Sedimentation of helminth eggs in water

• Published in: Water research (Oxford) Vol. 45; no. 15; pp. 4651 - 4660
• Main Authors: Sengupta, Mita E., Thamsborg, Stig M., Andersen, Thorbjørn J., Olsen, Annette, Dalsgaard, Anders
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2011; Elsevier
• Subjects: Animals; Applied sciences; Ascaris suum; crops; Density; Eggs; Exact sciences and technology; Helminth eggs; Helminths; Irrigation; Oesophagostomum; Parasite Egg Count; Particles; Pollution; risk; Sedimentation; Settling; Settling velocity; Stokes’ law; Tap water; Trichuris; Trichuris suis; Tubes; viscosity; Waste water; wastewater; Water; Water - parasitology; water quality; Water Supply - standards; Water treatment and pollution; Water; Settling velocity; Stokes’ law; Sedimentation; Particles; Helminth eggs; Viscosity; Irrigation; Stokes' law; Parasite; Tap water; Modeling; Waste water; Health and environment; Water quality; Health hazards; Public health
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2011.06.017

Helminth parasite eggs in low quality water represent health risks when used for irrigation of crops. The settling velocities of helminth eggs (Ascaris suum, Trichuris suis, and Oesophagostomum spp.) and wastewater particles were experimentally determined in tap water and in wastewater using Owen tubes. The settling velocities of eggs in tap water was compared with theoretical settling velocities calculated by Stoke’s law using measurements of size and density of eggs as well as density and viscosity of tap water. The mean settling velocity in tap water of 0.0612mms−1 found for A. suum eggs was significantly lower than the corresponding values of 0.1487mms−1 for T. suis and 0.1262mms−1 for Oesophagostomum spp. eggs. For T. suis and Oesophagostomum spp. eggs the theoretical settling velocities were comparable with the observed velocities in the Owen tubes, while it was three times higher for A. suum eggs. In wastewater, the mean settling velocity for A. suum eggs (0.1582mms−1) was found to be different from T. suis (0.0870mms−1), Oesophagostomum spp. (0.1051mms−1), and wastewater particles (0.0474mms−1). This strongly indicates that in low quality water the eggs are incorporated into particle flocs with different settling velocities and that the settling velocity of eggs and particles is closely associated. Our results document that there is a need to differentiate the sedimentation of different types of helminth eggs when assessing the quality of low quality water, e.g. for irrigation usage. The results can also be used to improve existing models for helminth egg removal. ► Helminth parasite eggs in low quality water represent health risks when used for irrigation of crops. ► Not all helminth eggs settle according to Stokes’ law. ► In wastewater, the helminth eggs are incorporated into the particle flocs. ► There is a need for differentiating between helminth egg types when assessing the water quality.