Flocculants and clarifiers
Flocculation is a process where suspended particles, called colloids, come out of suspension in the form of larger particles. It differs from precipitation in that precipitation occurs where dissolved ions react to form an insoluble particle that falls out of solution.
The impact on water quality occurs where turbidity is reduced due to removal of colloids from solution. However, it is important to note that flocculants or clarifiers do not remove the colloids per se; they simply prepare them to be removed by other means. It should also be noted that flocculants and clarifiers operate according to the same mechanisms, which means they essentially do the same thing. The difference within the industry is products that enhance filtration are generally called clarifiers, while products intended to drop a large amount of debris to the pool floor for vacuuming are generally called flocculants.
To understand the mechanism of flocculation, the interaction between colloids in a solution should be appreciated first. For instance, the way various particles act in water depends largely on their charge. If the particles have the same charge, they are repelled from each other. Typically, colloids carry a negative surface charge, so they naturally repel. If the charge on the colloids is neutralized, they are free to agglomerate (collect) into larger particles upon collision, ultimately to settle out of solution.
Flocculating agents and clarifiers operate to neutralize the charge of colloids. Alum, for example, reacts in the water to form aluminum hydroxide (Al[OH]3) salts. It has a positively charged surface, which absorbs the colloids’ negative surface and neutralizes their charge to allow for subsequent particle agglomeration. This reaction must take place in the presence of sufficient alkalinity in order to prevent the aluminum component from dissolving to form Al+3 ion, rather than reacting to form its aluminum hydroxide salt.
In addition, the aluminum hydroxide is concurrently precipitating out of solution. Due to its very low solubility, aluminum hydroxide precipitates out of solution rapidly. As it precipitates, it settles to the pool floor collecting colloids in the process.
This method of removing colloids, called ‘sweep floc,’ causes unorganized crystallization, which tends to trap additional metal ions in the structure, removing them from solution.
Similarly, cationic polymers operate by the principles of charge neutralization. They consist of long polymer chains, with many positive sites from which to collect negatively charged colloids. As colloidal particles are connected, they grow into microflocs, which ultimately bridge to form flocs that are removed by the filtration system or fall to the bottom of the pool for further removal.
A cloud on the horizon
As long as pools remain in existence, there will always be occasions when they turn cloudy. It is the pool professional’s job to prescribe the right treatment programs that will return the pool water to an inviting, pristine environment for the pool owner to enjoy.
By understanding cloudy water is a symptom of a problem, rather than the disease, pool professionals will be able to ask targeted questions that lead to the right solution. The ability to provide a solution to customers illustrates the service company’s value as professionals, while also driving customer loyalty and sustainable profitability.
Karen Rigsby is the leader of technical services for BioLab, a Chemtura Company. She has been involved with the recreational side of water treatment since 2001, focusing on education, problem resolution and new product development. She began her career in the water treatment industry at BioLab as an analytical chemist in the research and development group. Prior to recreational water, Rigsby was employed by the Georgia Bureau of Investigation as a forensic chemist. Rigsby received her bachelor of science in chemistry from Georgia Tech and is a member of the Association of Pool & Spa Professionals (APSP) Recreational Water Quality Committee and a National Swimming Pool Foundation (NSPF) certified instructor.
Zach Hansen is a technical services engineer for BioLab, where he started his career working in automated controller and feeder equipment development. Over the last four years he has focused on new product commercialization and development for the company. Hansen received his bachelor of science degree in chemical engineering from Auburn University in 2004. He can be reached via e-mail at zach.hansen@chemtura.com.
