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By Dave Carson, Burt Process Equipment
PolymerPlus Polymer Feed System
Developed to tackle the industry's need for advanced technology that maximizes polymer activation.
Hydro-dynamic principles deliver reliability and can increase polymer savings
Whether you’re a visitor or a longtime resident, you know the city of West Haven has a lot to offer as a seacoast community. The city has a beautiful view of Long Island Sound, well-manicured beaches and a boardwalk that is just right for a summer stroll. However, there is a little-known place, seldom talked about or even acknowledged, whose work is vital to the city they serve: The West Haven Wastewater Pollution Control Facility. They service approximately 55,000 residences in West Haven and a portion of the neighboring town of Orange.
West Haven Reviews Wastewater Treatment Processes
After a decade-long relationship with an independent municipal wastewater management firm, the City of West Haven resumed operation of its 12.5 million-gallon-per-day water pollution control plant (WPCP). The WPCP team immediately began to review their current processes to recognize target areas for improvement. The goal was to identify ways to increase equipment reliability, enhance overall efficiency, and promote operator safety while reducing operational costs and the environmental impact on New Haven Harbor. One of several processes targeted was the plant’s three polymer activation systems.
The Importance of Polymer in Wastewater Treatment
Polymer is used to coagulate suspended solids and aid in the dewatering process of active sludge. Emulsion polymer, also known as liquid polymer, requires a unique activation process that disperses the right amount of energy to allow for the polymer chain to maximize to its full potential. Polymers are very long chained molecules that attract suspended particles, thereby forming larger solids that can be easily removed during the dewatering process. Polymers are normally shipped in a concentrated oil or surfactant-based solution. Emulsions normally contain oil or surfactant and up to 35 percent active polymer. One of the disadvantages of emulsion polymer is that the oil or surfactant needs to be stripped away so the polymer molecule can hydrate. Hydration causes the polymer chain to uncoil itself and fully extend. It’s at this point of full extension that a polymer is most effective, but also susceptible to damage.
Challenges of Polymer Systems
The energy needed to remove the oil and surfactant can also damage the polymer chain once fully extended. It’s this balance and complexity which makes an advanced emulsion polymer activation technology necessary. Many polymer activation systems on the market today do not provide enough energy at the earliest point of hydration or provide too much energy once fully extended. Both cases reduce the effectiveness of the polymer, which ultimately increases polymer usage and the cost associated with its increased use.
The West Haven Pollution Control Facility dewaters activated sludge through three belt filter presses and uses liquid emulsion polymer to assist in the dewatering process of their bio-solids. Their original polymer systems were not intuitive, and operators could not interact with them. The units in general had limited control functions other than pump speed adjustment. The final straw was the continued need for additional polymer to ensure proper plant operation.
Previous systems used by West Haven were designed with a hydro-mechanical mixing device that isolates agitation energy in zones. These systems use the same rotational speed while applying different mixer impeller blade geometries to reduce energy per zone. High energy mixing removes oil and surfactant, then light agitation helps the polymer chain uncoil. Since these systems use a fixed speed device, they have no means to compensate or self-adjust in a real-world environment. It’s particularly true when inlet dilution water flow or pressures fluctuate. These fluctuations do not allow the mixer geometries to deliver the right amount of energy needed to activate polymer correctly.
One of the ways you can determine that a polymer system is not working properly is the identification of agglomeration in the active polymer solution. Agglomeration indicates wasted undissolved polymer. The larger the size of the agglomeration, the more significant the operating cost, due to a poorly functioning system.
Proven technologies can compensate for flow or pressure fluctuations while generating ultra-high activation energy and exposing this energy at the earliest point in hydration. Systems incorporating hydro-dynamic principals deliver reliability, ease-of-use and the opportunity to maximize polymer to its full potential, translating to reduced polymer use and significant annual savings.
PolymerPlus Advanced Activation System
Burt Process Equipment developed the PolymerPlus with liquid and dry polymer feed systems, designed to tackle the industry’s need for advanced technology that maximizes polymer activation. The PolymerPlus activation system activates polymers through a patented, motorless, hydro-dynamic, high energy activation chamber. The chamber uses the energy available in the dilution water flow to activate all types of liquid polymer.
The polymer is activated as it passes through the high turbulence generated by the patented orifice. As the polymer passes through the annular nozzle orifice, the system operates like a low-pressure homogenizer. The pressure required to operate the chamber is less than 10 pounds per square inch (psi). The orifice opening automatically compensates for solution flow changes. This assures that the polymer activation energy level remains adequate for the flow range of the polymer feed system.
While the activation technology is vitally important, two other key components of the polymer feed system, pump technology, and control options, were discussed with West Haven. It’s these components that will govern long term maintenance, operator interaction and overall satisfaction with the designed system.
Pumps used to meter activated polymer are of a positive displacement design and are either reciprocating or rotary type. The most common pumps used are the single diaphragm, peristaltic, or progressing cavity. Understanding the pros and cons of each type will help determine the right pump selection and the long-term maintenance required.
Larger single diaphragm pumps are often used for pumping heavy sludge and wastes containing heavy debris from catch basins and manholes. Smaller single diaphragm pumps are helpful in proportioning and chemical metering, for applications where a primary requirement is a specific quantity or constant flow of liquid. In addition to sludge, diaphragm pumps can be used to handle corrosive fluids and abrasives.
Advantages of diaphragm pumps include energy efficiency (when properly maintained), lower operating cost and low leakage. However, if not maintained, they may occasionally lose their prime. Diaphragm pumps also may be difficult to prime when there is considerable backpressure.
Peristaltic pumps are typically used for metering, dispensing and transfer applications. With media confined to the pump’s tubing, there is no chance of contamination. This makes peristaltic ideal for applications that require the strictest level of purity — for example, semiconductor, food, and pharmaceutical technologies. The low shear of peristaltic pumps makes them well-suited for handling sensitive materials since the gentle pumping action won’t damage the fluid.
Other advantages of peristaltic pumps include self-priming and variable speed models, various tubing sizes and fewer parts to clean since fluids stay in the tubing. Since peristaltic pumps are non-siphoning, there is no backflow.
For the West Haven application, the progressing cavity pump was selected. A progressing cavity pump uses a single helix rotor through a double helix elastomer core stator. As the rotor rotates inside the stator, it progressively opens and closes displacement cavities from suction to discharge. The pumping motion provides a gentle, non-shearing, near pulseless flow, which is beneficial when metering neat or solution polymers.
The progressing cavity pump design can also handle a broad range of viscosities which might require special options when using other technologies. Since a progressing cavity pump can be easily calibrated for a known fixed displacement, they are easily integrated with flow rate controls and use speed control via a variable frequency drive.
The West Haven operators wanted to interact with the system and make planned adjustments with a high degree of knowledge. Historically, they had been operating manually without supervisory control and a data acquisition (SCADA) system. However, having the ability to operate remotely made sense for further advancements. The system was customized with a programmable logic controller (PLC) based control panel and a human-machine interface (HMI) touchscreen display. Operators were now able to easily calibrate, adjust, and confirm both polymer and dilution water, allowing them to fine-tune operations. Understanding the long-term needs of the plant and its operators was vital to the success of this project.
Today, all three systems continue to meet the demands of the city and the expectation of its wastewater operators. PolymerPlus is solidifying annual polymer savings and substantiating the benefit of using a system with advanced hydro-dynamic activation technology.