Sewage sludge is one of the most promising fronts from a circular economy and recovery of value point of view. The waste par excellence is actually a potential source of numerous nutrients, and the purification process itself has great potential in producing energy, biogas and biofuels. In this perspective, the purifiers, which have always been considered by citizens as problematic elements of the area, are gradually turning into real cathedrals of nature, with an immense energy potential.


In more detail

The Sesto San Giovanni Bioplatform is the industrial symbiosis project that combines a waste-to-energy plant and purifier, transforming them into a structure dedicated to the carbon neutral circular economy, which includes two production lines: the first for the treatment of sludge deriving from water purification for production of thermal energy and fertilizers; the second of anaerobic digestion for the treatment of OFMSW for the production of biomethane.

The sludge line will recover 65,000 tons/year of wet sludge equal to 14,100 tons/year of sludge produced by the CAP Group purifiers, generating 11,120 MWh/year of heat for district heating and phosphorus as fertilizer. On the other hand, the OFMSW line will treat 30,000 tons/year of wet waste for the production of biomethane. The new plant will be made operational in October 2022 with the commissioning of the first line and in March 2023 with the entire industrial complex operating.

The Robecco sul Naviglio plant is an innovative drying plant with a low environmental impact and reduced energy consumption that above all treats dehydrated sludge, mainly recovering agricultural waste through anaerobic digestion.

In this context, in March 2021, CAP started a collaboration with Milano Ristorazione  for the recovery of food waste which involves the treatment of 100 tons/year of liquid waste consisting of the waste water from the "Cooking Centre" located in Milan, in via Sammartini.

The plant also makes it possible to recover sands that are reused in maintenance activities of the CAP Group's aqueduct and sewerage networks, such as the laying of pipes.

Lastly, the production of VFA (Volatile Fatty Acids) from sewage sludge, which takes place through a controlled mesophilic fermentation phase with mixed microbial cultures, should be noted.

The Life Freedom project is active at the Cassano D’Adda treatment plant. The four-year project consists of the design and construction of a demonstration plant for Hydrothermal Liquefaction to transform sewage sludge into renewable biofuels, bituminous conglomerates and phosphorus, crucial natural resources for agriculture and various industrial sectors.

The amount of sludge treated will be around 4,000 tons.


Quality biomethane from purification sludge is produced at the Bresso-Niguarda treatment plant,  through an anaerobic digestion process.

Launched in April 2019, the Bresso-Niguarda plant is the first in Italy to pump biomethane from sewage waste into the SNAM network.

Thanks to the seven CAP Group biodigesters, since 2019 until today over one million cubic metres of biomethane have been produced, capable of powering 558 cars (15,000 km/year).

Around 1200 m3 of biomethane are produced per day. Overall in 2020, 598,207 Sm3 were pumped into the SNAM network.

PAn innovative project for the recovery of cellulose from waste water was launched at the Trucazzano treatment plant.

The pilot project, launched in November 2020, will adapt the innovative technology of the Dutch CirTec to the purification process, testing the performance and quality of the raw material extracted, with the external support of the Milan Polytechnic.

The cellulose, extracted through a multi-filtering system and then cleaned and dehydrated, will be reused for the production of composite materials and monomers for the bioplastic industry, and in the production of construction materials such as road asphalt.

In this first phase, the plant will produce 150 kilograms of cellulose, deriving mainly from toilet paper, and which at full capacity are estimated to become 1,000 tons in a year.

Since 2017, CAP has launched a process aimed at recovering products no longer usable in the food chain by using them as a secondary raw material and source of energy, according to the principles of the circular economy.

In fact, food waste, through its treatment in the anaerobic digester of the purification plants, can be reused as biogas, electricity and organic chemicals.

The first experiment that arose from the collaboration with Danone, has been active since March 2019 and will continue throughout 2021.

Two new projects have also been launched in this direction: the first in partnership with ThinkAbout (an innovative entrepreneurial reality that promotes solutions to combat food waste) and the second with Milano Ristorazione.