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Dual chemical injection capability provides flexibility
As the national debate on the future of chlorine use as a water disinfectant continues, many point-of-entry and point-of-use (POE/POU) systems could face a potential engineering redesign.
For decades, chlorine has been a reliable and efficient water disinfectant; however, with the ongoing debate over the potential of disinfectant byproducts (DBP) development, many POE/POU suppliers are seeking ways to engineer flexibility into their systems.
Deploying Hydrogen Peroxide
One POE/POU solution developed by Charger Water Treatment Products is a chemical disinfectant system capable of injecting chlorine or hydrogen peroxide. In order to effectively deploy a dual chemical system, solutions to several technical and market issues needed to be resolved.
The popularity of hydrogen peroxide as a water treatment disinfectant is increasing. It is an effective disinfectant against bacteria and viruses and has been shown effective in treating nontoxic water contaminants such as iron and sulfur, reducing bacteria that can affect taste, color and odor. In contrast, the resulting byproducts of hydrogen peroxide—oxygen and water—are naturally beneficial with the residual oxygen in the flow stream acting to deter sulfide production.
The challenge to hydrogen peroxide is the handling. As a powerful oxidant, the U.S. Department of Transportation requires special handling and certifications for solutions of 8% or above. Chemical suppliers offer 7% solutions, reducing the liability to the dealer and end-user. Hydrogen peroxide should be handled and stored diligently.
The technical issues posed from a flexible chemical disinfection system using chlorine or hydrogen peroxide are the gasification of the chemical disinfectant experienced as vapor-lock in a diaphragm metering pump, fluid handling and preparation and the rangeability or turndown in the chemical pump.
Using Peristaltic Pumps
In some chlorine injection systems, Charger has provided systems using peristaltic pump technologies. Peristaltic pumps perform well in both chlorine or hydrogen peroxide injection systems because of their ability to handle the gasification of both liquids and provide the turndown required. The downside is their initial cost and resulting repair cost of replacing the tube, gear train and motor if the tube loop was installed horizontally versus vertically. If the tube in a vertical installation ruptures, chlorine will drip down the loop before accumulating inside the gear train and motor, allowing time for tube replacement before the onset of corrosion.
To handle the turndown rates, chemical metering pumps were also well-suited, but many of the diaphragm metering pumps suffered from vapor lock as the chlorine and hydrogen peroxide turned to gas. Vapor lock is a particular problem during the hot summer months.
During their research, Charger Water located the QP diaphragm metering pump from EMEC Americas that retained the turndown and integrated a self-venting head design to handle the gasification of chlorine and hydrogen peroxide.
Charger began testing the QP pump at select locations around their market area. Rangeability in the QP pump gave it a 150:1 turndown, allowing the pump to operate at a high injection rate of 24 gal per day (gpd), 22 gpd when venting gas and a minimum of 0.5 gpd within the required injection range for both chemicals. The benefit of venting gas vapor back into the tank proved to be an asset during the summer months.
“At first I was skeptical that a self-venting metering pump would work, but when we put it in the field we found that it actually vented the chlorine gas back into the tank and did not lose its prime,” said Eric Beck, Charger’s Port Richey, Fla., branch manager.
With initial tests complete, Charger began deploying a few of the QP pumps to select dealers for further field trials. The plan was to use one QP pump for either chlorine or hydrogen peroxide injection with the expectation of lower equipment costs. Initial installations went well, with installers commenting on the ease of installation of the wall-mount design. Water treatment dealers appreciated the fact that the wall-mount configuration saved them installation time versus a foot-mounted pump, which required a mounting base or pump head rotation.
Most of the initial installations went into systems that injected chlorine for POE applications. As the debate on chlorine use has intensified, end-users as well as water treatment dealers began inquiring about the option to inject hydrogen peroxide.
“That’s when we stepped in with our plan,” Beck said. “We worked with our dealers to calculate the hydrogen peroxide requirement for the installation, flushed the chlorine from the QP pump and reset the injection rate to meet the demand. So far the systems are working as expected. The pumps are still operating with their original diaphragms, which is an added benefit.”
“Returning comments indicate that users are witnessing lower electric consumption with the QP versus that of a peristaltic pump,” said David Wood, operations manager for Charger, Port Richey. “We suppose that is because the solenoid operates with one stroke versus the rotation of a peristaltic.”
“We’re excited about what this means for the industry—we now have one pump that can inject both chemicals without losing its prime,” Beck said.
It is not known where the debate on chlorine use will go, but developing options for the use of additional disinfectants such as hydrogen peroxide will make this industry better prepared to meet the opportunity as it develops.