The ARETUSA Consortium has been established in 2001 and associates an urban water utility (ASA Azienda Servizi Ambientali Spa) in PPP with industry (Solvay Chimica Italia Spa) and technology provider (TME Termomeccanica Ecologia Spa). Thanks to ARETUSA water reclamation facility, Solvay replaces high-quality groundwater with fit-for-purpose treated municipal wastewater for industrial use, while groundwater is more exploited for drinking water production to serve the coastal areas. Up to 3.8 Mio. m3 per year of treated municipal wastewater is already reused by the industrial partner Solvay, freeing up Solvay private industrial wells for drinking water use. Currently, the Solvay plant has highly expanded both in terms of production and variety, which further increases the water demand. The plant produces sodium carbonate, sodium bicarbonate (also for pharmaceutical use), calcium chloride, chlorine, hydrochloric acid, chloromethane, plastic materials, peracetic acid and hydrogen peroxide. The ARETUSA water reclamation facility was designed to treat the secondary effluent coming from the two municipal Wastewater Treatment Plants (WWTP) of Cecina and Rosignano by chemical, physical, and biological processes in order to reach the quality requirements of Solvay. The catchments of Cecina and Rosignano WWTPs are impacted by currently unpredicted and relevant seawater intrusion that increases the chloride up to levels higher than acceptable and agreed by the contract in force among the ARETUSA partners. In addition, other parameters (e.g., surfactants and COD) can irregularly and unpredictably exceed the quality standard required for industrial reuse in Solvay. The successful results of ULTIMATE will be integrated in the definitive and executive design and implemented in full scale for real long-term operation. Three million euros investments to revamp, upgrade and digitalize the reclamation plant and system are currently envisaged by ARETUSA PPP.