Portable water purification

Portable water purification devices are self-contained, easily transported units used to purify water from untreated sources (such as rivers, lakes, and wells) for drinking purposes. Their main function is to eliminate pathogens, and often also of suspended solids and some unpalatable or toxic compounds.

Techniques include heat (including boiling), filtration, activated charcoal adsorption, chemical disinfection (e.g. chlorination, iodine, ozonation, etc.), ultraviolet purification (including SODIS), distillation (including solar distillation), and flocculation. Often these are used in combination.

Drinking water hazards

Untreated water may contain potentially pathogenic agents, including protozoa, bacteria, viruses, and some larvae of higher-order parasites such as liver flukes and roundworms. Chemical pollutants such as pesticides, heavy metals and synthetic organics may be present. Other components may affect taste, odour and general aesthetic qualities, including turbidity from soil or clay, colour from humic acid or microscopic algae, odours from certain type of bacteria, particularly Actinomycetes which produce geosmin,[1] and saltiness from brackish or sea water.

Most portable treatment processes focus on mitigating human pathogens for safety and removing particulates matter, tastes and odours. Significant pathogens commonly present in the developed world include Giardia, Cryptosporidium, Shigella, hepatitis A virus, Escherichia coli, and enterovirus.[2] In less developed countries there may be risks from cholera and dysentery organisms and a range of tropical enteroparasites.

Giardia lamblia and Cryptosporidium spp., both of which cause diarrhea (see giardiasis and cryptosporidiosis) are common pathogens. In backcountry areas of the United States and Canada they are sometimes present in sufficient quantity that water treatment is justified for backpackers,[3] although this has created some controversy.[4] (See wilderness acquired diarrhea.) In Hawaii and other tropical areas, Leptospira spp. are another possible problem.[5]

Less commonly seen in developed countries are organisms such as Vibrio cholerae which causes cholera and various strains of Salmonella which cause typhoid and para-typhoid diseases. Pathogenic viruses may also be found in water. The larvae of flukes are particularly dangerous in area frequented by sheep, deer, or cattle. If such microscopic larvae are ingested, they can form potentially life-threatening cysts in the brain or liver. This risk extends to plants grown in or near water including the commonly eaten watercress.

In general, more human activity up stream (i.e. the larger the stream/river) the greater the potential for contamination from sewage effluent, surface runoff, or industrial pollutants. Groundwater pollution may occur from human activity (e.g. on-site sanitation systems or mining) or might be naturally occurring (e.g. from arsenic in some regions of India and Bangladesh). Water collected as far upstream as possible above all known or anticipated risks of pollution poses the lowest risk of contamination and is best suited to portable treatment methods.

Techniques

31st Marine Expeditionary Unit (MEU) Service Support Group 31

Not all techniques by themselves will mitigate all hazards. Although flocculation followed by filtration has been suggested as best practice[6] this is rarely practicable without the ability to carefully control pH and settling conditions. Ill-advised used of alum as a flocculant can lead to unacceptable levels of aluminium in the water so treated.[7] If water is to be stored, halogens offer extended protection.

Heat (boiling)

Heat kills disease-causing micro-organisms, with higher temperatures and/or duration required for some pathogens. Sterilization of water (killing all living contaminants) is not necessary to make water safe to drink; one only needs to render enteric (intestinal) pathogens harmless. Boiling does not remove most pollutants and does not leave any residual protection.

The CDC recommends a rolling boil for 1 minute. At high elevations, though, the boiling point of water drops. At altitudes greater than 6,562 feet (2000 meters) boiling should continue for 3 minutes.[8]

All bacterial pathogens are quickly killed above 60 °C (140 °F), therefore, although boiling is not necessary to make the water safe to drink, the time taken to heat the water to boiling is usually sufficient to reduce bacterial concentrations to safe levels.[9] Encysted protozoan pathogens may require higher temperatures to remove any risk.[10]

Boiling is not always necessary nor sometimes enough. Pasteurization where enough pathogens are killed typically occurs at 63 °C for 30 minutes or 72 °C for 15 seconds. Certain pathogens must be heated above boiling (e.g. botulism – Clostridium botulinum requires 118 °C (244 °F), most endospores require 120 °C (248 °F),[11] and prions even higher). Higher temperatures may be achieved with a pressure cooker. Heat combined with ultraviolet light (UV), such as SODIS method, reduces the necessary temperature + duration.

