Cryptosporidium surrogate removal in five commonly used point-of-use domestic filters

Point-of-use filters are the major means of treating household drinking-water from non-reticulated water supplies, especially in developing communities, but their effectiveness at removing protozoa varies greatly. We custom built a full-scale filter test rig to simulate typical household use conditions (40 psi, 21.6 L water/day treated, intermittent operation), and assessed the efficiencies of five commonly used low-cost household filter cartridges at removing glycoprotein-coated 4.5 mu m polystyrene microspheres that had been validated as a surrogate for Cryptosporidium oocysts. The filter cartridges included 1 mu m nominal activated carbon, 1 mu m nominal polypropylene, 1 mu m nominal polyester, 1 mu m absolute pleated-paper and 2 mu m nominal silver-impregnated carbon. The data from 120 test runs (duplicate filters, 24 replicate runs per filter type) indicated that the surrogate particles' log10 reduction values (LRVs) were 3.93-4.54 in the 1 mu m activated carbon filters, 1.95-2.94 in the 2 mu m silver-impregnated carbon filters, and 1.0 in the 1 mu m polypropylene, 1 mu m polyester and 1 mu m pleated-paper filters. To achieve an LRV 3, which is a requirement of domestic drinking-water treatment units for protozoan reduction, 1 mu m activated carbon filters are recommended. To satisfy protozoan removal requirements when using the other four filter types tested, additional treatment, for example, water boiling or ultraviolet disinfection, is necessary.

Automated summary

Point-of-use filters are commonly used in developing communities to treat household drinking water, with activated carbon filters proving more effective than other types in removing protozoa. Additional treatment such as water boiling or ultraviolet disinfection is necessary when using other filter types to meet protozoan removal requirements.