Coagulation water treatment uses chemical processes to prepare water for human use or to return it to the environment. Through coagulation, water treatment plants can remove the waste particles in water and further treat it to be usable again. Treated water is also less harmful when returned to the natural environment. Here are a few more facts about coagulation water treatment.
How It Works
Water in its natural and waste water forms includes small particulates. In water, those particulates with the same charge are suspended into a colloid (a mixture with properties between a fine suspension and a solution). The repulsion process--the physical property of particles with the same charge (i.e., negative and negative) repelling each other--stops the particulates from combining into a settled form. Coagulation water treatment applies chemicals to assist water particulates in combining together. When particulates are aggregated, they can be more easily removed from the treated water.
Use of Chemicals
The particulates that are easy to settle in water are removed through a settling process called sedimentation. The harder-to-settle particulates must react with a chemical in water. For example, when a chemical like ferric sulfate is added to the water, this chemical reacts with the water particulates. In other words, the coagulant introduces positive charges that destabilize the negative charges of the particulates. The next step is a process called flocculation. Polymers adsorb onto the particulates, causing them to combine together into clumps or aggregates called "flocs."
The difference between coagulation and flocculation is that the former neutralizes the charges of the particulates and the latter causes the flocs to be formed through the formation of polymer bridges between the particulates.
Common Types of Chemicals
There are two types of coagulant chemicals, the primary coagulants and the coagulant aids. According to the Pennsylvania Department of Environmental Protection, coagulant aids are "added after the primary coagulant to produce a stronger and more settleable floc. These chemicals can also help reduce the amount of primary coagulant needed and the amount of sludge produced during the treatment process." Four common chemicals used as coagulants are aluminum sulfate, ferrous sulfate, ferric sulfate and ferric chloride. Even after these chemicals are used to treat water, the water will progress through other steps, including filtration and disinfecting (at which point more chemicals will be used).
Water Purification Alternatives
Water is treated in several steps in most water treatment systems. When natural or waste water is filtered into a plant, it will first be screened for the removal of larger components, including soil, leaves and pieces of trash. The introduction of chemicals occurs at the coagulant stage. Water treatment can also use less environmentally harmful processes like multiple steps of filtration (using membranes and a substance like sand) to remove particles from water and then desalinizing the water instead of using chemicals.
Remove Harmful Microorganisms
The processes of sedimentation, coagulation and flocculation combine to treat waste water successfully. This water treatment method has been applied in the United States since the early twentieth century.
In April 2009, researchers at the University of Michigan discovered that the amount of bacteria killed by modern waste water treatment causes the development of superbacteria that are resistant to antibiotics. This new finding presents a public health concern. More research must be done to determine how much bacteria should remain in U.S. waste water, and the Environmental Protection Agency (EPA) may have to revise national water safety standards. For more information about the EPA's water standards, see the link below.