3.2 Results and Discussion .1 Formation of FeCHPLCOM
3.2.2 CHPL and FeCHPLCOM degradation in FP, PFP and UVP
The use of Fe(II) as initial specie together with high initial concentrations of iron and hydrogen peroxide implies a high initial radicals generation. Consequently, the production of additional radicals is not important and that is why FP and PFP exhibited similar decomposition behaviour. The irradiation level used (12 W/m2) was medium favouring Fenton’s importance. Moreover, the role of UV was insignificant because that some intermediates of CHPL could reduce Fe3+ (Chen et al., 2009; Du et al., 2006). There was a slight higher removal in PFP which was confirmed from the repetition of experiments. Fe2+
and H2O2 doses were optimized in the concentration range from 1 to 2 and 5 to 25 mM (Figures 3.7 and 3.8). The optimal pH was found out by varying it in the range from 2 to 4 (Figures 3.9). The experimental optimization to maximize CHPL degradation was performed on the basis of PFP. The same condition (optimized) was in FP without UV light and UVP without Fe2+.
TOC reduction of around 56-60, 62-70 and 33-55% were observed at 2.5 and 10 min of oxidation in FP, PFP and UVP, respectively. The faster initial rate of TOC removal was due to mineralization of amide chain. The second stage was related to the opening and
mineralization of substituted benzene ring. Usually, the large molecular weight intermediates are either mineralized or broken to lower molecular weight fragments like oxalic and acetic acids. Kavitha et al. (2004) indicated that carboxylic acids are eliminated quickly in PFP during the first stage of oxidation. The faster CHPL and TOC removal also can be corroborated from the residual concentration of H2O2 and Fe2+. It was 1.3 and 45.2% for H2O2 and Fe2+, respectively, after 45 min of Fenton reaction. The results are in well accordance with the literature (Du et al., 2007; Kavitha et al., 2004).
Iron-chelation played an important role on CHPL mineralization. PFP exhibited higher degradation ability of such complexes under UV luminesces. Oxalic acid is formed during Fenton reactions. An iron(III)-oxalate complex gets stability through conjugation with Fe(III) due to availability of a vacant 3d orbital. But it could lose its stability because of UV light absorption (Kavitha et al., 2004; Kemp et al., 1991). We didn’t visualize any sludge formation in PFP. Sludge formed in FP was separated by filtration using 0.45 μm cellulose ester filter at the end of the experimental run with 1.75 mM Fe2+, 20 mM H2O2 and pH 3. It was washed with distilled water and dissolved in conc. H2SO4. CHPL and TOC reduction of 3.9 and 1.8% were observed due to adsorption on iron-sludge.
The decrease in peak intensities of CHPL and FeCHPLCOM is shown Figure 3.10. About 12.9 mg/L of CHPL was found to form FeCHPLCOM with 1.75 mM Fe2+ at pH. It gave an initial FeCHPLCOM (MW 381.2 g/mol) of 14.9 mg/L. H2O2 was added after 10 min of chelation time and the variation of CHPL and FeCHPLCOM concentrations is shown in Figure 3.11. In FP, around 92.7 and 80.7% decomposition of CHPL and FeCHPLCOM was noted in 45 min. It was 95.4 and 94.1% in PFP. Around 2.7 and 13.4% more CHPL and FeCHPLCOM decomposition took place in PFP. Only 2.3% more TOC reduction was found in PFP when both the reagents (Fe2+ and H2O2) were added together in CHPL solution.
FeCHPLCOM concentration was around 14.9, 7.3 and 0.63 mg/L at pH 3, 7 and 10, respectively. It is possible that the lone electron pair could be free at acidic pH. However, at neutral or alkaline medium, hydroxyl group (-OH) attached to C1 position gets deprotonated.
Therefore, the extent of FeCHPLCOM formation should gradually decrease with increase in pH. CHPL removals were of 95.4 and 92.7% in 45 min of PFP and FP treatment, respectively. Whereas UVP showed 82.9% removal (Figure 3.12). TOC removal efficiency decreased to 65.9% in UVP against 71.9 and 69.5% in PFP and FP, respectively.
0 10 20 30 40 50 30
40 50 60 70 80 90 100
Removal, %
Reaction time, min
Fe2+, mM:
1.0 1.25 1.5 1.75 2.0
Figure 3.7. Effect of Fe2+ on removal of CHPL in PFP. Experimental conditions: [CHPL]0 = 100 mg/L, H2O2= 20 mM, pH = 3.0 and temperature = 25°C. Photo-reaction with an UV lamp of 12 W/m2 (9W).
0 10 20 30 40 50
20 30 40 50 60 70 80 90 100
Removal, %
Reaction time, min
H2O2, mM:
5 10 15 20 25
Figure 3.8. Effect of H2O2 on removal of CHPL in PFP. Experimental conditions: [CHPL]0 = 100 mg/L, Fe2+ 1.75 mM, pH = 3.0 and temperature = 25°C. Photo-reaction with an UV lamp of 12 W/m2 (9 W).
0 10 20 30 40 50 20
40 60 80 100
Reaction time, min
Removal, %
pH:
2.0 2.5 3.0 3.5 4.0
Figure 3.9. Effect of pH on removal of CHPL in PFP. Experimental conditions: [CHPL]0 = 100 mg/L, Fe2+ 1.75 mM, H2O2 = 20 mM and temperature = 25°C. Photo-reaction with an UV lamp of 12 W/m2 (9 W).
2 4 6 8 10 12 14
2x105 4x105 6x105 8x105 1x106
Fe2+
NH
Cl Cl
O
N+
O- o OH
O
Retention time, min
OH
NH
Cl Cl
O
N+ O- o OH
Peak Area, mV
Pure CHPL Photo-Fenton
Fenton
Figure 3.10. Chromatogram of residual CHPL and FeCHPLCOM found in FP and PFP at 10 min of reaction. Experimental conditions: [CHPL]0 = 100 mg/L, Fe2+ 1.75 mM, H2O2 = 20 mM, pH = 3.0 and temperature = 25°C. Photo-reaction with an UV lamp of 12 W/m2 (9 W).
0 10 20 30 40 50 0
20 40 60 80 100
Reaction time, min
Concentration of CHPL and FeCHPLCOM, mg/L
PFP:
CHPL concentration FeCHPLCOM FP:
CHPL concentration FeCHPLCOM
Figure 3.11. CHPL Concentration (after to form up the complex with Fe2+ in 10 min) and FeCHPLCOM with reaction time in FP and PFP. Experimental conditions: [CHPL]0 = 100 mg/L, Fe2+ 1.75 mM, H2O2 = 20 mM, pH = 3.0 and temperature = 25°C. Photo-reaction with an UV lamp of 12 W/m2 (9 W).
0 10 20 30 40 50
0 20 40 60 80 100
Removal, %
Reaction time, min
CHPL:
PFP FP UVP TOC:
PFP FP UVP
Figure 3.12. CHPL and TOC removal with reaction time. Experimental condition: [CHPL]0
= 100 mg/L, pH = 3.0, Fe2+ = 1.75 mM (in FP and PFP), H2O2 = 22.5 mM (in FP, PFP and UVP) and temperature =25°C. Photo-reaction with an UV lamp of 12 W/m2 (9 W).