Oxidation reduction is one of the most common reactions occuring in nature, but how it's used for water treatment remains a mystery to many water treatment dealers.
　Redox media remove dissolved gases such as chlorine, hydrogen sulfide and methane from water. They can also remove virtually any soluble heavy metal, help prevent mineral hardness scale accumulation and reduce levels of microorganisms.
　What makes these media unique, however, is that all the energy necessary to remove contaminants from water is inherent in the electrochemical and catalytic potential of the redox alloy. Because they're also versatile, they're a good choice for a wide veriety of water treatment applications, including:
   
Ⅰ.Dechlorinating.
　High purity copper-zinc redox media consistently remove 99 percent of free chlorine from drinking water by electrochemically reducing dissolved chlorine gas to water-soluble chloride ions. Because municipalities continue to chlorinate (and overchlorinate) water, the market for dechlorination is growing
   
Ⅱ.Removing dissolved heavy metals.
　Redox media remove up to 98 percent of water-soluble cations of lead, mercury, copper, nickel, chromium, cadmium, arsenic, antimony, cobalt and most other dissolved heavy metals upon direct contact. The removal mechanism is electrochemical and partially catalytic.
　Soluble lead cations are reduced to insoluble lead atoms and electroplated onto the surface and interstices of the granular media. Metallic contaminants are bonded to the redox alloy until the filter materials are recycled in a copper smelter.
 
Ⅲ.Controlling microorganisms.
　 The oxidation / reduction potential (ORP) shift from +200mV for untreated water to -500mV for water filtered through redox media controls microorganism growth. In general, different types of bacteria can only grow within a particular range of redox potential.
　Water treated with one redox medium comprised of a copperzinc alloy reduces bacteria and other microorganisms by disrupting electron transport, causing a cascade of cellular damage. Redox media also kill bacteria by direct electrochemical contact and by the flash formation of hydroxyl radicals and hydrogen peroxide, both of which interfere with a microorganism's ability to function.
   
Ⅳ.Preventing hardness scale accumulation.
　Redox alloy media prevent the formation and accmulation of mineral hardness scale, primarily calcium carbonate.
　Electron microscopy and X-ray crystallography demonstrate that hardness scale from untreated water is formed by relatively large, irregularly shaped acicular crystals of calcium and magnesium mineral salts. These salts form a hard, insoluble and interlocking network of vitreous limestone scale which plugs plumbing, interfering with heat transfer and damaging equipment.
　Water filtered through redox alloy media alters the morphology of insoluble calcium and magnesium carbonate and sulfate crystals to relatively small, evenly shaped, rounded grains and rods. These form an unconsolidated powdery compound that won't adhere to metallic surfaces and is removed by 5-micron physical filtration.

Ⅴ.Removing iron.
　Redox filter media combine dissolved oxygen and soluble ferrous (Fe2)+ iron. The (Fe2)+ is catalytically removed on contact in the form of insoluble ferric hydroxide and ferric oxide. This also contributes to reducing iron bacteria and the hydrogen sulfide byproduct from decomposing iron bacteria colonies.
　 Dissolved H2S gas gains an electron (reduction) while atomic copper from the redox filter media loses an electron (oxidation). The resultant copper sulfide is precipitated as a harmless insoluble ionic compound that's removed by backwashing.
　The primary virtues of redox filter media are their synergistic compatibility with other point-of-use (POU) filter media including ion exchange resin, granular activated carbon, activated alumina, silver impregnated carbon and sodium hexametaphosphate. In fact, many POU devices are 1/3 redox filter media and 2/3 activated carbon.
   

How Redox Media Work

Redox potential (ORP) is a measure of the readiness to part with electrons and is calculated in millivolts (mV). Metals such as copper and zinc are classified into an activity series where the most reactive are placed above the less reactive.
　 Zinc is more reactive than copper and is more electropositive. In redox filter media, there are multitudes of granular high-purity bimetallic couples with copper as the permanent cathode and zinc as the sacrificial anode.
　The metals are given a value in the activity series, known as the standard electrode potential, with zinc having a value of -0.76 volts and copper +0.36 volts. The net result is a 1.1 volt difference with zinc as the electron donor.
　 A number of elemental metals and metallic alloys will provide redox potential, but high-purity copper and zinc provide the most effective formulation for water treatment and purification.
　 A single pass through copper-zinc redox filter media rapidly changes the ORP from +200mV to -500mV. This has a profound effect on most bacteriologic, solubility and ionic reactions.

   
By Thomas M.Lotts is a technical writer and a sales representative for KDF Fluid Treatment,Inc.,Constantine, MI.