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

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.