Cleaning Water: Making water safe at home, at work and in agriculture

Iron

Why is there iron in ground water?

When rain falls, the water has a naturally aggressive, slightly acidic nature. This water then dissolves chalk/metallic deposits present in the local rock strata which contaminate the water. This results in ground and borehole water containing a number of elements that would not normally be present in mains water. These contaminants (such as iron and manganese) then cause problems when the water is put to use. Iron contamination can be found in two general forms, ferric iron which consists of particles of solid iron (rust) that can be removed by mechanical water filters (sediment filters), and ferrous or dissolved iron which must be removed from water by special iron water filters. In addition to causing an unpleasant metallic taste, iron in drinking and household water can cause unsightly staining of plumbing fixtures and laundry.

Iron correction media

Types of treatment media and equipment will vary according to the levels of iron or manganese, e.g. type of iron, daily water usage and other water parameters. A water quality test report should be obtained to ensure the appropriate equipment is chosen.

Catalytic oxidation is a tried and tested method of both oxidising the iron and manganese to form a precipitate and then holding on to it until it is automatically backwashed to drain.

How does it work?

Water flows into the valve at the top, down through the media and then up through the ‘riser’ tube in the middle of the vessel. As the water travels through the media the iron and manganese are oxidised bringing the metals out of solution and trapping them so only clean clear water flows out to service. These systems also act as sediment filters trapping any natural turbidity. As the media act as a catalyst they do not need to be topped up or replaced on a regular basis. There are timer options that can be set to automatically self clean (backwash) and wash away any of the accumulated iron and manganese.

The media filters require dissolved oxygen in the water to oxidize the metals. This normally is present naturally but can be added by aerator or as an air filtration option.

How to size

On average 160 litres of water is used per person per day. This normally occurs in two peak periods, one in the morning and one in the evening. A family of four typically uses 700 litres of water per day but may use 300 litres in an hour in the morning. Larger households, farms, stables and irrigations systems all use more water.

When sizing a system the peak flow rate need to be taken into account. The size of the pump also needs to be taken into account as these filters normally use twice the service flow rate to lift the bed and backwash away the trapped iron and manganese. If the backwash flow is not available two smaller units running side by side is often a good solution. The vessel size is given as the diameter and the height (in inches). Recommended operating pressure range is 20 to 120 psi. Water temperature ranges from 2 to 38°C.

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A water quality test report should be obtained to ensure the appropriate equipment is suggested.