Parasites in Southern Sludges and Disinfection by Standard Sludge Treatment

摘要

Major objectives were to: (a) assess types and densities of parasites in municipal wastewater sludges in the southern United States, (b) investigate the inactivation of parasites by lime stabilization of sewage sludges seeded with selected intestinal parasites, (c) assess conventional sewage sludge treatment processes from laboratory and field data for the control of parasites. Sludge samples examined in each of the four seasons from 27 municipal wastewater treatment plants indicated the following: (a) viable eggs of Ascaris and Toxocara were observed at least once from every plant; (b) viable eggs of T. vulpis and T. trichiura were observed at least once from 26 and 15 plants, respectively, and (c) viable eggs of at least 10 other helminths and cysts of a few protozoa were observed in fewer numbers and less frequently. Certain drying bed conditions such as previous sludge stabilization, high temperature, and low moisture content appear to inactivate parasite eggs synergistically between 60% to 5% sludge moisture content. Laboratory studies indicate that destruction of resistant parasite eggs is primarily due to temperature and not to a specific digestion process. The application of lime to primary, aerobic digested, and anaerobic digested sludge was found to be effective with greater than 80% reduction of Ascaris viability in 5 days following aerobic digestion at a lime dosage of about 1,000 mg/gram of sludge solids. Laboratory experiments showed that at certain combinations of ultrasonic frequency intensity, and exposure time Toxocara eggs could be destroyed.