A feasibility study of in-line rheological characterisation of a wastewater sludge using ultrasound technology

Abstract

The rheological characteristics of sludge affect transportation, treatment and the disposal processes involved in sludge system design and management operations such as dewatering, including flocculation and filtration. The concentration of solid matter in the sludge has an effect on rheological parameters such as yield stress and viscosity. These rheological properties of sludge are almost exclusively obtained today using commercially available instruments, such as conventional rotational rheometers or tube (capillary) viscometers. Since these methods are time-consuming and unsuitable for realtime process monitoring, the ultrasonic velocity profiling coupled with pressure drop (UVP+PD) methodology becomes very attractive for in-line flow behaviour monitoring for quality control and process optimisation. The main objective of this research work was to evaluate the UVP+PD technique in a concentrated sludge as found in a wastewater treatment plant. A portable pump test rig with tube viscometer fitted with a UVP+PD system was used to determine the rheological parameters. Conventional UVP installation techniques were tested as well as a new delay line UVP transducer. The results obtained from different installation techniques and transducers are compared. Finally, rheological parameters obtained using UVP+PD compared within 15% of that obtained using the tube viscometer. The results showed that UVP+PD is a feasible and promising technique for in-line real time flow visualisation and rheological characterisation for treated wastewater sludge which, when used as in-line process control, could lead to significant savings in chemicals and will optimise processes producing drier sludges and filter cakes.

In-line rheological characterisation of wastewater sludges using non-invasive ultrasound sensor technology

“…Pressure measurements were conducted using differential pressure transducers (Fuji Electric) with maximum ranges of 0-6 kPa and 0-130 kPa and an accuracy of ±0.25%. The complete pipe viscometer setup is described in more detail in Haldenwang et al (2010Haldenwang et al ( , 2012 and Kotzé et al (2014a).…”

“…The emission voltage was set to 90 V, and 256 pulse repetitions were used (the same settings were used for all measurements). Kotzé et al (2014a) used an emission voltage of 150 V and number of pulse repetitions of 512 in order to measure a velocity profile across the pipe radius (when using the delay line sensors). This means that almost double the energy input and number of ultrasound pulse emissions for one profile was needed.…”

“…The pipe rig used was slightly modified from the one used in Kotzé et al (2014a). The rig consisted of two polyvinyl chloride (PVC) pipes with inner diameters of 63.2 and 22.5 mm.…”

“…This was due to the delay line material absorbing ultrasonic energy which prevents measurements in larger pipe diameters in attenuating fluids. Kotzé et al (2014a) concluded that initial results obtained in a concentrated sludge suspension showed that the UVP + PD methodology is a feasible and promising technique for flow visualisation and rheological characterisation in the wastewater engineering and treatment industry. However, an important limitation was that the transducer installation (delay transducer setup) is not non-invasive.…”

“…In a recent study, Kotzé et al (2014a) investigated and presented an ultrasonic velocity profiling combined with pressure difference (UVP + PD) methodology for in-line rheological characterisation of a wastewater sludge. Feasibility tests were carried out using delay line and standard ultrasound transducers as well as different sensor installation techniques.…”