Table 7.8Reductions of bacteria, viruses and protozoa achieved by household water treatment technologies

Treatment processEnteric pathogen groupBaseline removal (LRV)Maximum removal (LRV)Notes
Chemical disinfection
Free chlorine disinfectionBacteria36Free chlorine × contact time predicts efficacy; not effective against Cryptosporidium oocysts. Turbidity and chlorine-demanding solutes inhibit this process; hence, turbidity should be kept below 1 NTU to support effective disinfection. Where this is not practical, the aim should be to keep turbidities below 5 NTU, although disinfection should still be practiced if 5 NTU cannot be achieved. At turbidities of more than 1 NTU, higher chlorine doses or contact times will be requireda
Viruses36
Protozoa, non-Cryptosporidium35
Cryptosporidium 01
Membrane, porous ceramic or composite filtration
Porous ceramic and carbon block filtrationBacteria26Varies with pore size, flow rate, filter medium and inclusion of augmentation with silver or other chemical agents
Viruses14
Protozoa46
Membrane filtration (microfiltration, ultrafiltration, nanofiltration, reverse osmosis)Bacteria2 MF; 3 UF, NF or RO4 MF; 6 UF, NF or ROVaries with membrane pore size, integrity of filter medium and filter seals, and resistance to chemical and biological (“grow-through”) degradation; maximum reductions associated with filtered water turbidity of < 0.1 NTUa
Viruses0 MF; 3 UF, NF or RO4 MF; 6 UF, NF or RO
Protozoa2 MF; 3 UF, NF or RO6 MF; 6 UF, NF or RO
Fibre and fabric filtration (e.g. sari cloth filtration)Bacteria12Particle or plankton association increases removal of microbes, notably copepod-associated guinea worm (Dracunculus medinensis) and plankton-associated Vibrio cholerae; larger protozoa (> 20 μm) may be removed; ineffective for viruses, dispersed bacteria and small protozoa (e.g. Giardia intestinalis, 8–12 μm, and Cryptosporidium 4–6 μm)
Viruses00
Protozoa01
Granular media filtration
Rapid granular, diatomaceous earth, biomass and fossil fuel–based (granular and powdered activated carbon, wood and charcoal ash, burnt rice hulls, etc.) filtersBacteria14+Varies considerably with media size and properties, flow rate and operating conditions; some options are more practical than others for use in developing countries
Viruses14+
Protozoa14+
Household-level intermittently operated slow sand filtrationBacteria13Varies with filter maturity, operating conditions, flow rate, grain size and filter bed contact time
Viruses0.52
Protozoa24
Solar disinfection
Solar disinfection (solar UV radiation + thermal effects)Bacteria35+Varies depending on oxygenation, sunlight intensity, exposure time, temperature, turbidity and size of water vessel (depth of water)
Viruses24+
Protozoa24+
UV light technologies using lamps
UV irradiationBacteria35+Effectiveness of disinfection depends on delivered fluence (dose), which varies with intensity, exposure time and UV wavelength. Excessive turbidity and certain dissolved species inhibit this process; hence, turbidity should be kept below 1 NTU to support effective disinfection. Where this is not practical, turbidities should be kept below 5 NTU with higher fluencesa
Viruses25+
Protozoa35+
Thermal (heat) technologies
Thermal (e.g. boiling)Bacteria69+Values are based on vegetative cells; spores are more resistant to thermal inactivation than are vegetative cells; treatment to reduce spores by boiling must ensure sufficient temperature and time
Viruses69+
Protozoa69+
Sedimentation
Simple sedimentationBacteria00.5Effective due to settling of particle-associated and large (sedimentable) microbes; varies with storage time and particulates in the water
Viruses00.5
Protozoa01
Combination treatment approaches
Flocculation plus disinfection systems (e.g. commercial powder sachets or tablets)Bacteria79Some removal of Cryptosporidium possible by coagulation
Viruses4.56
Protozoa35

LRV, log10 reduction value; MF, microfilter; NF, nanofilter; RO, reverse osmosis; UF, ultrafilter

a

See Turbidity: Information for regulators and operators of water supplies (Annex 1).

From: 7, Microbial aspects

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Guidelines for drinking-water quality: Fourth edition incorporating the first and second addenda [Internet].
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