CEE 697K - University of Massachusetts Amherst

20 Pages·2013·0.91 MB·English

11/19/2013
Updated: 19 November 2013 CEE 679 Kinetics Lecture #19 1
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CEE 697K
ENVIRONMENTAL REACTION KINETICS
Lecture #19
Chloramines Cont: Primary Literature
Enzyme Kinetics: basics
Brezonik, pp. 419-450
David A. Reckhow Introduction
Conclusions
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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
on pipe walls”
But this seems to contradict their introductory conclusion –how to reconcile?
CEE 679 Kinetics Lecture #19 David A. Reckhow
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What could they have concluded?
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Variability vs diurnal demand

30
25
20
Q/Qavg
15 u (ft/s)
t (hr)
C (ug/L)
10
5
0 CEE 679 Kinetics Lecture #19 David A. Reckhow
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Objective/hypothesis
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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
of physical parameters (e.g., fluid velocity) and biological
parameters (e.g., biodegradation kinetics, biomass density) on
HAA removal”
CEE 679 Kinetics Lecture #19 David A. Reckhow
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What could they have said?
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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
of biodegradation in distribution systems
CEE 679 Kinetics Lecture #19 David A. Reckhow
What could they have done?
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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?
CEE 679 Kinetics Lecture #19 David A. Reckhow
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What else?
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Consider mass

transfer
resistance within
biofilm
CEE 679 Kinetics Lecture #19 David A. Reckhow
What should be done next?
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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
CEE 679 Kinetics Lecture #19 David A. Reckhow
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 B1: biologically fixed bacteria
 B2: adsorbed bacteria
SANCHO Model
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Input Internal Processes Output
(H1, H2, B3)
BDOC CO2
H2
Cl Cl
2 2
Free
Bacteria
H1 S B3 Mortality
Cl
2
B2
Mortality B1
Fixed Bacteria
CEE 679 Kinetics Lecture #19 David A. Reckhow
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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.
CEE 679 Kinetics Lecture #19 David A. Reckhow
Enzymatic Reactions
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Many ways of illustrating the steps

Substrate(s) bond to active site
Product(s) form via transition state
Product(s) are released
CEE 679 Kinetics Lecture #19 David A. Reckhow
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Note that some
Basic Enzyme Kinetics
references use k
2
for k , and k for k
-1 3 2
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 Irreversible E + S ←→ k 1 ES k2 E + P
Single intermediate k-1
The overall rate is determined by the RLS, k
2
d[S] d[P]
r    k [ES]
dt dt 2
But we don’t know [ES], so we can get it by the SS mass
balance d[ES]
0k [E][S]k [ES]k [ES]
dt 1 1 2
Again, we only know [E ] or [E ], not free [E], so:
o tot
 
0 k [E ][ES][S]k [ES]k [ES]
1 o 1 2
CEE 679 Kinetics Lecture #19 David A. Reckhow
Reactants, products and Intermediates
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Simple Progression of

components for simple
single intermediate enzyme
reaction
 Shaded block shows steady
state intermediates
 Assumes [S]>>[E]
t
 From Segel, 1975; Enzyme
Kinetics
CEE 679 Kinetics Lecture #19 David A. Reckhow
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Basic Enzyme Kinetics II
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And solving for [ES],

k [ES][S]k [ES]k [ES] k [E ][S]
1 1 2 1 o
k [E ][S]
[ES] 1 o
k [S]k k
1 1 2
[E ][S]
[ES] o
[S] k1k2
k
1
CEE 679 Kinetics Lecture #19 David A. Reckhow
Michaelis-Menten
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 Irreversible E + S ←→ k 1 ES k2 E + P
Single intermediate k-1
d[P]
r   k [ES]
dt 2
[E ][S]
[ES] o
[S] k1k2
k
1
d[P] k [E ][S] r [S]
r   2 o  max
dt k1k2 [S] K [S]
k s
1
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Michaelis Menten Kinetics
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Classical substrate plot

rmax
100
80
e
at
R
n 60
ctio 0.5rmax
a
e
R 40
K d[P] r [S]
s r   max
dt K [S]
20 s
0
0 20 40 60 80 100 120
CEE 679 Kinetics Lecture #19 David A. Reckhow
Substrate Concentration
Substrate and growth
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d[P] d[S] 1 dX
 If we consider Y r   
dt dt Y dt
We can define a microorganism-specific substrate

utilization rate, U dX
r 
U   dt 
X YX Y
And the maximum rates are then 
 U k max
max Y
1 d[S] k[S] 1 d[X]  [S]
U   and   max
X dt K [S] X dt K [S]
s s
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