The rheology of sewage sludge at different steps of treatment

Rheological parameters are very important in sewage sludge management, not only as designing parameters in transporting, storing, landfilling and spreading operations, but also as controlling ones in many treatments, such as stabilisation and dewatering. To study how different treatments affect sludge rheological behaviour, research has been undertaken at CNR-Istituto di Ricerca Sulle Acque (CNR-IRSA), and the preliminary results are discussed in this paper. Sludge samples taken from three municipal wastewater treatment plants at different steps of treatment have been tested by a rotational viscometer and data interpreted through both Bingham plastic and Ostwald pseudoplastic models. Coefficients of those models have been then correlated to solids concentration. Results confirmed that solids concentration is the main parameter affecting sludge rheology and evidenced that a single parameter is not sufficient to represent the rheological behaviour, thus indicating that other parameters should be introduced and characteristics considered for a better understanding of the phenomenon. (C) 1997 IAWQ. Published by Elsevier Science Ltd.