The Effects of Exposure Time, Temperature, Ph, and Ammonia Concentration on the Inactivation Rate of Ascaris Eggs

Wastewater treatment produces solid residuals. Land application provides a sustainable, beneficial alternative for solids disposal, but it increases the threat of public exposure to disease. As such, regulatory agencies in many countries limit the number of pathogens allowable in residuals. One of the most common and resistant pathogens is the egg of the intestinal parasitic worm, Ascaris. Alkaline stabilization is one alternative to costly thermal inactivation of pathogens, but the mechanisms of inactivation during alkaline stabilization are still undetermined. This work quantified the effect of ammonia on the inactivation of Ascaris eggs in an alkaline setting. Ascaris eggs were exposed to a range ammonia concentrations, pHs, and temperatures for various exposure periods, then viewed microscopically to determine the level of inactivation. The results showed that Ascaris inactivation was a function of the concentration of the uncharged ammonia species and that ammonia inactivation played a significant role in Ascaris egg inactivation over a 72-hour period. These results have a number of implications for wastewater treatment. Firstly, they may help explain the wide range of reported times needed for Ascaris inactivation in alkaline stabilized sludge. Secondly, these findings may have implications for the design of sludge treatment. Engineering sludge storage systems to take advantage of ammonia inactivation may decrease both the time and the heating requirements needed for pathogen inactivation.