Filtration

Portable pump filters are commercially available with ceramic filters that filter 5,000 to 50,000 litres per cartridge, removing pathogens down to the 0.2–0.3 micrometer (µm) range. Some also utilize activated charcoal filtering. Most filters of this kind remove most bacteria and protozoa, such as Cryptosporidium and Giardia lamblia, but not viruses except for the very largest of 0.3 µm and larger diameters, so disinfection by chemicals or ultraviolet light is still required after filtration.

While the filtration elements may do an excellent job of removing most bacteria and fungi contaminants from drinking water when new, the elements themselves can become colonization sites. In recent years some filters have been enhanced by bonding silver metal nanoparticles to the ceramic element and/or to the activated charcoal to suppress growth of pathogens.

Small, hand-pumped reverse osmosis filters were originally developed for the military in the late 1980s for use as survival equipment, for example, to be included with inflatable rafts on aircraft. Civilian versions are available. Instead of using the static pressure of a water supply line to force the water through the filter, pressure is provided by a hand-operated pump, similar in function and appearance to a mechanic's grease gun. These devices can generate drinkable water from seawater.

The Portable Aqua Unit for Lifesaving (short PAUL) is a portable ultrafiltration-based membrane water filter for humanitarian aid. It allows the decentralized supply of clean water in emergency and disaster situations for about 400 persons per unit per day. The filter is designed to function with neither chemicals nor energy nor trained personnel.

Activated charcoal adsorption

Portable water purification unit used by International Red Cross and Red Crescent.

Granular activated carbon filtering utilizes a form of activated carbon with a high surface area, and adsorbs many compounds, including many toxic compounds. Water passing through activated carbon is commonly used in concert with hand pumped filters to address organic contamination, taste, or objectionable odors. Activated carbon filters aren't usually used as the primary purification techniques of portable water purification devices, but rather as secondary means to complement another purification technique. It is most commonly implemented for pre- or post-filtering, in a separate step than ceramic filtering, in either case being implemented prior to the addition of chemical disinfectants used to control bacteria or viruses that filters cannot remove. Activated charcoal can remove chlorine from treated water, removing any residual protection remaining in the water protecting against pathogens, and should not, in general, be used without careful thought after chemical disinfection treatments in portable water purification processing. Ceramic/Carbon Core filters with a 0.5 µm or smaller pore size are excellent for removing bacteria and cysts while also removing

Chemical disinfection with halogens

Chemical disinfection with halogens, chiefly chlorine and iodine, results from oxidation of essential cellular structures and enzymes. The primary factors that determine the rate and proportion of microorganisms killed are the residual or available halogen concentration and the exposure time.[12] Secondary factors are pathogen species, water temperature, pH, and organic contaminants. In field-water disinfection, use of concentrations of 1–16 mg/L for 10–60 min is generally effective. Of note, Cryptosporidium oocysts, likely Cyclospora species, Ascaris eggs are extremely resistant to halogens and field inactivation may not be practical with bleach and iodine.

Iodine

Iodine used for water purification is commonly added to water as a solution, in crystallized form, or in tablets containing tetraglycine hydroperiodide that release 8 mg of iodine per tablet adaptation to chronic tetraglycine hydroperiodide.

Iodine should be allowed at least 30 minutes to kill Giardia.

A potentially lower cost alternative to using iodine-based water purification tablets is the use of iodine crystals although there are serious risks of acute iodine toxicity if preparation and dilution and not measured with some accuracy. [13] [14] This method may not be adequate in killing Giardia cysts in cold water.[15] An advantage of using iodine crystals is that only a small amount of iodine is dissolved from the iodine crystals at each use, giving this method of treating water a capability for treating very large volumes of water. Unlike tetraglycine hydroperiodide tablets, iodine crystals have an unlimited shelf life as long as they are not exposed to air for long periods of time or are kept under water. Iodine crystals will sublimate if exposed to air for long periods of time. The large quantity of water that can be purified with iodine crystals at low cost makes this technique especially cost effective for point of use or emergency water purification methods intended for use longer than the shelf life of tetraglycine hydroperiodide.

Halazone tablets

Chlorine-based halazone tablets were formerly popularly used for portable water purification. Chlorine in water is more than three times more effective as a disinfectant against Escherichia coli than iodine.[16] Halazone tablets were thus commonly used during World War II by U.S. soldiers for portable water purification, even being included in accessory packs for C-rations until 1945.

