Topics in Current Chemistry (2020) 378:29
1 3
immersed tubes should be at a location where there is no interference with the passage of the ultrasound. The system can be tuned to use the appropriate combination
of solar and UV irradiations, depending on the operating conditions (incident intensity of solar irradiation, initial loading of the effluent, etc.). The irradiation time for
UV irradiations can be adjusted to a minimum based on the composition of the effluent, which should result in savings due to the maximum use of natural resources.
Agitation would be required so as to appropriately distribute the solid catalyst in
suspension as well as to achieve mixing of any supporting oxidants introduced in
the system. The proposed design should offer flexibility in both batch and continuous modes of operation, depending on the application to a specific effluent treatment
plant.
4.2 Synergy Index
The synergy index is an important factor governing the efficacy of the hybrid processes, and it has been quantitatively measured in most of the studies conducted to
date. The value of this index provides a quantitative estimate of the enhancement of
performance by using the combination of sonolysis with photocatalysis. Synergy is
measured using the rate constants obtained for US + catalyst, UV + catalyst and the
SPC oxidation process; however, there are variations in the calculations based on the
individual processes studied [49]. The general representation of the synergy index
can be given as:
where K is the rate constant for the specific processes mentioned in the subscript in
the equation. For the process to be synergistic, or for a positive enhancement using
combinations, the synergy index has to be more than unity. The actual value of the
synergy index has been seen to strongly depend on the type of pollutant, mostly on
the rate of utilization of the generated hydroxyl radicals by the pollutants depending on the specific reactivity. For example, the kinetic rate constant reported for the
combined US + UV + TiO 2 approach applied for the degradation of ofloxacin was
0.1054 min
−1
, whereas the combined rate constants for the individual approaches
were 0.0916 min
−1
, giving an synergistic index of 1.15 [56]. In another study on
the degradation of rhodamine B [57], a synergy index of 2.76 was reported for the
combined operation at the optimum ultrasonic operating condition of a power of
210 W. Sunasee et al. [58] reported a synergy index of 2.2 for the degradation of
bisphenol A using ultrasound at the optimum power of 50 W and TiO 2 (Degussa
P25) as the photocatalyst. Vinoth et al. [59] studied the SPC degradation of methyl
orange as the model pollutant using TiO 2 –NiO photocatalysts obtained with different NiO loading. These authors reported that under optimum 10 wt% NiO loading,
a synergy index of 4.8 was obtained for the combination approach applied using
the diffused sunlight [59]. For selecting the possible combination of ultrasound with
photocatalysis, the synergy index needs to be established based on feasibility studies
Synergy Index =
K US+UV+Catalyst
K US or US+Catalyst + K UV+Catalyst
,
86
Reprinted from the journal
1 3
immersed tubes should be at a location where there is no interference with the passage of the ultrasound. The system can be tuned to use the appropriate combination
of solar and UV irradiations, depending on the operating conditions (incident intensity of solar irradiation, initial loading of the effluent, etc.). The irradiation time for
UV irradiations can be adjusted to a minimum based on the composition of the effluent, which should result in savings due to the maximum use of natural resources.
Agitation would be required so as to appropriately distribute the solid catalyst in
suspension as well as to achieve mixing of any supporting oxidants introduced in
the system. The proposed design should offer flexibility in both batch and continuous modes of operation, depending on the application to a specific effluent treatment
plant.
4.2 Synergy Index
The synergy index is an important factor governing the efficacy of the hybrid processes, and it has been quantitatively measured in most of the studies conducted to
date. The value of this index provides a quantitative estimate of the enhancement of
performance by using the combination of sonolysis with photocatalysis. Synergy is
measured using the rate constants obtained for US + catalyst, UV + catalyst and the
SPC oxidation process; however, there are variations in the calculations based on the
individual processes studied [49]. The general representation of the synergy index
can be given as:
where K is the rate constant for the specific processes mentioned in the subscript in
the equation. For the process to be synergistic, or for a positive enhancement using
combinations, the synergy index has to be more than unity. The actual value of the
synergy index has been seen to strongly depend on the type of pollutant, mostly on
the rate of utilization of the generated hydroxyl radicals by the pollutants depending on the specific reactivity. For example, the kinetic rate constant reported for the
combined US + UV + TiO 2 approach applied for the degradation of ofloxacin was
0.1054 min
−1
, whereas the combined rate constants for the individual approaches
were 0.0916 min
−1
, giving an synergistic index of 1.15 [56]. In another study on
the degradation of rhodamine B [57], a synergy index of 2.76 was reported for the
combined operation at the optimum ultrasonic operating condition of a power of
210 W. Sunasee et al. [58] reported a synergy index of 2.2 for the degradation of
bisphenol A using ultrasound at the optimum power of 50 W and TiO 2 (Degussa
P25) as the photocatalyst. Vinoth et al. [59] studied the SPC degradation of methyl
orange as the model pollutant using TiO 2 –NiO photocatalysts obtained with different NiO loading. These authors reported that under optimum 10 wt% NiO loading,
a synergy index of 4.8 was obtained for the combination approach applied using
the diffused sunlight [59]. For selecting the possible combination of ultrasound with
photocatalysis, the synergy index needs to be established based on feasibility studies
Synergy Index =
K US+UV+Catalyst
K US or US+Catalyst + K UV+Catalyst
,
86
Reprinted from the journal