Pumps & Systems, March 2013
Many manufacturers are committed to sustainable practices to improve their environmental, economic and social performances. Companies that use or produce fluids in manufacturing processes face the challenge of properly disposing of the byproducts. For example, chemical manufacturers, food and beverage processors and metal finishers generate fluids that have to be treated in accordance with local government regulations before waste fluid is discharged into sewer systems.
The manufacturing sustainability trend is driven by customers; shareholders; government regulations; and the increasing costs of process inputs, such as water. As the cost of water increases, the industry is investing heavily in treatment processes using recycled water.
Industrial pumps are at the core of wastewater treatment systems, and different pumps are used in the treatment process. Positive displacement pumps are used to transfer liquids from tank to tank because they are durable enough to handle a wide range of fluids and solid particles.
Metering pumps play a vital role in the treatment process as well. This type pump has the technology required to accurately dose and meter chemicals at low flow rates and is one of the smallest positive displacement pumps on the market.
Air operated diaphragm pumps (AODP) are the workhorse of the wastewater treatment system. This type of positive displacement pump is durable enough to withstand submersion and continuous flow rates inherent in wastewater applications. AODPs are ideal for low- to mid-range flow rates—up to 350 gallons per minute—and produce enough back pressure, up to 250 psi, to move high viscosity fluids and sediment.
AODPs are used in multi-step, batch waste treatment systems to remove metal precipitation. One AODP moves the solution from the collection tank to the treatment tank. Others move the treated waste from the treatment tank to the drain.
The Pump’s Role
Positive displacement pumps have three main applications in the wastewater treatment process:
- Transferring fluids from the sump to the reactor
- Dosing chemicals into the reactor and neutralizer tanks
- Drawing slurry off the clarifier tank to feed the filter press
A typical wastewater treatment process begins as fluid builds in a sump tank. A positive displacement pump is used to move the fluid to a second tank where the rinse water flow is equalized and pushed into a reactor tank. The composition and temperature of the fluid running through the system must be considered when specifying this pump because the fluids can be corrosive and abrasive. AODPs can be configured to meet the chemical compatibility of the fluids, making them a low-risk solution.
Once the waste fluid is transferred from the sump to the reactor, concentrated chemicals are introduced to neutralize the pH balance. An electromagnetic or mechanically actuated simplex diaphragm pump, a highly controllable type of metering pump, doses treatment chemicals at a low flow rate.
This level of accuracy ensures that the fluids are treated, neutralized and clarified to adhere to local regulations.
Finally, the neutralized liquid flows into the flocculator where a chemical is added that adheres to particulates, causing them to coagulate on the bottom of the clarifier tank. AODPs are used to draw the slurry from the bottom of the tank and prime the filter press.
AODPs can handle this abrasive and corrosive mixture and produce enough back pressure to force the fluid into the filter, leaving only solid waste behind. The clean fluid returns to the treatment process before being discharged to the sewer or reused. The cake is removed from the filter press and disposed as solid waste.
Selecting the Right AODP
Pumps are critical to manufacturing processes. If one fails, it may force the entire plant to stop production until operators can find a way to restore it. Specifying the right pump for the application to increase reliability and prevent unexpected downtime is critical.
Pumps must be compatible with the fluids they transfer to prevent abrasive and corrosive materials from reacting with the composition material of the pump. Plant managers can ask a pump manufacturer to specify the best composition material for the application.
Polymer fluid chambers made from nonreactive materials, such as polypropylene or polyvinylidene fluoride (PVDF), are commonly used with elastomeric ball checks and diaphragms to prevent corrosion and increase a pump’s longevity.
Pump manufacturers can consult with plant managers to determine if continuous-duty pumps should be installed to meet the heavy-duty cycle required in wastewater treatment. Continuous-duty pumps prevent icing and stalling, and pulsation dampeners can be added to help equalize the pressure flow and keep the system running reliably.
AODPs offer several unique advantages over other positive displacement pumps:
- They are powered by compressed air and do not require electrical hookups at the installation sites, which dramatically reduces installation costs.
- Some AODPs can be submerged in fluids, making them a convenient option for sumps and pits.
- These pumps can be integrated with electric interface control devices, such as solenoids and tank fill, to control the pump’s operation.
- AODPs are not damaged by downstream blockages in the system.
- They are more compact than other pumps.
- These pumps have reduced purchase prices because they do not require electric motors or gear boxes.
- AODPs do not have mechanical seals that could leak or need replacement.
- They are portable and have plug-and-play capability for easy installation.
Total Cost of Ownership
When evaluating if an AODP is right for a facility, plant managers should note the initial purchase price and then include the total cost of ownership. These factors will help plant managers determine if an AODP is the most economical pump for the application:
- Compare the time required for maintenance on the AODP and how that affects productivity.
- Calculate the downtime costs of the plant and whether it is cost effective to keep an extra AODP in stock so it can be replaced quickly.
- Determine whether the AODP pump shares common parts with other units in the plant and manage inventory accordingly.
- Select a modular pump design that allows maintenance teams to repair one piece of the AODP without disabling the entire unit.
- Consider the installation costs and energy consumption required to get the pump up and running.
If specified correctly, AODPs can be an effective and reliable solution to a facility’s wastewater treatment process. Plant managers should contact an authorized pump manufacturer to determine if an AODP is the right choice for their application. P&S