Model and analysis of belt drainage thickening

A gravity drainage model was developed that included terms for cake resistance, filter resistance, and initial pending. Laboratory scale batch drainage tests were performed at sludge volume loadings between 0.013 and 0.006 m(3)/m(2). Results were compared with limits established from the model for ponded and nonponded sludge drainage. At low volumetric loadings, the series of drainage curves represented a smooth family of curves with increased drainage rates at the volume was increased. However, at higher volumetric loadings, a discontinuity in the family of curves was observed in which the rate of filtrate flow decreased with an increase in sludge volume. The change in the shape of the filtrate curves corresponded with the observance of standing water on top of the forming sludge cake, or pending. The effects of plowing during drainage were investigated. One effect of plows was to diminish the effects of pending, noted as an increased drainage rate, for sludge loading conditions that had a tendency to pond in the absence of plows. A second effect was to cause the release of more water from sludges that were not prone to pending than that seen in the absence of plows.