CHLORINE
Chlorine has a number of problems when used for field treatment of water. When chlorine reacts with organic material, it attaches itself to nitrogen containing compounds (ammonium ions and amino acids), leaving less free chlorine to continue disinfection. Carcinogenic trihalomethanes are also produced, though this is only a problem with long-term exposure. Trihalomethanes can also be filtered out with a charcoal filter, though it is more efficient to use the same filter to remove organics before the water is chlorinated. Unless free chlorine is measured, disinfection can not be guaranteed with moderate doses of chlorine.
One solution is super chlorination, the addition of far more chlorine than is needed.
This must again be filtered through activated charcoal to remove the large amounts
Of chlorine, or hydrogen peroxide can be added to drive the chlorine off. Either
Way there is no residual chlorine left to prevent recontamination. This isn’t a problem, if the water is to be used at once.
Chlorine is sensitive to both the pH and temperature of the treated water.
Temperature slows the reaction for any chemical treatment, but chlorine treatment
Is particularly susceptible to variations in the pH as at lower pHs, hypochlorous
Acid is formed, while at higher pHs, it will tend to dissociate into hydrogen and
Chlorite ions, which are less effective as a disinfectant. As a result, chlorine
Effectiveness drops off when the pH is greater than 8.
One solution is super chlorination, the addition of far more chlorine than is needed.
This must again be filtered through activated charcoal to remove the large amounts
Of chlorine, or hydrogen peroxide can be added to drive the chlorine off. Either
Way there is no residual chlorine left to prevent recontamination. This isn’t a problem, if the water is to be used at once.
Chlorine is sensitive to both the pH and temperature of the treated water.
Temperature slows the reaction for any chemical treatment, but chlorine treatment
Is particularly susceptible to variations in the pH as at lower pHs, hypochlorous
Acid is formed, while at higher pHs, it will tend to dissociate into hydrogen and
Chlorite ions, which are less effective as a disinfectant. As a result, chlorine
Effectiveness drops off when the pH is greater than 8.
Calcium Hypochlorite, also known as High Test Hypochlorite (HTH) is supplied
In crystal form; it is nearly 70% available chlorine. One product, the Sanitizer
(Formally the Sierra Water Purifier) uses these crystals to superchlorinate the water
To insure pathogens were killed off, then hydrogen peroxide is added to drive off
The residual chlorine. This is the most effective method of field chlorine treatment.
In crystal form; it is nearly 70% available chlorine. One product, the Sanitizer
(Formally the Sierra Water Purifier) uses these crystals to superchlorinate the water
To insure pathogens were killed off, then hydrogen peroxide is added to drive off
The residual chlorine. This is the most effective method of field chlorine treatment.
IODINE
Iodine’s use as a water purification method emerged after World War 2, when the
U.S. military was looking for a replacement for Halazone tablets. Iodine was found
To be in many ways superior to chlorine for use in treating small batches of water.
Iodine is less sensitive to the pH and organic content of water, and is effective in
Lower doses. Some individuals are allergic to iodine, and there is some question
About long term use of iodine. The safety of long-term exposure to low levels of
Iodine was proven when inmates of three Florida prisons were given water
Disinfected with 0.5 to 1.0 ppm iodine for 15 years. No effects on the health or
Thyroid function of previously healthy inmates was observed. Of 101 infants born
To prisoners drinking the water for 122- 270 days, none showed detectable thyroid
Enlargement.
U.S. military was looking for a replacement for Halazone tablets. Iodine was found
To be in many ways superior to chlorine for use in treating small batches of water.
Iodine is less sensitive to the pH and organic content of water, and is effective in
Lower doses. Some individuals are allergic to iodine, and there is some question
About long term use of iodine. The safety of long-term exposure to low levels of
Iodine was proven when inmates of three Florida prisons were given water
Disinfected with 0.5 to 1.0 ppm iodine for 15 years. No effects on the health or
Thyroid function of previously healthy inmates was observed. Of 101 infants born
To prisoners drinking the water for 122- 270 days, none showed detectable thyroid
Enlargement.
