactor models.


Calibration

Transparent and consistent biofilm model calibration methods do not exist.

Most biofilm-reactor model users do not know the role of radio dials nor how much to adjust the dial.

The true effectiveness of biofilm models cannot be gauged if over calibration is required

The inherent danger is creating a much larger black boxthan existed with previous design protocol

100

LL LF kde or kat

100




reactor models Discussing biofilm-reactor modeling uncertainty:

the mass transfer boundary layer problem Conclusions Questions



Conclusion

Practice demands a more fundamental biofilm reactor design approach. 1-D biofilm models are adequate for engineering practice. Not all biofilm reactors are well described with existing biofilm reactor

models. No consensus biofilm model exists as for activated sludge. Uncertainty in existing biofilm reactor models includes:

extent of RL fate of Xi biofilm distribution detachment

MTBL thickness exemplifies the existence inadequate methods of quantifying parameters of interest

Transparent and consistent biofilm model calibration methods do not exist.


Questions

Documents

Biofilm2009_JoshuaBoltz.pdf