Iron in groundwater
Iron in rural groundwater supplies is a common problem: its concentration level ranges from 0 to 50 mg/l, while WHO recommended level is < 0.3 mg/l. The iron occurs naturally in the aquifer but levels in groundwater can be increased by dissolution of ferrous borehole and handpump components. Iron-bearing groundwater is often noticeably orange in colour, causing discoloration of laundry, and has an unpleasant taste, which is apparent in drinking and food preparation.
Iron dissolved in groundwater is in the reduced iron II form. This form is soluble and normally does not cause any problems by itself. Iron II is oxidised to iron III on contact with oxygen in the air or by the action of iron related bacteria. Iron III forms insoluble hydroxides in water. These are rusty red and cause staining and blockage of screens, pumps, pipes, reticulation systems etc. If the iron hydroxide deposits are produced by iron bacteria then they are also sticky and the problems of stain and blockage are many times worse. The presence of iron bacteria may be indicated by rusty slime inside headwork’s, reduced water flow form the bore and unpleasant odor from water pumped from the bore, slimy deposits blocking main and lateral lines, severe staining on pavements, walls foliage .
Biological iron removal is a means of removing iron from groundwater within water filters. Microbiologists have known for many years that certain bacteria are capable of oxidizing and immobilizing iron. The bacteria responsible for the process appear to be natural inhabitants of the well environment.