INACTIVATION OF ASCARIS-SUUM EGGS DURING STORAGE IN LIME TREATED SEWAGE-SLUDGE

Survival and development of Ascaris suum eggs in sewage sludge mixed w ith 10% w/w of quick lime (85% CaO) has been examined. Fresh collected A. suum eggs were mixed in sewage sludge during lime treatment. The d evelopment of the eggs was followed every second week during a 10 week s period and again after 5 months, parallel with control eggs. Lime tr eatment of sewage sludge resulted in a pH > 12 and development of A. s uum eggs was strongly reduced during the observation period. When the Ascaris eggs were isolated from the lime treated sewage sludge and sus pended at neutral pH, the proportion that developed to larvated eggs d ecreased with time. Thus, the inactivation of A. suum eggs was reversi ble following short time storage while prolonged storage of sludge wit h pH > 12 completely destructed the ability of A. suum eggs to embryon ate. A. suum eggs uniformly mixed into the sludge lost the ability to embryonate at a faster rate than eggs deposited in nylon bags. After 5 months no intact eggs could be identified in the sludge. Incubation o f A. suum eggs at neutral pH imitate spreading on agricultural land, w here the eggs could be a potential infective hazard. In conclusion, li me treatment and storage of sewage sludge at pH > 12 for at least 3 mo nths can be recommended as a hygienic measure before application on ag ricultural land.