32 Outbreaks of Cryptosporidiosis Surface and groundwater sourcesRunoffSewage spillsCoagulationFiltrationrate changesBackwash recycleContaminated distribution system
33 Particle Counts Continuous on-line monitoring Low operating costs High sensitivityDetachment of aggregates
34 Cyst Removal vs Particle Removal Nieminski and Ongerth (1995)
35 Minimizing Risk of Outbreaks Optimal destabilization of particlesFilter-to-wasteCoagulants in backwashSlow-start filtrationMinimizing flow rate changes in dirty filtersTreatment of backwash waterFilter effluent turbidity < 0.1 NTU
36 Concluding StatementIn the multiple-barrier concept, filtration is the “great” barrier to particles, parasites and organics.
37 Summary and Conclusions Importance of particle destabilizationMicromechanical force modelBiofiltration for organics removalEffectiveness of collapse-pulsing air scourMultiple-barrier concept
38 ReferencesAmirtharajah, A., “Some Theoretical and Conceptual Views of Filtration,” JAWWA, Vol. 80, No. 12, 36-46, DecAmirtharajah, A., “Optimum Backwashing of Filters with Air Scour - A Review,” Water Sci. and Tech., Vol. 27, No. 10, , 1993.Ahmad, R. et al., “Effects of Backwashing on Biological Filters,” JAWWA, Vol. 90, No. 12, 62-73, Dec
39 AcknowledgmentsThis paper includes the work of several former students at Georgia Tech:M.S. students T.M. Ginn, L. Zeng and X. Wang and Ph.D students, Drs. P. Raveendran, R. Ahmad, K.E. Dennett and T. Mahmood.They were not only students but teachers too! Their work is acknowledged with gratitude.