The inactivation rate of Ascaris eggs was studied in the sludge layer of a primary, facultative wastewater stabilization pond located in Mexico City. Two independent methods, sludge cores and dialysis chambers, were used to determine the inactivation rates through which a comprehensive
picture of the inactivation was gained. The dialysis chambers provided a detailed picture of the initial inactivation (14 months) at one location in the pond, whereas the sludge cores provided less precise information about the inactivation rate at several locations and over the entire lifetime
of the pond (10 years). The inactivation curve was characterized by an initial lag phase, a period of roughly first-order inactivation, and a tailing region. During the first year, 50 to 60% of the eggs were inactivated, after which the rate decreased. Although the observed, initial first-order
rate constant was greater than 0.002 d−1, the average, long-term rate constant was closer to 0.001 d−1.
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