Viscous heating analysis of simulant feces by computational fluid dynamics and experimentation

Abstract

Highly viscous substances, such as feces, produce significant heat when layer deformation occurs. We describe the use of viscous heating sufficient to destroy disease-causing microorganisms and whipworms in feces. Computational fluid dynamics (CFD) was used to evaluate preliminary design and provide initial geometric specifications for a laboratory-scale unit. The laboratory device has a rotating core separated from a fixed shell wall by a defined space. Data were obtained over a range of operating conditions with simulant materials. The CFD model was validated with the experimental results. The temperature observed with the smallest spacing was 190 °C. Alternative geometries are considered for high-volume sludge processing. Potential design modifications include enhancing efficient water evaporation and recovery.

Review of synthetic human faeces and faecal sludge for sanitation and wastewater research

“…et al, (2013). The alternatives included contents from pig caecum (a section of the pig lower intestine) (Takahashi and Sakata 2002), content from chicken caecum (Takahashi et al, 2004), wheat flour (Podichetty et al, 2014), different types of mashed potatoes (Podichetty et al, 2014) and simulant stool (simulant based on Susana.org.2008, simulant #13 presented later in Table 3, viscosity profile of the simulant was made by Podichetty et al, 2014). While wheat flour had the closest match to the rheological behaviour of human faeces, they selected red potato mash since it had a higher resemblance in terms of moisture content (simulant #3).…”

“…Most of the developed simulants mimic specific physical, chemical or thermal characteristics of human faeces important to the research objectives for which they are developed. Physical properties such as shape, size, density and rheology are of importance for simulating phenomena such as faeces settling, transport in sewer pipes, dewatering, viscous heating for pathogen destruction, and physical disintegration (e.g., Butler et al, 2003;Veritec Consulting Inc. & Koeller and Company, 2010;Podichetty et al, 2014). Chemical properties including chemical and biological oxygen demand, nutrient concentration, pH and conductivity are of importance for simulating biological disintegration, treatment of faeces and biogas production (e.g., Kaba et al, 1989;Wignarajah et al, 2006;Miller at al., 2015).…”

The inactivation of Ascaris suum eggs by short exposure to high temperatures

“…Increased temperatures have been found to be effective and cost efficient for inactivation of faecal-sludge pathogens (Podichetty et al 2014 ; Belcher et al 2015 ). This study is an extension of a short communication by Naidoo & Foutch ( 2017 ) and aimed to fill the knowledge gap with regards to the effects of short exposures of Ascaris eggs to heat.…”

The time–temperature relationship for the inactivation of Ascaris eggs

“…eggs in faecal sludge (Podichetty et al . 2014 ). A key design variable of VH is the faecal sludge residence time at a specific operating temperature.…”