Water is one of the most important resources on the planet. Clean water is necessary to support life itself and is the basis for countless water-based products, including food products, medical formulations, personal hygiene products, and more. The purification of water, however, spans municipal processes resulting in potable water and the treatment of wastewater from industry. The chemical reactions that are utilized in the purification of water are highly controlled and require precise dosing, flow rates, and agitation levels. Below are some exam­ples of how industrial mixers are utilized in key steps in the municipal and industrial treatment of water.

Municipal Water Purification
The purification of groundwater that flows from rivers, lakes, or streams is the focus of the continuous process of municipal water purification facilities. Through a series of chemical and physical processes, contaminants are separated, and organisms are mediated to produce clean drinking water. A few of the common steps in the overall municipal water purification process are chemical makeup and addition, flash mixing, flocculation, chlorination, and polymer addition. Each step in the process can have unique needs for agitation level and shear (the stress imparted to the liquid and suspended particles as a result of encountering a mixing blade).

Water purification chemicals are produced in dry powder or concentrated liquid form. Therefore, dilution, either in portable tanks or intermediate bulk containers (IBCs), is common prior to introduction into the general process flow. Portable direct-drive clamp-style mixers are ideal for use in any necessary pre-mixing steps, including for rapid mixing of low-viscosity formulations or when there is a desire to limit shear. Direct-drive and gear-driven mixers are often used when mixing in IBC totes.

Flash mixing is the rapid integration of chemicals into the water purification process. It is characterized by high-rpm mixing to maximize agitation and therefore achieve homogeneity in a short period of time. Portable mixers can be used for smaller scale processes, while more powerful top-mounted mixers may be required for turbulent agitation in larger-volume flash mixing basins.

Flocculation is the process of introducing compounds called flocculants, often aluminum sulfate (alum), into the water to attract solid particles to form clumps, or flocs. These flocs then settle to the bottom of the basin as the flow of water is gently agitated. While it’s critical that complete agitation is generated to maximize the agglomeration of the solids, it’s equally important that shear be minimized to prevent destruction of the same flocs. Therefore, a gear-driven, top-mounted mixer with a hydrofoil-style impeller is the best choice to achieve both goals. Such mixers utilize a hydrofoil impeller design, which provides the maximum agitation per unit of energy input with the lowest shear input.

Chlorination is a sanitization step in the process to ensure that bacteria and other organisms are eliminated from the water. Chlorination is generally achieved through intense agitation to completely disperse sodium hypochlorite into the water, using either a direct-drive or gear-driven mixer design optimized to provide the agitation necessary for the chlorination tank or basin used in the process. Similarly, polymers may be added to achieve the desired water chemistry. A variety of mixers may be used for chlorination and polymer addition based on the working volume and container geometry.

Industrial Wastewater
Industrial wastewater processes are often designed to settle out solids resulting from chemical or other production, dilution of chemical contents to meet EPA disposal requirements, or adjustment of acidity and alkalinity. Therefore, from an agitation standpoint, the range of applications can be similar to those for municipal treatment.

However, it’s the nature of the elements to be removed and the operating environments that can be quite different. For example, solid waste may be denser and thus require higher horsepower and torque, or highly acidic processes may need to be neutralized inside a sealed mixing tank, thereby requiring more chemically resistant mixer components and perhaps a mechanical seal.

For these and myriad other industrial wastewater mixing applications, standard or customized mixers can be created to meet application-specific needs. Mechanical seals prevent hazardous fumes from escaping the vessel and are typically available with a wide range of metallic and elastomer components. Mixing shafts and impellers are typically 316 stainless steel but can be upgraded to include Hastelloy and other alloys, as well as Teflon, Halar, and other chemically resistant coatings for tougher applications.
When in doubt about materials of construction, horsepower required, number or type of impellers, or any other aspect of the mixer in question, consult with your mixing equipment manufacturer—the organization’s engineers should be happy to assist.

About the author
Mark Hennis is President of INDCO and has held the position for 13 years. Hennis holds a BS in Mechanical Engineering from the University of Tennessee. He can be reached at mhennis@INDCO.com.

About the company
Located in New Albany, IN, INDCO is a leading manufacturer of industrial mixers. Since 1975 they have designed and manufactured a completed lineup of mixers for batch sizes up to 50,000 gallons. In addition to premier equipment, INDCO prides itself on providing fast, friendly customer service and immediate technical support. For more information, visit www.INDCO.com.

 

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