19.07.2016

Chemical Coagulants Used In Water Treatment

water coagulants in treatments

Coagulation and flocculation have been used to clarify water since ancient times – as early as 2000BC, when the Egyptians used almonds to clarify river water. There is also evidence to suggest that the Romans were using alum as a coagulant at around 77AD.

Today, coagulation and flocculation are still essential components of treatment processes, e.g. for reducing water turbidity. Wastewater treatment operations also require coagulation, e.g. for chemical phosphorus removal and for reducing suspended solids.

Organic Coagulants VS Inorganic Coagulants
Chemical coagulants used in wastewater treatment fall into two main families: organic and inorganic.

Organic coagulants are generally used for solids & liquids separation and sludge generation. Organic formulations are based on the following chemistries:

  • Polyamines, e.g. polydiallyldimethyl ammonium chloride (AKA. polyDADMAC) – The most widely used class of organic coagulants, which function by charge neutralization alone. Polyamines are effective at treating higher turbidity raw water and wastewater.
  • Melamine Formaldehydes and Tannins – These coagulate the colloidal material in the water, and absorb organic materials such as oil and grease. This choice of coagulant is particularly well suited to operations that generate hazardous sludge.

Inorganic coagulants are both cost-effective and applicable for a broad variety of water and wastewater. Inorganic coagulants are particularly effective on raw water with low turbidity and will often treat this type of water when organic coagulants cannot.

Once added to water, the inorganic coagulants form aluminium or iron precipitates. These absorb impurities in the water as they fall, serving to clean the water. This process is known as the ‘sweep-floc’ mechanism. However, a downside of metal hydroxide precipitate sweep-floc is that they add to the overall sludge volume that must be treated and removed.

Examples of inorganic coagulants are as below:

  • Aluminum Sulfate (Alum) – One of the most commonly used water treatment chemicals in the world despite being mildly hazardous to health. Alum is manufactured as a liquid, from which the crystalline form is dehydrated.
  • Aluminum Chloride – A second choice to Alum as it is more expensive, hazardous and corrosive.
  • Polyaluminum Chloride (PACl) & Aluminum Chlorohydrate (ACH)
  • Ferric Sulfate & Ferrous Sulfate – Ferric sulfate is the more commonly used, but ferrous sulfate is typically used in applications where a reducing agent or excess soluble iron ions are required. Iron coagulants work similarly to aluminum coagulants but the cost may vary based on the local source of supply.
  • Ferric Chloride – The least expensive inorganic coagulant, as it is generated as a waste material from steel making operations. However, it’s by far the most corrosive and hazardous inorganic coagulant, and its use is limited to facilities equipped to handle it safely.

SNF supply a range of Flocculants and Coagulants. For more information or advice, please get in touch.

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