Chlorine bleach tablets give a more stable platform for disinfecting the water than liquid bleach (sodium hypochlorite) as the liquid version tends to degrade with age and give unregulated results unless assays are carried out – not practical on the spot. Still, despite chlorine-based halazone tablets falling from favor for portable water purification, chlorine-based bleach may nonetheless safely be used for short-term emergency water disinfection. Two drops of unscented 5% bleach can be added per liter or quart of clear water, then allowed to stand covered for 30 to 60 minutes. After this treatment, the water may be left open to reduce the chlorine smell and taste. Guidelines are available online for effective emergency use of bleach to render unsafe water potable.

The Centers for Disease Control & Prevention (CDC) and Population Services International (PSI) promote a similar product (a 0.5% - 1.5% sodium hypochlorite solution) as part of their Safe Water System (SWS) strategy. The product is sold in developing countries under local brand names specifically for the purpose of disinfecting drinking water.[8]

Bleach

Common bleach including calcium hypochlorite (Ca[OCl]2) and sodium hypochlorite (NaOCl) are common, well-researched, low-cost oxidizers.

Neither chlorine (e.g., bleach) nor iodine alone is considered completely effective against Cryptosporidium, although they are partially effective against Giardia. Chlorine is considered slightly better against the latter. A more complete field solution that includes chemical disinfectants is to first filter the water, using a 0.2 µm ceramic cartridge pumped filter, followed by treatment with iodine or chlorine, thereby filtering out cryptosporidium, Giardia, and most bacteria, along with the larger viruses, while also using chemical disinfectant to address smaller viruses and bacteria that the filter cannot remove. This combination is also potentially more effective in some cases than even using portable electronic disinfection based on UV treatment.

Chlorine dioxide

Chlorine dioxide can come from tablets or be created by mixing two chemicals together. It is more effective than iodine or chlorine against giardia, and although it has only low to moderate effectiveness against cryptosporidium, iodine and chlorine are ineffective against this protozoan.

Mixed oxidant (MiOx)

A simple brine {salt + water} solution in an electrolytic reaction produces a powerful mixed oxidant disinfectant (mostly chlorine in the form of hypochlorous acid (HOCl) and some peroxide, ozone, chlorine dioxide)[17] to inactivate viruses, bacteria, Giardia and Cryptosporidium killing 99.9% of all organisms without the need to filter.

Chlorine tablets (NaDCC)

Sodium dichloroisocyanurate or Troclosene Sodium more commonly shortened as NaDCC, is a form of chlorine used for disinfection.

NaDCC tablets are available in a range of concentrations to treat differing volumes of water[18] to give the World Heath Organisation's recommended 5ppm[19] available chlorine. They are effervescent tablets allowing the tablet to dissolve in a matter of minutes.

Other chemical disinfection additives

Silver ion tablets

An alternative to iodine-based preparations in some usage scenarios are silver ion/chlorine dioxide-based tablets or droplets.

Hydrogen peroxide

One recent study has found that the wild Salmonella which would reproduce quickly during subsequent dark storage of solar-disinfected water could be controlled by the addition of just 10 parts per million of hydrogen peroxide.[20]

Ultraviolet purification

Ultraviolet (UV) light induces the formation of covalent linkages on DNA and thereby prevents microbes from reproducing.

A concern with UV portable water purification is that some pathogens are hundreds of times less sensitive to UV light than others. Protozoan cysts were once believed to be among the least sensitive, however recent studies have proved otherwise, demonstrating that both Cryptosporidium and Giardia are deactivated by a UV dose of just 6 mJ/cm2 [21] However, EPA regulations and other studies show that it is viruses that are the limiting factor of UV treatment, requiring a 10-30 times greater dose of UV light than Giardia or Cryptosporidium.[22][23] Studies have shown that UV doses at the levels provided by common portable UV units are effective at killing Giardia[24] and that there was no evidence of repair and reactivation of the cysts.[25]

Water treated with UV still has the microbes present in the water, only with their means for reproduction turned "off". In the event that such UV-treated water containing neutered microbes is exposed to visible light (specifically, wavelengths of light over 330-500 nm) for any significant period of time, a process known as photo reactivation can take place, where the possibility for repairing the damage in the bacteria's reproduction DNA arises, potentially rendering them once more capable of reproducing and causing disease.[26] UV-treated water must therefore not be exposed to visible light for any significant period of time after UV treatment, before consumption, to avoid ingesting reactivated and dangerous microbes.

