IRON FILTRATION AT IT'S BEST!

I

Forms of Iron Found in Water

Iron will cause an orange stain and will many times be accompanied by manganese and hydrogen sulphide gas odor. In combination with manganese, Iron staining will sometimes be chocolate or brown. At high concentration (> .3ppm ) the iron will cause the water to have a metallic taste and metallic odor.

The iron itself can exist in four forms:

1. Ferrous iron (often referred to as clear-water iron) - This form of iron is invisible in the water just like dissolved sugar is. Just like sugar water, the iron can not be mechanically filtered from the water.
2. Ferric (often referred to as red-water iron) - It is called red water iron because it gives the water a cloudy colour appearance. The iron has precipitated and formed a solid that is no longer in solution - it has turned to rust - "oxidized". This form of iron can be mechanically filtered. An easy way to remember which kind of iron is visible (ferrous or ferric) is to remember that the "I" and the "c" at the end of the word ferric say the same thing as "I see" it.
3. Organic iron (sometimes called heme-iron or pink water iron)- This form is actually iron combined with the dissolved organic matter (tannins) in the water and is held in solution with the organic materials. The water will appear clear but may or may not have color. Sometimes this iron will begin to oxidize and form a suspension in the water. We refer to this suspended iron mixture as colloidal iron.
4. Colloidal iron - This will look like red-water iron but cannot be easily filtered. The iron has precipitated (turned to ferric iron) but the molecules formed do not stick together to form large enough pieces to settle to the bottom of a container or be trapped with normal filtration. This water/solid combination is called a colloidal mixture. To test if you have this type of water, collect a sample in a clear glass container. Shine a flashlight beam through the water and see if you can see the light  in the water. Then, let the water set overnight. If after setting over night you can still see the beam of light as it passes through the water and there was no settling of material on the bottom of the container, the chances are very good that you have colloidal iron.

Treatment

Ferrous iron can be treated two ways. The most common way is to use a water conditioner or softener to remove the iron by ion exchange This method can be used on almost any level of iron. We have treated iron concentrations in excess of 100ppm successfully with a water conditioner. This method will only be successful by itself if all the iron is in the ferrous form, the TDS is relatively low (generally <500ppm), the ph is low ( generally <7) and there is very little oxygen in the water. The TDS has to be low to assure that there is no bleed through due to the iron being removed from the resin once attached. High TDS  indicates there are other minerals (ions) in the water competing for the sites on the resin (media) the iron has attached to. The low pH and low oxygen content assure that the iron will not oxidize to ferric iron while attached to the media (resin). If the iron oxidizes once attached to the media, it can not be removed during regeneration.

A second method to remove iron, is a two step process called oxidation filtration. The iron is first oxidized by the use of either oxygen, chlorine or potassium permanganate. The oxidation causes the ferrous iron to form ferric iron. The ferric iron is then removed by filtration. This method is not typically used on very high concentrations (> 8 or 10ppm) of iron because the filter beds will require more frequent back washing (automatic cleaning) then is reasonably possible. This method may also require the use of some kind of pH correction because iron will not oxidize below a pH of 6.8. There are several types of oxidation filtration systems used today. They are-

1. Air Injection - Oxygen in the air is used to oxidize the iron. The system requires the use of a venturi or an air pump (compressor) to inject the air. The system is therefore called an air injection system. There are many brand names for this type of system but they all require a minimum flow (usually at least 5 gpm) from the well pump to make the venturi work. This flow must be tested before this type of system can be used. Good systems will consist of 3 parts- venturi, air release tank, and filter tank. The air release tank removes any undissolved air and allows for the retention of the water. If the air is not released, severe spitting will result at the faucet. The retention allows time for some of the oxidation reaction to take place. The rest of the oxidation occurs in the filter on a catalytic media. The filter tank media removes the precipitated (ferric) iron that was formed by the oxidation process. THESE SYSTEMS DO NOT WORK WELL WITH WATER THAT HAS LOW pH AND LOW ALKALINITY.

