Techno-economic analysis of a novel hybrid system for the valorisation of SWRO brines in a minor Sicilian island

Abstract

In small remote islands, freshwater scarcity is an issue to which several viable solutions have already been found employing constantly evolving desalination technologies. The several RO plants in the Canary and minor Sicilian Islands are just an example . However, the beneficial application of seawater desalination is accompanied by a problematic matter: the production of high salinity brines. Not only do they compromise the aquatic ecosystem but their treatment in order to respect environmental regulations is costly too. Worth noting how these so-called “wastewater streams” present a high concentration of valuable raw materials, such as magnesium and calcium or sodium chloride, that are essential to many industrial sectors (food, pharmaceutical, etc.) . In this work, a novel hybrid system is introduced to valorize SWRO brines produced in the minor Sicilian island of Pantelleria. The treatment chain consists in the coupling of four different separation processes, each with a specific purpose: (i) Nanofiltration (separation of bivalent from monovalent ions), (ii) MF-PFR crystallizer (selective recovery of magnesium and calcium), (iii) Multi-effect distillation (freshwater production and NaCl brine concentration) and (iv) Evaporative crystallizer (recovery of sodium chloride). The chain not only recovers valuable minerals and fresh water but contemporarily reduces the volume of the final brine that will be discharged into the Mediterranean Sea and enhance the overall process sustainability by utilizing waste or solar thermal energy for powering some of the integrated units. Process models for each technology have been developed and integrated in an advanced simulative platform, which includes tools for the estimate of economic performance indicators, allowing to perform a full techno-economic analysis. Numerous scenarios, characterized by different operating conditions and energy sources of the single technologies, are taken into examination. The purpose is to identify the set of operative conditions that best yields an economically and environmentally sustainable brine treatment process, thus implementing the concept of circular economy.