Solar photocatalytic degradation and adsorption of emerging pharmaceutical contaminants in wastewater
Loading...
Date
2014-09-15
Authors
Akach, John Willis Juma Pesa
Journal Title
Journal ISSN
Volume Title
Publisher
Vaal University of Technology
Abstract
Pharmaceutical pollutants in wastewater have become an increasing concern in recent years. Adsorption and photocatalytic degradation of pharmaceutical pollutants have proved to be very efficient in the removal of pharmaceutical contaminants. In this study, a composite catalyst of powdered activated carbon (PAC) and TiO2 bound by silica xerogel (CTS composite) was synthesized and characterised using SEM, XRD and XRF. The composite catalyst was then used to adsorb and photodegrade the pharmaceuticals sulfamethoxazole (SMX), diclofenac (DCF) and carbamazepine (CBZ) in a three phase fluidised bed photocatalytic reactor using sunlight to activate the TiO2. The solar radiation intensity at the Vaal University of Technology and the hydrodynamic behaviour of the reactor were also investigated. Additionally, the effect of catalyst composition and loading, hydrodynamics and solution characteristics on the adsorption and photodegradation of the substrates was investigated.
It was found that the solar radiation intensity varied with the hour of day, weather and seasons of the year. SEM showed that the porosity of the composite catalyst increased with increase in the PAC loading and a decrease in the silica xerogel loading. The XRD results showed that the silica xerogel and the PAC did not alter the composition of the P25 TiO2. XRF showed that the method used in the preparation of the substrates resulted in the desired composition of the catalyst. The optimum CTS composition was 60% silica xerogel loading and 10% PAC/TiO2 ratio. The best mass of the composite catalyst was 1.5 g/l. Using the optimal composite composition resulted in over 90% removal of the substrates with low residual solution turbidity of less than 3.5 formazin attenuation units (FAU). The optimum hydrodynamic condition was obtained when the reactor inclination angle and superficial air velocity were 75° and 0.014 m/s, respectively. However, a reactor inclination angle of 75° and a superficial velocity of 0.007 m/s gave the best adsorption and photodegradation of the substrates. Reducing the initial concentration of the substrates resulted in an increase in the efficiency of removal of the substrates. The adsorption and photodegradation of SMX was observed to increase with a decrease in pH and was maximum at pH 4. The adsorption of SMX and DCF was found to follow the Langmuir isotherm model. These results show that the use of the synthesised composite catalyst in the fluidised bed reactor provided a stable and efficient system capable of long term use. The results from this work also show that this system can be used for the removal of pharmaceutical substrates at low concentrations.
Description
M. Tech. (Department of Chemical Engineer, Faculty of Engineering and Technology), Vaal University of Technology.
Keywords
Pharmaceutical pollutants, Solar photocatalytic degradation, Adsorption, Pharmaceutical contaminants