Wastewater Treatment Plant in Olazagutía, Navarre

The public company of the Government of Navarre, NILSA, decided to build a new wastewater treatment plant due to the increase in flow rate and the high pollutant load recorded in recent decades.  

This new facility, which is much more modern, efficient, and larger, is being constructed next to the old treatment plant, which will be demolished due to its obsolescence.  

The project features a combined activated sludge and moving bed biofilm reactor (MBBR) system, a biological wastewater treatment method that requires no added chemicals and delivers a high level of purification, thanks to IFAS (Integrated Fixed-Film Activated Sludge) technology. 

The process involves microorganisms that attach to small plastic media pieces and feed on the organic matter in the water. 

With aeration and mixing in the bioreactor, these microorganisms are evenly distributed, maximising their effectiveness in removing pollutants.  

As a result, the treated water meets the quality standards set by Directive (EU) 2024/3019 regarding the reduction of nitrogen and phosphorus, helping to improve the quality of the Arakil River. 

Key works carried out under this contract include: 

• ​Site grading: excavation and profiling of the slope surrounding the plot to level the surface and install the components of the new WWTP.  
• Construction of the storm water tank and bioreactor.
• Construction of the inlet works, primary clarifiers, and sludge pumping.  
• Construction of the sludge line and control building.
• Installation of equipment, hydraulic connections, and connection to the discharge works. 
• Functional testing and commissioning of the upgraded WWTP. 
• Landscaping and final finishes.