Microspheres as Surrogate Helminth Eggs: A Comparative Labscale Sedimentation Study for Tap- and Wastewater

Abstract

Re-use of water containing helminth eggs during irrigation for agricultural purposes poses health risks, and likewise during research, due to the potential of spreading on contact. Therefore, polystyrene latex microspheres could be used as surrogates for chemical or biological species during colloidal transport. The aim here is to compare the settling velocities of microspheres having varied surface coatings—that is, proteins A, G and A/G; with that of real helminth eggs obtained from literature. The settling velocities of the microspheres were experimentally determined in tap- and wastewater, as well as theoretically in tap water; which was found to be within the range of mean values for those experimentally determined. There were no differences amongst the microspheres types used for settling in wastewater (i.e., A = 0.072 ± 0.02; G = 0.060 ± 0.03; A/G = 0.053 ± 0.01 mm/s). The same applied for settling in tap water (i.e., A = 0.068 ± 0.02; G = 0.047 ± 0.004; A/G = 0.095 ± 0.02 mm/s), except for microsphere G being different from microsphere A/G. All three types of microspheres settled at velocities lower than that of the wastewater particles (=0.118 ± 0.03). T-test analyses of settling velocities of microspheres in both tap- and wastewater, versus that from literature (i.e., Ascaris, Trichuris and Oesophagostomum), showed that microsphere A and A/G may surrogate for Ascaris in tap water, the same as A/G for Oesophagostomum. In wastewater however, both microspheres A and G are a good fit for Trichuris.