Image analysis to estimate the settleability and concentration of activated sludge

A new method, using low magnification microscopy combined with image analysis to estimate settling properties of activated sludge, is presented. It is shown that the morphology of the activated sludge flocs correlates significantly with the settling properties of the sludge, as expressed by traditional settling tests. The morphology is expressed by two parameters: the mean equivalent circle diameter and the mean form factor of the sludge flocs. In contrast with traditional tests, the new method takes only between 10 and 20 min, is automated and can be incorporated in other sensors. In addition, a rapid and reliable estimate of the suspended solids concentration can be obtained by establishing a calibration between the mean field area of a series of images with the concentration of a certain type of activated sludge. The relevance of the novel method is clearly illustrated by its ability to monitor the rise and the subsequent cure of a severe case of bulking in an activated sludge pilot plant. It is shown that a more sensitive measurement of the sludge settleability is obtained by using image analysis. Consequently, the method presented may have good potential in being used as an early warning system.