In drinking water systems, ozone can be used to remove iron and manganese. Ozone can easily oxidize iron and manganese.
It is an extremely fast reaction when iron and manganese are exposed to ozone. Ozone can cause nuisance issues in many ozone applications because the soluble iron and manganese inadvertently oxidizes by ozone and falls out of solution in poor application locations.
Since iron and manganese cause discoloration of water, they must be removed in order to keep the water from causing health problems. The removal of iron and manganese from surfaces, such as pipes, fixtures, and other fittings, may also be needed.
Iron Fe(2) and Manganese Mn(2) are soluble (non-removable) in water, so they pass directly through conventional filtering without undergoing oxidation that would transform them into particulate (removable).
Iron Removal Using Ozone
It is called ferrous iron when the iron is soluble in water. Oxidation of ferrous iron to ferric iron by ozone involves ferrous iron Fe(II). As Ferric Iron Fe(III) hydrolyzes into FeOH, a particulate that is easily removed by filtration, it is known as Fe(OH)3. Ferric Iron Fe(II) is converted into ferrous iron Fe(II) by oxidation with ozone at a rate of 0.43 mg per mg.
Ozone can also be used to oxidize iron. In comparison to the calculated ozone demand of 0.43 mg per mg iron, an Ozone System for iron removal may be more efficient due to the oxidation of iron by oxygen. Oxidation of ferrous iron is a fast reaction since it only requires an electron exchange. In iron oxidation reactions, ozone is typically consumed almost entirely before manganese oxidation.
Manganese Removal Using Ozone
Manganese dioxide MnO2, a particulate that can be easily removed by filtration, is formed by oxidation of manganese soluble Mn(II). For every mg of manganese Mn(II), 0.88 mg of ozone is consumed.
The formation of soluble permanganate MnO4- occurs upon excessive manganese oxidation. It is best to design a manganese removal system with the proper ozone dosages and integrate controls to prevent overoxidation, as permanganate will normally return to manganese dioxide MnO2 over time (20-30 minutes).
When iron and manganese are exposed to ozone, they are oxidized and form insoluble particles that are easily filtered from water. The filter must be cleaned periodically to remove iron and manganese that accumulate on it. The best way to achieve these results is to use a back washable filter. Sand filters are designed to remove iron and manganese because of their simple design and long-lasting filter media. The back-wash cycles must be timed to occur at opposite times in continuous use systems where two filters must be used in parallel.
It is imperative that it be disposed of with care since the back-wash water from these filters is extremely high in iron and manganese. Although iron and manganese pose no health or safety risks, plumbing issues should be considered as iron and manganese buildup may obstruct drain pipes over time.
It has been widely used for many years to remove iron and manganese with ozone. It is relatively simple and straight forward to understand how ozone reacts with these metals. Prior to installing an Ozone System for iron and manganese removal, there are a few design considerations such as system sizing.
Iron and manganese oxidation by ozone can be an effective solution as compared to various other options. With no major maintenance costs or operational costs, ozone can be implemented quickly and easily. However, improper usage can make ozone difficult to manage so you have to carefully complete the process.
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