What Is Coagulation and Flocculation in Water and Wastewater Treatment?

Written by AOS Treatment Solutions on April 3, 2018
coagulation and flocculation in water and wastewater treatment

One of the challenges for any water or municipal wastewater treatment plant is being able to remove the vast majority of waste particles from the water, quickly and efficiently. Coagulation and flocculation for wastewater treatment represent tested ways to improve efficiency and remove a high volume of particles. Here’s what you need to know about these two processes.

What is coagulation in wastewater treatment?

Coagulation water treatment is the first step in chemical wastewater treatment. Instead of passing over particles that would otherwise slip through the filter and fall too slowly to be trapped as sediment, coagulation clumps them together so they are more easily removed. Most of us know coagulation from anatomy class. It’s what our blood does when it combines with oxygen, thereby making a scab or a blood clot. It’s the same principle with wastewater treatment.

In coagulation treatment, a harmless chemical such as alum causes all of the particles to give off a positive charge and thus clump together, making them easier to filter. Coagulation is especially useful in removing the chemical phosphorus from water. Yet coagulation water treatment is far from being a new process. In fact, it was in use by the Egyptians as early as 2,000 B.C. Later the Romans used the coagulation process in water treatment, as did the English in the 18th century.

What is flocculation in wastewater treatment?

Flocculation goes hand in hand with coagulation in wastewater treatment. Once the waste particles have clumped together using coagulation, flocculating agents in wastewater treatment are used to remove the clumps. Flocculants are lightweight, medium weight and heavy polymers that cause the destabilized clumps of particles to agglomerate and drop out of the solution, removing them from the filtered water. The weight used depends on the type of particle.

Flocculants are like a high-tech rope that ties all of the coagulated clumps together. Flocculants come in various charges, charge densities, molecular weights and forms, and they have also been around for centuries. Natural polymers, such as crushed nuts, have been used as flocculants since prehistoric times by some central African tribes.

Coagulation, flocculation and the EPA

Coagulation and flocculation processes have become more and more popular due to the increasingly stringent filtration requirements for industrial and municipal water treatment and wastewater treatment facilities levied by the U.S. Environmental Protection Agency (EPA.)

The U.S. EPA surface water treatment rule requires 99.9 percent (3-log) Giardia removal or inactivation, and at least 99 percent (2-log) removal of Cryptosporidium. The combination of coagulation and flocculation is particularly useful at exceeding these guidelines. Using these two treatment methods with sedimentation and filtration, assigned a 2.5-log removal credit for Giardia, will leave only 0.5-log inactivation.

Would you like to know more about how coagulation and flocculation can help your treatment facility become more efficient and effective? To learn more about coagulation and flocculation in water and wastewater treatment, contact AOS Treatment Solutions today.


Posted Under: Wastewater Treatment Solutions