Shear rheological properties of fresh human faeces with different moisture content

Abstract

Dry sanitation requires the handling of faeces, which vary in age and degree of transformation. Rheological data are necessary to support the design of equipment to handle faeces. The rheological properties of fresh human faeces were measured using a variable-speed rotational rheometer. Samples were further tested for moisture content, total solids, volatile content, and ash content. Faecal samples were found to have a yield stress; there was a decrease in apparent viscosity with increasing shear rate. For any given shear rate, higher apparent viscosities are associated with lower moisture contents. Across a range of water contents of 58.5% to 88.7%, apparent viscosities of 27 Pa•s to 2 014 Pa•s were measured at a shear rate of 1 s -1 . During constant shear tests, the apparent viscosity of all faeces was found to decrease asymptotically, where the minimum apparent viscosity value increased with decreasing moisture content. A structural recovery test indicates that human faeces are thixotropic in behaviour, where the viscosity permanently decreases to 0.5% of the initial value after a 20 s exposure to a shear rate of 10 s -1 . A linear relationship between viscosity and temperature was found, with a recorded 30.6% decrease in viscosity for a 35.6 °C increase in temperature from 13.4°C.

The Characterization of Feces and Urine: A Review of the Literature to Inform Advanced Treatment Technology

“…Scales relating to the physical form of faeces also provides a further estimation of the solids composition by providing approximate estimations of the TS content of faeces across large sectors of populations. Research being carried out byWooley et al (2013) into assigning a TS value to the Bristol Stool Form scale will be of further benefit to technology development in this respect. Extremes in solids composition Downloaded by [SUNY Health Science Center] at 21:18 15 March 2015…”

A Physical Simulation to Investigate the Effect of Anorectal Angle on Continence

“…It forms a homogenous substance with physical properties of density and viscosity comparable to those reported for soft faeces [43].…”

“…The method here adapts that presented by Woolley et al [43] for analysing the effect of shear rate on dynamic viscosity of VEEGUM solutions.…”

“…The measured moisture contents of human faeces range from 58.5% to 88.7% by mass [43], with apparent viscosities at 1s -1 ranging between 52.8 and 3306.3 Pa.s based on a power law relationship. In this study a stool simulant was selected at 90.5% water content, producing an apparent viscosity of 47.065 (Pa.s), within the bounds of high moisture content semisolid faecal samples.…”

Rheology of Un-Sieved Concentrated Domestic Slurry: A Wide Gap Approach

“…Of the many articles published to characterise the rheology of wastewater slurries, to the author's knowledge, none characterise concentrated domestic slurry. For faecal sludge, the only article addressing its rheology by Woolley [18] is not comprehensive enough and is regarded to be at most a preliminary analysis. Therefore, this paper presents a detailed rheological study of un-sieved concentrated domestic slurry in a wide gap Couette-flow Searle type rheometer (MCR 302 Anton Paar, Graz, Austria).…”