Impurities may make water unfit for human consumption or unusable for other purposes in the residence or business. Some of the impurities found in water that may degrade waters usability are:
4. Acid or alkaline
5. Turbidity, suspended matter and colour
6. Taste and odor
Hard water is water that has picked up considerable amounts of calcium and magnesium compounds from the earth it has passed through. These compounds in the water prevent soap from producing a lather, harms clothing and causes a scale which is detrimental to the system, to form on the inside of pipes, boilers and hot water tanks when heated. Soft water is relatively free from these compounds of calcium and magnesium. There are two types of hardness classifications:
1. Temporary Hardness - Caused by the presence of dissolved bicarbonates.
2. Permanent Hardness - Caused by the presence of dissolved carbonates, sulfates, chlorides and nitrates.
Temporary hardness may be overcome by boiling the water. If the water is hard due to calcium bicarbonate, boiling will change the soluble bicarbonate to the insoluble calcium carbonate, which will then settle to the bottom of the container and the water will then be soft.
Calcium bicarbonate [Ca(HCO3)2 ] + HEAT = Calcium carbonate CaCO3+H2O+CO2
Hardness measurement is expressed in terms of grains per gallon (gpg), parts per million (ppm) or milligrams per liter (mg/l).
- To convert from ppm or mg/l to gpg (U.S.) divide by 17.1.
- (1 gpg (U.S.) equals 17.1 ppm or 17.1 mg/l)
- To convert from ppm or mg/l to grains per Imperial gallon use 14.3.
- One grain equals 1/7000 of a pound
Hardness removal methods
Lime can be used to remove carbonate or permanent hardness.
Soda can be used to remove non-carbonate hardness
Lime and Soda combined will remove both types of hardness from the water. This process is known as the Soda-Lime Process.
Ion Exchange hardness removal by the zeolite process was introduced in about 1910. Zeolite is a complex compound made up of sodium, aluminum, silicone, and oxygen. It may simply be referred to, however, as Sodium Zeolite. The reaction involved here is simply an exchange process, where sodium (which does not tend to produce insoluble compounds) is substituted for the calcium (which does form the salts, which create the hardness). This is achieved by passing the water through a bed of sodium zeolite where hardness ions of calcium are exchanged with the sodium ions as the water passes through the sodium zeolite. When the zeolite bed is completely exhausted, a strong brine solution of common salt (NaCl) is drawn through the zeolite to regenerate.
- Water volume - before installation, ensure the well and water system will supply enough water to backwash the softener.
- Pressure - a minimum pressure of 20 psi is required (avoid excessive pressure).
- Water temperature - cold water is softened and then it may be heated.
- Drain - unit should be located close to a drain.
- By-pass - Softeners should have an external three-valve or built in bypass using non-restrictive gate or full-port ball valves for softener service.
- Unions - should be installed so that the softener can be easily removed.
- Filters - iron or sand filters should be installed before the softener.
- Pressure drop - water softeners can cause a fairly high pressure drop.
Sizing a Softener
1. Determine water hardness in grains per gallon.
a,) field test kit
b,) lab report
c,) Provincial analysis
2. Estimate daily water usage.
(50-60 gallons per person per day) x number of people
3. Determine daily hardness capacity requirements.
- Multiply daily water usage times the water hardness (gpg).
4. Determine frequency of regeneration.
Divide the daily capacity requirements into the zeolite capacity to determine the number of days between regeneration (maximum 3 days if iron present).
