Flocculants And Coagulants For Wastewater Treatment

How Are Flocculation and Coagulation Use in Wastewater Treatment

Flocculation and Coagulation in water treatment are used to remove suspended solids through a process that destabilizes the suspended particles in water solutions. The difference between the two is coagulation is the coming together, or clumping of particles, and flocculation is the settling of coagulated particles. Their purpose is to remove and neutralize charge density of particles with coagulation and then facilitate particle bounding through flocculation so that the larger aggregated particles easily separate from the water and settle to the bottle.

Common applications include:

• Slurry Pond Management
• Wastewater solids dewatering
• Effluent wastewater treatment
• Recycled plastics wash water treatment
• Mining wastewater treatment

View our Flocculants and Coagulants

Why Use Flocculants and Coagulants?

Flocculants and Coagulants when used in conjunction with each other provided efficient and cost effective means to remove suspended particles in water solutions or slurries. Some particles would settle out of the water on their own, given enough time. But other particles would resist settling for days or months due to small particle size and to electrical charges between the particles. Coagulants are primarily used to remove extremely small suspended particles in solution which do not settle rapidly. The flocculant primary use is to bind and agglomerate suspended particles in water to form large particles to assist in their settling and facilitate removal through particle and water separation processes.

The primary purpose of the coagulation/flocculation process is the removal of turbidity from the water. Turbidity is a cloudy appearance of water caused by small particles suspended therein. Water with little or no turbidity will be clear.

Turbidity is not only an aesthetic problem in water. Water with a high turbidity can be very difficult or impossible to properly disinfect. As a result, the maximum allowable level of turbidity in water is 0.5 NTU, while the recommended level is about 0.1 NTU. (NTU, or TU, stands for nephelometric turbidity units, a measurement of the turbidity of water.)

In addition to removing turbidity from the water, coagulation and flocculation is beneficial in other ways. The process removes many bacteria which are suspended in the water and can be used to remove color from the water.

Turbidity and color are much more common in surface water than in groundwater. As surface water flows over the ground to streams, through streams, and then through rivers, the water picks up a large quantity of particles. As a result, while aeration is more commonly required for groundwater, treatment involving coagulation and flocculation is typical of surface water.

What is Flocculation?

Flocculation is the process particles undergo when their interactions in water are destabilized in the presence of another molecule causing them to come together and bind with each other to form large, agglomerated particles that are easily settled. Polymeric molecules are often used to facilitate this process because they can be customized to increase or decrease their destabilizing potential by the surface charge of the molecules. The higher the charge density, the more destabilizing affect they can have. The lower the charge density, the less affect they will have on the particles in suspension. As a result, scientists deploy various combinations of charges, molecular structures and even elemental makeup of the flocculants to tailor their water treatment protocols to each individual application.

How Flocculants Works?

Used in a wide range of industries and applications, flocculants help to remove suspended solids from wastewater by aggregating contaminants into flakes or “flocs” that float to the surface of the water or settle at the bottom. They can also be used for lime softening, sludge thickening, and solids dehydration. Natural or mineral flocculants include activated silica and polysaccharides, while synthetic flocculants are most commonly based on polyacrylamide.

Depending on the charge and chemical composition of your wastewater, flocculants can either be used on their own or in combination with coagulants. Flocculants differ from coagulants in that they are often polymers, whereas coagulants are typically salts. They can range in molecular size (weight) and charge density (% of the molecule with either anionic or cationic charges), which is used to “balance” the charge of the particles in the water and cause them to come together and dewater. Generally speaking, anionic flocculants are used to catch mineral particles while cationic flocculants can capture organic particles.

Top Chemicals Used for Flocculation

At ChemREADY, our high-quality FlocREADY line of flocculants and coagulants are designed to improve wastewater treatment and lower overall costs in a wide range of mineral processing applications. We offer a wide range of cationic, anionic, and non-ionic flocculants, we well as organic and inorganic coagulants for all of your chemical treatment needs.  You can also learn more about our equipment partner Matec for use in dewatering after pretreatment.

What is Coagulation?

Coagulation is a somewhat simple chemical process that involves bringing insoluble materials together by manipulating the charges of particles, by adding iron or aluminum salts, such as aluminum sulfate or ferric sulfate, to a wastewater stream. The primary purpose of using a coagulant besides removing vary fine particles from suspension is that this process results also in less turbidity of the water, i.e. clearer water.

With coagulants’ positive charge, the negatively charged particles in the water are neutralized. This causes the suspended solids in the water to bind together into larger flocs. These larger flocs begin to settle at the base of the water supply. The larger the size of the particles, the quicker the floc settles.

Coagulation helps to remove a number of different pollutants that cause your water to become dirty or toxic, including:

• Organic compounds and certain dissolved organic materials, commonly referred to as Natural Organic Matter (NOM) or Dissolved Organic Carbon (DOC)
• Suspended inorganic precipitates like iron and some metals
• Certain viruses and bacteria

Through coagulation, industrial water supplies are put into the perfect chemical state for easy mechanical filtration. Once the flocs settle at the bottom of your clarifier, equipment like a filter press can then take those larger clumps of aggregated particles and remove them, delivering clean water back into your system.

When used together, coagulants, clarifiers and filter presses offer maximum water reclamation of over 95 percent. With so little water actually discharged with the solids, you can create a nearly closed-loop process.

Types of Coagulants

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.

More About Our Products

Our proprietary sieving process serves to eliminate many dust fines and reduce human exposure and slippery residue in the makedown area. Together with our dry polymer process, which achieves high molecular weights, this often results in a cost savings. Our portfolio also includes high-performance emulsion flocculants. Our proprietary emulsion breaker and carrier systems result in reduced polymer emulsion settling rates and low formation of insoluble material.

• Specifically formulated to enhance liquid/solid separation (How Industrial Wastewater Pretreatment Works?).
• Our experienced and highly trained chemists and technicians can create an optimized chemistry plan that ensures your system works at peak efficiency.
• Without this guidance you run the risk of damaging your equipment by using the wrong chemicals, spending too much money on wasted chemicals, paying costly non-compliance fees, and running up higher energy bills because your system is operating inefficiently.