Viability of six species of larval and non-larval helminth eggs for different conditions of temperature, pH and dryness

Helminth eggs are the most difficult biological parasites to inactivate in wastewater and sludge. In developing countries, in particular, they are present in high concentrations and are the cause of many diseases that impact seriously on the human population. The process conditions for affordable inactivation are very variable, leading to different inactivation efficiencies. Temperature, dryness, pH and the developmental stage of the eggs must be taken into consideration to achieve complete inactivation. The objective of this research was to study the inactivation of six species of larval and non-larval helminth eggs of medical importance in developing countries under controlled conditions of temperature, pH, dryness and contact time. Results showed considerable differences in inactivation conditions among helminth eggs and a high level of resistance was confirmed for the eggs of Ascaris lumbricoides and Ascaris suum. The appropriate conditions for inactivation of all types of eggs were found by applying combinations of pH, temperature and dryness. At 45 °C it was possible to inactivate all species with a pH of 5.3 and 90% dryness within 6 days. If alkalization was applied, a pH of 12.7 was sufficient over 19 days at the same conditions of dryness and temperature. From these results it is proposed that both Ascaris spp. and Taenia solium may be used as indicators of biological contamination in wastewater and sludge.

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► Helminth eggs are more vulnerable to acidification than to alkalization.
► Larval eggs are inactivated faster than the non-larval ones (coefficients provided).
► Ascaris and Taenia are more resistant than Toxocara, Trichuris and Hymenolepis.
► Except for Trichuris, pH changes were more inactivating than dryness changes.
► Full inactivation is achieved by properly combining pH, temperature and dryness.