Parasite removal by waste stabilisation pond systems and the relationship between concentrations in sewage and prevalence in the community

Abstract

Waste stabilisation pond (WSP) performance for the removal of nematode eggs is generally considered to be excellent. In this paper, the performance of WSPs for parasite egg removal is reviewed. A simplified membrane filtration method for enumeration of parasites in sewage was introduced and applied to evaluate emergency anaerobic and permanent sanitation units in Bangladesh. With short retention times of 48-72 hours 99% egg removal efficiencies were achieved in the emergency unit using sewage from a cholera hospital complex. Permanent units gave poorer performance and, in a 23 day WSP system in Grand Cayman, it is possible that removal efficiency may have been impaired and hookworm eggs carried over to the final effluent. Evidence for carry over of eggs is critically re-assessed. Publications relating levels of prevalence of helminth parasites and concentrations in sewage are summarised, and data are interpolated to provide an understanding of the response-dose relationship. A classification of end emicity is proposed to assist in evaluating the success of helminth control programs.