Effect of temperature and shear stress on the viability of Ascaris suum

Abstract

Ascaris eggs are commonly used as a bioindicator to test the success of waste treatment systems. The ability to inactivate this organism's eggs indicates probable destruction of a variety of pathogens. The intent of these experiments was to determine operational parameters for a conical-augur device to treat human solid waste in a time-efficient manner (seconds), without exogenous chemicals (e.g. lime, an alkalizing agent) or an external heat source. Literature reviews and independent viscometry experiments established a target temperature range and residence time within the device. The ability of applied shear force to inactivate Ascaris suum, directly or indirectly, was assessed using viscometry. Shear force alone, as friction, failed to inactivate A. suum eggs. However, shear force was used to generate sufficient heat in a human-fecal simulant to inactivate A. suum eggs under a variety of test conditions. Target operating conditions for the conical-augur device were 70 °C with a 6-s residence time; increasing the temperature allowed for reduced residence time to achieve A. suum inactivation.