Effect of aerobic and anaerobic digestion on the viability of<i>Cryptosporidium parvum</i>oocysts and<i>Ascaris suum</i>eggs

Abstract

The viability of Cryptosporidium parvum oocysts and Ascaris suum eggs inoculated into aerobic and anaerobic digesters was measured. The digesters were maintained at 37 degrees C, 47 degrees C, and 55 degrees C, with 10-day detention times. Eggs and oocysts were added to each digester in a single spike or in chambers placed in the digesters for varying periods. Oocysts were inactivated very rapidly in all systems as determined by a dye permeability assay, > 99% inactivated after 10 days at 37 degrees C, 4 days at 47 degrees C, and 2 days at 55 degrees C. Eggs were more rapidly inactivated in anaerobic digesters than in aerobic digesters. At 55 degrees C, eggs in both anaerobic and aerobic digesters were > 99% inactivated within 1 h. At 47 degrees C, anaerobic digestion inactivated around 95% eggs in 2 days, but around 25% of the eggs were still viable after 10 days in aerobic digesters. At 37 degrees C, anaerobic digestion inactivated more than 75% of the eggs after 10 days, but in the aerobic digester at 37 degrees C, 10 days of treatment had no effect on viability. The oocysts and eggs added in chambers appeared to behave similarly to these pathogens added directly to the biosolids within the digesters.