[PDF] - CEE 670 TRANSPORT PROCESSES IN ENVIRONMENTAL AND WATER RESOURCES PDF Document

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CEE 670

TRANSPORT PROCESSES IN ENVIRONMENTAL AND WATER RESOURCES ENGINEERING

Surface Reactions

David A. Reckhow

CEE 670 Kinetics Lecture #10 1

Updated: 8 December 2011

Print version

Kinetics Lecture #10

Surface Reactions: Pipe walls & degradation in Distribution Systems Primary Literature

Seasonal Variability & Biodegradation

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 Chen & Weisel study  JAWWA, April 1998  Intensive study of Elizabethtown, NJ system  125 MGD conventional plant  4.9 mg/L DOC (raw water average)  pH 7.2

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Elizabethtown, NJ: THMs

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Elizabethtown, NJ: TCAA

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HAA Degradation

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 Biodegradation:

dihaloacetic acids degrade more readily than

trihaloacetic acids

On BAC

 MHAA>DHAA>THAA  Wu & Xie, 2005 [JAWWA 97:11:94]

In distribution systems

 DHAA>MHAA>THAA  Many studies

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Degradation in Dist. Systems

6 Town Hall; Norwood, MA

Date

1 / 1 / 1 9 9 9 1 / 1 / 2 1 / 1 / 2 1 1 / 1 / 2 2 1 / 1 / 2 3 1 / 1 / 2 4 1 / 1 / 2 5 1 / 1 / 2 6

Concentration (g/L)

20 40 60 80 100 120 TTHM HAA5

Pier 1; Norwood, MA

Date

1 / 1 / 1 9 9 9 1 / 1 / 2 1 / 1 / 2 1 1 / 1 / 2 2 1 / 1 / 2 3 1 / 1 / 2 4 1 / 1 / 2 5 1 / 1 / 2 6

Concentration (g/L)

20 40 60 80 100 120 TTHM HAA5

Example: Norwood, MA

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Degradation of HAAs

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 Norwood, MA example

Percentile

20 40 60 80 100

HAA/THM Ratio (g/g)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 Town Hall Pier 1 No Degradation Degradation David A. Reckhow

CEE 670 Kinetics Lecture #6

Why the loss of HAAs?

 Homogeneous Chemical Decomposition ?  Decarboxylation  What is half-life

 Is it too slow to be very important?

 Dehalogenation

 Probably too slow for chlorinated HAAs  Reaction with reduced pipe materials?

 Abiotic reductive dehalogenation not likely either,

especially for DCAA

 Biodegradation?

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A few recent studies

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 Modeling HAA Biodegradation in Biofilters and

Distribution Systems

 Alina S. Grigorescu and Ray Hozalski, University of

Minnesota at Minneapolis

Journal AWWA, July 2010, 102(7)67-80

Background conclusion?

 “Thus aerobic biodegradation is believed to be the

dominant HAA degradation process in ….…..water distribution systems”

 Citing: Tung & Xie, 2009; Zhang et al., 2009a; 2009b;

Bayless & Andrews, 2008

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Objective/hypothesis

 Not really stated, but they did end the intro with:  “In this work, computer simulations were performed to predict

the fate of three HAAs (MCAA, DCAA, and TCAA) along a distribution system and within a biologically active filter. Sensitivity analyses were performed to investigate the effects

f physical parameters (e.g., fluid velocity) and biological

parameters (e.g., biodegradation kinetics, biomass density) on HAA removal”

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Transport Model

 Loss of HAAs in a pipe  One dimensional plug flow  Overall rate is a combination of rate of

biodegradation (kra) and mass transfer (kma)

 

U x

verall

k

e C C





ra ma

k k

verall

k

1 1

1  

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Biodegradation model

 Monod model  Simplified for low C

C K kXC dt dC

M 

  XC k XC K k dt dC

r M

   

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Biodegradation model II

 Biodegradation rate (kra; in day-1) is the pseudo-

first order biodegradation rate constant (kr; in L/day/µg-protein) times the biofilm density (X; in µg-protein/cm2) and the specific surface area (a; in m-1)

   

L m cm r L m cm r ra

d X k Xa k k

2 2

10 10

4  

Where d is the pipe diameter in meters

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Mass Transfer Model I

 Mass transfer constant (kma) is the mass transfer velocity (km;

m/s) times the specific surface area; and km is related to the Sherwood number

 combining  Linton & Sherwood (1950) found the following correlation for

flow in pipes (fn(Reynolds and Schmidt numbers)):

2

4 d ShD a d ShD a k k

w w m ma

  

33 . 83 .

Re 023 . Sc Sh 

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d ShD k

w m 

a k k

m ma 

Compare to equ 7.126 in Clark Eq 7.164 in Clark

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Mass Transfer Model II

 The Schmidt number is the ratio of mass to viscous diffusion

timescales, and calculated from the viscosity, the density and the diffusion coefficient:

 And the Reynolds number can be calculated from the pipe

diameter, velocity, density and viscosity:

w w w

D Sc   

w w

du    Re

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Compare to equ 7.82 in Clark

Model Predictions

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 “Overall the model calculations suggest that

biodegradation is…..not likely to play a major role in most water distribution systems”

 “the conditions needed for significant HAA removals in a

distribution system (i.e., total biomass densities > 105 cells/cm2 over long distances of pipe) are unlikely in the US water distribution systems where total chlorine residuals typically are high and thus inhibit the development of biofilm

n pipe walls”

But this seems to contradict their introductory conclusion – how to reconcile?

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What could they have concluded?

 Variability vs diurnal demand

5 10 15 20 25 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Q/Qavg u (ft/s) t (hr) C (ug/L) David A. Reckhow

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Objective/hypothesis

 Not really stated, but they did end the intro with:  “In this work, computer simulations were performed to predict

the fate of three HAAs (MCAA, DCAA, and TCAA) along a distribution system and within a biologically active filter. Sensitivity analyses were performed to investigate the effects

f physical parameters (e.g., fluid velocity) and biological

parameters (e.g., biodegradation kinetics, biomass density) on HAA removal”

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CEE 670 Kinetics Lecture #10

What could they have said?

 To determined if observed HAA loss could be

attributed to biodegradation on pipe walls given known physical and microbial characteristics of distribution systems

 To estimate spatial and temporal variability of HAA

concentrations based on a rational physical model

f biodegradation in distribution systems

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What could they have done?

 Find some direct evidence for biodegradation of

HAAs in distribution systems

 A product of the enzymatic reaction?  Chlorohydroxyacetate?  Evidence of abiotic reactions?  Increase in MCAA?

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What else?

 Consider mass

transfer resistance within biofilm

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What should be done next?

 Experimental Work  In-situ controlled study of flow velocity vs DCAA loss in

a pipe segment?

 Effect of biocide in above segment?  Model Refinement  Account for internal mass transfer resistance  Combine with growth model for HAA degraders

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SANCHO Model

 B1: biologically fixed bacteria  B2: adsorbed bacteria 30

B1 B2 H1

H2

S CO2

Cl2 Mortality

B3

Cl2 Cl2

Mortality

BDOC

Fixed Bacteria

Free Bacteria

Input (H1, H2, B3) Output Internal Processes

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Effect of Zn on HAAs

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 Effect of Zinc on the Transformation of HAAs in

Drinking Water

 Wei Wang and Lizhong Zhu  Journal of Hazardous Materials 174:40-46.

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 End