Industrial Wastewater Treatment – Pros and Cons of Iron Based Coagulants

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Coagulants are chemical compounds that aid coagulation, where the particles become destabilized, begin to come together, and then form clumps. Iron is a very common metal that is used in coagulants, and most compounds made with it are relatively inexpensive. Iron is an effective coagulant because it is a transition metal. This means that has valence electrons, which allow it to combine with other elements.

Further, these electrons are present in more than one shell, giving them the ability to have several different oxidation states. Because Iron based coagulants are soluble over a very broad pH range, they are very useful for any industrial wastewater treatment applications. There are several types of iron-based coagulants, and each has pros and cons that you should be aware of before choosing the right one for your water.

Ferric Chloride (FeCl₃)

Pros:

· Reacts with phosphates and/or alkalinity to form insoluble iron salts, causing them to precipitate out of solution. This interaction makes Ferric Chloride ideal for removing metals such as Cu, Ni, and Zn, solids, and phosphorous.

· Can be combined with hydrogen peroxide to formFenton’s Reagent, which is used to oxidize organic contaminants in water. The reaction is exothermic (so it does release heat).

Cons:

· Is a highly corrosive compound.

· Does stain on contact, so the water treatment equipment may take on a brownish color.

· Generates a large amount of sludge during chemical precipitation.

Ferrous Chloride (FeCl₂)

Pros:

· Is less corrosive than ferric chloride.

· Used for a hexavalent chrome reduction, phosphorous removal, metals removal (especially arsenic and selenium), and as an aid to flocculation.

Cons:

· Does stain on contact, so the water treatment equipment may take on a brownish color.

· Generates a large amount of sludge during chemical precipitation.

Ferric Sulphate (Fe₂(SO4)₃)

Pros:

· Is very effective in treating oily water, removing turbidity and phosphorus, and removing metals.

· Is also effective for sludge dewatering.

Cons:

Does stain on contact, so a water treatment equipment may take on a brownish color.

Ferrous Sulphate (FeSO₄)

Pros:

· Is used for odor control, sludge conditioning, TSS reduction, and phosphorous removal.

· Is less corrosive than ferric chloride

Cons:

· Does stain on contact, so a water treatment equipment may take on a brownish color.

· Not as effective at removing metals

Advantages of proprietary iron-based coagulants over commodity iron -based coagulants

The coagulant types that are described above are commodity compounds. In other words, you can purchase them by these names, and the product will be identical regardless of the vendor. Commodity chemicals are often not the most effective treatment for a facility’s waste stream. They are meant to serve a specific purpose and solve problems seen by the majority. A lot of facilities, however, have a more complex waste stream that requires a tailored coagulant. That is why some wastewater treatment chemical vendors manufacture proprietary blends (or custom blends). Iron based coagulants are used as the basis of many custom coagulant blends.

Pros:

· Can be tailored to a specific waste stream

· Include other compounds that enhance their performance and reduce the number of chemicals that need to be dosed during water treatment processes.

· Remove some of the disadvantages you may find with commodity compounds or add advantages that are not otherwise present with the commodity compound.

Cons:

The wastewater treatment chemical vendor will need to test your water in order to develop the right blend for your water. This may take require laboratory fees and more time than if you buy a commodity blend from that vendor.

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