Determination of ozone mass transfer coefficient in a tall continuous flow counter-current bubble contactor

Preliminary experiments in a continuous flow counter-current bubble type ozone contactor, 3 m in length and 25 mm diameter, indicated that the gas phase hold-up (ɛG) in the contactor increased linearly from 8 to 15% when gas flow rate (Qg) was increased from 500 to 1000 mL min−1 (8.33 × 10−6 to 1.67 × 10−5 m3 s−1). The liquid phase dispersion coefficient (DL) in the contactor increased from (2.02 ± 0.83) × 10−3 to (2.34 ± 0.46) × 10−3 m2 s−1 when Qg was increased from 500 to 1000 mL min−1 (8.33 × 10−6 to 1.67 × 10−5 m3 s−1). The contactor was mathematically modeled considering the hydrostatic pressure variation along reactor height, and assuming the gas and liquid phases in the reactor to be plug flow and mixed flow, respectively. Using this model, aqueous ozone concentration was simulated at various reactor heights as a function of time. The simulation results using an ozone mass transfer coefficient (KLa) of 0.025 s−1 matched well with the corresponding experimental data. Experimental data on gaseous ozone concentration effluent from the reactor was also obtained as a function of time. This data also matched well with corresponding simulation results for a KLa value of 0.025 s−1. Sensitivity analysis indicated that the model simulation results were relatively insensitive to changes in KLa value in the range of 0.015–0.035 s−1. The work described in this paper is the first part of a continuing study to develop a fully mechanistic model of a tall ozone contactor for degradation of micro-pollutants in water.