Improving water flow in aeration tanks to boost treatment efficiency

What is it about?

Wastewater treatment plants are essential for protecting nature and public health. One of the key units in these facilities is the aeration tank, where air is mixed with wastewater to support biological processes. However, the way water and air move inside these large tanks is often not well understood in real operating conditions. Poor circulation may cause “dead zones,” where the water moves very slowly. These zones can reduce treatment performance and increase energy costs. In this study, we explored how water flows in a large, full-scale aeration tank. We combined on-site flow measurements with computer simulations to better understand the movement of water and air in the tank. First, we carried out field measurements using special flow sensors at different locations and depths. These data were then used to build and validate a computer model, which allowed us to visualise the flow behaviour in three dimensions. The results highlighted areas where the flow was too slow or did not mix properly. These “low-velocity zones” were mainly located near the inlet and outlet structures and along the walls of the tank. By testing alternative design options in the computer model, we found that changing the position and shape of the inlet and outlet could significantly improve circulation and reduce dead zones. This work shows how combining field measurements with computer modelling can help engineers identify problems in existing wastewater treatment systems and test practical solutions without expensive on-site trials. The findings can guide the design of more energy-efficient aeration tanks and support upgrades to improve the performance of existing plants.

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Why is it important?

This study stands out by combining extensive full-scale field measurements — including 98 points across 15 depth levels — with the use of an innovative ADCP device for cross-sectional flow monitoring. By linking these detailed measurements with high-resolution CFD modelling, it provides new insights into flow behaviour inside operational aeration tanks. Importantly, it demonstrates that optimising the inlet and outlet geometry can significantly improve flow distribution and energy efficiency, offering practical design guidance for upgrading existing treatment plants.

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