LAUSR

Abstract Bubble size, bubble rise velocity and the corresponding distributions were directly measured by a dual-tip electro resistivity probe and to present empirical correlations to estimate the average bubble size and bubble rise velocity in activated sludge. Experiments were conducted in a 9 cm diameter bubble column while superficial gas velocity was in range of 0.5–7 cm/s. Four samples of activated sludge with mixed liquor suspended solid (MLSS) concentrations from 1.082 to 10.82 g/L were used in the experiments. It was found that increasing the MLSS concentration resulted in increase in the bubble chord length and bubble rise velocity and decrease in the gas hold up. It was shown that in the homogeneous regime, the probability distributions of bubble chord length and bubble rise velocity are sharp and unimodal. To estimate bubble size and bubble rise velocity in activated sludge, correlations were developed which includes effect of MLSS concentration besides physical properties and operating conditions. The experimental results of this study were compared with the proposed correlations in literature obtained in two and three phase bubble column. It was shown that neither of the previous correlations can predict the bubble size and bubble rise velocity in the activated sludge system properly while the proposed correlation in this work shows a good precision for estimating these parameters.