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Manganese Greensand

Removal of iron/manganese

Nanotech supplies custom designed manganese greensand filtration units which can be used for a specific application or integrated into a turnkey Nanotech water treatment system. The units we supply have the following features:

Vessels are constructed from GRP, mild steel or stainless steel. Choice of material is dependant on application and operating features.
System control can be either manual, time control or volume demand.
Configurations are available in either CR (Continuous Regeneration) or IR (Intermittent Regeneration).

To properly design and integrate the water softener into a new or existing application, Nanotech has to understand the existing site conditions. We therefore ask potential customers to complete our water system enquiry form. This information will give us a snapshot of their site conditions and allow us to recommend a system/equipment that will meet all expectations.

What is a manganese greensand filter?

These filter systems use a high quality manganese greensand media. The system is installed in the main water line. When the raw water enters your iron filter, it passes down through the filter media and becomes oxidised. This causes precipitation of the minerals and any iron, manganese or hydrogen sulfide present in your water supply are trapped, resulting in a clean, filtered water flow to your household. The filter media is continuously or periodically regenerated automatically, either by a dosing and oxidising agent (chlorine, potassium permanganate,etc) upfront of the filter or by backwashing the trapped minerals to drain and then regenerating with potassium permanganate to replace the oxygen. The system is supplied with a potassium permanganate container. With proper installation, this system removes the following contaminants, resulting in healthier water:

15 ppm of both ferric (oxidised) and ferrous (clear) iron
5 ppm of hydrogen sulfide (rotten egg odour)
10 ppm of manganese

Note: These systems are designed for water supplies with a pH between 6.2 and 8.8. If your water supply has a pH of 6.1 or less, you need to neutralise pH before passing it through this system.

Next to hardness, the presence of iron is probably the most common water problem faced by consumers and water treatment professionals. The secondary (aesthetic) maximum contaminant levels (MCL) for iron and manganese are 0.3 milligrams per litre (mg/l) and 0.05 mg/l, respectively. Iron and manganese in excess of the suggested maximum contaminant levels (MCL) usually results in discoloured water, laundry, and plumbing fixtures.

Small amounts of iron are often found in water because of the large amount of iron present in the soil and because corrosive water will pick up iron from pipes. Clothing washed in water containing excessive iron may become stained with a brownish colour. The taste of beverages, such as tea and coffee, may also be affected by iron. Manganese produces a brownish colour in laundered clothing, leaves black particles on fixtures and as with iron, affects the taste of beverages, including coffee and tea.

Well water from the tap is usually clear and colourless. However, when water containing colourless, dissolved iron is allowed to stand in a cooking container or comes in contact with a sink or bathtub, the iron combines with oxygen from the air to form reddish-brown particles (commonly called rust). Manganese forms brownish-black particles. These impurities can give a metallic taste to water or to food.

The rusty or brown stains on plumbing fixtures, fabrics, dishes and utensils cannot be removed by soaps or detergents. Bleaches and alkaline builders (often sodium phosphate) can make the stains worse. Over time, iron deposits can build up in pressure tanks, water heaters and pipelines, reducing the quantity and pressure of the water supply.

Iron and manganese can often be quite difficult to treat. This is primarily due to the fact that iron can be present in several forms and each form can potentially require a different method of removal.

Types of iron

There are three main forms of iron and manganese. Other types are much rarer:

Ferrous - This type of iron is often called "clear water iron" since it is not visible in poured water. It is found in water which contains no oxygen, such as water from deep wells or groundwater. Carbon dioxide reacts with iron in the ground to form water-soluble ferrous bicarbonate, which, in the water, produces ferrous ions (Fe++).
Ferric - Ferric iron is also known as "red water iron". This type of iron is basically ferrous iron which has been exposed to oxygen (oxidised), usually from the air. As carbon dioxide leaves the water, oxygen combines with the iron to form ferric ions (Fe+++). These oxidised particles are generally visible in poured water.
Bacterial iron - Slime depositing in toilet tanks or fouling water filters and softeners is a good indication of the presence of bacterial iron. Better described as iron biofouling, the iron bacteria problem is both complex and widespread. It attacks wells and water systems around the world in all sorts of aquifer environments, both contaminated and pristine. In some places, it causes great damage; in others, it is considered a minor nuisance.

