Organic Coagulation
Organic coagulants are best used for solid-liquid separation. They are also good options to use when trying to reduce sludge generation. Being organic in nature, these coagulants offer the added benefits of working at lower doses and having no effect on the pH of your water.
Organic coagulants are typically based on the following formulations:
PolyAMINEs and PolyDADMACs – These cationic coagulants work by charge neutralization alone and are the most widely used organic coagulants. PolyAMINEs and PolyDADMACs neutralize the negative charge of colloids in your water, forming a spongy mass called a “microfloc.” Since they only coagulate through charge neutralization, they don’t offer any advantages in regard to the sweep-floc mechanism (explained later with inorganic coagulants).
Melamine Formaldehydes and Tannins – These natural coagulants work somewhat similarly to inorganic coagulants in that they both coagulate colloidal material in the water and also contribute their own precipitated floc. This sweep-floc precipitate can absorb organic materials such as oil and grease while coagulating unwanted particles together in your water. Since the precipitate dewaters everything to low moisture concentration, these coagulants are great for operations that generate hazardous sludge, such as what’s found in oil refineries.
The main advantages of organic coagulants include; lower dosage, lower volume of sludge produced and no effect on the pH.
Inorganic Coagulant
Inorganic coagulants are typically cheaper than their organic counterparts, making them a cost-effective solution for a broad range of water treatment applications. They are especially effective when used on raw water with low turbidity.
When added to water, inorganic coagulants form aluminum or iron precipitates. These help to clean the water by absorbing impurities in the water as they fall. This process is known as the “sweep-floc” mechanism. However, this can add to the overall sludge volume that must be treated and removed, so it’s not the right choice in every scenario.
The main types of inorganic coagulants include:
Aluminum Sulfate (Alum) – As one of the most common water treatment chemicals used in industrial processes, alum is the go-to coagulant choice for many. Manufactured as a liquid, alum’s crystalline form is created when the liquid is dehydrated. It should be noted that alum is mildly hazardous and has similar health effects/corrosion characteristics as diluted sulfuric acid.
Aluminum Chloride – This coagulant works similarly to alum, but it’s more expensive, hazardous and corrosive. As such, it’s usually only picked as a second choice in processes where alum could not be used.
Polyaluminum Chloride (PAC) and Aluminum Chlorohydrate (ACH) – These inorganic coagulants are best used for more basic water supplies.
Ferric Sulfate and Ferrous Sulfate – While ferric sulfate is more commonly used, both iron coagulants work similarly to aluminum coagulants. Ferrous sulfate is typically a good choice in applications where you need a reducing agent or excess soluble iron ions are required.
Ferric Chloride – Since it is generated as a waste material from steel making operations, ferric chloride is the least expensive inorganic coagulant. However, it’s only used in facilities that can handle its reputation as the most corrosive and hazardous inorganic coagulant.
Once you have the right coagulant, you add these chemicals to your dirty water and mix rapidly. That way, the coagulant is quickly and easily circulated throughout the water.
The residuals or by-products of these coagulants generally do not pose a water quality issue, so long as they were applied properly and with the right dosage. This is why having a water treatment expert is key. Professionals who are experienced with wastewater treatment can even set up the coagulation process so that the coagulant chemicals are removed with the floc during filtration.
