Iron Removal Plants and Filters

Origin of Iron Contamination in Water

Iron is one of the natural minerals abundantly available in the earth’s crust. Also an inorganic chemical, about 5% of the earth’s crust is made up of iron. The rainwater that infiltrates the soil and the underlying rock formations dissolves the iron present in the crust and causes it to seep into aquifers that serve as sources of groundwater. Iron is thus released (geogenic) into the water from such natural deposits and exists in rivers, lakes and underground water in various forms.

Concentration of iron in water is also adversely impacted by industrial wastes, refining of iron ores and corrosion of iron-containing metals. Iron content in water, in many parts of India, is higher than the permissible limits and sometimes it is as high as 25 mg/L (or ppm).

As per the standards laid down by WHO (World Health Organization), the permissible limit of iron in water is less than 0.3 mg/L (or) ppm (parts per million). Standards set by the Indian Government is also the same. Water with iron content more than this limit is regarded as contaminated.

Forms of Iron present in water

Presence of iron in water is largely in two forms. It is either in the soluble / dissolved form (Ferrous) or in the insoluble / suspended form (Ferric Oxide / Ferric Hydroxide).

Ferrous Iron

In the ferrous (soluble) form, water will be colourless since the iron content remains dissolved in water. However, the water will carry an offensive odour. This form occurs primarily in deep bore wells due to lack of sufficient oxygen in the water. Removal of this type of iron warrants additional oxygenation / aeration of water followed by filtration processes.

Ferric Iron

In the ferric oxide-hydroxide (insoluble) form, the water will have a yellow brown or reddish brown colour, depending on the iron content present in the water, since the iron is in suspended state. This form of iron is basically the ferrous iron that has turned into suspended form on account of being exposed to oxygen. Removal of this type of iron can be done using a series of properly sized depth filtration and adsorbtion filters.

Mostly, iron-contaminated water will have both the forms of iron. The treatment process for iron removal in such cases is dependent on the type and content of iron present in the water along with other factors such as site conditions, applications of the treated water etc.

pH level of water largely determines the form of iron in the water. Low pH (6) can lead to more dissolved iron and higher pH ( >7.5) results in more suspended iron. Hence, while deciding on the iron removal treatment scheme, the pH needs to be factored in along with other key parameters for effective removal of iron.

Other types of iron

Sometimes iron may be present in colloidal form. Unlike the ferric iron, colloidal iron remains scattered as tiny particles since they repel each other and do not coagulate into large flakes. Their small size makes it difficult to filter them out and hence a coagulating agent may be required to achieve the same.

Bacterial iron is another nuisance factor. When bacteria use the iron content to survive, they combine to form a foul-smelling biofilm / slime, also known as iron bio-fouling. This type of slime is noticeable, among other places, in the toilet tank when the lid is removed. This bacterial iron can be controlled by periodic chlorination of water sources or the storage tanks.

Symptoms of Iron Presence in Water

Iron content in the water generally gives it an offensive (rusty) odour and metallic taste. Iron, if in oxidized state, also imparts a slight yellowish brown or reddish brown colour to the water depending on how much iron is present in the water.

Using this water for general utility purposes can discolour and stain the overhead tanks, bathroom walls, fittings, pipes, kitchen utensils, sinks, tiles and even the clothes.

In the water analysis labs, iron concentration is determined through atomic absorption spectrometry or using colorimetric methods.

Harmful Effects of Iron Contamination

Iron is an essential nutrient for good health. It is a major component of haemoglobin that is used to transport oxygen and carbon dioxide in the blood. In fact, iron deficiency can increase absorption of lead and toxicity in the body. However, overload of iron can result in chronic health issues and the forms of iron generally found in water are not advisable for human ingestion.

Iron-contaminated water is basically unpalatable due to its metallic taste and offensive odour. Regular consumption (drinking and cooking) of iron-contaminated water result in chronic constipation, loss of appetite, nausea, gastrointestinal diseases and can also damage blood vessels, liver, heart, kidneys, tissues in the long term.

While a low level of iron may not be harmful in itself, iron content often carries with it the bacteria that feed off the iron to survive. These bio organisms can be harmful to human health.

If used for bathing, it can clog skin pores leading to skin itching, wrinkles (due to loss of skin moisture), hair loss, potentially damage the skin cells and scalp.

When used for washing and cleaning, iron-contaminated water can permanently discolour / stain clothes and kitchen utensils.

