Environmental Engineering Reference
In-Depth Information
h
tr
+
+ H
2
O
2
2H
+
+ O
2
(Eq. 3.22)
h
tr
+
+ H
2
O
2
+ OH
-
H
2
O + HO
2
•
(Eq. 3.23)
HO
2
• + OH• H
2
O + O
2
(Eq. 3.24)
Aeration is generally adopted for this purpose to provide economic source of
oxygen as well as providing homogenous mixing. Jeon et al. (2005) have reported that
the degradation of TCE in 80 min is 33% for the reactor supplied by nitrogen, 54% for
that without gas flow, and 70% for that with oxygen supply (Figure 3.13). The results
also indicate that there is no significant difference in the final conversion when air or
pure oxygen is used as a gas source. However, some research groups have reported that
there is no appreciable inhibition in the absence of oxygen (Dijkstra et al., 2001;
McMurray et al., 2006). This observation could be reasoned as that the oxygen
depletion requires about 20 min to exhibit a rate difference, which, obviously, also
depends on the individual reaction system (Jeon et al., 2005). Thus, air can be safely
used as commercial scale operation instead of pure oxygen, which is expected to be the
most cost effective method to improve the photocatalytic performance.
80
100
(a)
(b)
80
60
60
40
40
20
Without Gas Flow
Oxygen
Nitrogen
20
0
0
0
20
40
60
80
0
5
10
15
20
25
30
Reaction Time, min
Reaction Time, min
Figure 3.13
Variation of photodegradation conversion with oxygen, without gas, and
nitrogen supplies. (a) 0.2 wt% Degussa P-25 TiO
2
, 4 BLB lamp (k = 365 nm), Q
1
= 0.2
L/min, 40 ppm TCE, () oxygen, () without gas, and (
) nitrogen. (b) 0.2 wt% Degussa
P-25 TiO
2
, 4 BLB lamps, Q
l
= 0.2 L/min, ε
g
= 0.035, 40 ppm TCE, () nitrogen supply,
() air supply, () oxygen supply; and 0.1 wt% Degussa P-25 TiO
2
, 1 BLB lamp,
g
= 0,
5.3 ppm phenol, Q
l
= 0.3 L/min, (
) air, (
U
) oxygen (Replotted from Jeon et al., 2005).
3.4.5 Solution pH
The solution pH has multiple effects on the photocatalytic process (Tseng and
Huang, 1990; Konstantinou and Albanis, 2004). Tseng and Huang (1990) have
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