By Carl Hammonds
Summary: Until not too long ago, those seeking water treatment for small applications were reduced to two options—chlorine gas and bleach. Meanwhile, larger users always had the alternative of tablet chlorination methods. But now smaller users are offered a new system that provides the same benefits only previously available on a larger scale.
Small water treatment users such as resorts, mobile home villages, towns and community parks have traditionally relied on either chlorine gas or sodium hypochlorite as a disinfectant for both their potable and wastewater systems. When carefully managed, both methods can be effective. However, they each have issues of safety, maintenance and efficiency that continue to make them ill-suited for the small volume user. While larger users avoid the liability of chlorine gas and the inefficiencies of sodium hypochlorite by switching to tablet chlorination systems, those with lower water flows have been left wondering when such systems will be available to them.
The wait is over.
A new, advanced tablet disinfection system brings performance that has proven itself successful on a large scale to smaller users. Until now, the leading tablet technology required site specific custom engineering for every application. However, this new concept—which features a simple “plug and play” design—requires no custom engineering. A single system has the ability to cover a broad range of chlorine demand, treatment volume and operating pressures. This functional flexibility makes it ideal for most disinfection applications including rural, county and city water supplies, food and beverage processing, meat processing, cooling tower disinfection and more. It’s ideal for anyone with a need to safely chlorinate water flows of 50-to-2,000 gallons per minute (gpm). Most importantly, the technology is being scaled down even more, which means it can be configured to serve users such as churches, schools, restaurants and even homeowners that utilize individual wells at flow rates less than 50 gpm.
Nuts and bolts
Here’s how it works. The technology manipulates the chemical solution to better control the tablet erosion process. It uses a magnetic stir bar to create a powerful vortex in a small water chamber. The vortex creates positive and negative pressures within the chamber allowing for controlled recirculation of the solution, thus making it possible to precisely control the solution generating process. In short, the specially configured vortex continually blends chemical and water to mix just the right solution strength, and since small batches of solution are generated on an “as needed” basis, the system always delivers consistent chemistry. In comparison, since sodium hypochlorite can lose almost half its strength in 10 days, it’s not hard to see how maintaining consistent chlorine residuals in fractions of 1 part per million (ppm) is almost impossible without constant adjustments of the metering system. The process utilizes 3-inch calcium hypochlorite tablets to produce a consistent solution that can be metered at controlled rates into the water supply (see Figure 1).
This advanced tablet technology offers several advantages over other methods of chlorine disinfection. First, it provides significantly better control. For example, in the case of smaller commercial users, mixing bleach for use in a diaphragm pump is inherently inaccurate. Even while in a store or on warehouse shelves, beach loses its strength due to temperature and age (see Figure 2). Adding further to the margin for error, standard bleach is typically diluted further before being injected by using less than accurate methods in the hand blending process.
On the other hand, solid calcium hypochlorite tablets are extremely stable, with a dry storage life of up to one year. Having the ability to blend small, consistent batches of solution at less than 1 percent concentration provides a steady supply of stable disinfectant.
Solutions at less than 1 percent concentration don’t require containment, are less corrosive and fall outside regulatory guidelines requiring special hazardous materials handling and emergency response plans. Actual field tests of a manually controlled system have produced consistencies within ±0.3 ppm of the original residual set-point and didn’t require constant adjustments due to changes in solution strength.
In addition to being non-hazardous, the solution doesn’t cause maintenance problems such as clogging and scaling associated with bleach or calcium hypochlorite concepts that depend on much higher concentration levels. Producing a stable, low concentration solution is only half the disinfection process. Metering either bleach of calcium hypochlorite solution at pressures as high as 125 pounds per square inch (psi) is a challenging pump application.
The advanced technology tablet feeder utilizes a balanced diaphragm pump capable of handling highly corrosive materials that often contain solids such as sand found in well water, and the calcium precipitates that can form from mixing calcium hypochlorite in hard water. The pump is configured within the system so that a flooded suction is always provided, thus eliminating loss of prime, which is commonly associated with pumps mounted on top of bleach barrels. One by one, this concept attempts to eliminate or significantly reduce the maintenance liabilities normally found in small disinfection systems since operators of such installations have neither the manpower nor training to provide constant hands-on attention.
The advanced technology tablet feeder is powered by any 110 volt AC outlet with a capacity of at least 5 amps, placing it within the capacity of most lighting circuits. A system to treat a 2,000-gpm well requires a 2-gpm potable water supply and can inject at any pressure up to 500 psi. That same system can be scaled down to disinfect a well of only 50 gpm and, while that may not be an ideal economic choice, it demonstrates the broad versatility of this concept in a single piece of equipment. Smaller versions of this same system offer performance that matches the requirements and budgets of smaller users.
Cost vs. effectiveness
Finally, it’s important when considering any form of disinfection to weigh the total cost of disinfection. This concept compares favorably with the total equipment and operating costs of gas or bleach disinfection systems. Although solid chemical costs are somewhat higher than bleach or gas, issues of safety, dependability and performance are primary considerations since the amount of chemistry consumed in small installations is nominal.
This versatile technology is already finding its way into a variety of unique applications. For example, it can be configured in fluid powered systems that require no electricity and can be readily adapted to provide safe water for global humanitarian efforts in developing nations and disaster relief. Whether used by a remote village, city park or dairy farmer, its versatility, range of application and reliability offer disinfection solutions never before available to smaller applications.
About the author
Carl Hammonds is founder and president of Houston-based Hammonds Technical Services Inc. He introduced the first factory engineered and manufactured pressurized tablet chlorination system in 1994, which became the industry standard alternative to chlorine gas and liquid bleach. Hammonds has over 30 years of experience designing and manufacturing water chlorination systems, fluid powered additive injectors, hydrostatic testers and related materials handling equipment. He can be reached at (800) 582-4224 or email: http://Carl@waterchlorination.com