Portable water purification
Portable water purification devices are self-contained, easily transported units used to
These units provide an
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
and saltiness from brackish or sea water.Common metallic contaminants such as copper and lead can be treated by increasing the pH using soda ash or lime, which precipitates such metals. Careful decanting of the clear water after settlement or the use of filtration provides acceptably low levels of metals. Water contaminated by aluminium or zinc cannot be treated in this way using a strong alkali as higher pHs re-dissolve the metal salts. Salt is difficult to remove except by reverse osmosis or distillation.
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
Less commonly seen in
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
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 use 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 WHO states bringing water to rolling boil then naturally cooling is sufficient to inactivate pathogenic bacteria, viruses and protozoa.[8]
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 (2,000 meters) boiling should continue for 3 minutes.[9]
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.[10] Encysted protozoan pathogens may require higher temperatures to remove any risk.[11]
Boiling is not always necessary nor sometimes enough.
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. It is worth noting that not all bacteria are removed by 0.2 µm pump filters; for example, strands of thread-like Leptospira spp. (which can cause leptospirosis) are thin enough to pass through a 0.2 µm filter. Effective chemical additives to address shortcomings in pump filters include chlorine, chlorine dioxide, iodine, and sodium hypochlorite (bleach). There have been polymer and ceramic filters on the market that incorporated iodine post-treatment in their filter elements to kill viruses and the smaller bacteria that cannot be filtered out, but most have disappeared due to the unpleasant taste imparted to the water, as well as possible adverse health effects when iodine is ingested over protracted periods.
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. 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
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 chemicals.
Chemical disinfection with halogens
Chemical disinfection with
Iodine
Similarly to
Iodine should be allowed at least 30 minutes to kill Giardia.[17]
Iodine crystals
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 are not measured with some accuracy.
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.[21] 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.
Sodium dichloroisocyanurate (NaDCC) has largely displaced halazone tablets for the few remaining chlorine-based water purification tablets available today.
Bleach
Common bleach including calcium hypochlorite (Ca[OCl]2) and sodium hypochlorite (NaOCl) are common, well-researched, low-cost oxidizers.
Chlorine bleach tablets give a more stable platform for disinfecting the water than liquid bleach as the liquid version tends to degrade with age and give unregulated results unless assays are carried out, which may be impractical in the field. Still, liquid bleach may nonetheless safely be used for short-term emergency water disinfection.
The EPA recommends two drops of 8.25% sodium hypochlorite solution (regular, unscented chlorine bleach) mixed per one quart/liter of water and leave to stand covered for 30 to 60 minutes. Two drops of 5% solution also suffices. Double the amount of bleach if the water is cloudy, colored, or very cold. Afterwards, the water should have a slight chlorine odor. If not repeat the dosage and let stand for another 15 minutes before use. After this treatment, the water may be left open to reduce the chlorine smell and taste.[22][6]
The
Neither chlorine (e.g., bleach) nor iodine alone is considered completely effective against
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.[9] The cost of chlorine dioxide treatment is higher than the cost of iodine treatment. [citation needed]
Mixed oxidant
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).[23]
Chlorine tablets
Sodium dichloroisocyanurate or troclosene sodium, more commonly shortened as NaDCC, is a form of chlorine used for disinfection. It is used by major non-governmental organizations such as UNICEF[24] to treat water in emergencies.
Sodium dichloroisocyanurate tablets are available in a range of concentrations to treat differing volumes of water[25] to give the World Health Organization's recommended 5ppm[26] 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. These solutions may disinfect water more effectively than iodine-based techniques while leaving hardly any noticeable taste in the water in some usage scenarios.[citation needed] Silver ion/chlorine dioxide-based disinfecting agents will kill Cryptosporidium and Giardia, if utilized correctly. The primary disadvantage of silver ion/chlorine dioxide-based techniques is the long purification times (generally 30 minutes to 4 hours, depending on the formulation used). Another concern is the possible deposition and accumulation of silver compounds in various body tissues leading to a rare condition called argyria that results in a permanent, disfiguring, bluish-gray pigmentation of the skin, eyes, and mucous membranes.
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.[27]
Ultraviolet purification
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 [28] 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.[29][30] Studies have shown that UV doses at the levels provided by common portable UV units are effective at killing Giardia[31] and that there was no evidence of repair and reactivation of the cysts.[32]
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.[33] 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.
Solar water disinfection
In solar water disinfection (often shortened as "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
See also
- Ceramic water filter
- Desalination
- Self-supply of water and sanitation
- Solar water disinfection
- Traveler's diarrhea
- Water quality
- Wilderness acquired diarrhea
References
- ^ Problem Organisms in Water: Identification and Treatment, 3rd Ed. (M7). Amewrican Waterworks Associan. 2004.
- ^ Geldreich E. Drinking water microbiology—new directions toward water quality enhancement. Int J Food Microbiol 1989;9:295-312.
- PMID 12681456.
- PMID 10737847.
- ^ "What is Leptospirosis?" (PDF). Hawaii State Department of Health. September 2006. Retrieved 26 November 2009.
- ^ PMID 11774083.
- ^ Clayton D.B:date=1989. Water pollution at Lowermoore North Cornwall. Lowermoore incident health advisory committee, Cornwall District Health Authority. p. 22.
{{cite book}}
: CS1 maint: numeric names: authors list (link) - ^ "Boil Water" (PDF). Archived from the original (PDF) on July 6, 2015.
- ^ a b c d "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.
- ^ 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
- ^ Lawley R (1 January 2013). "Cryptosporidium". Food Safety Watch.
- ^ Foundations of Microbiology
- ^ Hoff J. Inactivation of microbial agents by chemical disinfectants. Cincinnati: US Environmental Protection Agency; 1986. EPA/600/2-86/067.
- ^ "Equipped to Survive - Repackaging Potable Aqua". www.equipped.com. Retrieved 3 June 2018.
- PMID 7829615.
- ^ "Guidelines for Iodine Prophylaxis following Nuclear Accidents" (PDF). World Health Organization. 1999. Archived (PDF) from the original on 13 August 2013.
- ^ "National Forest Service". 20 September 2023. Retrieved 20 September 2023.
- PMID 165639.
- PMID 7281653.
- PMID 7405206.
- PMID 4959984.
- ^ EPA, OW, US (2013-02-20). "Ground Water and Drinking Water - US EPA". US EPA. Retrieved 3 June 2018.
- ^ Electrochemcially Generated Oxidant Disinfection In the Use of Individual Water Purification Devices, US Army Public Health Command, Prepared by: Steven H. Clarke, Environmental Engineer, March 2006, updated January 2011
- ^ "UNICEF - Progress on Drinking Water and Sanitation" (PDF).
- ^ "Water Purification Tablets".
- ^ "WHO - Guidelines for drinking-water quality, fourth edition". Archived from the original on July 7, 2011.
- PMID 20060566.
- ^ USEPA, Ultraviolet Disinfection Guidance Manual for the final LT2ESWTR, Nov 2006
- ^ "National Primary Drinking Water Regulations: Long Term 2 Enhanced Surface Water Treatment Rule". Federal Register. 71 (3): 783. 5 Jan 2006. Retrieved 17 Apr 2010.
- PMID 12092585.
- PMID 11848367.
- PMID 12075814.
- PMID 15528503.
External links
- Household Water Treatment Knowledge on CAWSTwebsite