The Drents Overijsselse Delta water authority faced a substantial challenge at its wastewater treatment plant in Echten. The organisation had to close the central sludge digestion plant due to various safety concerns and problems. In addition, biogas utilisation via CHP was no longer eligible for a permit due to the associated nitrogen emissions.  
 
With the exception of a few components, the mechanical plant was no longer suitable for use in the fully renovated plant. In short, a significant part of the wastewater treatment plant needed a radical redesign, specifically the part where biogas is upgraded to produce green gas and the heat supply arrangement for the central sludge digestion plant.

Witteveen+Bos prepared an integrated detailed design for part of the wastewater treatment plant. For example, we designed the heat supply system for the sludge digester. A heat pump installation heats the sludge using residual waste heat from the clean wastewater (effluent). An array of large heat exchangers recovers the waste heat from the digested sludge to preheat the fresh sludge. This reduces electricity usage. 

The biogas utilisation system which upgrades the biogas to natural gas quality and feeds it into the existing 8-bar gas grid was also designed by W+B in close collaboration with the construction team. The electrical system and existing process automation were no longer usable and were completely redesigned by our experts.

After a 1.5-year construction phase, the new plant was officially put into service in October 2025. The water authority expects to supply sustainable gas to about 2,000 households. ‘This ‘gas factory’ fits perfectly with our goal of integrating sustainability and circularity into our work as much as possible’, says board member Miranda Wesselink on the Drents Overijsselse Delta website. ‘That means using fewer resources, reducing greenhouse gas emissions and recovering energy and heat from wastewater.’