    

2. Chlorination Systems - Chlorine is introduced into the water by one of two methods. The chlorine can be pumped in with a solution feed pump or it can be dropped in tablet form directly into the well. The water is then either sent to a retention tank and then to a filter or it can be sent directly to a filter. The choice of methods will be determined by the severity of the iron problem and the type of media chosen for the filter tank. If chorine is used, it may be desirable to remove it with carbon. If the iron levels are low (<2ppm), the carbon can also be used as the filter that removes the ferric iron that is formed. If the iron is greater than this (2ppm) than a separate filter with filter A.G media should be used to remove the ferric iron so the carbon will not be fouled. Some customers will opt to use filter AG in the filter and only use carbon at a sink as a P.O.U (point of use) treatment to remove the chlorine from the drinking water. If this is done, there will still be chlorine in the water at all other faucets and showers. The chlorine should be able to be regulated so that it is of no higher a concentration than that found in city water. CARBON IS NOT TO BE USED UNTIL THE WATER IS CHECKED FOR RADON BECAUSE THE CARBON CAN BECOME A RADIOACTIVE SOURCE.

    

3. Greensand Systems (NOT USED BY US)- This method uses a catalytic media (called greensand) coated with manganese that is treated periodically (like the salt regeneration of a softener) with potassium permanganate. The potassium permanganate acts as an oxidant (like the chlorine or oxygen). When the iron in the water comes in contact with the surface of the media it oxidizes and the ferric iron is then filtered out by sticking to the media before it finds it way through the filter. We do not use this method because these systems can easily bleed manganese into the water, they general require a lot of maintenance and the potassium permanganate is not only poisonous, but, if spilled, stains badly. The manganese that bleeds into the water can get to levels high enough to be toxic. You will hear these filters referred to as iron filters, greensand filters or potassium permanganate filters.

Shock Chlorination and Control of Iron Bacteria

Iron bacteria are a common nuisance in water wells, but are not considered a health hazard. They use dissolved iron in the water as an energy source and leave slimy deposits of red iron hydrate as a by-product.

This slime will coat the inside of the well casing, water piping and equipment, creating problems such as reduced well yield, restricted water flow and red staining of plumbing fixtures and laundry. However, all iron- staining problems are not necessarily caused by iron bacteria. The iron naturally present in the water can also cause significant problems.

Conditions for Iron Bacteria Growth

Iron bacteria thrive in water which contains 0.5 to 4 mg/L of dissolved oxygen, and as little as 0.01 mg/L dissolved iron. They prefer a temperature range of 5 to 15^oC. Water wells will almost always produce these conditions. Iron bacteria also create an environment which encourages the growth of sulphate-reducing bacteria in the well. Some of these sulphate-reducing bacteria can produce hydrogen sulphide as a by-product, resulting in a "rotten egg" or sulphur odour in the water. Others produce small amounts of sulphuric acid which can corrode well casing and pumping equipment. The easiest way to check a well and water system for iron bacteria is to examine the inside surface of the toilet flush tank. If a greasy slime or growth is present, then iron bacteria are probably present.

Shock Chlorination Treatment

Shock chlorination is used to treat iron and sulphate- reducing bacteria in a water system. To be effective, shock chlorination must disinfect:
 

• the entire well depth
• the formation around the bottom of the well
• the pressure system
• some water treatment equipment
• the distribution system

To accomplish this result, a large volume of super chlorinated water is poured down the well to displace all the water in the well and some of the water in the formation around the well.

Figure 1. Typical water system .

Effectiveness of Shock Chlorination

With shock chlorination, the entire system (from the water-bearing formation, through the well bore and the distribution system) is exposed to water which has a concentration of chlorine strong enough to kill iron and sulphate-reducing bacteria. Bacteria collect in the pore spaces of the formation and on the casing or screened surface of the well. To be effective, you must use enough chlorine to disinfect the entire cased section of the well and adjacent water-bearing formation.

The described procedure does not completely eliminate iron bacteria from the water system, but will hold it in check. To control the iron bacteria, you must repeat the procedure each spring and fall as a regular maintenance procedure. If your well has never been shock chlorinated or has not been done for some time, it may require two or three treatments before you notice a significant improvement.

