• Project: Wastewater treatment plant, Baix Llobregat.
• Entity: Sociedad Depuradora del Baix Llobregat, S.A.
• Location: Prat de Llobregat, Barcelona (Catalonia). Spain.
• Capacity:
• Flow: 420,000 m³/day.
• Population: 2,275,000.

Objective:

Regeneration of the Llobregat River Delta and of the coastline near the river mouth, thus improving the bathing waters of the beaches located between Barcelona and the Garraf Massif.

Description:

It is one of the largest purification plants in Europe, combining two large processes that operate in parallel: water line and sludge line.

• Prefilter wells with screens with grids with 100 mm of separation between bars and 2 bivalve grabs with 500 litre capacity.
• Raw water pumping with 8+1 centrifugal pumps with the capacity to elevate up to 6,526 m3/h each and with trim.
• Discharge of thick and thin solids, in 8 channels equipped in 2 lines. Elimination of sand and oils using 12 desanders-deoilers.
• Measurement of the flow and by-pass to limit the flow entering the biological treatment to 35,000 m³/h.
• Twelve 20x60 m rectangular primary decanters.
• Biological treatment in 8 lines through activated sludge, combining anaerobic, anoxic and oxygenation processes.
• 14 circular secondary decanters with a diameter of 45.5 m.

• Sifting and thickening of sludge using 4 thickeners.
• Thickening of excess biological sludge using 4 centrifuges of 260 m³/h.
• Anaerobic sludge digestion using 8 digesters, each 7,180 m³.
• Four centrifuges, each 60 m³/h for the dehydration of digested sludge.
• Low storage of gas in 2 membrane tanks.
• Thermal drying of dehydrated sludge.
• Energy recovery from the digestion gas using 4 motor generators, each 2.8 MWe.
• Odour treatment for pre-treatment deodorising.