Although a wastewater treatment plant is an industrial installation that benefits the environment, it also has a visual impact on the surroundings and produces disagreeable odours. In certain areas where tourism is important or where the terrain is difficult, a hidden plant can treat the urban wastewater without the consequences of a problematic location.

The civil work for the municipal wastewater plant in Llanes was a real challenge due to the special characteristics of the cavern where it is located and the complexity of a plant that had to be designed with compact technologies to economize space without increasing the investment.