[Analysis of effect of sludge recirculation on setting efficiency in horizontal sedimentation tank]

The problem that the present sediment theory does not consider sludge recirculation effect on the efficiency of particle settling is studied. Based on the longitudinal mixing settling theory, an imperfect sediment model that takes reflux ratio in consideration is built. According to the established model, the study analyzes the effect of sludge recirculation taken by suction dredge on particle setting, in horizontal sedimentation tank. Specifically, the relation between overplus of sewerage suspension and sedimentation rate was chosen as an example. Shown as a result, when sludge recirculation is not taken in consideration, efficiency of particle settling is 72.8%. However, when sludge recirculation increases from 0.5 to 3.0, efficiency of particle settling decreases from 71.1% to 50.9%, which is smaller than efficiency of particle settling without recirculation; and when sludge recirculation is 3.0, efficiency of particle settling is 50.9%, which is approximately 30% less than efficiency of particle settling without recirculation. So, sludge recirculation make efficiency of particle settling is smaller than efficiency of particle settling without recirculation, and the efficiency of particle settling reduces with the increase of reflux ratio.