Iodine is normally used in doses of 8 PPM to treat clear water for a 10 minute contact time. The effectiveness of this dose has been shown in numerous studies. Cloudy water needs twice as much iodine or twice as much contact time. In cold water (Below 41˚ F or 5˚ C) the dose or time must also be doubled. In any case doubling the treatment time will allow the use of half as much iodine. These doses are calculated to remove all pathogens (other than cryptosporida) from the water. Of these, giardia cysts are the hardest to kill, and are what requires the high level of iodine. If the cysts are filtered out with a microfilter (any model will do since the cysts are 6 µm), only 0.5 ppm is needed to treat the resulting water.
Water treated with iodine can have any objectionable taste removed by treating the
Water with vitamin C (ascorbic acid), but it must be added after the water has stood for the correct treatment time. Flavored beverages containing vitamin C will accomplish the same thing. Sodium thiosulfate can also be used to combine with
Free iodine and either of these chemicals will also help remove the taste of chlorine as well. Usually elemental iodine can’t be tasted below 1 ppm, and below 2 ppm the taste isn’t objectionable. Iodine ions have an even higher taste threshold of 5 ppm. Note that removing the iodine taste does not reduce the dose of iodine
Ingested by the body.
Water with vitamin C (ascorbic acid), but it must be added after the water has stood for the correct treatment time. Flavored beverages containing vitamin C will accomplish the same thing. Sodium thiosulfate can also be used to combine with
Free iodine and either of these chemicals will also help remove the taste of chlorine as well. Usually elemental iodine can’t be tasted below 1 ppm, and below 2 ppm the taste isn’t objectionable. Iodine ions have an even higher taste threshold of 5 ppm. Note that removing the iodine taste does not reduce the dose of iodine
Ingested by the body.
Average American iodine intake is estimated at 0.24 to 0.74 mg/day, higher than the RDA of 0.4 mg/day. Due to a recent National Academy of Science recommendation that iodine consumption be reduced to the RDA, the EPA discourages the use of iodized salt in areas where iodine is used to treat drinking water.
SILVER
Its use is currently out of favor due to the EPA’s establishment of a 50 ppb MCL (Maximum Contaminate Level) limit on silver in drinking water.
This limit is set to avoid argyrosis, a cosmetic blue/gray staining of the skin, eyes,
And mucous membranes. As the disease requires a net accumulation of 1 g of silver in the body, one expert calculated that you could drink water treated at 50 ppb for 27 years before accumulating 1 g. Silver has only be proven to be effective against bacteria and protozoan cysts, though it is quite likely also effective against viruses. Silver can be used in the form of a silver salt, commonly silver nitrate, a colloidal suspension, or a bed of metallic silver.
Electrolysis can also be used to add metallic silver to a solution. Some evidence has suggested that silver deposited on carbon block filters can kill pathogens without adding as much silver to the water.
This limit is set to avoid argyrosis, a cosmetic blue/gray staining of the skin, eyes,
And mucous membranes. As the disease requires a net accumulation of 1 g of silver in the body, one expert calculated that you could drink water treated at 50 ppb for 27 years before accumulating 1 g. Silver has only be proven to be effective against bacteria and protozoan cysts, though it is quite likely also effective against viruses. Silver can be used in the form of a silver salt, commonly silver nitrate, a colloidal suspension, or a bed of metallic silver.
Electrolysis can also be used to add metallic silver to a solution. Some evidence has suggested that silver deposited on carbon block filters can kill pathogens without adding as much silver to the water.
POTASSIUM PERMANGANATE
Potassium permanganate is no longer commonly used in the developed world to kill pathogens.
