1. Field of the Invention
The present invention relates generally to apparatus for liquid purification or separation with means to add a treating material. More particularly, the present invention relates to a method for cleaning contaminated water using ion exchange media.
2. Description of the Related Art
Water's hardness is determined by its concentration of multivalent cations (i.e., positively charged metal complexes with a charge greater than 1+). The hardness of water is typically classified into two types: soft and hard. Surface water, such as rainwater, is classified as soft water and considered to be relatively free of multivalent cations. By contrast, well water and ground water is classified as hard water because it is often found to have significant concentrations of calcium ions (Ca2+) and magnesium ions (Mg2+). These ions enter a water supply by leaching from minerals within an aquifer.
Hard water is generally not harmful to one's health, but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water. In domestic settings, hard water is often indicated by a lack of suds formation when soap is agitated in water. Wherever water hardness is a concern, water softening is commonly used to reduce hard water's adverse effects.
To resolve water hardness problems, water softeners are widely used. For this softening function, a water softener typically includes essentially a water softening tank, a regeneration tank and the necessary plumbing and control valves to control the flow of water between these tanks. The water softening tank is filled with an ion exchange resin of a particular polymer compound with sodium ions that are reduced by continuous contact with raw hard water. Thus, when water softening is carried out for a long period, the concentration of sodium ions in the ion exchange resin is diminished and the resin must consequently be periodically regenerated. The regeneration tank contains a regeneration material for the ion exchange resin, such as salts which release sodium ions when dissolved in water so as to create a brine solution. See, for example, U.S. Pat. Nos. 7,285,220, 6,436,293 and 2,711,465.
The water softening tank and the regeneration tank both have raw water, inflow piping. A piping line connects the upper part of the water softening tank to a lower part of the regeneration tank. A valve in this line is opened to begin a back-washing operation that supplies brine water from the regeneration tank to the water softening tank. After the resin has been sufficiently rejuvenated, this valve is closed and the brine water is flushed from the water softening tank. Its resin is now again available for use in softening the incoming raw water. A timer and a programmable control valve are often used to control the flow between the tanks and the various phases (softening or back-washing) of the water softener's operation.
Conventional water softeners often have several disadvantages. The regeneration phase of their operation can be time-consuming which can limit their available service time for softening water and yield higher than desired operating costs. They can also be bulky in size which can limit the number of places where they might be installed in a residence.
Well water, particularly water drawn from “deep” wells (i.e., below thirty feet), may also contain significant quantities of soluble gases, such as hydrogen sulfide (H2S) which has a distinctive “rotten egg” smell that makes the treatment of H2S-contaminated water desirable.
Water softeners are not effective for removing soluble H2S from water. Most methods for treating H2S-contaminated water rely on oxidizing H2S so as to make a solid precipitate that can be filtered from the water. If H2S concentrations exceed 6 mg/L, oxidation via chlorination is typical. On the other hand, if H2S concentrations fall below 6 mg/L, oxidation with manganese greensand is more common.
Chlorination is a widely used method for oxidizing H2S. Chlorine is usually added to a supply of water in the form of sodium hypochlorite (NaOCl), liquid bleach. Treated water may, unfortunately, have lingering tastes or odors caused by residual chlorine and byproducts of the reaction between NaOCl and H2S. Therefore, before human consumption, treated water should be passed through an activated carbon filter to remove suspended chlorine and sulfur compounds.
Chlorination systems are available as a pellet-drop unit or a liquid feeder. A pellet-drop unit automatically dispenses a measured amount of NaOCl in solid form into a well casing or into a retention tank during a pumping cycle. A liquid feeder, as the name suggests, delivers NaOCl dissolved in a liquid to an energized well pump.
Manganese greensand carries a coating of manganese oxide (MnO2). During use, MnO2 reacts with H2S to form solid particles that are captured by the greensand itself. When the MnO2 is depleted, the greensand can be regenerated with potassium permanganate (KMnO4). When greensand is used to treat water with high H2S concentrations, frequent regeneration is often required.
Catalytic carbon provides an alternative. Essentially, catalytic carbon is activated carbon with a modified surface. Catalytic carbon retains all of the adsorptive properties of activated carbon, but it further exhibits an ability to catalyze chemical reactions. During water treatment, catalytic carbon first adsorbs H2S and, then, in the presence of dissolved oxygen, converts H2S into an inert solid.
Aeration is another common treatment for water having dissolved H2S. See, for example, U.S. Pat. Nos. 6,627,070, 6,325,943 and 5,354,459. During aeration, H2S is removed by agitating water in contact with air in a special mixing or aeration tank. The unwanted H2S is, after agitating, removed as a gas by venting it with the air from the tank. Aeration is most effective when H2S concentrations are lower than 2 mg/L. At higher concentrations, aeration may not remove all of the H2S and supplemental filtration may be necessary.