Shock Chlorination Procedure for Drilled Wells

Caution: If your well is slow yielding or tends to pump any silt or sand, you must be very careful using the following procedure. Over-pumping a well that pumps sand may damage the well. To avoid this, siphon the solution down the well very slowly and pump the well out very slowly.

Step 1. Store sufficient water to meet farm and family needs for 8 to 48 hours.

Step 2. Pump the recommended amount of water (see Table 1) into a clean water storage container. A clean galvanized stock tank or pick-up truck box lined with a 4 mil thick plastic sheet is suitable. The recommended amount of water is the amount required to provide twice the volume of the well casing. To calculate the depth of water in the casing, refer to the water well driller’s report. Subtract the “static water level” from the “total depth of the well”. If this information is not available use a water well depth sounder to find the static water level. Always disinfect the well sounder before and after use.

Example: Drilling records indicate the casing is 250 ft. deep and the static water level is 150 ft. The length of casing with water is 100 ft. (250 -150). If your casing is 6 inches in diameter you need to pump 2.4 gal. of water for every foot of water in the casing into your storage container. Since you have 100 ft. of water in the casing, you will pump 2.4 gal./ft. x 100 ft. = 240 gal. of water into the clean water storage container.

Using Table 1, calculate how much water you need to pump into clean storage.

Table 1. Amount of chlorine and water required to shock chlorinate a well at 1,000 PPM

Casing diameter		Volume of water needed		5.25% domestic chlorine bleach	12% industrial sodium hypochlorite	*70% high test hypochlorite
		Water needed per 1 ft. (30cm) of water in the casing		Liters needed per 1 ft. (30cm) of water	Litres needed per 1 ft. (30cm) of water	Dry weight* per 1 ft. (30cm) of water
in.	mm	gallons	litres	litres	litres	grams
4	100	1.1	5.0	0.095	0.042	7.2
6	150	2.4	10.9	0.21	0.091	15.6
8	200	4.2	19.1	0.36	0.16	27.3
24	600	**extra 200 gal.	**extra 1,000 L	1.7	0.74	127
36	900	**extra 200 gal.	**extra 1,000 L	3.8	1.7	286

* Since a dry chemical is being used, it should be mixed with water to form a chlorine solution before placing it in the well.
** See modified procedure for large-diameter wells.

Step 3. Mix the recommended amount of chlorine with the water. Equivalent strengths of chlorine are shown in Table 1. This works out to be 1000 ppm chlorine solution. Example: If your casing is 6 inches in diameter and you are using 12 per cent industrial sodium hypochlorite, you will require 0.091 L per foot of water in the casing. If you have 100 ft. of water in the casing, you will use 0.091 L x 100 ft. = 9.1 L of 12 per cent chlorine.

Step 4. Siphon this solution into the well. (See Figure 2.)

Figure 2. Siphoning water down a well.

Step 5. Open each outlet (including dishwashers, washing machines, etc.) in the water distribution system until the water coming out has a chlorine-like odour. Note: you may want to bypass treatment equipment to prevent damage. Check with your water treatment supplier.

Step 6. Leave the chlorine solution in the well and distribution system for 8 to 48 hours. The longer the contact time, the better the results.

Step 7. Open an outside tap and allow the water to run until the chlorine odour has disappeared.

Step 8. Flush the chlorine solution from the hot water heater and household distribution system. The small amount of chlorine in the distribution system will not harm the septic tank.

Step 9. Backwash and regenerate any water treatment equipment. Use the worksheet at the end to determine how much water and chlorine you need to shock chlorinate your well.

Modified Procedure for Large-diameter Wells

Due to the large volume of water in many bored wells, the above procedure can be impractical. A more practical way to shock chlorinate a bored well is to mix the recommended amount of chlorine right into the well. An extra 200 gallons of chlorinated water is then used to force some of the chlorine solution into the formation around the well. Follow these steps to shock chlorinate a large-diameter bored well.

Step 1. Pump 200 gal. (1000 L) of water into a clean storage tank at the well head.

Step 2. Mix 20 L of 5.25 per cent domestic chlorine bleach (or 8 L of 12 per cent bleach or 1.4 kg of 70 per cent calcium hypochlorite) into the 200 gal. of stored water. This mixture will be used later in Step 5.

