Water Disinfection

For the International and Adventure Traveler

The Problem for Travelers

High density population, rampant pollution, and absence of sanitation systems means that raw water is wastewater.

Contaminationof tap water is to be assumed. Greater than 1 billion people have non access

to potable water. Inoculum size which is determined by volume

of water and concentration of organisms. Virulence of organisms.Some organisms

cause infection with small inoculum size ( eg., Giardia, Shigella, Hep A, Crypotosporidum, enteric viruses, E Coli enterohemmorhagic).

Heat Inactivation

Heat inactivation is exponential , thus thermal death is faster using higher temperature or using longer contact time at lower temperature.

Enteric pathogens are killed rapidly at >60C any watewr boiled for 1 min is safe at any altitude .

For travelers, a mutli-fuel backpacking stove or a heating coil can be useful.

Heat Inactivation

Neither improves or worsens taste or smell of water.

Single step process that inactivates all enteric pathogens.

Efficacy is not compromised by contaminants or particles.

Fuel sources may be expensive or unavailable.

Filtration

Filtration is both a physical and chemical process as electochemical attraction may cause viruses and other organisms to adhere to the filter.

Filters are simple to operate, add no taste but do add bulk.

As the filter clogs, higher pressures to drive water thru the devices can force microrganisms thru the filter.

Filter Types

Portable filters are depth filters using ceramicmaterial, fiber, or compressed GAC.

These filters have a large capacity for holding particles and don’t clogfor a long time.Flow can be partially restored by backflushing or surface cleaning.

A prefilter is often incorporated into the intake tubing, if not use a paper filter or cheese cloth.

Filter Effectiveness

Portable filters can easily remove protozan cysts and bacteria but can’t always remove all viruses .

Semi-permeable membranes in RO filters can.

EPA standard for virus removal is a 4 log reduction. Only the First Need filter by Sweet Water meets this standard.

Most filters do reduce viral load by 2-3 logs.

Filter Utility

In prestine water sheds, fecal contamination by humans is minimal and filtration of bacteria and protozoal cysts is the goal.

For foreign travel, surface H2O may be heavily contaminated with fecal or sewage matter. In this setting mechanical filters should not be used as the sole means of water disinfection.

Treatment with heat or halogens before, or after filtration is advised.

Halogens

The use of halogens, chiefly iodine or chlorine is used worldwide to disinfect water.

Germicidal activity results from the oxidation of essential cellular structures and enzymes.

Germicdal activity is based on concentration and contact time.

The goal is 4mg /L for clear H2O. In cloudly H20 either clarify first or double the

concentration and allow more contact time.

Halogens contd.

Cold slows reaction time. Protozal cysts are more resistant than enteric

bacteria or viruses but can be inactivated by doses of halogen used in the field.

Cryptosporidum oocysts are extremely resistant to halogens , cyclospora is asumed to be as well.

Resistance between iodine and chlorine are similar.

Iodine reacts less with organic compounds. Adding ascorbic acid helps improve taste.

Halogens contd.

Hypochlorite is currently the preferred means of disinfection in municipal water systems and has no known toxicity in this setting.

Iodine in low concentrations is effective in killing bacteria, viruses , and cysts.

High levels of iodine, such those found in iodine tabs should not be used for > than 1 mo. Consider TFT,s for long term use .Repeat q 6-12mos.

Demand Disinfectants

The concept of demand disinfectants has important implications for field dis-infection. Small filters that contain an iodine resin are insoluable in water , as organisms contact the rfesion the iodine binds to the microorganisms and are exposed to high concentrations.

Most also incorporate a 1-um filter to remove crytosporium and giardia.

Carbon removes residual iodine but may not allow sufficient time for destruction of cysts.

Miscellaneous Disinfectants

Ozone and chlorine dioxide are highly effective disionfectants and are used in municipal water systems and have recently been miniturized.

A process that uses an electrochemical process to convert a simlpe salt into a mixed oxidant solution containing free chlorine, chlorine dioxide and ozone .

The Miox device is the size of a cigar.

Preferred Technique

Heat is effective as a 1 step process in all situations, but won’t improve asthetics of water.

Optimal proctection may require a 2 step process of either coagulation-floculation, followed by halogenationn or filtration.

New methods using chlorine dioxide or ozone may prove to be an effective 1 step technique.

Sanitation

Personal hygiene especially important to prevent enteric infections.

Careful food prep.Dishes and utensils should be

disinfected by rinsing in water to which enough household bleach has been added to produce a distinct chlorine odor.

Cooking for oneself is associated with < risk of diarrheal disease !!

Etiology and Risk

Infectious agents include bacteria, viruses, protozoa and parasites.

The primary reason to disinfect water is to destroy microorganisms from humans or animals.

Water may also be contaminated wioth organic or inorganic chemicals.

Treatment Methods for Travelers

Bottled water is convinent and popular the bottles create ecological problems in countries that can’t recycle.

Disinfection means the removal , or destruction of microorganisms to make water potable not sterile.

A reduction of 3-5 log is the goal .

Purification

Purification and disinfection are often used interchangeably.

Purification is the removal of organic or inorganic chemicals and particulate materials to improve color , taste, and odor.

Purification may not remove enough micoorganisms to assure safety.

Clarification

Facilitates disinfection. Sedimentation is the separation of suspended

particles. Coagulation/floculation in use since 2000

B.C. is the removal of smaller suspended particles too small to settle with gravity.

Coagulation is the use of chemicals to cause particles to stick together.

Flocculation is a physical process to promote larger particles byb gentle mixing.Alum/Lime.

Coagulatiom/Floculation

Removes 60-98% of micoorganisms, heavymetals, and some minerals and chemicals.

Adda pinch Alum to 1gal water shake/stir briskly for 1min to mix, then agitate gently fo 5 min.Add more Alum if still cloudy.Wait 30 min and filter through paper or cheesecloth.

Use baking powder or white fireplace ash in an emergency.

GAC , or granular activated carbon is often found in portable field filters.

Risk of Infection