A: The process of oxidation is either naturally occurring or part of a method used in reducing unwanted ions from water. These ions are typically iron and manganese. There are a number of methods used. Introduced air (oxygen) is one method, another is the use of strong oxidisers, chlorine and less commonly ozone. When water containing soluble ferrous iron (+2) ions is exposed to air, the ions react with oxygen to form insoluble iron (+3) ions. The insoluble iron can then be physically removed from the water body by settling and/or filtration. The oxidation process can be described in the following manner

The formation of iron rust is thought to begin with the oxidation of iron to ferrous. This is the point at which iron enters the water and is described as a substance in solution. While iron remains in solution it rarely represents any serious problem.

When water containing iron contacts oxygen the reaction further oxidises soluble ferrous iron (+2) to form ferric (iron +3) ions.

The electrons provided from both oxidation steps are used to reduce oxygen in the following manner.

Insoluble iron (iron oxide) over time will usually settle from the water it is contained within. It normally appears as a brown sediment on or near the base of the container.

Iron reducing bacteria through the action of their metabolism can reduce iron from soluble to insoluble. The electrons that are liberated during this process is used by the iron reducing bacteria as a source of energy. The resultant chemistry is somewhat different to the normal iron oxygen process. Typically IRB are responsible for the biomass usually seen in pumping and distribution systems. The red/brown slime seen is chemically described as hydrated ferric hydroxide (FeOH³) .

With the addition of extracellular bipolymer or slime produced by the bacteria (which is already combined with the altered iron chemistry). Biofouling becomes a serious problem. Other than the obvious hazards this material represents to irrigation, attempts to remove the iron through aeration and precipitation are foiled or made more difficult as the added buoyancy created by the additional chemistry prevents the material from settling out of the water column.

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