Overflows is a major and growing societal and environmental problem. It is also a challenge that most Swedish municipalities more or less struggle with on a daily basis. However, there are smart solutions that limit or eliminate these problems.

Additional water is water that does not come from the municipalities' own waterworks. Among other things, it could be rainwater that enters the pipes due to a leak or because someone has incorrectly connected their stormwater to the municipalities' wastewater pipes. Another source is groundwater, which in various ways finds its way into the wastewater pipes.

Today, the municipalities' pumping stations are unable to handle the situation with larger amounts of water flowing in at the same time. This leads to overflows with difficult environmental problems as a result.

- The big concern when it overflows is that large amounts of wastewater risk spreading into nature. And then we are not just talking about eutrophication of our waterways, lakes and seas. Wastewater that overflows contains, among other things, nutrients, chemicals and medicines, sometimes even remnants of paper, tops and other things that people flush down their toilets. All this has a negative environmental impact, where some recipients and water protection areas are more sensitive than others, says Arvid Nelehag, Group Manager Water at Sweco Sweden.

A major future environmental hazard

The systems and infrastructure that were built several decades ago were then adapted for a certain future capacity. In 1940, Sweden's population was 6.3 million, in 2022 it is 10.4 million and in 2030 it is estimated to amount to 11 million, ie almost a doubling during these 90 years.

- The problem is that our cities are growing and new residential areas are being added, with the result that the overflow challenges are only increasing. Add to that the expected impact of climate change on the country's water levels. Overflows and floods are a major future environmental threat, says Arvid Nelehag.

The negative effects of overflows and flooding of land, roads, infrastructure and properties are significant. It is manifested in extensive material damage, eutrophication, sewage odors, fish deaths and bathing bans.

- The societal costs and environmental problems associated with this are enormous, says Arvid Nelehag.

Ancient infrastructure

Most municipalities today have ancient VA systems, which are unable to handle growing populations and a more capricious climate. The additional water flowing into the pipes should simply not be there. The water and sewerage networks are not dimensioned for this. The growing urbanization is increasing the amounts of both wastewater and stormwater.

- When former nature areas are transformed into urban development areas, the possibility of run-off that previously existed decreases. Nature and forest land can normally absorb large amounts of rainwater, but so cannot rock, concrete and asphalt. Houses with roofs, new streets, squares and roads also lead to faster runoff, where large amounts of water collect during heavy rainfall and drain away at the same time, says Arvid Nelehag.

The municipalities' big challenge then will be to constantly ensure that they do not have too much water in the pipes. One way to prevent this is to invest in newer and larger sewage treatment plants, as well as in new transmission lines, where the water is transferred from one area to another.

In the future, environmental legislators will also demand costly measures.

- It is an inevitable development no one really wants. These measures will cost huge sums for the municipalities, says Arvid Nelehag.

The demands will increase further

There are very large sums to earn for the municipalities if they can even out the water flows to the treatment plants.

- In the event of heavy rainfall with overflows and floods as a result, it is difficult to maintain a high quality of treatment. Therefore, you want as even a flow to the treatment plants as possible, then the treatment will be the best, says Arvid Nelehag.

Water is in many places a scarce commodity and a finite resource. In the long run, our communities will therefore also want to use the purifying wastewater for industrial use, but reuse it as drinking water is also conceivable.

- Then the requirements will be even tougher on water purification and flow control.

Water as a resource and scarce commodity is also a topic that has high priority in the EU. Over the years, several important decisions have been made to reduce the strain on Europe's strained water resources. One of the most well-known initiatives is the Water Framework Directive (WFD), which was adopted in 2000 to protect European waters in terms of both quantity and quality, thus ensuring their long-term availability to Member States.

Weak team follow-up

When it comes to overflows, such are already banned for the municipalities. The problem is that the authorities find it difficult to follow up on this legislation and today no fines are usually issued.

The technology available for measuring overflows is expensive. Many municipalities today lack measurement options, others choose to attach blocks to the pipes for detecting when overflows have occurred and of course there are those who regularly perform accurate flow measurements, says Arvid Nelehag.

There is a smart solution

A well-proven way for authorities to make demands on municipalities is to refer to the use of BAT - best available technology. This of course presupposes that there is also one available.

One of these is now being developed by Sweco and Calejo, which with the help of advanced AI have developed a technology for smarter and more optimized control of pumps and pumping stations in order to prevent overflow. The ultimate goal is to together create a completely new intelligent water supply and sewerage platform for the municipalities under the name Smart Water.

With the help of AI and so-called hybrid intelligence, a so-called digital twin of the pump control is built. The model is initially trained on historical data based on precipitation data, power consumption and water levels in the pump sumps.

- The digital twin is fed with data in real time and then shows alternatives to how each pumping station should pump more efficiently to prevent overflows. In the next step, the pumps will be controlled directly or via existing control systems, says Arvid Nelehag.

Successful investment

With the help of Calejo's and Sweco's new optimization technology, the problems can be limited without the need for extensive investments in new infrastructures and the construction of new, expensive and cumbersome collection dams.

- We can eliminate a significant part of the overflow - especially "first flush", which is the dirtiest part, says Arvid Nelehag and concludes:

- The technology also contributes to increased energy efficiency and in the long term, the Smart Water platform will also be supplemented with optimization tools for drinking water and more efficient treatment at treatment plants.