In a typical aeration system, air is supplied to a mixing tank by a pump or is aspirated into the water with a mixing or aspiration valve. The tank usually maintains a pocket of air in its upper portion of the tank. If the tank does not maintain an air pocket, there may insufficient time for dissolved H2S to escape and foul odors and tastes may return.
Aeration is not always practical for in-home water treatment, especially if H2S concentrations exceed 10 mg/L. First, large mixing tanks must be set up in a home to allow air and water to mix for long times. Also, objectionable odors must be vented outside the home. Finally, aerated water may need to be repressurized for distribution within the home.
One's water supply may also contain troubling levels of iron. Making up at least five percent of the earth's crust, iron is one of the earth's most plentiful resources. Rainwater as it infiltrates the soil and underlying geologic formations dissolves iron, causing it to seep into aquifers that serve as sources of groundwater for wells. Although present in drinking water, iron is seldom found at concentrations greater than 10 milligrams per liter (mg/L) or 10 parts per million. However, as little as 0.3 mg/l can cause water to turn a reddish brown color.
Iron is mainly present in water in two forms: either the soluble ferrous iron (Fe+2) or the insoluble ferric iron (Fe+3). Water containing ferrous iron is clear and colorless because the iron is completely dissolved. When exposed to air in the pressure tank or atmosphere, the water turns cloudy and a reddish brown substance begins to form. This sediment is the oxidized or ferric form of iron that will not dissolve in water.
Iron is not hazardous to health, but it is considered a secondary or aesthetic contaminant. Essential for good health, iron helps transport oxygen in the blood. Most tap water in the United States supplies approximately 5 percent of the dietary requirement for iron.
Dissolved ferrous iron gives water a disagreeable metallic taste. When the iron combines with tea, coffee and other beverages, it produces an inky, black appearance and a harsh, unacceptable taste. Concentrations of iron as low as 0.3 mg/L will leave reddish brown stains on fixtures, tableware and laundry that are very hard to remove.
When iron exists along with certain kinds of bacteria, a smelly biofilm can form. To survive, the bacteria use the iron, leaving behind a reddish brown or yellow slime that can clog plumbing and cause an offensive odor. Iron can also combine with different naturally-occurring organic acids or tannins. Organic iron occurs when iron combines with an organic acid. Water with this type of iron is usually yellow or brown, but may be colorless. As natural organics produced by vegetation, tannins can stain water a tea color.
Ion exchange techniques and various oxidation methods are commonly used to treat water containing ferrous iron. The ion exchange technique involves the use of a water softener's ion exchange resin to also remove low to moderate levels of ferrous iron through the exchange process. This treatment method is reported to have good results when other water quality parameters are within tolerable ranges—including the absence of ferric iron, and the pH level not being so high as to oxidize iron.
Oxidation methods convert soluble ferrous iron into insoluble ferric iron which can then be filtered out using appropriate filtration techniques. Oxidation methods use chlorine, ozone (O3), ambient air, various types of oxidizing filter media or the relatively new technique of electrolytically producing oxygen in the water.
Chlorine for treating ferrous iron can be injected with a chemical feed pump between the well pressure tank and a retention tank. The treated water then is held in the retention tank, where the iron precipitates, some settles and the remainder can then be removed by filtering. A variety of filtration systems can be used, such as oxidizer-treated minerals, manganese greensand, sand and multi-media or catalytic media filters.
Alternately, ozone (O3), which is created by an ozone generator, can be similarly fed into the water stream via a pump or air injector. Another alternative is to introduce significant quantities of air into the water. This is usually achieved by aspirating or pulling air from the surrounding atmosphere into a relatively high speed, water jet stream which is partially exposed to the atmosphere or by using a compressor to inject air into the water flowing through a pipe. A still further alternative is to use manganese greensand as an oxidizing media, which must be periodically rejuvenated by backwashes that utilize potassium permanganate (KMnO4). Yet another alternative is the relatively new technique of electrolytically producing micro-bubbles of pure oxygen from the water itself—this involves having the water flow through a bypass loop which has a unit containing titanium electrodes for generating oxygen microbubbles that are 400 times smaller than standard aeration bubbles.
In light of the problems associated with the hardness and iron- and H2S-contamination of household water supplies and despite the existence of many types of water softeners and means for treating iron- and H2S-contaminated water, there is still a need for improved water treatment systems—e.g., systems that are more compact, require less maintenance, operate more efficiently and have lower investment and operating costs.