The “aerobic” and “facultative” sewage stabilization ponds, according to the laboratory findings, are not likely to suppress the hatching of the eggs or significantly affect the survival of miracidia of Schistosoma mansoni or the vector snails. The results indicate, however, that the deep, heavily loaded, anaerobic pond will curtail the hatching of the eggs, significantly affect the survival of the miracidia, and discourage the survival of vector snails. Under tropical conditions the inclusion of a preliminary anaerobic chamber in the stabilization pond design should effectively remove the eggs and miracidia of S. mansoni.
In support of the above conclusion, the following experimental results are summarized:
The viability of S. mansoni eggs harvested from livers of infected mice does not extend beyond the second day in sewage or sewage stabilization ponds of any classification.
All waters devoid or nearly devoid of dissolved oxygen were found to inhibit hatching and reduce the viability of the eggs.
Environmental factors in raw sewage other than the dissolved oxygen content inhibited the hatching of eggs.
Eggs remaining in the bottom sludge of sewage stabilization ponds for more than nine hours cannot be induced to hatch.
The maximum and mean survival times of miracidia in the “anaerobic pond” water were 6 and 2 hours, while in the “aerobic pond” water they were 10 and 4 hours.
Present address: Department of Social and Preventive Medicine, Christian Medical College, Ludhiana, Punjab, India.