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Advanced Oxidation Technologies for Wastewater Treatment: An Overview 179

2 mm

22.61 6.4
17 mm

10 mm 18 mm 67 mm 10 mm
1mm
Figure 3.13 Schematic of cavitating device (circular venturi).

pressure gauges, and valves (see Figure 3.10). The degradation of imidaclo-
prid using HC was first optimized in terms of operating inlet pressure and
solution pH by carrying out experiments at different inlet pressures and
pHs. Further experiments were then conducted at the optimum inlet pressure
and solution pH of 2.7. The experiments using the combined process of HC
and H 2 O 2 were carried out at a different molar ratio of imidacloprid:H 2 O 2 to
establish the optimum loading of H 2 O 2 for the degradation of imidacloprid
using combined processes of HC and H 2 O 2 . Fenton chemistry was

employed along with HC at the optimum loading of imidacloprid:H 2 O 2
as 1:40 with the concentration of H 2 O 2 as 3.91 mmol/L and a varying molar
ratio of ferrous sulfate:H 2 O 2 as 1:50, 1:40, 1:30, and 1:20. Photo-Fenton
alone and HC+photo-Fenton processes were employed at the molar ratio
of imidacloprid:H 2 O 2 as 1:40 and a molar ratio of ferrous sulfate:H 2 O 2 as
1:40. Photocatalytic process alone and HC+photocatalytic processes were
employed using niobium pentoxide as a photocatalyst, due to its adequate
band gap of 3.4 eV and stability in acidic conditions. The amount of catalyst
used was 200 mg/L without any pretreatment. UV assembly was placed cen-
trally in a feed tank for UV irradiation as per the requirement.

3.6.1.1 Degradation of Imidacloprid Using HC-Based Hybrid Method
The degradation of imidacloprid using HC was carried out at different oper-
ating inlet pressures and solution pHs. The results obtained for different pro-
cesses are shown in Table 3.1. It was observed that the rate of degradation of
imidacloprid increases with an increase in the inlet pressure until 15 bar, after
which an increase in the inlet pressure does not have a significant effect on
the rate of degradation of imidacloprid. Also a lower pH of 2.7 is favorable
for the degradation of imidacloprid using HC. The maximum extent of deg-
radation of 6.15% was obtained with a reaction rate constant of