Improving water quality and reducing energy consumption for Pidpa’s water towers

Pidpa is a Belgian water service provider. Their goal is to deliver drinking water of impeccable quality. Bacterial regrowth is one of the significant quality risks during the conservation stage of water. There are various drivers for regrowth, and water’s residence time is an important one.

The company's distribution network consists of 13,000 kilometres of pipelines with 42 operational water towers. These water reservoirs vary widely in shape and dimensions, and Pidpa categorises them into four different types. They never empty the water towers completely to retain a strategic water supply.

What’s inside?

To better understand what’s happening inside their reservoirs, Pidpa turned to us. To check the actual mixing conditions inside the reservoirs we modelled each of the four water tower types. We performed transient CFD simulations of complete 24-hour cycles to visualise and quantify residual old water in the water towers. Real measurements were practically not feasible and would have been very costly while delivering less information.

To capture the main hydraulic mixing patterns using advanced modelling methodology compartmental modelling, we calculated the water ageing for seven consequent days.

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Better mixing and lower energy consumption

One of the CFD simulation scenarios showed that they could improve their mixing conditions by using the sub-merged pipe for filling instead of using the pipe from the top of the water tower. This allowed Pidpa to save energy too, as the water doesn’t need to be pumped to the top of the reservoirs anymore.

We came to the same conclusion for the other water reservoirs. By combining their own geographic dashboard with the findings from our CFD modelling, Pidpa could decrease and optimise residence times across their water reservoir network. This led to optimal use of resources and uncovered non-ideal mixing conditions inside the commonly considered well-mixed water towers.  

Discover the full story

David Geysen, Process Engineer at Pidpa, explains the project in the video below:

Check out the simulations

The following videos show the mixing conditions in the water towers with the current design, where the inlet pipe is at the top of the tower.

The video below zooms in on another design where the inlet pipe is at the bottom of the water tower. It clearly shows energy savings that resulted from doing the filling differently.

Learnings

What did we learn from this project?

• Even in smaller volumes (eg 600m³),  mixing must be accounted for
• Positions of inlet and outlet and operational settings are crucial
• Aspect ratio and filling height impact mixing significantly

Read more on CFD for water towers

Want to learn more about 3D modelling for water towers? Read our dedicated blog on this topic.