Waste water sludge pipeline predictions using conventional viscometry and ultrasound based rheometry

Abstract

To optimise the design and operational management of wastewater treatment plants (WWTP’s) there needs to be an understanding of the viscous properties of wastewater sludges, which at higher concentrations become non-Newtonian. Worldwide, there is more and more pressure to attain higher sludge concentrations which complicates mixing and pumping. Pipeline design at higher concentrations also requires prior knowledge of sludge rheology. The comparison of the rheological parameters of wastewater sludge world-wide has been hampered due to different rheological measurement techniques and interpretation of results used. For the past seven years wastewater sludges have been rheologically characterised in Sweden and in South Africa, using the same tube viscometer. Seventy-six sludges were tested in tube and rotary viscometers at 16 WWTPs in Sweden and South Africa with solids concentrations ranging from 2 to 8%. A correlation could be obtained of the rheological parameters as a function of sludge concentration. In addition to this, a real-time in-line fluid visualisation and characterisation system, was also used to determine the rheology of the sludge. Three wastewater sludge concentrations were rheologically characterised using the FlowViz system and a conventional tube viscometer. It is demonstrated that a significant effect on pressure drop predictions occurs when using results from the Flow-Viz system compared to tube viscometry, which is mainly due to more accurate determination of the yield stress. This work provides confidence for the pursuit of the development of a universal correlation for sludge rheological parameters using in-line real time rheological parameters for improved pipeline design.