MORE TOPICS | Corrosion Resistance
Water Management & Corrosion Resistance
Designing pumping systems for changing conditions.
Steve Mosley | Industrial Flow Solutions
Managing water and wastewater is rarely about designing for one predictable operating condition. Flow rates change throughout the day. Storm events can cause sudden volume increases, debris can enter the collection system and wastewater itself can create challenging operating environments for equipment and infrastructure.
For municipalities and engineers, effective water management requires looking beyond a pump’s ability to move a specified volume of water. The entire pumping system must be designed to accommodate changing hydraulic conditions, wastewater characteristics, solids, corrosion potential, energy use and long-term maintenance requirements.
This is especially important in combined sewer systems and other applications where flow and wastewater characteristics can change during wet-weather events.
Understanding Variable Flow Conditions
One basic challenge in wastewater management is variability. Under normal dry-weather conditions, a pump station may experience relatively predictable wastewater flows. During a significant rain event, however, incoming flow can increase dramatically.
Combined sewer systems present an especially demanding example because the same infrastructure may carry both wastewater and stormwater. A pumping system designed only around average conditions may struggle when those conditions change. Oversizing equipment to accommodate the maximum possible flow is not necessarily the answer, either. A system sized exclusively for peak conditions may operate inefficiently during the much more common periods of low or normal flow.
Instead, engineers can design pumping systems that provide multiple levels of pumping capacity. Duplex, triplex and quadruplex arrangements use multiple pumps that can be brought online as incoming demand changes. During lower-flow conditions, a single pump may be sufficient. As incoming flow increases, additional pumps can operate to provide the necessary capacity.
This approach lets a system handle normal, everyday wastewater flows and higher wet-weather conditions without relying on a single pump to cover the entire operating range efficiently.
| IMAGE 1: Cutaway image of a stainless-steel pump (Images courtesy of Industrial Flow Solutions)
Matching Pumping Capacity to Incoming Demand
The number of pumps operating is only one part of managing variable flow. Pump speed can also adjust to changing conditions.
When paired with variable frequency drives (VFDs) and intelligent controls, pumping equipment can increase or decrease speed based on system demand. Rather than operating continuously at full speed, the system can provide the pumping capacity required for current conditions.
As incoming flow increases, pump speed can increase and additional pumps can be brought online when necessary. When demand decreases, the system can reduce output accordingly. This is especially valuable in applications with large differences between minimum, average and peak flow. Operating equipment based on actual demand can also improve energy efficiency. Instead of consuming the energy associated with full-speed operation when it is not required, the system can regulate operation based on current hydraulic conditions.
However, always evaluate variable-speed operation as part of the complete hydraulic system. When establishing control parameters, consider pump curves, system curves, minimum velocities, solids transport, best efficiency point (BEP) and acceptable operating ranges.
The objective is not simply to slow a pump down whenever flow decreases; it is to keep reliable, efficient operation across the anticipated range of conditions.
Preparing for Debris
Mining and chemical containment is heavily regulated, and for good reason. Tailings storage facilities, heap leach pads and chemical secondary containment fall under a web of federal and state requirements, and increasingly under standards enforced by agencies such as the Environmental Protection Agency (EPA) and Mine Safety and Health Administration (MSHA). A containment system installed with full quality-control documentation, seam testing records and material certifications is not just more reliable; it is what demonstrates compliance when a facility is inspected or a permit is renewed. Building to those standards from the start is far cheaper than retrofitting a system that was not designed to meet them.
Corrosion Is a System-Level Consideration
Water management also requires consideration of what the pumped liquid and surrounding environment can do to the equipment over time. Wastewater environments can expose infrastructure to moisture, corrosive gases, chemicals, chlorides and other conditions that can degrade materials. Hydrogen sulfide is a particular concern in wastewater systems because it can contribute to odor problems and corrosion within collection and pumping infrastructure.
Material selection therefore plays an important role in long-term system reliability. Engineers should evaluate wastewater chemistry, pH, chloride concentrations, temperature, expected gases and environmental exposure when selecting materials for pumps, piping, valves, fasteners, enclosures and other system components. Stainless steels and other corrosion-resistant materials may be appropriate in demanding environments, but specifying a corrosion-resistant pump alone does not necessarily make the entire installation corrosion-resistant.
A system-level approach is important. Evaluate piping connections, hardware, instrumentation, electrical enclosures, structural components and other materials exposed to the environment together. Also consider material compatibility between components to avoid causing new corrosion mechanisms. The goal is to select materials based on actual site conditions rather than assuming one material suits every wastewater application.
| IMAGE 2: Debris and flooding from a storm
Can System Design Reduce Exposure to Corrosive Conditions?
