Four main technologies are available, and plant operators can optimize operations by selecting the best combination of these options.
by Tom O'Donnell
October 17, 2016
Hydraulically actuated diaphragm metering pumpsImage 2. Hydraulically actuated diaphragm metering pumps are a technology of choice for many wastewater treatment plants because they can handle the hardest chemicals, can pump against higher pressures, offer highly repeatable dosing accuracy and have been designed for 20 years of service.

Hydraulically balanced means that the hydraulic fluid is on the oil side of the diaphragm, while the chemical being pumped is on the other side (wetted or process side) of the diaphragm. The piston, internal to the pump, pushes oil against the diaphragm but never comes in direct contact with it. These pumps are capable of pumping against extremely high pressures, so long discharge lines are not a problem.

Hydraulic diaphragm pumps are equipped with an adjustable internal relief valve that prevents an over-pressurized situation, which could damage the pump. They also offer a repeatable dosing accuracy of +/-1 percent.

3. Solenoid Diaphragm Metering Pumps

Solenoid-actuated, or electronic, metering pumps are an economical option in wastewater treatment operations for low-flow/low-pressure chemical-dosing applications. They are generally available to a maximum of 20 gallons per hour (gph) (76 liters per hour). At those capacities, maximum pressures are about 30 psi (2 bar).

Solenoid-actuated diaphragm metering pumpsImage 3. Solenoid-actuated diaphragm metering pumps offer reliable dosing accuracy, even when working with low flow rates and operating pressures.

The lower and medium capacities are compatible with pressures of 100 to 150 psi with low flows (less than 1 gph) to more than 200 psi (14 bar). They offer a repeatable dosing accuracy of +/-3 percent. They are normally provided with an on-board relief valve to prevent pump damage resulting from over-pressurization.

4. Peristaltic Pumps

This pump technology, simplistic in its design, is well-suited for handling viscous and abrasive chemicals. Because the design features a rotor with shoes or rollers that squeeze the hose or tube and force the liquid to the discharge port, peristaltic pumps are able to run dry—a feature that technologies like some progressive cavity pumps cannot provide because their rotors and stators may be damaged in dry-run conditions.

Peristaltic pumps also do not have valves that can become clogged. This is an important consideration when the pump needs to be shut down during a product run. The lack of valves in a peristaltic pump eliminates any clogging issues, especially when handling viscous liquids or those that will solidify or become gelatinous when resting. This also makes the peristaltic pump ideal for handling abrasive or corrosive chemicals.

Help from Manufacturers

While these pump technologies can provide a list of benefits for wastewater treatment plant operators, the challenge is knowing which pump is best for which chemical-metering application. This is where the pump manufacturer can lend a hand.

Complete Chemical-Feed SystemImage 4. Because many pump manufacturers also design the other components that make up a complete chemical-feed system, they can be a significant source of assistance, or even a provider of comprehensive turnkey systems, for wastewater-handling operations.

Many pump manufacturers also design and manufacture many of the components that are included in a complete chemical-feed system; for example, relief and backpressure valves, calibration columns, tanks, mixers, injection quills, and control panels.

Some offer the complete chemical-feed system as an option and can build a system that meets the specific needs of the treatment plant. While the task of properly outfitting a treatment facility may be overwhelming, manufacturers of the various components that will be used to optimize the system, or the manufacturer of a complete system, can assist in determining how to best outfit the plant.

Optimizing Operation

Ensuring that communities have the cleanest water possible places a great amount of pressure on water and wastewater treatment facilities to perform their jobs as effectively, efficiently and safely as possible. The various chemicals that may be required in the different treatment processes only increase the plant operator’s risk.

An operation will reach the pinnacle of proper performance only if the best pump technologies are chosen for each of the many critical chemical-metering processes.

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