ABSTRACT
In the present work, the degradation of magenta dye has been investigated using ultrasonic (US) and ultraviolet (UV) irradiation at a laboratory scale. Additionally, the investigation was conducted at a semi-pilot scale by employing hydrodynamic cavitation and a novel air-marble cavitation reactor. Initially, optimization studies such as the effect of initial dye concentration and catalyst loading of TiO2 and MnO2 followed by the effect of combined catalyst loading (TiO2 /MnO2 ) on the extent of degradation have been studied at a capacity of 3 L. It was observed that the US irradiation results in 87.1% and 68.2% of degradation, whereas the UV irradiation results in 79.8% and 56.4% extent of degradation at 1 g/l of TiO2 and 0.8 g/l of MnO2 , respectively. The maximum degradation was 92.1% at the combined loading of 0.6 g/l (1:0.8; TiO2 :MnO2 ) using US irradiation with a capacity of 3 L and 81.3% using a hydrodynamic cavitation reactor with a semi-pilot scale capacity of 7 L. The chemical oxygen demand (COD) analysis also showed the highest COD removal of 92% at a small scale using the US irradiation and 76% at a semi-pilot scale using hydrodynamic cavitation. On a small scale, the cost of a US/TiO2 + MnO2 treatment scheme is US$ 0.01/L, whereas on a semi-pilot scale using HC/TiO2 + MnO2 , the cost is US$ 0.04/L. Both of these treatment schemes offer viable pathways for degradation based on energy and economic assessments. Overall, the current work has clearly demonstrated the effectiveness of the cavitational reactor for the efficient degradation of magenta dye from lab to semi-pilot scale operation. PRACTITIONER POINTS: Small-scale dye containing wastewater treatment using ultrasound and ultraviolet irradiation Combined use of catalysts at large-scale operations with novel cavitation techniques Novel cavitation techniques studied for dye degradation. Energy efficiency and cost analysis evaluated for AOPs studies.
