The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO2) as the solid catalysts. Experiments have been carried out at the operating capacity of 2 L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5-4.5 g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5 g/L whereas for TiO2 maximum degradation was observed as 51.2% at a loading of 4 g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH3OH) and n-butanol (C4H9OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO2 (4 g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.

The present work deals with achieving viscosity reduction in polymer solutions using ultrasound-based treatment approaches. Use of simple additives such as salts, or surfactants and introduction of air at varying flow rates as process intensifying parameters have been investigated for enhancing the degradation of polyvinyl pyrrolidone (PVP) using ultrasonic irradiation. Sonication is carried out using an ultrasonic horn at 36 kHz frequency at an optimized concentration (1%) of the polymer. The degradation behavior has been characterized in terms of the change in the viscosity of the aqueous solution of PVP. The intrinsic viscosity of the polymer has been shown to decrease to a limiting value, which is dependent on the operating conditions and use of different additives. Similar extent of viscosity reduction has been observed with 1% NaCl or 0.1% TiO2 at optimized depth of horn and 27°C, indicating the superiority of titanium dioxide as an additive. The combination of ultrasound and ultraviolet (UV) irradiation results in a significantly faster viscosity reduction as compared to the individual operations. A kinetic analysis for the degradation of PVP has also been carried out. The work provides a detailed understanding of the role of the operating parameters and additives in deciding the extent of reduction in the intrinsic viscosity of PVP solutions.

No abstract

The conventional chemical oxidation methods have not been very successful for the treatment of dyes due to higher stability against the oxidizing agents. The present work investigates the application of an improved treatment approach based on the ultrasonic and ultraviolet irradiations for treatment of dye containing wastewaters. Magenta dye, which is commonly used in textile industries, has been used as a model compound. Initially, the experiments have been performed using individual operation of ultrasonic and ultraviolet irradiations. Studies related to effect of concentration revealed that the extent of degradation increased with an increase in the concentration of dye solution till an optimum loading. Intensification of the extent of degradation using ultrasonic irradiation has been investigated using different additives such as NaCl, TiO2, air and starch. Also the efficacy of combined treatment approaches based on different approaches involving ultrasound, ultraviolet irradiation and additives for the removal of magenta dye from the aqueous solution have been evaluated. For the use of additives, maximum intensification was achieved for TiO2 followed by use of NaCl and least effect was observed for starch. For the combined treatment approaches, the maximum extent of degradation (98.8%) and maximum COD removal (94.0%) has been obtained for the combination of ultrasound with 1 g/L TiO2 and air. The present work has clearly demonstrated the efficacy of combined treatment approaches for removal of dyes from the wastewater.

No abstract