79
Figure 4. 6 Effect of initial concentration of MDEA on TOC removal after 360
minute reaction time.
In this preliminary study on effect of initial concentration of MDEA, there was found no optimum concentration for degradation. However, based on the observed
results, the suitable initial concentration for this experiment was found to be 2000 ppm of MDEA =1000 ppm TOC. The maximum degradation occurs at 3 hours, and
for this concentration it was found to be accurate and easy to follow the TOC profile with time. Hence all the further experiments were conducted using 2000 ppm of
MDEA.
4.1.3 Effect of UV Intensity in Combination with H
2
O
2
Experiments were conducted to study the effect of the UV intensity on the organic carbon degradation at three intensity level 3.67
– 12.06 mWcm
2
. For an initial concentration of MDEA = 2000 ppm, initial concentration of H
2
O
2
= 0.12 M, initial pH = 7.0, temperature = 30 ºC, the percentage of TOC removal was found to be
80 19.37, 42.42, and 58.95, for the UV intensity of 3.67 mWcm
2
, 7.35 mWcm
2
, and 12.06 mWcm
2
respectively with 180 minutes of reaction time Figure 4.7.
Figure 4. 7
The degradation profile of organic carbon for different UV intensities.
The results showed that degradation rate increased with an increase in UV intensity, which might be attributed to the reason that the effective role of light power
towards the formation of high amount of hydroxyl radical in the solution, which are in concurrence with the reported literature [137
– 140]. Qiao et al. [135] reported that by increasing UV intensity from 0 to 7.35 mWcm
2
, the degradation of microcystin-RR was complete within 60 minutes of reaction time Asilian et al. [138] reported the
same trend for the degradation of polychlorinated biphenyl PCB in the water solution by using photochemical process. The degradation efficiency of this
compound significantly increased with an increase in UV intensity. Increasing UV intensity will increase the driving force for photolysis reaction, which involves UV
energy to excite PCB molecule followed by the cleavage of C-Cl bond. Xu et al. [129] reported that increasing UV intensity enhances the degradation of diethyl
phthalate in the UVH
2
O
2
process. In addition, oxidative degradation of microsystin-
81 LR by using UVH
2
O
2
also enhanced by increasing the UV intensity as reported by Ren et al. [140].
Based on the results of these experiments and also based on our laboratory limitation, the UV intensity at 12.06 mWcm
2
was the highest intensity that gave the highest degradation efficiency i.e. 58.95 TOC removal Figure 4.8, and hence an
intensity of 12.06 mWcm
2
was used for further degradation experiments.
Figure 4. 8 Effect of different UV intensity on TOC removal.
4.1.4 Effect of Initial Concentration of H
