Water and wastewater processes are important to cities and towns of all sizes. These operations are complex and involve a wide range of flow measurement applications. They demand high flow meter accuracy and reliability as well as long-term stability and a low cost of ownership.
Flow measurement is a basic and important control parameter for ensuring that clean, high-quality water is available to commercial, residential and industrial users. Applications ranging from water storage and transmission to wastewater treatment, leak detection and pump management require flow meter technology.
As sewage networks and wastewater treatment plants strive for greater efficiency and cost reduction, it is imperative that they monitor and control operations more precisely. When heavy rainfall or other abnormal events occur, wastewater levels in the collection system and wet wells can rapidly reach critical levels and accurate information from flow metering equipment is needed to take appropriate actions.
Municipalities have a significant financial stake in the performance of lift stations. When groundwater and stormwater enter city collection systems, treatment processes become less efficient and sanitary sewer systems become strained. Lift station pumps run for a longer duration after a rain event and have a larger number of starts and stops—indicating stormwater has entered the sanitary sewer system and is on its way to be treated. This additional stormwater costs municipalities money by increasing pump operation and wastewater treatment.
Meeting Today’s Demands
With greater awareness that water resources exist in limited quantities, there is an urgent need to save, reuse and recycle water, as well as develop methodologies to improve resource management and optimize water treatment efficiency.
Municipalities in particular are facing concerns about the effectiveness of their water and wastewater operations. Regulatory standards established by the U.S. Clean Water Act (CWA), National Pollutant Discharge Elimination System (NPDES), Effluent Limitation Guidelines (ELGs) and the National Sanitation Foundation (NSF) dictate effective water usage, treatment and disposal techniques.
Water and wastewater operations require plant-wide process control, integrated measurement and monitoring capabilities, and data reporting. Plants also need effective solutions to minimize energy usage and reduce risks to assets and the community.
Importance of Measuring Flow
Water and wastewater processes involve a range of flow measurement tasks and, as such, demand high meter accuracy and reliability, as well as long-term stability and a low cost of ownership. Flow meters must be able to measure liquid across all phases, including large volumes of fluid carrying suspended solids and other materials.
Typical flow measurement applications include:
- monitoring water flow
- dosing water treatment chemicals
- monitoring water consumption
- detecting and reducing leakage
- monitoring network load
- optimizing water usage
- monitoring influent water quantity
- monitoring discharge water quantity
- monitoring flow between reservoirs
Flow meters measure, monitor and control many water-related processes. The question is which technology to use, since a wide variety of meter designs are available. Each type of meter has pros and cons and must be properly deployed to achieve optimal performance.
For example, experience has shown that flow measurement is a valuable tool for optimizing lift station operation. Accurate flow data helps operators understand whether systems are running efficiently. Monitoring flow in lift stations provides important reference points for general billing processes, evaluating pump efficiency, analyzing the impact of inflow and infiltration (I&I), and planning maintenance programs.
Using Ultrasonic Meters
A growing number of municipal wastewater departments are finding that ultrasonic transit time flow meters are a good solution for lift stations. The meters enable improved diagnostics to measure flow, help identify potential pump failures and initiate appropriate preventative maintenance programs on equipment at the stations—which extends asset life.
Transit time ultrasonic flow meters measure flow rate by propagating ultrasound waves into liquid-filled pipes and measuring the time of flight. With clamp-on technology, the meter is nonintrusive—a design that provides advantages such as:
- reduced installation costs
- uninterrupted production
- installation flexibility across a wide range of pipe sizes
- no pressure head loss
- no contact with internal liquid
- no moving parts to maintain
This approach allows for routine maintenance activities throughout the life of the meter without having to cut into piping. For installations below the water line, such as in meter pits or manholes, ultrasonic flow meters can be paired with submersible, IP68-rated transducers coupled with silicon-based room temperature vulcanizing (RTV) characteristics, which can reduce the need for future maintenance.
For today’s supervisory control and data acquisition (SCADA) systems, ultrasonic flow meters with Modbus or Ethernet communication can provide flow rates, volumetric totals and diagnostic information. This data and all lift station metrics can be trended and transmitted back through the SCADA system and made available to keep a close eye on real-time flow conditions, pump run times and other operating parameters. Ultrasonic meters with a built-in data-logging feature can record flow rates and totals as a backup to SCADA historical data logs.
In addition, ultrasonic flow meters provide dry and wet weather flow readings from the lift station so that operations and maintenance personnel can extrapolate pertinent information and analyze I&I conditions related to sump pumps, leaky laterals and sewer mains. This allows them to focus future repair work in basins using the data supplied by the meters.
Noninvasive flow measurement instruments, such as ultrasonic clamp-on flow meters, are a good solution when users cannot shut down water and wastewater operations to install a traditional inline meter. As ultrasonic meters measure from the pipe wall outside, there is no wear on the device.
Ultrasonic clamp-on meters are also easy to install, which helps to reduce overall project costs. Municipalities can use accurate flow data to better plan for capital improvement projects related to I&I and verify the costs from the wastewater treatment plant in order to prioritize their budget allocations.
