PRIVATE WATER SYSTEMS EDUCATION SYSTEM

Treatment Devices

Addition of Chlorine Compounds (2)

There are a number of chlorinator units on the market, each designed to meter small amounts of chlorine solution into a water supply as the water is being used. They are roughly divided into three types:

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Chlorine Solution

There are three common ways to make the chlorine solution used in disinfection: 1) dissolve calcium hypochlorate in water; 2) dissolve sodium hypochlorate in water; and 3) bubble chlorine gas through water.

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Pump type

Pump Type The pump type is powered with an electric or water motor. The pump delivers a fixed amount of chlorine solution with each discharge stroke.

The amount of chlorine delivered can be adjusted by either changing the length of each stroke, adjusting the pump speed, or adjusting the amount of time the pump works.
Strokes

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Injector type

Injector type An injector-type chlorinator is also called an aspirator or a jet. In this type, chlorine is drawn into by jet action into the water supply system. Press the space bar to see a picture. The chlorine input is regulated by adjusting the feed adjusting screw.

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Tablet Type

Tablet Type With a tablet-type chlorinator, a small amount of water is circulated through a container of chlorine tablets and back into the delivery line. The restricting valve forces a certain amount of water into the container with the tablets. The amount of water allowed to circulate determines the concentration of chlorine in the water.
Tablet Type

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Aeration (7)

The process of aeration is used for the removal of dissolved gasses, such as carbon dioxide, hydrogen sulfide, and methane, and the addition of oxygen necessary for the removal of iron and manganese from the water. Oxygen entering the water will increase the corrosiveness of the water. Aeration is not always efficient in removing taste and odor from things that are not in the gaseous form. Also, aeration should not be used if the water is subjected to airborne contamination.

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Activated Carbon Filter (7)

activated carbon filter Activated carbon filters are used for the removal of offensive tastes and odors, color, chlorine, and certain pesticides such as DDT, parathion, dieldrin, and lindane. Carbon filters can also remove more than 90 % of cadmium, chromium, manganese, mercury, silver, and tin, and it also can remove turbidity.

Problems not corrected by carbon filters include: hardness; dissolved metals such as iron, lead, manganese, and copper or chlorides, nitrates, and fluorides; and bacteria. In fact, carbon filters may promote bacteria growth especially when not used for a few days or when not changed at proper intervals. Despite some manufacturers claims that carbon filters containing silver discourage the growth of bacteria, research shows that silver-impregnated filters do not significantly reduce bacteria growth and may increase the silver content of the drinking water.

There are two types of activated carbon filters:

Activated carbon is made of specially-treated hardwood, selected coals, and pecan nutshells all ground into a fine powder to increase adsorptive capacity.

The length of time a filter will last depends on the concentra- tion of impurities in the water as well as the quantity of water being conditioned. For an average household, one filter will last from one to three years.

Precoat cartridge filters (2)

Maintenance of smaller precoat cartridges consists of replacing the entire cartridge when the water pressure starts to lower noticeably. This pressure decrease is a result of the build- up of material on the filter surface.

With the larger types of precoat cartridges, the filter is removed and cleaned by washing off the dirt particles that have accumulated. After several cleanings, and when the carbon material has absorbed all the taste and odor it can hold, the filter is replaced.

Carbon-bed Type Filters (2)

Maintenance of the carbon-bed filter consists of back- washing the filter bed to remove suspended dirt from under the filter bed. Under most conditions, more than one or two back- washings will be required every month.

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Coagulation and Sedimentation (2)

Coagulation and sedimentation is a process that causes the fine sediment in water to collect into larger particles and settle to the bottom of a pond, before the water reaches the filter. The addition of 12 pounds per 7000 gallons of pond storage of powdered gypsum should cause the fine particles to cluster (coagulate) and settle to the bottom.

Turbidity Treatment Systems (2)

Turbidity Treatment Systems A turbidity treatment system commonly consists of a screened intake and piping for conducting the water from the intake to the first unit of the system, a settling tank for coagulation and sedimentation, a filter, and a storage compartment. If the turbidity is less than 40 units, the settling tank can be left out and the filter will do the whole job.

