Modeling of the Fouling Probability of an Activated Sludge Dryer

Better understanding (and so better control) of the stickiness phenomenon of drying sludge is critical for proper operation of a variety of industrial dryers, as is the case for the combined centrifuge-dryer system used on the Monsanto Europe site in Antwerp, Belgium. In this paper a binary logistic regression analysis is performed on a 4-years data base, which resulted in an empirical model for the evaluation of the dryer fouling probability as function of changes in the Sludge Volume Index (SVI) and the dosing of clay additive and tertiary (flotation) sludge to the main secondary (biological) sludge feed to the system. According to the research results, a decreasing SVI increases the probability of obtaining fouling in the dryer. Furthermore, in periods of low SVI, the fouling probability can be reduced significantly by reducing the clay dosing. This extended analysis confirms the hypothesis formulated earlier (Peeters et al., 2009a) that a wetter cake (induced by high SVI and low clay dosing) at the beginning of the drying stage of this system is better to avoid drying sludge fouling the dryer wall. Copyright © 2010 IFAC