Last October 1st, the Utebo WWTP came into operation, according to the contract for the Construction Project of the Infrastructures necessary for the treatment of Wastewater in the municipalities of Utebo, La Joyosa, Pinseque, Sobradiel, Torres de Berrellen and Zaragoza, which has executed a joint venture formed by MLN, Ferrovial and Cadagua.

These works are part of a 20-year concession contract awarded by the Aragonese Water Institute.

The works have been completed within the 22-month contract period and consist mainly of a WWTP with a capacity of 28,000 m3/day, 18 km of collectors with diameters between 1800 and 400 mm, in which two 1800 mm pipes below the AP-68 motorway and the railway line stand out, and two pumping stations with capacities of 11,200 and 16,800 m3/day.

The plant is of the type of active sludge with anaerobic digestion and to be discharged into a sensitive area, an additional reduction of nutrients (nitrogen and phosphorus) is required to avoid eutrophication problems in the river Ebro and its downstream reservoirs and provides service to 70,000 equivalent inhabitants.

The treatment of the wastewater consists of roughing by means of automatic cleaning sieves, sanding and degreasing with its corresponding sand washer and grease concentrator.

Afterwards, the emergency physical-chemical treatment is carried out to stabilise the pH in the event of aggressive industrial discharges, including mixing and flocculation chambers with ferric chloride, anionic polyelectrolyte and sodium hydroxide dosing.

The biological process is then carried out with a primary settling process by means of circular decanters with articulated scrapers and mobile bridge, after passing to the biological reactor by means of activated sludge with configurations of the DN type, with suitable sizing for nitrification/denitrification and elimination of phosphorus by biological means, with its corresponding internal recirculation and excess sludge pumping.

Finally, secondary decanting is carried out using circular decanters with articulated scrapers and a mobile bridge before it is discharged into the River Ebro.
The sludge line of the WWTP consists of the following processes:
Pumping of primary sludge by means of automatic sieves of 3 mm pitch. The excess sludge is pumped to the thickeners by gravity in a thickener with a diametric scraper bridge and then pumped to anaerobic sludge digestion with biogas generation.