Let's begin by reviewing water filtration processes is for water treatment plant. The American Water Works video produce this video that explains the process.

When iron and manganese are oxidized to insoluble forms by aeration, chlorination, or permanganate, the oxidation processes are usually followed by filters to remove the insoluble material.

Iron tests should be made monthly on the water entering a filter to be sure that iron is in the ferric state. Collect a sample of the water and pass the water through a filter paper. Run an iron test on the water that has passed through the filter. If the iron is still in the soluble ferrous state, iron is in the water. If aeration is being used to oxidize the iron from the soluble ferrous to the insoluble ferric state and iron is still present in the soluble state in the water entering the filter, try adding chlorine or potassium permanganate. If chlorine or potassium permanganate is being used and soluble iron is in the water r entering the filter, try increasing the chemical dose. If potassium permanganate is being used, the sand may be replaced by greensand to improve the efficiency of the process.

If oxidation is being accomplished by aeration or chlorination, a free chlorine residual must be maintained in the effluent of the filter to prevent the insoluble ferric iron from returning to the soluble ferrous form and passing through the filter.

Most iron removal treatment plants are designed so that the filters are backwashed according to head loss. If iron break-through is a problem, filters should be backwashed when break-through occurs or just before break through is expected. Accurate records can reveal when break through occurs and when break thorough can be expected.