Water Disinfection

1. Water Disinfection For the International and Adventure Traveler

2. 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).

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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 !!

16. 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.

17. 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 .

18. 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.

19. 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.

20. 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.

21. Risk of Infection