Removal of Cryptosporidium parvum oocysts by rapid sand filtration with ballasted flocculation-filtration and intermediate downwashes

A novel and efficient protocol optimising deep-bed filtration of surface water was developed. The innovation lies in ballasted-flocculation filtration and an intermediate downwash. The approach is based on the assumption that kaolin particles with a partial positive charge may adsorb onto the surface of C. parvum oocysts and neutralize their negative charge. Application of this technology enhanced removal of inorganic particles and Cryptosporidium, parvum oocysts by approximately 30% and shortened the ripening stage of the filtration process from 1 h to about 10 min.