Milan San Rocco
The Milan San Rocco treatment plant started operation in December 2004; it serves the western Milan drainage basin, the Settimo Milanese Municipality and generally the drainage basin flowing into the Southern Lambro tributary. This plant is located south of the township pf Ronchetto delle Rane, close to the west Tangenziale ring highway within the Milan municipal jurisdiction. The collection system is formed of a main sewer collector used for the wastewater discharged from several sub-basins in the western part of the City. Degrémont Spa runs and manages the treatment plant under contract.
Plant operations
The plant pre-treatment stages involve: initial screening to remove large objects; grit removal, a primary settlement tank, oil skimming and fat removal. The activated sludge process is used for biological treatment and includes denitrification, oxidation, nitrification, final clarification. Tertiary treatment includes removal of phosphorus, gravity sand filtration and final disinfection using UV radiation, with the possibility of additional disinfection, depending on the final use of the recycled water. The sludge line continues with a dynamic thickening section, aerobic digestion, chemical treatment, mechanical dewatering using plate filter presses and thermal depolymerisation. The process is completed in and odour-control section which treats the odours in three stages: alkaline, acid and oxidizing. All treatment sections are installed in closed buildings. The disinfection treatment in particular, consists of a UV radiation system fitted with low-pressure mercury vapour lamps, an engineering solution recommended by the Ministry of the Environment during the executive design stage.
Final water destination
The water discharged from the plant is taken to three surface destinations: the Lambro Meridionale tributary downstream of the plant in Ponte Sesto di Rozzano, the canals of Carlesca and Pizzabrasa southwest of the plant, still in Rozzano, near the Tangenziale Ovest (western ring highway). The Lambro Meridionale is a public waterway that originates from a spillway of the Naviglio Grande at San Cristoforo in Milan, where it also receives some of the water from the Olona river, close to the City’s outer ring highway. After leaving the City, this watercourse flows for a few dozen miles into the Lambro Settentrionale river downstream of Sant'Angelo Lodigiano in the Province of Lodi. The Roggia Carlesca canal originates from the Naviglio Grande in Milan then, after leaving the City it goes on to irrigate a large district extending in the southern Milan area to the Province of Pavia. The Roggia Pizzabrasa canal originates from the Lambro Meridionale spillway in Municipality of Rozzano and flows from north to south, continuing to irrigate a large district extending in the south of Milan, bordering with the Province of Pavia.