Screened Intake
Most recommendations are that the screened intake be located about 12 to 18 inches below the surface of the pond to take advantage of the less turbid water.
Settling Tank
The water enters the settling tank first. An arrangement where an alum tank is used with the settling tank is shown in the figure. Alum is fed into the tank in proportion to the amount of water that is fed in from the pond. The alum forms a floc, or glob, which the fine particles from the pond attach to and sink to the bottom of the tank. There are also polymer compounds available instead of alum.

Maintenance of the settling tank consists of occasionally removing the mud and floc accumulated on the bottom of the tank. This will not be necessary more than every 6 to 8 months in a well designed system.

Alum will need to be added about every two weeks.

Filters (2)
If a settling tank is being used, a slow sand filter will be needed. If there is no settling tank, then the water will enter the filter directly. In this case, either a diatomite or rapid sand filter is likely to be used.

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Slow Sand Filters (2)

This type of filter is used extensively for pond water treatment. Water moves through the filter by gravity, and, as a result, it moves through very slowly - about 27 to 75 gallons per day per square foot of filter-bed surface.

As the water deposits dirt particles, they build up on the surface of the sand layer and assist in the filtering action. Although the filter becomes more effective as more material is deposited on it, the rate of water flow through the filter decreases.

Maintenance of the filter consists of removing the dirt and about 1 to 1 1/2 inches of the top layer of sand when the filtration rate becomes too slow. The time between servicings may vary between two weeks to six months depending on the turbidity of the water and the amount of water being filtered.

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Diatomite Filters (2)

Sometimes called diatomaceous- earth filters, these filters are made from the remains of marine algae called diatoms. When these shell-developing plants die, their shells accumulate on the sea floor to form diatomaceous earth.

The filtering element usually consists of a cylinder of porous called a septum. It may be made of wire cloth, plastic fiber, or any other material that will allow water to pass readily. A coating of diatomite-filter material is then applied to the septum to form a precoat.

The diatomite filter removes suspended solids in the same manner as the sand filter, but it filters greater amounts 10 to 100 times faster.

Maintenance consists of adding diatomite-filter-aid material as the filtering action starts to slow. When the addition of the filter aid no longer has any effect, the filter cake must be replaced. If the filter is properly sized, filter cake replacement should not be necessary any more than about every 2 months.

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Rapid Sand Filters (2)

Rapid Sand Filters The rapid-sand filter is a tank-type arrangement containing fine sand which rests on top of a bed of coarse sand and gravel.

The filter is connected into the delivery line from the pump so it works under whatever pressure is developed by the pump. The capacity of the filter is usually around 2 to 3 gallons per minute per square foot of sand surface. Water flows through the sand from top to bottom, so the dirt particles collect on the top of the filter bed.

The rapid sand filter works best if the particles are few and large. It is the least effective filter for small-sized particles, therefore it is rarely considered appropriate for use in filtering pond water.


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The Neutralizer Tank (2)

The Neutralizer Tank The neutralizing tank is similar in appearance to the water softener tank except it contains a bed of limestone or marble chips. The acid in the water reacts with these materials and gradually "eats" them until they to be replaced. This action neutralizes the water until most of the corrosive action has been overcome. Flow through the neutralizer should be slow to allow the reaction to take place.

Since limestone is dissolved, water hardness will increase slightly. This can be overcome by installing a softener just after the neutralizer.

Maintenance consists of backwashing regularly - perhaps weekly - to loosen and clean the neutralizing bed. Every year the neutralizing bed should be checked and the dissolved portion replaced.


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Continuous Soda Ash Feeder (2)

Continuous Soda Ash Feeder If a chlorinator is already in place, the soda ash can be mixed with the chlorine solution and added through the chlorinator. If no chlorinator is in use, a chemical feeder of the same type (as is used for chlorinators) is satisfactory for feeding in soda ash by itself.

Feeding the soda ash directly in the well not only helps to prevent corrosion of the piping system, as intended, but corrosion of the casing, well screen, and pump is also avoided.

Soda ash adds no hardness to the water and has no marked effect on water used for bathing, drinking, or clothes washing. Soda ash does add sodium bicarbonate to the water, however.