Treatment Methods

Iron Bacteria

Iron bacteria can be controlled by periodic well chlorination or it can be treated in the building. The treatment involves the following: chlorination, retention and filtration. Activated carbon is usually used as the filter material, also allowing the excess chlorine to be removed.

Ferric iron

In theory, the elimination of ferric iron is simple use a properly sized media filter to filter it from the water. In practice, however, there may be other issues:

Some iron may be present in colloidal form. Unlike ferric iron, which will generally stick together to form large flakes, the tiny particles of colloidal iron do the opposite. Their large surface area and charge relative to their mass causes the individual particles to repel one another. As a result they will not coagulate and their small size, makes them difficult to filter, often requiring a coagulating agent to achieve adequate filtration.
Most water containing ferric iron also contains ferrous iron. This can add complexity to the process, since some of the methods for removing ferrous iron will also remove ferric iron.

Ferric iron.

There are a variety of ways for removing ferrous iron, each with its own strengths and limitations. These methods fall into two categories: Ion exchange and Oxidation / filtration

Ion Exchange (water softener)

Many companies claim that water softening is a viable option to remove iron and manganese from water. With our extensive experience in water treatment Nanotech believes that this is not an option. Water softening resin is used to remove Ca and Mg hardness ions from water, not Fe and Mn ions. The Fe and Mn ions coat the resin leaving the resin useless to perform its intended function.

Oxidation / filtration

Oxidation followed by filtration is a relatively simple process. The oxidant chemically oxidises the iron or manganese (forming a particle), and kills iron bacteria and any other disease-causing bacteria that may be present. The filter then removes the iron or manganese particles.

Oxidation

Before iron and manganese can be filtered, they need to be oxidised to a state in which they can form insoluble complexes. Oxidation involves the transfer of electrons from the iron, manganese, or other chemicals being treated to the oxidizing agent. Oxidation methods fall into two groups: those using additives like chlorine, ozone or air; or those using an oxidising filter media.

Ozonation - An ozone generator is used to make ozone that is then fed by pump or by an air injector into the water stream to convert ferrous iron into ferric iron. Ozone has the greatest oxidising potential of the common oxidisers. This is followed by a contact time tank and then by a catalytic medium or an inert multilayered filter for removal of the ferric iron.
Chlorination - Chlorine can be introduced into water in one of several forms: a gas as calcium hypochlorite; or commonly, as sodium hypochlorite. The treated water is then held in a retention tank where the iron precipitates out and is removed by filtering with manganese greensand, anthracite/greensand or activated carbon. If applied this way, a dosage of one part of chlorine to each part of iron is used and 0.2 parts of potassium permanganate per part of iron is fed into the water downstream of the chlorine. The potassium permanganate and any chlorine residual serve to continuously regenerate the greensand.
Aeration - Air is also used to convert dissolved iron into a form that can be filtered. This approach mimics the process that occurs when untreated dissolved iron comes into contact with the air after leaving its outlet or tap. Aeration methods can be of a two-tank or a single-tank variety. In a two-tank system, air is introduced into the first tank using a pump or other injection device. The dissolved iron precipitates in the first tank and is carried into the second tank where it is filtered in a Birm or multi-media filter. One drawback to this system is that water bearing the precipitated iron goes through the head of the first unit and the piping between the units. Particularly at lower flow rates, the sticky ferrous hydroxide tends to foul the valve on the first unit and may require cleaning every six to 24 months. A single-tank system essentially combines the two tanks of a single tank system into one. The iron is oxidised at the top of the tank before falling into the filter medium at the bottom. There is no potential fouling of the head. The iron is filtered before it goes through the outlet port of the valve. For very high levels of iron, chlorination with continuous regeneration is the only practical approach.