Removal of intestinal nematode eggs in tropical waste stabilization ponds.

The removal of intestinal nematode eggs in waste stabilization ponds treating domestic waste-water was studied in northeast Brazil. Anaerobic and primary facultative ponds achieved Ascaris spp. removals of 88-98% and 99-100%, and hookworm removals of 91-97% and 98-100%, respectively. Egg-free effluents were produced by a single primary facultative pond with a retention time of 18.9 days, and by an anaerobic and a secondary facultative pond in series with retention times of 6.8 and 5.5 days. It is concluded that effluents with less than or equal to 1 egg per litre can be produced by a 1 day anaerobic pond followed by a 5 day secondary facultative and a 5 day maturation pond.