A simple and low cost technique for determining the granulometry of upflow anaerobic sludge blanket reactor sludge

Four techniques (microscope sizing, calculation from settling velocities, image and laser analysis) are available nowadays for determining the particle size distribution of upflow anaerobic sludge blanket (UASB) reactor sludge. These techniques present however the disadvantage of being 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. In this study, a granulometry procedure based on manual humid sieving was evaluated. It was shown that no solid loss occured during the screening and that the particle size profiles were reproducible when performed with sludge samples of 5, 10, 25 and 150 ml, but not 1 ml. Only the results between 10 and 25 ml were however fully identical. It was shown also that the sieving could be performed on sludge samples stored for as long as 50 days at refrigerator temperature and that tap water could be use for the wash and backwash operations without any impact on the particle size profile. The granulometry obtained by image analysis was not comparable to that given by sieving. Nevertheless, no evidence of granule erosion could be found. In any case, the technique allowed us to follow the evolution of sludge granulometry perfectly over time. As a consequence, the manual humid sieving appears to be an adequate technique for determining the granule size distribution of UASB sludges.