E.g. Water with a hardness of 33 gpg with a six person usage, and regenerating the softener every 3 days, the proper size of softener is
33 gpg x (6 x 50 gal) x 3 days = 33 x (6 x 50) x 3 = 29700 grains
(Chose a 30,000 grain softener or regenerate sooner)
(2) IRON IN WATER
Iron in water is undesirable, as it tends to discolor everything it touches. It is found in the following forms
1. ferrous (in solution - clearwater iron)
2. ferric (solid in suspension - usually iron oxide)
3. Iron bacteria (living organisms that build slimes or feed on pumps, piping, tanks and fixtures causing damage.
4. heme iron (biological iron in blood)
Iron Reduction Methods
Water Softener Trace levels of Iron may be removed by using a softener. A softener will filter suspended iron but must be backwashed and cleaned regularly. The iron will tend to foul the softener “bed” and will “bleed” iron through. Since iron is heavier than the softener mineral the job of backwashing the iron out becomes very difficult. Softeners will remove iron if the upper limit does not exceed 3 ppm.
Manganese Zeolite Filter These filters oxidize the ferrous iron to participate it and then filter it out in the same unit. The mineral bed contains manganese dioxide, which converts the ferrous iron to ferric oxide, thus precipitating the iron. The oxygen in the filter is replenished by regenerating with potassium permanganate (KMnO4). Manganese Zeolitefilters will remove iron concentrations up to 10 ppm. These filters will not remove iron bacteria.
Air Injection Iron Filter These filters use a “micronizer” (nozzle and venturi) to inject air into the water, which oxidizes the ferrous iron converting it to ferric oxide through the use of a contact tank and then filters it through back washable lava rock or manganese zeolite. Air injection iron filters will remove iron concentrations up to 20 ppm. These filters will not remove iron bacteria.
Chlorinating A chlorinator should be used when iron bacteria are present. Chlorine is an excellent oxidizing agent and when fed into the water supply will oxidize (contact time required) and precipitate the iron in the water. In addition, chlorine will also destroy the iron bacteria. A carbon filter or sand filter is necessary to filter the iron from the water. Chlorinating will treat water with concentrations up to 100 ppm (becomes cost prohibitive)
1) Up to 3 ppm iron remove with softener.
2) 3 - 10 ppm iron remove with manganese zeolite or air injection filter.
3) 10 - 20 ppm iron remove with air injection filter or chlorinator and filter
4) Above 20 ppm iron remove with chlorinator and filter.
5) Iron bacteria is removed with chlorinator and filter.
*Note* - Poly-phosphates are occasionally used for iron water. They are injected into the water with the use of a chemical feed pump and hold the iron in solution (Ferrous) thus preventing staining. They also coat the insides of tanks, pumps etc. for further protection.
(3) SULFUR IN WATER
Sulfur water is primarily H2S dissolved in water. This imparts a “rotten egg” odor and taste to the water. Hydrogen sulfide is very corrosive and will eat away pump parts, piping and hot water tanks. Treatment of sulfur in water by
1. Aeration - Oxygen is mixed with water to help precipitate the sulfur. The water is then filtered to remove the sulfur.
2. Manganese zeolite filter - will remove up to 5 ppm of sulfur.
3. Chlorinating - Chlorine oxidizes the hydrogen sulfide and rids the water of the taste and smell of sulfur.
(4) ACIDIC or CORROSIVE WATER
Water is acidic, neutral or alkaline in nature. To denote its nature, an artificial symbol, pH (potential of Hydrogen)has been established. The pH scale is a measure of acidity or alkalinity. pH is a number between 0 and 14 with 7 being neutral and anything below 7 is acidic and above 7 is alkaline. The further away from 7 the stronger the acidity or alkalinity.
Correction of acid and corrosive waters The pH may be raised by a neutralizing filter or by soda ash feeding. Using a neutralizing filter may increase the hardness of the water. Soda ash feeding does not increase the hardness of the water but does increase the alkalinity of the water and neutralizes it.
(5) TURBIDITY, SUSPENDED MATTER AND COLOUR
Turbidity and suspended matter may be in the form of oxidized iron, fine sand, clay, or organic matter. Colour in water is found generally to be from decaying vegetable growth.
A sand filter may remove turbidity and suspended matter.
Colour can be removed by Chlorination followed by activated carbon filtration.
(6) TASTE and ODOR
Taste or odor are effectively removed with activated carbon filters