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The Scientific World Journal
Volume 2014, Article ID 590961, 6 pages
Research Article

Rheology Measurements for Online Monitoring of Solids in Activated Sludge Reactors of Municipal Wastewater Treatment Plant

Dipartimento di Chimica, Fisica e Ambiente, Università degli Studi di Udine, Via Cotonificio, 108, 33100 Udine, Italy

Received 5 August 2013; Accepted 20 October 2013; Published 14 January 2014

Academic Editors: J. A. Baeza and A. Rodriguez

Copyright © 2014 Luciano Piani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Rheological behaviour of recycled sludge from a secondary clarifier of a municipal wastewater treatment plant was studied by using the rate controlled coaxial cylinder viscometer Rotovisko-Haake 20, system M5-osc., measuring device NV. The tests (hysteresis cycles) were performed under continuous flow conditions and following an ad hoc measurement protocol. Sludge shear stress versus shear rate curves were fitted very satisfactorily by rheological models. An experimental equation correlating the solid concentration of sludge to relative viscosity and fitting satisfactorily flow curves at different Total Suspended Solids (TTS%) was obtained. Application of the empirical correlation should allow the monitoring of the proper functioning of a wastewater treatment plant measuring viscosity of sludge.