Simple estimation of granule size distribution and sludge bed porosity in a UASB reactor

Abstract

Granular sludge is the key factor for an efficient operation of an upflow anaerobic sludge blanket (UASB) reactor. In order to monitor the granularity of anaerobic sludge, the determination of the granule size distribution is of vital importance. Another critical parameter for the UASB reactor performance is the sludge bed porosity. For this reason, several techniques have been proposed, however they are either tedious, imprecise or expensive and hardly applicable in full scale treatment plants. There was then the need for a simple and low cost technique. This technique involves the determination of the settling velocities of a sludge sample and of extrapolating the corresponding diameters using a mathematical algorithm. In the proposed algorithm, the granules density was calculated, the flow regime was examined and finally the granule size distribution was obtained. Some very important correlations were suggested by the experimental results. The granule density and diameter as well as the sludge bed porosity were strongly correlated with the VSS/TSS ratio.