The photocatalytic degradation characteristics of TCE/toluene by $TiO_2$ powders have been determined in an internally-circulating slurry bubble column (15 cm diameter and 60 cm high) reactor.
Gas holdup is not affected by liquid velocity (up to 200 ml/min) and the solid loading (0.1-0.4 wt%). Gas holdup in the slurry bubble column is lower than that in the bubble column since the presence of solid increases the liquid viscosity.
Direct photolysis efficiency of TCE without air is higher than that with air flow due to air stripping of TCE.
The photocatalytic degradation efficiency of TCE with air is higher than that without air. Therefore, supply of enough oxygen and proper mass transfer are necessary for degradation of TCE during photocatalytic reaction.
It has been reported that the optimum loading of $TiO_2$ in the laboratory-scale experiments is 0.1 wt%. In this study, 0.2 wt% of $TiO_2$ was used for efficient illumination with geometrically symmetrical arrangement of the lamps and the increase of light penetration length due to bubble formation.
The rate constant (k) and adsorption equilibrium constant (K) are found to be $6.687×10^{-6}$ moles/L-min and $9.2838×10^2L/mol$, respectively. The Langmuir-Hinshelwood model equation fits well with the experimental data. Therefore, the Langmuir-Hinshelwood model can apply to TCE photocatalytic reaction system.
The air stripping fraction of TCE increases, but, the photodegradation fraction of TCE decreases with increasing TCE initial concentration in water. It has been found that air stripping is superior to photodegradation of TCE.
Toluene at a low concentration (62 ppm) does not affect the photodegradation of TCE, but, at a high concentration (218 ppm) exhibits "toluene quench of TCE effect".
Regarding on the TCE photodegradation efficiency, the externally-recirculating system is more efficient than the internally-circulating slurry bubble column photoreactor system. For TCE total removal, the total removal efficiency (photodegradation and air stripping) in the internally-circulating slurry bubble column photoreactor system is higher than the total removal efficiency by photodegradation in the externally-recirculating photoreactor system.
