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Bacteria Disinfection

Bacteria Disinfection Bacterial contamination of drinking water is a serious health problem for many private well water systems. Coliform bacteria may not cause disease, but can be indicators of disease-causing organisms such as E. Coli or fecal coliform. The latter can cause intestinal infections, dysentery, hepatitis, typhoid fever, cholera and other illnesses.

If contamination is present, an attempt should be made to identify and eliminate the source of the contamination. Human and animal wastes are a primary source of bacteria in water. These sources of bacterial contamination include runoff from yards, feedlots, pastures, dog runs, and other land areas where animal wastes are deposited. Insects, rodents or animals entering the well are other sources of contamination. Another way bacteria can enter a water supply is through inundation or infiltration by floodwaters or by surface runoff. Floodwaters commonly contain high levels of bacteria.

We offer four main types of disinfection systems with a wide range of options:

• Chlorination Systems
• Hydrogen Peroxide Systems
• Ozone Systems
• Ultraviolet Sterilizers

For most of our customers, the selection of their water treatment system begins with an accurate water analysis

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When to Test for Coliform Bacteria

Owners of private water supplies are responsible for having their water supply tested to ensure it is safe from bacterial contamination. Generally, private water supplies should be tested for bacterial safety as follows:

1 At least once a year;
2 When a new well is constructed;
3 When an existing well is returned to service;
4 Whenever a component of the water system is opened for repair
5 Whenever the well is inundated by flood waters or surface runoff;
6 Whenever bacterial contamination is suspected, as might be indicated by continuing illness;
7 When a laboratory test indicates high nitrate and human or livestock waste is suspected.

Well Water Treatment Using Chlorinators

Many residential water wells will use a chlorine bleach injector or chlorinator to kill bacteria and viruses.

Chlorinators come in two main types, liquid bleach injectors and solid pellets feeders. Whichever type of water treatment system is used, there must be sufficient chlorine present for a certain length of time in the water for disinfection to occur. The manufacturer of the chlorinator will provide instructions, but there must be sufficient time, usually 10 to 30 minutes after the chlorine has been injected, for disinfection to occur. A contact or retention tank or small storage tank is used for this purpose and can be pressurized or a non-pressurized tank. The goal is to be able to test for a .5 to 1.0 ppm of free-chlorine residual after the retention tank, at the furthest point in the piping away from the tank.

Common household bleach can used in an automatic chlorinator system to kill coliform bacteria and provide disinfected water, but to be safe an approved bleach designed for drinking water is recommended. Calcium hypochlorite or powdered bleach designed for drinking water can be mixed as a solution and injected with a chlorinator. Liquid bleach chlorinators use a small pump to inject a small amount of bleach automatically and in a precise dose, each time the well pump turns on. Both types work well but the concentration of chlorine is easier to control with the liquid metering pumps. Pellet chlorinators typically drop a small pellet of chlorine down the well, into a contact tank, or in small chamber to chlorinate the water. The chlorine residual is harder to control with the pellet type, but they can be effective for many small applications.

Hydrogen Peroxide Systems

Hydrogen peroxide (“H2O2”) is a powerful oxidizing agent, much more powerful than aeration, chlorine or potassium permanganate. Hydrogen peroxide decomposes into oxygen and water leaving no trace of chemical residues. For problem well water containing iron, iron bacteria, manganese and/or “rotten-egg” sulfur odor “H2S” (hydrogen sulfide gas) hydrogen peroxide systems are an excellent choice.

When peroxide is added to water a large amount of dissolved oxygen is released and a powerful oxidizing effect occurs. Coliform and iron bacteria are killed, and tannins are oxidized. Even though contact times can be shorter than with chlorination, the water must have a certain length of time after the peroxide has been injected in order for disinfection to occur.

Hydrogen peroxide costs about three times the cost of chlorine bleach. After the peroxide is added, no residual disinfection agent exists in the water. With chlorine, it can be adjusted so there is some chlorine left in the water to continue to disinfect long distribution lines, or if there is a community system where a chlorine residual is desired or required. Generally however water treated with peroxide is great and has an excellent effect on water quality, making it taste and smell great, especially when combined with catalytic type activated carbons.

Water Treatment Systems Using Ultraviolet Light

Ultraviolet light or "UV" is effective at inactivating coliform bacteria, viruses and protozoa, such as Cryptosporidium and Giardia, which may be present in well waters. Ultraviolet light, in the 200 to 300-nm (UV-C) range, is the most effective at killing bacteria and viruses by altering their DNA. This natural, non-chemical method of treatment penetrates and permanently alters the DNA of the bacteria and make them unable to reproduce or infect.

UV systems are available in different sizes. The size chosen depends on the flow rate of the water, or how fast the water is flowing through the water treatment system. The UV manufacturer has sizing guidelines that make it easy to select a UV for a home application. The water to be treated with UV must be good quality, low in minerals and metals such as iron, that might scale or cloud up the UV light and prevent it from shining into the water. Depending on the concentrations of the minerals, water hardness for example, can affect the performance of the UV system, as water hardness can cause scale to form on lamp sleeves. This can reduce UV light transmission and the rate at which bacteria is killed.

Common water quality parameters for best performance from a UV system in a residential well water are:

• < 0.3 ppm iron
• < 7 grains per gallon (120 ppm) hardness
• > 75-percent UVT (UV transmission through the water)

The advantages of ultraviolet sterilizers are:

• Low lifetime cost
• No moving parts
• Minimal maintenance
• No change to the taste or odor of the water
• No handling or mixing of chemicals

Ozone Gas As An Alternative Water Treatment System

Ozone (O3) is an unstable form of oxygen produced on site by an ozone generator. It is a very strongly oxidizing gas that is injected into water to instantly kill bacteria. It is faster acting than chlorine and sanitizes the water, rapidly destroying any microbiological contamination.

Unlike chlorine, dissolved ozone reverts back to harmless oxygen in a matter of minutes, depending on the temperature and pH of the water. Ozone leaves virtually no harmful breakdown products. Ozone systems are automatic and require no chemicals be mixed or solutions be measured or monitored. The fast acting time and lower maintenance requirements are two of the most desirable features of using ozone for killing bacteria. The biggest drawback to using ozone is the higher initial cost.

Ozone generators operate by passing dry air or oxygen next to high voltage electrodes where a corona discharge converts some of the oxygen to ozone much as occurs in a lightning storm. That gas mixture is then contacted with the water, either in a tank diffusion system or in a pipe with venturi injector.

While reaction times are faster than chlorine, like chlorine sufficient contact time must be present for the bacteria and viruses to be destroyed. Since ozone is a gas, a system must be designed to remove the excess gas from the water for residential uses. Ozone gas is harmful to breathe so properly designed ozone water treatment systems vent off excess ozone gas and then remove any trace of dissolved ozone before the water enters the home.

Multi-Barrier Approach Best for Residential Wells

A multi-barrier water treatment system uses more than one method to prevent bacteria from entering the home. This is especially important when there is surface water present (such as water from creeks, springs, lakes, or rivers); when the well is contaminated with sewage; or when animals are the source of contamination.

Bacteria (including E. coli) and viruses are easily prevented from entering finished drinking water by combinations of filtration and disinfection for surface waters, and disinfection of ground waters that are under the direct influence of surface waters. For example a combination of chlorination, filtration and UV light is a good multi-barrier approach. Ozone gas injection followed by filtration and a ceramic filter designed to filter bacteria is excellent for surface water sources. The water source and water chemistry is carefully considered in choosing which multi-barrier water treatment system to use.

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