It is much weaker than the other alternatives cited, more expensive, and leaves a
Objectionable pink or brown color. Still, some underdeveloped countries rely on it,
Especially in home-use applications. If it must be used, 1 gram per liter would
Probably be sufficient against bacteria and viruses (no data is available on it
Effectiveness against protozoan cysts). Hydrogen Peroxide can be used to purify
Water if nothing else is available. Studies have shown of 99 percent inactivation of
Poliovirus in 6 hr with 0.3 percent hydrogen peroxide and a 99% in-activation of
Rhinovirus with a 1.5% solution in 24 minutes. Hydrogen Peroxide is more
Effective against bacteria.
Potassium permanganate is no longer commonly used in the developed world to kill pathogens.
It is much weaker than the other alternatives cited, more expensive, and leaves a
Objectionable pink or brown color. Still, some underdeveloped countries rely on it,
Especially in home-use applications. If it must be used, 1 gram per liter would
Probably be sufficient against bacteria and viruses (no data is available on it
Effectiveness against protozoan cysts). Hydrogen Peroxide can be used to purify
Water if nothing else is available. Studies have shown of 99 percent inactivation of
Poliovirus in 6 hr with 0.3 percent hydrogen peroxide and a 99% in-activation of
Rhinovirus with a 1.5% solution in 24 minutes. Hydrogen Peroxide is more
Effective against bacteria.
COAGULATION/FLOCCULATIONA GENTS
While flocculation doesn’t kill pathogens, it will reduce their levels along with
Removing particles that could shield the pathogens from chemical or thermal
Destruction and organic matter that could tie up chlorine added for purification. 60-98% of coliform bacteria, 65-99% of viruses, and 60-90% of giardia will be
Removed from the water, along with organic matter and heavy metals.
Some of the advantages of coagulation/flocculation can be obtained by allowing the particles to settle out of the water with time (sedimentation), but it will take a while for them to do so. Adding coagulation chemicals, such as alum, will increase the rate at which the suspended particles settle out by combining many smaller particles into larger floc, which will settle out faster. The usual dose for alum is 10-30 mg/liter of water. This dose must be rapidly mixed with the water, then the water must be agitated for 5 minutes to encourage the particles to form flocs. After this at least 30 minutes of settling time is need for the flocs to fall to the bottom, and them the clear water above the flocs may be poured off.
Most of the flocculation agent is removed with the floc, nevertheless, some question the safety of using alum due to the toxicity of the aluminum in it. There is little to no scientific evidence to back this up. Virtually all municipal plants in the US dose the water with alum. In bulk water treatment, the alum dose can be varied until the idea dose is found. The needed dose varies with the pH of the water and the size of the particles. Increase turbidity makes the flocs easier to produce not harder, due to the increased number of collisions between particles.
Removing particles that could shield the pathogens from chemical or thermal
Destruction and organic matter that could tie up chlorine added for purification. 60-98% of coliform bacteria, 65-99% of viruses, and 60-90% of giardia will be
Removed from the water, along with organic matter and heavy metals.
Some of the advantages of coagulation/flocculation can be obtained by allowing the particles to settle out of the water with time (sedimentation), but it will take a while for them to do so. Adding coagulation chemicals, such as alum, will increase the rate at which the suspended particles settle out by combining many smaller particles into larger floc, which will settle out faster. The usual dose for alum is 10-30 mg/liter of water. This dose must be rapidly mixed with the water, then the water must be agitated for 5 minutes to encourage the particles to form flocs. After this at least 30 minutes of settling time is need for the flocs to fall to the bottom, and them the clear water above the flocs may be poured off.
Most of the flocculation agent is removed with the floc, nevertheless, some question the safety of using alum due to the toxicity of the aluminum in it. There is little to no scientific evidence to back this up. Virtually all municipal plants in the US dose the water with alum. In bulk water treatment, the alum dose can be varied until the idea dose is found. The needed dose varies with the pH of the water and the size of the particles. Increase turbidity makes the flocs easier to produce not harder, due to the increased number of collisions between particles.
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