Viability of Ascaris and other helminth genera non larval eggs in different conditions of temperature, lime (pH) and humidity

Abstract

Helminth eggs are the pathogens most resistant to inactivation during sludge and wastewater treatment. For this reason, in several regulations and the WHO guidelines for wastewater and excreta reuse for agriculture and aquaculture they are considered as indicators of the performance of the treatment process. Conditions required to inactivate helminth eggs, notably Ascaris lumbricoides, are recommended in the literature, but in practice these have not always proven effective, not only for Ascaris but also other genera of helminth eggs. The objective of this research was to study the inactivation of a high total content of non larval Ascaris and other genera of helminth eggs of medical importance to developing countries under controlled conditions of (a) temperature (30 °C to 80 °C) and humidity (80, 90 and 95%) and (b) lime doses (15 and 20% of CaO w/w dry basis) and humidity (90 and 80%), using different contact times in both cases. The inactivation data obtained for different genera of non larval helminth eggs is presented. Results showed that there is a combination of conditions (temperature, pH and humidity) that is optimal for inactivation. To completely inactivate any genera of non larval helminth eggs: (a) a temperature above 70 °C and 80% humidity for a duration of 120 min; and, (b) a 20% CaO dose (pH 12.5) and a humidity level of 80% for a duration of 8 months are needed. With regard to the resistance of different genera of helminth eggs, Ascaris, Toxocara and Taenia, in that order, were the most resistant, while the most sensitive were Trichuris and Hymenolepis. For most of the conditions tested Ascaris showed the highest resistance, probably due to the chemical arrangement of its membrane.