Integrating Chemical Dosing and Flow Verification for Reliable Water Sanitation

As regulations tighten and staffing becomes more limited, treatment plants are increasingly finding that reliable water sanitation requires an integrated system. Sanitation of Water and Wastewater can be a delicate balancing act. The quality of the water is of utmost importance, it must be free of harmful pathogens, maintain precise pH levels, and contain sufficient disinfection residuals to meet regulatory requirements.

Chemical metering pumps are central to the sanitation process and when they work in conjunction with complimentary components, such as flow meters and pressure gauges, it creates an enhanced system that will manage chemical dosing and achieve consistent water quality and regulatory compliance (Figure 1).

The Gap Between Setpoint and Reality

Facilities can battle inaccurate or unverified chemical dosing. An operator may set the pumps chemical dosing rate and assume that the intended dose is reaching the contact basin. However, without a flow meter to provide real-time flow verification, operators must rely on downstream residual samples to tell them if something has gone wrong. This process is time consuming and not always accurate. Moreover, by the time a manual sample indicates a low residual, inadequately treated water may have already entered the distribution system.

Several factors can cause the dose ordered to differ from the dose delivered, including:

• Vapor lock. Off-gassing chemicals like sodium hypochlorite can cause vapor locking which in turn will prevent the unit from pumping efficiently or may even shut the pump down completely.
• Scaling and clogging. Mineral buildup or debris in the piping, tubing or other components can increase backpressure or foul valves, reducing flow rates.
• Suction lift changes. As chemical tanks empty, the pump must work harder to pull the liquid, which can cause the flow rate to drift.
• Calibration drift. Over time, mechanical wear on pump components may impact delivery rates even if the motor speed remains constant.

Closing the Loop

Simple steps can be taken to close the gap between the pump setpoint and actual chemical dosing. One example is to incorporate a flow meter that is designed to provide this type of verification. Caution should be used when choosing the flow meter, not all will be suitable for use with the aggressive chemicals used for water treatment. For this reason, non-invasive technologies, like ultrasonic flow meters can be the most effective choice. These meters never come into contact with the fluid being pumped and thus there are no wetted parts to corrode or clog. This can be critical when dosing harsh chemicals like sulfuric acid, peracetic acid (PAA), or sodium hypochlorite.

Matching Capabilities and Chemistry

Of course, accurate and repeatable dosing requires matching the metering pump’s capabilities with the chemical in use. The required duty cycle must also be considered. It’s equally important not to undersize or oversize the metering pump. Two of the most common pump types used in water treatment are peristaltic and diaphragm pumps, and each has its distinct advantages. Peristaltic pumps are the preferred choice for use with offgassing chemicals and high-viscosity and delicate fluids, such as polymers and slurries. Diaphragm pumps perform well in high-pressure applications.

The Case for Pre-Engineered Skid Systems

While large utilities may have the in-house engineering staff to design and build custom chemical feed systems, small to mid-sized utilities are increasingly turning to preengineered skids. There are several advantages to pre-engineered, preassembled skid systems. For example, there is no need for the plant to source components from several vendors. In addition, Blue- White® CHEM-FEED® Skid Systems arrive pre-assembled with all the necessary components such as the plant’s choice of diaphragm or peristaltic metering pump(s) (Figure 2), flow meter, pressure gauge, valves, and calibration columns. Blue- White’s CHEM-FEED® Skid Systems undergo rigorous factory testing prior to shipment. Skids also offer single-source support and reduce potential field plumbing errors. Prefab, preassembled skid systems simplify installation which can help keep labor costs in check. In addition, custom work, including special materials and components, is available.

For facilities with limited floor space or crowded equipment rooms, Blue-White® offers wall-mounted skid systems, as well as lightweight and compact plastic skid systems. These designs help to streamline the water treatment process.

In addition, a pre-engineered skid removes integration risk, ensuring that every elastomer, valve, and tube is chemically compatible and correctly sized. This helps mitigate operational mistakes, such as under sizing tubing, which can lead to premature failure.

Ensuring Proper Installation

Even the best equipment can fail when installed incorrectly. Common mistakes can include:

1. Omitting pressure gauges. Although this may save money, it leaves operators unaware when a pump is operating above its rated capability.
2. Inadequate labeling. It’s good practice to label pumps with the name of the chemical being injected. This simple system can reduce the risk of mix-ups.
3. Incorrect Material Selection for Components. Using the wrong tube material can lead to rapid tube failure and potentially dangerous accidents.

Reliable water sanitation is the foundation of public health. As such, it requires more than just a set-andforget mentality. By moving beyond the pump and adopting an integrated strategy utilities can turn their sanitation and disinfection processes into a predictable, reliable and verifiable system. This systematic approach protects the community is cost-effective and saves operators’ time.

Written by:
Blue-White® Industries
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