What causes sewage pumping stations to overflow (and how can we stop it?)

Sewage pumps are globally critical on the road to zero pollution incidents

Water utilities around the world are actively committed to ending sewage spills into the environment. Their prevention efforts address every part of the wastewater system, from the pipes that initially receive waste from homes and businesses all the way to the end of the treatment cycle in the sewage treatment plant. In this article, we zoom in on the many pumps along the sewer network that keep untreated water moving through the system. We’ve used research data from England to frame the conversation, but the problems (and solutions) are relevant for water utilities around the world.

1. How can sewage pumping stations cause sewer overflows?

When pumps in the sewer network fail, the water they’re supposed to pump away builds up instead. With nowhere else to go, this wastewater overflows into the surrounding area. There are several reasons why sewage pumping stations (SPS) might fail, but the four below account for the vast majority of pollution incidents.

1.1 Wet wipes and cooking oil

Items like wet wipes, diapers, feminine hygiene products, cotton swabs, and other non-biodegradable materials don’t break down easily, so flushing them down the toilet can lead to blockages in the sewer system.

Grease and oil are another major culprit. Many people (and businesses such as restaurants) don’t realize that fats, oil and grease solidify as they pass down the network, accumulating over time into “fatbergs” that block the flow of wastewater.

Both sewage pipes and sewage pumps can become clogged by these improperly disposed items. A clogged pump is unable to work at full speed, and in the worst case may stop working altogether.

1.2 Equipment wear and tear

Pumping stations contain many mechanical and electrical components, including pumps, motors, valves and control systems. If not properly maintained, these components will deteriorate and eventually fail.

Sewage pumping stations are particularly difficult to maintain. There are more than 30,000 of them in England [2], and they are constantly exposed to debris that can damage them — not just wet wipes and cooking oil, but also hard items such as rocks, branches and even toys that make their way into the sewers. This means they need frequent attention, but they tend to be widely spaced across a large geographical area, making staff size and travel time a limiting factor. Once personnel arrive, they must enter confined spaces where they are exposed to raw sewage, toxic gases, and potentially harmful pathogens, requiring time-consuming safety protocols. All these factors make it hard to service every SPS on an adequate schedule.

1.3 Power outages

Failures in the electrical grid bring pumping stations to a decisive halt. Backup generators help mitigate the problem, but there’s a tradeoff between how often they are needed and the immense cost of installing and maintaining them. Renting instead of buying can help control this cost, but introduces a possibly unacceptable delay for delivery and setup in an emergency.

What’s more, these systems rely on a fossil fuel for power, which means the water utility must either have a connection to the gas mains at every SPS or store a reserve of propane, diesel or gasoline nearby. Many pumping stations are in residential areas, creating a safety hazard and limiting the available space to store fuel. If the power outage lasts longer than the fuel, the pumping station will eventually stop working and the sewer will overflow.

1.4 Extreme weather & growing populations

Climate change and population growth have drastically increased the flow of untreated water into systems designed for much less, and that mismatch is only going to get worse. Both factors stress existing wastewater infrastructure, leading not only to immediate pollution incidents but also to long-term system failure.

Though the problem is urgent, there is no quick fix. A full solution will be a massive undertaking that spans decades and involves not just water utilities, but also technology companies, equipment manufacturers, and local and national governments.

2. How can water companies get sewage pumping station spills down to zero?

Water utilities work hard to prevent SPS overflows — but three of the four main causes lie outside their control. Even so, water utilities must find ways to stop sewage spills from happening (at pumping stations and everywhere else). What options do they have?

2.1 Better infrastructure

The only solution for climate change and population growth is to increase the resilience of the wastewater system. In the short term, that means extra storm tanks to capture excess water during periods of hydraulic overload. In the long term, it means redesigning the network to separate stormwater and sewage, designing green infrastructure such as sustainable urban drainage systems (SUDS) to capture surface runoff, and building more or larger treatment facilities, sewers, and pumping stations.

2.2 Smarter sewers

Water utilities can only indirectly influence the disposal of inappropriate materials through awareness and education campaigns. Until consumers change their behavior, the only direct solution is to detect and resolve pumping station blockages before they cause an overflow. Fortunately, smart sensors that can detect a clogging pump before it becomes critical are part of the real-time monitoring and analytics that are making today’s sewer systems intelligent.

2.3 Better backup

To avoid overflows caused by power outages, a robust power backup plan is critical. Such a plan addresses every facet of a power loss, from communication with the electric company to preparing for widespread, long-duration outages.

2.4 Smarter maintenance

To address equipment failure from age or damage — the one factor directly under water utilities’ control — every company we analyzed is already putting proactive maintenance strategies in place. Nearly all of them include preventive (schedule-based) and/or predictive (condition-based) maintenance initiatives in their pollution incident reduction plans. Preventive maintenance improves on traditional reactive strategies by regularly servicing equipment to keep it healthy. Predictive maintenance goes a step further, using artificial intelligence to continuously analyze incoming sensor data and assess the machine’s actual condition. By determining which machines need attention and which are still healthy, a predictive strategy lowers the daily workload, which lessens the impact of staff shortages and travel time on utilities’ ability to keep all pumping stations in good working order.

Summary table of SPS overflow causes and fixes

Footnotes

[1] T. Giakoumis and N. Voulvoulis, Combined sewer overflows: relating event duration monitoring data to wastewater systems’ capacity in England (Environ. Sci.: Water Res. Technol., 2023, 9, 707).

[2] S. Purnell, N. Mills, K. Davis and C. Joyce, Assessment of the pollution incident performance of water and sewerage companies in England. (PLoS ONE 16(10): e0251104, 2021).