Step 3. Using Table 1 calculate the amount of chlorine you require per foot of water in the casing and add directly into the well. (Note that the 70 per cent hypochlorite powder should be mixed with water to form a solution before syphoning it into the well.)

Step 4. Circulate chlorine added to the water in the well by hooking a garden hose up to an outside faucet and placing the other end back down the well. This circulates the chlorinated water through the pressure system and back down the well. Continue this procedure for at least 15 minutes.

Step 5. Syphon the 200 gal. bleach and water solution prepared in Steps 1 and 2 into the well.

Step 6. Complete the procedure as described in Steps 5 to 9 for drilled wells.

Worksheet for Calculating Water and Chlorine Requirements for Shock Chlorination

Complete the following table using your own figures to determine how much water and chlorine you need to shock chlorinate your well.

Worksheet

 

* Since a dry chemical is being used, it should be mixed with water to form a chlorine solution before placing it in the well.
** See modified procedure for large-diameter wells.

 

Water used for drinking and cooking should be free of pathogenic (disease causing) micro organisms that cause such illnesses as typhoid fever, dysentery, cholera, and gastroenteritis. Whether a person contracts these diseases from water depends on the type of pathogen, the number of organisms in the water (density), the strength of the organism (virulence), the volume of water ingested, and the susceptibility of the individual. Purification of drinking water containing pathogenic micro-organisms requires specific treatment called disinfection.

Although several methods eliminate disease-causing micro-organisms in water, chlorination is the most commonly used. Chlorination is effective against many pathogenic bacteria, but at normal dosage rates it does not kill all viruses, cysts, or worms. When combined with filtration, chlorination is an excellent way to disinfect drinking water supplies.

This fact sheet discusses the requirements of a disinfection system, how to test the biological quality of drinking water, how to calculate the amount of chlorine needed in a particular situation, chlorination equipment, by-products of disinfection, and alternative disinfection methods.

Disinfection requirements

Disinfection reduces pathogenic micro-organisms in water to levels designated safe by public health standards. This prevents the transmission of disease.

An effective disinfection system kills or neutralizes all pathogens in the water. It is automatic, simply maintained, safe, and inexpensive. An ideal system treats all the water and provides residual (long term) disinfection. Chemicals should be easily stored and not make the water unpalatable.

State and federal governments require public water supplies to be biologically safe. The U.S. Environmental Protection Agency (EPA) recently proposed expanded regulations to increase the protection provided by public water systems. Water supply operators will be directed to disinfect and, if necessary, filter the water to prevent contamination from Giardia lamblia, coliform bacteria, viruses, heterotrophic bacteria, turbidity, and Legionella.

Private systems, while not federally regulated, also are vulnerable to biological contamination from sewage, improper well construction, and poor-quality water sources. Since more than 30 million people in the United States rely on private wells for drinking water, maintaining biologically safe water is a major concern.

Testing water for biological quality

The biological quality of drinking water is determined by tests for coliform group bacteria. These organisms are found in the intestinal tract of warm-blooded animals and in soil. Their presence in water indicates pathogenic contamination, but they are not considered to be pathogens. The standard for coliform bacteria in drinking water is "less than 1 coliform colony per 100 millilitres of sample" (<1/100ml).

Public water systems are required to test regularly for coliform bacteria. Private system testing is done at the owner's discretion. Drinking water from a private system should be tested for biological quality at least once each year, usually in the spring. Testing is also recommended following repair or improvements in the well.

Coliform presence in a water sample does not necessarily mean that the water is hazardous to drink. The test is a screening technique, and a positive result (more than 1 colony per 100 ml water sample) means the water should be retested. The retested sample should be analyzed for fecal coliform organisms. A high positive test result, however, indicates substantial contamination requiring prompt action. Such water should not be consumed until the source of contamination is determined and the water purified.

A certified testing laboratory provides specific sampling instructions and containers. Names and addresses can be obtained from the health department or county Cooperative Extension office.

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Chlorine treatment

Chlorine readily combines with chemicals dissolved in water, micro organisms, small animals, plant material, tastes, odours, and colors. These components "use up" chlorine and comprise the chlorine demand of the treatment system. It is important to add sufficient chlorine to the water to meet the chlorine demand and provide residual disinfection.

