Image Credit: Cannon Water Technology Inc. | Flygt, a Xylem brand

 

Lift stations, also called pumping stations, contain pumps, valves, and electrical equipment necessary to move liquids (usually water, wastewater, or sewage) from low to high elevation. They may be used to overcome inadequate head, to provide easy-to-install pumping solutions, or to provide economic alternatives to other pumping options. For example, wastewater may be transported by elevating it first (using a lift station) and letting it flow through a system by gravity. This may be more economical than installing pumps to move the fluid in the system itself.

 

Pump Types

Pumping stations may use a range of different types of pumps, but all can be described as either dynamic or positive displacement. Dynamic pumps, and their subtype centrifugal pumps, utilize fluid momentum and velocity to generate pump pressure while positive displacement pumps use expanding and contracting cavities to move fluids. Dynamic pumps produce a variable flow suited for generating high flow rates with low viscosity fluids, while positive displacement pumps produce a constant flow suited for producing high pressures (and low flow rates) with high viscosity fluids.

 

Specifications

There are a number of specifications to consider when selecting a lift station.

  • Reservoir size is the storage capacity of the lifting station tank or reservoir, usually measured in gallons.
  • Head defines the energy supplied to liquid (per unit weight) by the pump. It is expressed as a column height of liquid (either vertical lift or suction), given in feet of head (ft).
  • The number of pumps determines the overall capacity and achievable head of the pumping station, and also determines how much power must be provided for the system.
  • Maximum flow rate is the highest rate of liquid flow through the lift station system, usually given in gallons per minute (gpm).
  • Maximum pressure is the highest pressure that the system is designed to handle, usually at the outlet. It is given in pounds per square inch (psi) or bar.
  • Discharge size is the diameter or length of the outlet of the lift station.

For more information on the specifications and performance of pumps within these lift stations, visit the Industrial Liquid Handling Pumps Selection Guide on GlobalSpec.

 

Components

Lift stations can be comprised of many different types of materials.

 

Components of a lift station can include housing, pumps, level-sensing probes, pressure sensors, control systems, and stand-by generators.

  • Housing is the well, casing, or structure within which the pump and other lift station components are housed. Wells and similar structures designed for wastewater or sewage applications are typically made of concrete and are designed to be buried below ground.
  • Pumps (one or more depending on the size of the station) provide the actual pumping power to the lift station. Pumps may be submersible or external depending on the application of the pump.
    • Submersible pumps are designed to function inside the water source. They are less expensive and easier to install.
    • External pumps operate outside the reservoir or tank. They are typically more energy efficient and are easier to service when maintenance is required.
  • Level-sensing probes are used to sense the fluid level of the lift station's reservoir or tank. In addition to providing readouts for analysis and operations, these sensors may initiate a function when the liquid reaches a certain level, such as turning on the pump(s) or setting off an alarm.
  • Pressure sensors are designed to provide fluid pressure readings for a certain part of the process.
  • Control systems are used along with sensors to control lift station system operation.
  • Stand-by generators are used in conjunction with lift stations to provide pumping power should the external power source of the station be lost.

Corrosion Protection

Lift stations, especially those for sewage and wastewater, are installed in difficult operating environments. Both inside and outside are constantly subject to corrosion. Proper maintenance is required to maintain and protect the steel surfaces of these stations. In particular, grease and odors can result in major problems in an isolated, unmaintained lift station.

 

Odors - Odors are the result of the accumulation of sewage gases in oxygen deficient environments. They can develop into toxic or explosive gases if left untreated. Aeration is a way to prevent the buildup of these gases. Chemicals such as sodium nitrate can also be used to increase oxygen content in the water when mechanical sources of oxygen are not available.

 

Grease - Fats, oils, and grease (referred to as FOG in the industry) can cause blockage and other types of interference in wastewater systems. Problems with oils and greases are hard to solve because of their low solubility in water. Adding biological agents is one way to help eliminate the buildup of grease also and lower maintenance costs. Most chemicals designed to handle grease are used to aid its transport away from lift stations, but do not eliminate it from the system.

 

Grease deposits in a sewage system. Image Credit: Environmental Leverage

 

Applications

Lift stations are used in a variety of different situations and applications.

 

Water and Wastewater Systems

Wastewater systems typically use gravity to transport wastewater away from homes and businesses to provide water treatment at a central facility. For cities that have many changes in elevation, municipalities must use lift stations to pump the wastewater to a higher elevation. Lift stations for water systems work similarly, transporting water to sufficient elevation needed to provide communities with potable water.

 

Typical municipal lift station. Image Credit: Wika Instrument Corporation

 

Storm Water Control

Lift stations pump storm water and sewage away from low-lying areas, such as the parishes surrounding the city of New Orleans. A pump lift station is used in conjunction with other mitigating structures and features (such as canals and levees) to manage storm water. Lift stations are designed to handle a specific flow of water from rainfall, and many contain multiple pumps to manage a large drainage capacity, usually measured in cubic feet per second. Large storm water treatment facilities may have generator back-up for a pump station to ensure the proper drainage of water during a storm or power outage.

 

Production and Laboratory Systems

Lift stations may be designed as automatic pumping stations to economically collect and transfer wastes from production machines or laboratory sinks when drains cannot be used.

 

References

 

Environmental Leverage - Troubleshooting- Grease removal in Lift Stations

Multitrode.com - Water and Sewage Lift Station Management

Pollution Control Systems, Inc. - Lift Station/Pump Station Package System