Next generation water-smart management systems: large scale demonstrations for a circular economy and society (WATER-MINING)

Water security is among the most crucial challenges for water management today. As a consequence, innovative water management solutions and alternative water resources are required. The EU-funded WATER-MINING project will exhibit and validate innovative next-generation water resource solutions at the pre-commercial demonstration-scale in accordance with relevant legislation, such as the Water Framework Directive, Circular Economy and EU Green Deal packages. It will combine water management services with the improvement of renewable resources such as mining water. It is envisaged that the value-added end products will offer supplies of regional resources to increase economic growth. The project will examine different designs proposed for urban wastewater treatment and seawater desalination and innovative service-based business models aiming to improve the engagement of private and public stakeholders.

Objectives

The Water Mining project aims to face the challenge of ensuring access to clean water and sanitation by developing innovative solutions for the sustainable use of alternative water sources, including urban and industrial wastewater and seawater desalination. The project considers water as a resource, consumable and as a durable good. To capture the full potential of the circular water economy, WATER-MINING project proposes different strategies for each of these three water forms, involving six sector-specific case studies (CS).

PSA-CIEMAT, together with UAL-CIESOL, is responsible for CS2, corresponding to one of the two sea-mining case studies. In particular, CS2 aims to demonstrate that thermal desalination can improve the sustainability of current technologies (reverse osmosis) for seawater desalination, by reaching higher concentrations to facilitate the implementation of Zero Liquid Discharge schemes with lower consumption of primary energy (i.e., use of low temperature solar heat). To improve the efficiency of the thermal desalination process, the seawater to be fed to the MED will be pre-treated by a nanofiltration (NF) system to retain the divalent ions (Mg²⁺, Ca²⁺, SO₄^2-), resulting in a sodium chloride (NaCl) rich and purified permeate stream.  By using this as feed, the recovery of the MED plant can be increased, and also the operating temperature (typically limited to 70ºC to avoid scaling), enhancing the thermal efficiency significantly. The aim is to demonstrate the potential of reaching a record-breaking lowest energy consumption in thermal desalination (below 25 kWh_th/m³) without exceeding 100ºC in the Top Brine Temperature. In addition, the use of polymeric materials in the MED plant replacing metallic evaporator tubes will be evaluated to decrease the cost of the desalination plant. To achieve Zero Liquid Discharge desalination, the concentrated brine released from the MED plant will be treated with solar-powered crystallization. As the brine from the MED will be free from divalent ions, the salts produced in the crystallizer can be pure NaCl with higher added value. Furthermore, the brine from the NF system, with a larger concentration of divalent salts, will be used to remineralize the distilled water produced in the MED and in the crystallizer, to be used for irrigation. The divalent ions are tolerated by crops and some act as fertilizers.