Recent developments in semiconductor technology allows for the development of UV-C Light Emitting Diodes (LEDs). UV-C LED systems address disadvantages of mercury-based technology, namely: power-cycling penalties, high power needs, fragility, warm-up time, and mercury content.

Ozone water disinfection

In ozone water disinfection, microbes are destroyed by ozone gas (O3) provided by an ozone generator. Common in Europe, ozone gas is now becoming widely adopted in the United States. It is emerging across a wide array of industries; from municipal water treatment plants, to food processing plants, to healthcare organizations. It is being adopted due to its ability to sanitize water and surfaces without wasting water, and because there are no by-products. When its job is done, ozone gas quickly degrades into oxygen. Ozone is more effective than chlorine in destroying viruses and bacteria.

Ozone is most commonly created by a process called “corona discharge”, which causes oxygen molecules (O2) to temporarily re-combine into ozone (O3). This gas is very unstable, and the 3rd oxygen molecule reacts with pathogens by penetrating the cell walls of bacteria and viruses. This destroys the organisms.

Ozone is effective against pollutants for the same reason; it will react with long-chain carbon (organic) molecules, and break them down into less complex (and typically less harmful) molecules through oxidation.

Advances in ozone generation techniques, coupled with filtration, make this a viable new portable water purification method.

Solar water disinfection

In solar water disinfection (SODIS), microbes are destroyed by temperature and UVA radiation provided by the sun. Water is placed in a transparent plastic PET bottle or plastic bag, oxygenated by shaking partially filled capped bottles prior to filling the bottles all the way, and left in the sun for 6–24 hours atop a reflective surface.

Solar distillation

Solar distillation relies on sunlight to warm and evaporate the water to be purified which then condenses and trickles into a container. In theory, a solar (condensation) still removes all pathogens, salts, metals, and most chemicals but in field practice the lack of clean components, easy contact with dirt, improvised construction, and disturbances result in cleaner, yet contaminated water.

Homemade water filters

Water filters can be made on-site using local materials such as sand and charcoal (e.g. from firewood burned in a special way). These filters are sometimes used by soldiers and outdoor enthusiasts. Due to their low cost they can be made and used by anyone. The reliability of such systems is highly variable. Such filters can do little, if anything, to mitigate germs and other harmful constituents and can give a false sense of security that the water so produced is potable. Water processed through an improvised filter should undergo secondary processing such as boiling to render it safe for consumption.

Prevention of water contamination

Human water-borne diseases usually come from other humans, thus human-derived materials (feces, medical waste, wash water, lawn chemicals, gasoline engines, garbage, etc.) should be kept far away from water sources.

