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This paper will elucidate the data demonstrating that ASCARIS eggs are much more resistant to inactivation when compared to CRYPTOSPORIDIUM oocysts. In the last few years, there has been concern that CRYPTOSPORIDIUM is a very resistant pathogen. This paper will illustrate that properly coordinated Class B disinfection would inactivate CRYPTOSPORIDIUM oocysts but not ASCARIS eggs.

The difference between the Ascaris egg and the CRYPTOSPORIDIUM oocyst is the outer shell. The ASCARIS egg consists of three layers that have been observed to be highly resistant to many chemical disinfectants. The Crytposporidium oocyst wall is thinner and appears less resistant than the ASCARIS egg. Both of these organisms are susceptible to (1) non-charge biosolids (ammonia released during alkaline stabilization), temperature, and cavitation processing (ultrasound or pulse power).

In alkaline stabilization, it is the ammonia concentration that is the factor determining the effectiveness of alkaline agents to inactivate the contained helminth eggs and the protozoan oocyst. From our work, ASCARIS eggs require one magnitude greater concentrations of ammonia for inactivation than is required for the activation of oocysts, i.e., 1 to 3% ammonia for ASCARIS eggs and less than 0.1% ammonia for oocysts. Similarly, in the cavitation process, at 10,0000 PSI, over 80% of the oocysts were inactivated, but there was no effect on the eggs of Ascaris. Similarly, with respect to temperature, oocysts were inactivated much more rapidly at all temperatures between 30° to 60° than were the eggs of ASCARIS.

Thus, from this data it would appear that the choice of ASCARIS as the agent for verification of pathogen inactivation in Class A solids remains appropriate, at least with respect to this protozoan pathogen.

Document Type: Research Article


Publication date: January 1, 2000

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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