70
Figure 4.18
Continuous addition of H
2
O
2
and FeSO
4
;7H
2
O 5000 ppm DEA + 54.8 ml H
2
O
2
30 + 2.5 g FeSO
4
;7H
2
O at pH 3
4.1.7 Comparison of COD and TOC
The reduction profile of COD and TOC on DEA oxidation by Fenton’s reagent was similar. Degradation of COD and TOC decreased fast in the initial time
of reaction and than slower down. Figure 4.19 shows the corresponding of COD and TOC progress.
Oxidation of an organic compound by hydroxyl radical possibly proceed through abstraction of hydrogen atoms principal to formation of carboxylic acid.
Further degradation eventually leads to CO
2
and H
2
O. The presence of an organic acid such glycine has been identified in this study. The carboxylic acids are well
known react slowly with hydroxyl radical. Consequently it is predictable that degradation of COD should be faster than reduction of TOC.
71
Figure 4.19 COD and TOC profile
by Fenton’s reagent on DEA degradation {10000 ppm and 16000 ppm DEA initial concentration}.
The measurement was conducted in two different initial concentrations of DEA. Those are 10000 ppm and 16000 ppm of DEA under identical condition. The
reductions of COD were 36.3 and 43.2 respectively. While the TOC reductions were 9.8 and 16.53 respectively.
Since the COD removed by Fenton treatment mostly oxidize H atoms and the C atoms is slow to remove by Fenton’s reagent, hence the biological oxidation is to
be exploited in order to achieve of COD standard on wastewater effluent.
72
4.1.8 Degradation Intermediates after Fenton Oxidation
Oxidation of an organic compound such as MEA and DEA by hydroxyl radical may proceed through abstraction of hydrogen atoms or lead to the formation
of carboxylic acids which are further degraded to smaller fragment and eventually to CO
2
and H
2
O when enough hydroxyl radical is available. Under the acidic pH conditions, the amino group is protonated to certain level, which might deactivate the
α-CH bond. Consequently, a further located C- atom of the amine is oxidized. Thus an amino-acid is a possible product.
An attempt to identify the degradation interme diate products after Fenton’s
treatment was made. HPLC and FTIR were used to characterize the intermediates. The chromatogram Figure 4.20 shows a few peaks. One of the peaks is of glycine
that appears at 4 minute. Peak for MEA appears at 5.1 minute, while peak for DEA appears at 5.4 minute. FTIR spectrums give stronger evidence about functional group
of partially degraded alkanolamine. Infrared spectra of glycine and partially degraded alkanolamine were similar. The infrared spectra of partially degraded amine DEA
also gave a similar output. It indicates the presence of a common component. A carbonyl C = O peak appears around 1620 - cm
-1
[C = O as carboxylic acid] and bonding between C and N appear on the center of peak 1080cm
-1
[C – N as aliphatic
amine]. The sample was in aqueous solution and therefore a broad peak of water H
2
O appears in the region between 3000 – 3700 cm
-1
and covering many peaks for N
– H amine, O – H carboxylic acid and O – H alcohol that should be appear on that region. In addition, peaks with center 2090 cm
-1
appear as interaction of COO
-
from carboxylic group and N
+
from ammonium group [Silverstein et al 2005; Coates 2000]. Infrared spectra of partially degraded MEA and DEA depicted in
Figure 4.22 and 4.23.
73
Figure 4.20 A Chromatogram of MEA, partially degraded MEA and Glycine.
B Chromatogram of DEA, partially degraded DEA and Glycine.
Figure 4.21 Infrared spectra of Glycine
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Figure 4.22 Infrared spectra of partially degraded MEA
Figure 4.23 Infrared spectra of partially degraded DEA
75
4.1.9 A simplified Rate Model for Mineralization