The chlorine that does not combine with other components in the water is free (residual) chlorine, and the breakpoint is the point at which free chlorine is available for continuous disinfection. An ideal system supplies free chlorine at a concentration of 0.3-0.5 mg/l. Simple test kits, most commonly the DPD calorimetric test kit (so called because diethyl phenylene diamine produces the color reaction), are available for testing breakpoint and chlorine residual in private systems. The kit must test free chlorine, not total chlorine.

View our chlorine injection pumps

Contact time with microorganisms

The contact (retention) time (Table 1) in chlorination is that period between introduction of the disinfectant and when the water is used. A long interaction between chlorine and the micro organisms results in an effective disinfection process. Contact time varies with chlorine concentration, the type of pathogens present, pH, and temperature of the water. The calculation procedure is given below.

Contact time must increase under conditions of low water temperature or high pH (alkalinity). Complete mixing of chlorine and water is necessary, and often a holding tank is needed to achieve appropriate contact time. In a private well system, the minimum-size holding tank is determined by multiplying the capacity of the pump by 10. For example, a 5-gallons-per-minute (gpm) pump requires a 50-gallon holding tank. Pressure tanks are not recommended for this purpose since they usually have a combined inlet/outlet and all the water does not pass through the tank.

An alternative to the holding tank is a long length of coiled pipe to increase contact between water and chlorine. Scaling and sediment build-up inside the pipe make this method inferior to the holding tank.

Table 1. Calculating Contact Time

To calculate contact time, one should use the highest pH and lowest water temperature expected. For example, if the highest pH anticipated is 7.5 and the lowest water temperature is 42 °F, the "K" value (from the table below) to use in the formula is 15. Therefore, a chlorine residual of 0.5 mg/l necessitates 30 minutes contact time. A residual of 0.3 mg/l requires 50 minutes contact time for adequate disinfection.

minutes required = K / chlorine residual (mg/l)
 

Chlorination levels

If a system does not allow adequate contact time with normal dosages of chlorine, superchlorination followed by dechlorination (chlorine removal) may be necessary.

Superchlorination provides a chlorine residual of 3.0-5.0 mg/l, 10 times the recommended minimum breakpoint chlorine concentration. Retention time for superchlorination is approximately 5 minutes. Activated carbon filtration removes the high chlorine residual (see: Water Treatment Notes: "Activated Carbon Treatment of Drinking Water").

Shock chlorination, outlined below, is recommended whenever a well is new, repaired, or found to be contaminated. This treatment introduces high levels of chlorine to the water. Unlike superchlorination, shock chlorination is a "one time only" occurrence, and chlorine is depleted as water flows through the system; activated carbon treatment is not required. If bacteriological problems persist following shock chlorination, a continuous chlorination system should be used.

SHOCK CHLORINATION OF WELLS

Shock chlorinate after construction of well, improvements made in well, or positive coliform test

Use household bleach containing 5.25 percent available chlorine (sold in supermarkets)

Mix 2 quarts bleach in 10 gallons water; pour into well while pumping

-circulate solution until strong chlorine odor observed at all taps
-continue circulating one hour
-close taps and stop pump

• Mix additional 2 quarts bleach in 10 gallons water; pour into well without pumping
   

   
   
   

  -allow well to stand at least 8 hours (preferably 12-24 hours)
  -pump water to waste, away from grass and shrubbery, until chlorine odor dissipates
  -chlorine may persist 7-10 days

• 9 After complete chlorine removal (1-2 weeks after flushing), test water for biological contamination
• Repeat testing in 2-3 months

CHLORINATION GUIDELINES

Types of chlorine used in disinfection

Public water systems use chlorine in the gaseous form, which is considered too dangerous and expensive for home use. Private systems use liquid chlorine (sodium hypochlorite) or dry chlorine (calcium hypochlorite). To avoid hardness deposits on equipment, manufacturers recommend using soft, distilled, or demineralized water when making up chlorine solutions.

