The Castellar del Vallès Wastewater Treatment Plant (WWTP) treats the municipality’s water, with a processing capacity of up to 8,000 m³/day. Meanwhile, the Sant Celoni WWTP manages the wastewater from Sant Celoni and part of Santa Maria de Palautordera, with a treatment capacity of up to 6,000 m³/day. 

Both WWTPs serve a population of 114,667 people. 

One of the main challenges for these facilities was achieving better use of the sludge resulting from the treatment process, as until now it had been dehydrated and managed as waste. 

Sorigué’s intervention has provided a comprehensive three-pronged solution:

• Reduction in sludge volume. 
• Biogas generation. 
• Electrical energy production from biogas.

The work consisted of the design and assembly of digesters, motor generators and boilers, as well as the electrical and control installation integrated with the rest of the plant.

The new digesters are metallic, a material that is uncommon in urban wastewater treatment plants, where concrete is generally used. However, the process is identical: the sludge produced after wastewater treatment enters the anaerobic tank (that is, without free oxygen), where a ‘cow’s stomach’ effect causes fermentation, enabling part of the sludge to be transformed into biogas. 
In a circular process, the gas generated enables complete energy recovery and promotes electrical self-consumption. Thus, the Castellar del Vallès facilities produce up to 823 kWh/day and the Sant Celoni ones produce 564 kW/day. 

These initiatives, part of the recovery, transformation and resilience plan funded by the Next Generation EU fund, place these WWTPs at the forefront of clean energy generation and cement Sorigué’s position as an expert in processing wastewater sludge for biogas production.