Afonsoeiro and Seixalinho Wastewater Treatment Plants



Water Utilities






SOMAGUE Engenharia, S.A.

This detailed design entails the Wastewater Treatment Plants of Afonsoeiro and Seixalinho, dimensioned to serve an equivalent population of 48 000 (average flow: WWTP Afonsoeiro: 11.500 m³/day; WWTP Seixalinho: 4 400 m³/day). The WWTPs include the following operations:

  • Liquid Stage:

          - Reception and preliminary treatment of the septic tanks effluents; Preliminary treatment (screening and sand retention / degreasing, with aerobic biological treatment of grease); Equalisation-homogenisation in aerated lake; Intermediate pumping; Secondary treatment in 4 Sequential Batch Reactors (SBR); Final disinfection with UV radiation.


  • Solid Stage:

          - Thickening in gravitational thickener; Storage of thickened sludge; Mechanical dehydration in centrifuges; Lime addition.

  • Odor Treatment:

          - Ventilation system (polluted air extraction) in the entrance and sludge treatment buildings; Chemical deodorization unit.

The project also includes two underwater outfalls: one with a length of 200 m, in HDPE, DN 560, and another with a length of 300 m, in HDPE, DN 710.

Detailed Design including all the ancillary works and services.