The project involved the expansion and modernization of the Nerviano (MI) wastewater treatment plant, which serves the Parabiago urban area. The plant’s capacity was increased from 35,000 to 49,500 population equivalents, in order to also accommodate wastewater from the Rescaldina urban area—whose treatment plant was decommissioned due to its age—and to comply with the discharge limits set forth in Lombardy Regional Regulation No. 6/2019. To achieve this, a new 14,500 p.e. treatment line was added to the plant, built in place of the decommissioned structures and based on MBBR (Moving Bed Biofilm Reactor) technology, supplemented by filtration, UV disinfection, and a system for pumping treated water, along with an emergency system for periods of high water. The electromechanical components of the existing line were upgraded, while the sludge treatment line was expanded to handle sludge from both lines, featuring new thickening, stabilization, and dewatering compartments. The electrical system and remote control system were also upgraded to meet the new requirements, including a new transformer substation. Finally, to protect the plant from the risk of flooding from the Olona River, the perimeter was equipped with levees capable of withstanding a 100-year flood.