Insights into gas flow behavior in venturi aerator by CFD-PBM model and verification of its efficiency in sludge reduction through O3 aeration

Abstract

The use of ozone has become a new direction in residual sludge reduction. In order to improve the mass transfer efficiency and utilization efficiency of ozone, the structure of the venturi aerator was optimized by simulating the gas flow behavior with the CFD-PBM model. The gas volume fraction slowly decreased as the inlet angle increased. Besides, the ratio of throat diameter and throat length gradually increased, increasing bubble crushing rate and breakup probability. The turbulent eddy dissipation decreased with increasing outlet angle and moved from the central region to the sidewall, reaching a maximum at the throat. Thus, the optimal parameters for the venturi aerator were determined to be an inlet angle of 15°, a ratio of throat diameter to throat length of 1 and an outlet angle of 3°. Regarding the sludge reduction effect, the sludge dissolution efficiency after treatment with an optimized venturi aerator and traditional disc aerator was 35.3 % and 28.6 %, respectively. When the ozone dosage was 100 mg/g·MLSS, the venturi aerator had a better effect on ozone utilization than the disc aerator. At an ozone inlet flow rate of 2 L/min, the mass transfer coefficient of ozone in a venturi aerator was higher than that of the disc aerator. This study demonstrates the operational feasibility of ozone combined with a venturi aerator to reduce residual sludge production.