Environmental Engineering Reference
In-Depth Information
HþNO
2
! OHþNO
2
OH ! H
2
OþO
OþOH ! O
2
þH
with reaction constants
k
3
(Bradley et al.
1973
). Neglecting
transport, the entire set of reaction equations is as follows:
k
1
,
k
2
and
@
c
H
@t
¼
k
1
c
H
c
NO
2
þ
k
3
c
O
c
OH
@
c
H
2
O
@t
¼
k
2
c
OH
@
c
NO
@t
¼
k
1
c
H
c
NO
2
@c
NO
2
@t
¼
k
1
c
H
c
NO
2
@
c
O
@t
¼
k
2
c
2
OH
k
3
c
O
c
OH
@c
O
2
@t
¼
k
3
c
O
c
OH
@
c
OH
@t
¼
k
1
c
H
c
NO
2
k
2
c
2
OH
k
3
c
O
c
OH
with
k
1
¼
2.9,
k
2
¼
0.155 and
k
3
¼
1.1.
For high concentrations a maximum reaction rate
r
is approached, while for low
concentrations
q
is proportional to
c
(with proportionality constant
r=c
2
). If the
concentration
c
of the species coincides with the half-concentration parameter
c
2
,
half of the maximum rate is reached.
In some computer codes, the transition between linear and constant rate appears
at a specified characteristic value of the concentration. Such a distinction between
low and high concentration situations is used as a simpler alternative to Monod
kinetics. It is referred to as
Blackwell
kinetics and applied by van Cappellen and
Wang (
1995
) among others.
7.4 Bacteria Populations
In models one may also consider bacteria populations explicitly. If there is a high
abundance of bacteria, degradation processes are favoured. Vice versa, the abun-
dance of fuel favours bacteria population growth.
