The coal-deposit quay of Vado Ligure harbour hosts 3 different types of coal: the steel coal, for steam production, the coking coal, for cast-iron production, and a residual coal deriving from the coking process. In case of precipitation, all the runoff water washing the quay must be treated before being discharged into the sea, as it contains high concentrations of coal.

The rainwater treatment plant is built inside the very structure of the quay, which is composed of inter-connected hollow prestressed-concrete caissons: each tank comprising the treatment plant has been designed to be connected with the other tanks, and lodged inside one of the caissons comprising the quay-structure. 

The treatment plant has the following structure: 

• First sedimentation tank: it receives the coal-polluted runoff water, and allows the suspended coal solids to deposit on the tank floor: these solids will be gathered successively on one side of the tank, and pumped outside by a sludge uncloggable pump. On the other side of the tank, water will be pumped to the clarifying and coagulation tanks.
• Coagulation tank: in normal conditions, it’s not necessary to clarify the water coming from the sedimentation tank, so that it is directly sent to the coagulation tank, where the polyelectrolyte (sodium carbon) is added, in order to chemically separate the remaining suspended coal from water, and maintain the water pH at average levels (7-8).
• Secondary sedimentation tank: after coagulation, a secondary sedimentation is provided, identically to the first sedimentation stage.
• Turbidity tank: in this stage, a turbidity analyser measures water quality: in case of concentrations higher than 60 ppm, the water is directly pumped back to the first sedimentation tank, and then treated with polychloride aluminium coagulant in the clarifying tank.