R.M. Ayres

A design equation for human intestinal nematode egg removal in waste stabilization ponds

Abstract The percentage removal ( R ) of human parasitic nematode eggs in waste stabilization ponds can be described by the empirical equation R = 100 [1 − 0.141 exp (−0.38θ)] where θ is the mean hydraulic retention time (d). The lower 95% confidence limit of this equation. R = 100 [1 − 0.41 exp (−0.49θ+0.0085θ 2 )] is recommended for the design of ponds to meet the WHO microbiological guideline of ≤ one egg per litre for restricted irrigation.

Comparison of techniques for the enumeration of human parasitic helminth eggs in treated wastewater

Abstract Four methods for the enumeration of human parasitic nematodes in treated wastewater were compared in field trials in the northeast of Brazil. Effluents from a series of waste stabilisation ponds and a physico‐chemical lime treatment plant were used. Comparisons were made on a daily and 24 hour basis. The recovery of eggs was found to be consistently higher using the method currently recommended by the World Health organisation (1) (commonly known as the Bailenger method) but only when 10 1 samples, rather than 11 samples, were processed.

Wastewater reuse in agriculture and the risk of intestinal nematode infection.

The increasing use of wastewater for crop irrigation in arid and semi-arid zones means that wastewater parasitology is becoming on important research area. The World Health Organizations (WHO) current guideline states that only treated wastewater containing no more than one human intestinal nematode egg per litre should be used for irrigation. This guideline was based on very limited epidemiological evidence. In this article Rachel Ayres, Rebecca Stott, Duncan Mara and Donald Lee describe their recent work in Yorkshire and northeast Brazil and suggest that their results may be the first evidence for relaxing the WHO guideline for restricted irrigation to no more than ten intestinal nematode eggs per litre.

The accumulation, distribution and viability of human parasitic nematode eggs in the sludge of a primary facultative waste stabilization pond

Investigations into the enumeration, distribution and viability of nematode eggs in the sludge from a primary facultative waste stabilization pond showed that pond sludges are not nematologically safe for immediate land application. Up to 12% of Ascaris lumbricoides eggs were viable after the pond had been in operation for 2.5 years. Eggs were recovered from the sludge along the full length of the pond, although there were significant decreases in egg concentration and viability with increasing distance from the inlet.

Monitoring full scale waste stabilisation ponds in Kenya for nematode egg removal

Abstract The removal of human intestinal nematode eggs (specifically Ascaris lumbricoides, Trichuris trichiura and the human hookworms) was measured in two series of waste stabilisation ponds in Kenya. Egg removal was efficient despite overloaded conditions at both sites and the final effluents met the current World Health Organisation standards for unrestricted irrigation with respect to nematode eggs (≤ 1 egg 1‐1 ). The distribution of eggs in the facultative pond effluents followed a Poisson distribution.