Material selection is one way to address corrosion. System configuration can provide another. Traditional wastewater pumping stations commonly collect wastewater in a wet well before pumping it downstream. Depending on operating conditions, wastewater may remain in the wet well long enough to create odor, gas, maintenance and corrosion concerns.
One alternative approach is direct in-line pumping. Instead of relying on a conventional open wet well to store wastewater before pumping, direct in-line systems receive wastewater directly from the incoming sewer and move it into the discharge system. Eliminating or reducing wastewater storage can change the environment around the pumping equipment and may help reduce some conditions associated with traditional wet wells.
This does not eliminate the need for corrosion-resistant materials or proper wastewater characterization. It does, however, illustrate an important principle in water management: Corrosion should not always be addressed solely by selecting more resistant material. Engineers can also evaluate whether the overall system design can reduce exposure to the conditions causing corrosion in the first place.
Designing for Combined Sewer Systems
Combined sewer applications bring many of these considerations together. During dry weather, the system primarily handles wastewater. During a storm, the same infrastructure may experience substantially greater flow while also receiving stormwater and additional debris.
A pumping strategy for these applications therefore needs to consider several conditions at the same time:
- Minimum, average and peak flow rates
- Changes in flow during storm events
- Required solids passage
- Potential debris entering the system
- Wastewater chemistry and corrosion potential
- Pump staging and redundancy
- Variable-speed operation
- Energy consumption across the operating range
- Maintenance access and system reliability
Multiple-pump configurations can provide flexibility as demand changes. Intelligent controls can regulate pump speed and stage additional pumps as incoming flow increases. Appropriate pump hydraulics can help accommodate debris, while corrosion-resistant materials and thoughtful system configuration can address the wastewater environment.
The result is not a single piece of equipment solving every challenge. It is a coordinated pumping strategy designed around the range of conditions the system is expected to encounter.
The Growing Role of Intelligent Controls
Modern water management increasingly goes beyond the mechanical equipment itself. Intelligent control systems can provide operators with greater visibility into how pumping equipment is performing and how conditions are changing.
Depending on the control architecture, operators may monitor pump status, operating speed, alarms, run time, system demand and other parameters remotely. Remote monitoring becomes particularly valuable during severe weather events or at facilities that are not continuously staffed. Instead of relying entirely on physical inspections, operators can access system information and identify changing conditions from another location.
Some systems also provide read/write capabilities, allowing authorized operators to change certain operating parameters remotely. Remote access should include appropriate cybersecurity, permissions and operational safeguards, but when properly designed, it can give utilities another tool for managing dynamic systems.
Controls can also help transform pumping equipment from individual mechanical components into a coordinated system. Pumps can be staged, speeds adjusted, alarms generated and operational information collected to support future maintenance and system evaluation.
Designing for the Entire Operating Range
The most important lesson in water management is not to select equipment for a single point in time. A wastewater pumping system may need to operate during low overnight flows, normal daily conditions, seasonal changes, heavy rainfall and major storm events. At the same time, it may encounter changing solids loads, debris, corrosive conditions and evolving maintenance requirements.
Successful system design starts with understanding the full operating range. Engineers should ask not only, “What is the required flow and head?” but also: “What are the minimum and maximum expected flows? How quickly can those flows change? What solids and debris can enter the system? Is the wastewater screened? What are the chemical and environmental conditions? How should pumping capacity increase during a storm? What level of redundancy is required? How will operators know when conditions change?”
Those questions influence pump hydraulics, materials of construction, the number of pumps, control strategy, monitoring capabilities and complete system configuration.
A More Resilient Approach to Water Management
As wastewater infrastructure is asked to manage increasingly variable conditions, resilience depends on engineering systems that can adapt. No single pumping configuration fits every application.
Some installations may benefit from conventional wet-well designs, while others may be candidates for different approaches such as direct in-line pumping. Some applications require significant solids-handling capability, while screened systems may prioritize hydraulic efficiency.
The common principle is designing around the application rather than forcing the application to fit the equipment. By treating variable flow, wet-weather conditions, solids, corrosion, energy consumption, controls and monitoring as linked parts of the same system, engineers can develop pumping strategies better prepared for both everyday operation and more difficult conditions.
Effective water management is ultimately about more than moving water from one location to another. It is about understanding how conditions change and designing a system that can change with them.
Steve Mosley is a product manager at Industrial Flow Solutions. He holds a bachelor’s degree in civil engineering from the University of Hartford. For more information, visit flowsolutions.com.
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