86 Reaction between hydroperoxide anion HO
2 -
and hydroxyl radical HO
•
generates a less reactive radical i.e. hydroperoxyl radical HO
2
• Equation 2.32 and
hence decrease in degradation rate. Similar trend was also reported for the degradation of dimethyl phthalate DMP and microcystin-LR MCLR using UV
H
2
O
2
by Xu et al. and Ren et al., respectively [132, 140]. They concluded that, the optimum pH for MCLR was at 7.2 and that for DMP was 4.0, for the degradation of
the respective compounds using UVH
2
O
2
process. The optimum pH condition for the degradation of different compounds using UVH
2
O
2
process depends mainly on the characteristic of the individual compounds.
4.1.6 Effect of Temperature
The effect of reaction temperature on the removal of organic carbon during the MDEA degradation using UVH
2
O
2
is shown in Figure 4.13. The experiments were carried out at four different temperatures while maintaining the volume of liquid
400 ml, UV intensity 12.06 mWcm
2
, concentration of MDEA 2000 ppm, concentration of H
2
O
2
0.18 M, and pH 7 as constant. Range of temperature studied was 20
⁰C – 50 ⁰C.
The effect of temperature was reported by Xu et al. [139] for the degradation of diethyl phthalate DEP using UVH
2
O
2
. They concluded that, by varying reaction temperature from 15
⁰C to 31⁰C did not show any significant change in DEP removal 76.2 to 80.5, respectively. However it can be seen from Figure 4.13 that by an
increase in the temperature up to 40 ⁰C, reduction of organic carbon increases very
little and beyond which the degradation rate of organic carbon started decreasing. An increase in the degradation rate of organic carbon with an increase in
temperature 20 to 40 ⁰C may be due to the increasing collision frequency between
MDEA and hydroxyl radical in the system [142]. Masschelein [31] also stated that the highest effectiveness of LP Hg UV lamp the UV lamp that was used to emit the
photon was at 40 ⁰C. Therefore more photons were provided for photolysis of H
2
O
2
.
87 Hence, more hydroxyl radicals were generated and hence increased the removal of
organic carbon up to 67.94 during the MDEA degradation using UVH
2
O
2
process Figure 4.14. This result is in agreement with those reported by Li et al. [142]. They
reported that the degradation rate of clofibric acid in the effluent using UVH
2
O
2
increased by increasing the reaction temperature.
Figure 4. 13 The degradation profile of organic carbon at different temperature
When the temperature of reaction was at 10 ⁰C, 80 minutes reaction time was required
to nearly complete the degradation process, whereas the temperature of reaction was increased to 30
⁰C, a nearly complete degradation was achieved within 15 minutes of reaction time. In this present study, the reaction temperature beyond 40
⁰C was found to decrease the degradation rate. This might be due to the decomposition of H
2
O
2
itself at higher temperatures [29, 155].
88
Figure 4. 14 Effect of temperature on TOC removal.
4.1.7 Optimization Process of MDEA Degradation by using UVH