Iron water can also drastically reduce the life and efficiency of water-using appliances like washing machines, dish washers, water heaters and steam iron boxes in addition to clogging / corrosion of bathtubs, showers, sinks, plumbing accessories, fittings, faucets and pipes.

Multi-Stage Iron Removal Process - Working Principle

Dissolved iron cannot be filtered but suspended iron can be removed by filtration. In order to remove the dissolved iron, it needs to be effectively oxidized and converted into suspended iron.

Technology and Process Description

Effective removal of iron content in water consists of two stages. ie., Aeration Process and Filtration Process

Stage I – Aeration Process

Online Aeration

Source water (Bore well / Open well / Sump) is pumped into a specially designed aeration tank that is trifurcated into equal sized chambers. The water flows into the first chamber of the aeration tank through perforated pipes or other suitable mechanical devices to ensure sufficient water-spread. From this chamber, the water is allowed to travel to the other two chambers through multiple vents strategically placed on the baffle walls to produce the designed intensity of turbulence in the water.

In the aeration tank, the water establishes maximum contact with air by the time it reaches the third chamber and as a result the dissolved iron content in the water gets oxidized and converts into filterable suspended iron. In case of lower pH or higher iron content in the source water, dosing of appropriate oxidizing agents may be required to expedite and complete the oxidation process.

Aeration Tank - An aeration tank can be constructed either on the ground or on the terrace or underground (sump) based on site conditions. In case of underground aeration tanks, additional equipment ( Blowers | Diffusers | Sludge pumps ) will be required to ensure proper mix of air in the water and removal of precipitated sludge from the sump. Volume, dimensions and design of the aeration tank are vital parameters to maximize the aeration efficiency of the tank.

Offline Aeration

Bore well water is sent into a single chamber aeration tank through perforated pipes, sprinklers and other mechanical devices to ensure sufficient water-spread. This tank can be a civil tank (on-the-ground or underground) or an HDPE Tank. This water is allowed to stagnate in the tank for a period of 4 to 8 hours for effective aeration and the stagnation period is determined based on the iron content in the water. In case the feed water PH is acidic, dosing of appropriate oxidizing agents may be required to facilitate and complete the oxidation process.

Stage II - Filtration Process

Once the first stage is complete, the water that comes out of the aeration tank is sent through the Korgen Iron Removal Unit that uses OXYRICH DFT (Depth Filtration Technology). Korgen Iron Removers consist of a unique 5-layered composite media that completes the oxidation of the leftover dissolved iron content in the water and effectively filters the oxidized iron, turbidity, suspended solids, odour, colour and taste using the voids present throughout the media.

Operation and Maintenance of Iron Removers

Besides the design factor, proper operation and regular maintenance are the key requirements in the sustained efficacy of Iron Removal Plants. Following the prescribed operational and maintenance processes will ensure longer life and optimal functioning of the Iron Remover.

Backwash

Once the filtration cycle is completed, the suspended iron particles trapped in the filter media have to be removed from the Iron Remover Unit. In order to achieve this, water is sent through the Iron Remover Media in reverse direction. The reverse flow of water with sufficient pressure agitates the filter media and loosens the trapped impurities in the media including the suspended iron particles. These impurities then flow out with the water through the drain port available in the Iron Removal Filter.

In high-volume Iron Removal Plants, air scouring may be required to agitate and loosen the media for effective removal of iron and other related contaminants from the water.

Rinsing

Once the backwash cycle is completed, the loose media is allowed to settle by gently passing water through the filter media.

Features of Iron Remover Plants

Unless warranted under special conditions, Iron Removal Units generally comprise the following major parts

• iVessel
• iiValve
• iiiMedia

Correct composition and alignment of the media helps in ensuring even distribution of the oxidation and filtration load. It also facilitates easy maintenance of the Iron Removal Plant resulting in longer life of the media.

The basic design and dimensions of an Iron Remover are highly formula-driven and should be primarily based on the following factors.

• Iron Content in the Feed Water
• Other related feed water characteristics
• pH Level and DO Content in the Water
• Hourly Flow Rate (LPH) required
• Volume of water to be filtered per day
• Site Conditions and end use applications

General Applications of Iron-Free Water (Subject to other parameters being within the prescribed limits)

• Used for all domestic uses such as bathing, washing, gardening etc.
• Used for external uses in commercial buildings and industrial units.
• Used as feed water to other treatment units and equipment. ie., Softeners, DM units, RO Plants etc.