Maintenance consists of making up the soda-ash solution. About 1/2 pound of soda ash is added to one gallon of soft water. It is then either fed through a feeder or dumped into the well. It will need to be replenished about once every two weeks.


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Oxidizing Filter (2)

The oxidizing filter is much like a softener, but the material inside is and oxidizing material, usually manganese-treated greensand. The manganese bed provides oxygen which causes the iron to settle out as rust particles.

Maintenance consists of backwashing and rinsing the filter about every week, and recharging, either then, or at longer intervals. Flow rates as high as 8 to 10 gallons per minute per square foot of area of filter bed is recommended for backwashing.

The iron-removal filter is recharged with potassium permanganate. The potassium permanganate is placed on top of the tank, and the unit slowly rinsed with a down-flow of water. This recharges the mineral filter bed with oxygen. Recharging varies from weekly to monthly depending on the size of the filter and the amount of iron in the water.

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Controlling Water Hardness (7)

Hard water is caused by dissolved calcium and magnesium and has undesirable effects on skin, hair, clothes, and water fixtures. Hard water also causes bathtub rings, soap scum, and scale-filled pipes and water heaters. It is a common problem throughout a large part of the United States.

Water softeners usually consist of a tank containing an ion-exchange material such as zeolite or resin beads.

Water-softening capacity is given in terms of the number of grains of hardness it will remove between successive regenerations.

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Ion-Exchange

The Softening Process (1)

Ion-Exchange Water softening exchanges calcium and magnesium ions with sodium ions on the surface of an exchange resin in a tank. Sodium is released from the resin, and calcium and magnesium go on to the resin. The water flowing through the tank is softened as long as there are exchangeable sodium ions available in the resin. "Most softeners are fully automatic and require only a periodic resupply of salt. They will automatically backwash before regenerating to flush out accumulated sediment and iron "(7) .

The amount of sodium added to the daily diet is relatively small. For example, suppose that the had water contains 10 grains of calcium and magnesium. Assuming that the daily consumption of water is 1/2 gallon per person, then the daily increase in sodium in the daily diet is 0.3 grams (assuming 100% exchange efficiency).
Ion-Exchange

Regeneration of the Softener (7)

Ion-Exchange When the available sodium ions are almost all used up, the softener exchange resin should be regenerated. Regeneration is accomplished by flushing brine (strong salt solution) through the exchange material to replace the collected calcium and magnesium ions with sodium ions. The flush brine is waste and must be disposed of properly.


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Continuous Disinfection (1)

Three methods of disinfection are suggested for private water systems: adding chlorine compounds; heating water; or ultraviolet radiation. Before purchasing any water disinfection equipment, consult local or state health officials concerning codes governing its use.

Disinfection by Pasteurization (2)

Disinfection by Pasteurization
The water pasteurizer works under the same principle, and at the same temperature, as the pasteurization of milk. Untreated water enters a heat exchanger where it is heated to 150 degrees F. The water is then forced through a heating chamber where the temperature is raised to about 161 deg. F and maintained at that temperature for at least 15 seconds. This hot water is then routed back by the heat exchanger where it gives up some of its heat in heating the water that is to follow it. The water is then discharged into the treated-water storage.

Only small amounts of water can be pasteurized at one time so the treated water must be stored and pumped by a second pump to the points of use.

Disinfecting with Ultraviolet Light (2)

Disinfecting with Ultraviolet Light
Disinfecting with Ultraviolet Light In this method, a thin layer of water is passed around a set of ultraviolet lamps encased in a quartz sleeve. The killing action is the same as that provided by direct sunlight in killing bacteria in open streams. For one of these units to be effective, the water must be circulated in such a manner as to expose every droplet of water to as much light as possible. Also, the effectiveness decreases if there is sediment in the water, therefore a sediment filter may need to be installed ahead of the light. Units are available with a variety of safety devices to increase effectiveness. These include:
  1. An electric eye to detect when the lamp intensity gets too low;
  2. A time delay to allow the lamp to warm up before water is run by it;
  3. Electrical relays to insure the lamp is run with the proper amount of current;
  4. Wipers for cleaning small particles off of the quartz sleeves
The available sizes of units vary in capacity from 22 gallons per hour to 22000 gallons per hour.

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