See also

References

  1. ↑ Problem Organisms in Water: Identification and Treatment, 3rd Ed. (M7). Amewrican Waterworks Associan. 2004.
  2. ↑ Geldreich E. Drinking water microbiology—new directions toward water quality enhancement. Int J Food Microbiol 1989;9:295-312.
  3. ↑ Boulware DR, Forgey WW, Martin WJ (2003). "Medical risks of wilderness hiking". The American Journal of Medicine. 114 (4): 288–93. doi:10.1016/S0002-9343(02)01494-8. PMID 12681456.
  4. ↑ Welch TP (2000). "Risk of giardiasis from consumption of wilderness water in North America: a systematic review of epidemiologic data". International Journal of Infectious Diseases. 4 (2): 100–3. doi:10.1016/S1201-9712(00)90102-4. PMID 10737847.
  5. ↑ "What is Leptospirosis?" (PDF). Hawaii State Department of Health. September 2006. Retrieved 26 November 2009.
  6. ↑ Ericsson, Charles D.; Steffen, Robert; Backer, Howard (1 February 2002). "Water Disinfection for International and Wilderness Travelers". Clinical Infectious Diseases. 34 (3): 355–364. doi:10.1086/324747. Retrieved 3 June 2018 – via cid.oxfordjournals.org.
  7. ↑ Clayton D.B:date=1989. Water pollution at Lowermoore North Cornwall. Lowermoore incident health advisory committee, Cornwall District Health Authority. p. 22.
  8. 1 2 "A Guide to Drinking Water Treatment and Sanitation for Backcountry & Travel Use". Centers for Disease Control and Prevention. 10 April 2009. Retrieved 19 March 2018.
  9. ↑ Backer, H. Water Disinfection for International and Wilderness Traveler. Clinical Infectious Diseases. (2002) 34 (3): 355-364. Available from: http://cid.oxfordjournals.org/content/34/3/355.full
  10. ↑ Lawley R (1 January 2013). "Cryptosporidium". Food Safety Watch.
  11. ↑ http://www.bellarmine.edu/faculty/dobbins/Secret%20Readings/Lecture%20Notes%20202/Chapter%2011WO.pdf
  12. ↑ Hoff J. Inactivation of microbial agents by chemical disinfectants. Cincinnati: US Environmental Protection Agency; 1986. EPA/600/2-86/067.
  13. ↑ Kahn FH, Visscher BR (1975). "Water Disinfection in the Wilderness -- a simple, effective method of iodination". Western Journal of Medicine. 122 (5): 450–3. PMC 1129772. PMID 165639.
  14. ↑ Zemlyn S, Wilson WW, Hellweg PA (1981). "A caution on iodine water purification". Western Journal of Medicine. 135 (2): 166–7. PMC 1273058. PMID 7281653.
  15. ↑ Jarroll EL Jr.; Bingham AK; Meyer EA (1980). "Inability of an iodination method to destroy completely Giardia cysts in cold water". Western Journal of Medicine. 132 (6): 567–9. PMC 1272173. PMID 7405206.
  16. ↑ Koski TA, Stuart LS, Ortenzio LF (1966). "Comparison of Chlorine, Bromine, and Iodine as Disinfectants for Swimming Pool Water". Applied Microbiology. 14 (2): 276–9. PMC 546668. PMID 4959984.
  17. ↑ http://phc.amedd.army.mil/PHC%20Resource%20Library/Electrochemically%20Generated%20Oxidant%20Disinfection%20in%20the%20Use%20of%20Individual%20Water%20Purification%20Devices.pdf
  18. ↑ "Water Purification Tablets".
  19. ↑ "WHO - Guidelines for drinking-water quality, fourth edition".
  20. ↑ Sciacca F, Rengifo-Herrera JA, Wéthé J, Pulgarin C (2010-01-08). "Dramatic enhancement of solar disinfection (SODIS) of wild Salmonella sp. in PET bottles by H(2)O(2) addition on natural water of Burkina Faso containing dissolved iron". Chemosphere (epub ahead of print)|format= requires |url= (help). 78 (9): 1186–91. doi:10.1016/j.chemosphere.2009.12.001. PMID 20060566.
  21. ↑ USEPA, Ultraviolet Disinfection Guidance Manual for the final LT2ESWTR, Nov 2006
  22. ↑ "National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule". Federal Register. U.S. Environmental Protection Agency. 71 (3): 783. 5 Jan 2006. Retrieved 17 Apr 2010.
  23. ↑ Mofidi AA, Meyer EA, Wallis PM, Chou CL, Meyer BP, Ramalinham S, Coffey BM (2002). "The effect of UV light on the inactivation of Giardia lamblia and Giardia muris cysts as determined by animal infectivity assay (P-2951-01)". Water Research. 36 (8): 2098–108. doi:10.1016/S0043-1354(01)00412-2. PMID 12092585.
  24. ↑ Campbell AT, Wallis P (2002). "The effect of UV irradiation on human-derived Giardia lamblia cysts". Water Research. 36 (4): 963–9. doi:10.1016/S0043-1354(01)00309-8. PMID 11848367.
  25. ↑ Linden KG, Shin GA, Faubert G, Cairns W, Sobsey MD (2002). "UV disinfection of Giardia lamblia cysts in water". Environmental Science and Technology. 36 (11): 2519–22. doi:10.1021/es0113403. PMID 12075814.
  26. ↑ Qiu X, Sundin GW, Chai B, Tiedje JM (November 2004). "Survival of Shewanella oneidensis MR-1 after UV Radiation Exposure". Applied and Environmental Microbiology. 70 (11): 6435–43. doi:10.1128/AEM.70.11.6435-6443.2004. PMC 525172. PMID 15528503.
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