Liquid Chlorine   household bleach most common form available chlorine range:  5.25% (domestic laundry bleach)  18% (commercial laundry bleach) slightly more stable than solutions from dry chlorine protect from sun, air, and heat

Dry Chlorine   powder dissolved in water available chlorine: 4% produces heavy sediment that clogs equipment; filtration required dry powder stable when stored properly dry powder fire hazard near flammable materials solution maintains strength for 1 week protect from sun and heat

Equipment for continuous chlorination

Continuous chlorination of a private water supply can be done by various methods. The injection device should operate only when water is being pumped, and the water pump should shut off if the chlorinator fails or if the chlorine supply is depleted. A brief description of common chlorination devices follows.

chlorine pump (see Fig. 1):

• commonly used, positive displacement or chemical-feed device,
• adds small amount, of chlorine to the water,
• dose either fixed or varies with water flow rates
• recommended for low and fluctuating water pressure,
• chlorine drawn into device then pumped to water delivery line

suction device:

• line from chlorine supply to suction side of water pump,
• chlorine drawn into water held in well pump,
• dosage uniformity not assured with this system,
• some suction devices inject chlorine directly into well water, increasing contact time between micro organisms and disinfectant; water/chlorine mixture is then drawn into well pump

aspirator (see Fig. 2):

• simple, inexpensive mechanism,
• requires no electricity,
• vacuum created by water flowing through a tube draws chlorine into a tank where it mixes with untreated water,
• treated solution fed into water system,
• chlorine doses not consistently accurate

solid feed unit:

• waste treatment and swimming pool disinfection,
• requires no electricity,
• controlled by flow meter,
• device slowly dissolves chlorine tablets to provide continuous supply of chlorine solution

batch disinfection:

• used for fluctuating chlorine demand,
• three tanks, each holding 2 to 3 days' water supply, alternately filled, treated, and used

Disinfection by-products

Trihalomethanes (THMS) are chemicals that are formed, primarily in surface water, when naturally occurring organic materials (humic and fulvic acids from degradation of plant material) combine with free chlorine. Some of the THMs present in drinking water are chloroform, bromoform, and bromodichloromethane. Since groundwater rarely has high levels of humic and fulvic acids, chlorinated private wells contain much lower levels of these chemicals.

THMs are linked to increases in some cancers, but the potential for human exposure to THMs from drinking water varies with season, contact time, water temperature, pH, water chemistry and disinfection method. Although there is a risk from consuming THMs in chlorinated drinking water, the health hazards of undisinfected water are much greater. The primary standard (maximum contaminant level) for total THMs in drinking water is 0.10 mg/l, and activated carbon filtration removes THMs from water.

Other disinfection methods

Although chlorination is the method of choice for most municipal and private water treatment systems, alternatives do exist. Information about these other disinfection methods is on the right.

Summary

Chlorination is the most common disinfection method for public and private drinking water systems. This treatment has limitations and is not suitable for heavily-contaminated wells or springs, or sources where hazardous materials are present. With adequate residual chlorine and contact time between the disinfectant and the micro organisms, chlorination effectively kills many disease-causing bacteria. Additionally, chlorine is inexpensive, easy to control, generally safe to use, and adapts to municipal or private systems.

OTHER DISINFECTION METHODS

Ultraviolet radiation (UV)

 

	uses light to kill micro organisms
	lamp has 9-month to 1-year lifetime
	needs UV sensor to determine germicidal dose
	effective for bacterial contaminants (viruses more difficult, cysts and worms unaffected)
	advantage in no chemicals added to water
	disadvantage in no residual disinfection; cloudy or turbid water decreases effectiveness

Ozonation

 

	ozone more powerful disinfectant than chlorine
	disadvantage is ozone cannot be purchased, must be generated on-site
	machinery to generate ozone complicated and difficult to maintain
	effects of ozonation by-products not fully understood

Boiling

 

	two minutes vigorous boiling assures biological safety
	kills all organisms in water (chlorination reduces them to safe levels)
	practical only as emergency measure
	once boiled, cooled water must be protected from recontamination

Pasteurization

 

	uses heat to disinfect but does not boil water
	flash pasteurization uses high temperature for short time (160 °F, 15 seconds)
	low-temperature pasteurization uses lower temperature for longer time (140 °F, 10 minutes)

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