MEWAC – Collaborative Project EXALT: Coupling thermal desalination and extraction of dewatered salt with hydroponic greenhouse cultivtion via heat pumps - Middle East Regional Water Research Cooperation Program (MEWAC)

Abstract

The EXALT project, supported by the MEWAC funding initiative, aimed to deliver practical solutions to water scarcity in the Middle East through trinational collaboration between German, Jordanian, and Israeli partners (Figure 1). Crop production in the region is constrained by chronic water scarcity, exacerbated by climate change, recurrent droughts, and salinization of freshwater and soils. In the Jordan River Basin, per capita renewable water availability has declined by more than 80% over six decades, while agriculture remains the largest consumer of water, using roughly half of total freshwater withdrawals in both Jordan and Israel. The two countries pursue divergent strategies to address water scarcity: Jordan depends on declining groundwater and transboundary surface water, supplemented by limited freshwater imports from Israel, whereas Israel relies heavily on large-scale desalination and direct wastewater reuse. In this context, EXALT developed a blueprint for innovative hydroponic greenhouse systems to overcome both water scarcity and salinity constraints. By combining advanced climate control, water recovery, and thermal desalination, the project sought to maximize water-use efficiency, reduce environmental pressures, enhance year-round productivity, and provide a scalable model for arid, subtropical regions. From the outset, the consortium emphasized integrated collaboration across technical, scientific, and capacity-building dimensions, including controlled-environment trials, field assessments, stakeholder engagement, and training of young scientists. EcoPeace Jordan supported these efforts by organizing field trips for researchers, conducting interviews, and assisting with soil sampling campaigns, while a number of universities and public institutions contributed local knowledge, sample analysis, and networking support. Research at the University of Hohenheim examined the interplay of atmospheric demand, salinity, and plant performance in hydroponic systems. Three experiments with tomato, cucumber, and quinoa demonstrated genotype-specific responses in growth, ion partitioning, and stress tolerance. Salt-tolerant tomatoes effectively sequestered sodium and chloride in the petiole, protecting metabolically active leaf tissues, while cucumbers showed lower ionic homeostasis and increased vulnerability under high vapour pressure deficit (VPD). Evapotranspiration was strongly influenced by both VPD and light regime, with LED lighting reducing water loss relative to metal halide lamps. These findings underscore the importance of coordinating humidity, light, and salinity management to optimize plant performance and water-use efficiency. At the University of Jerusalem, experiments compared nutrient uptake in recirculating deep-water culture and nutrient film technique systems. Leaf nutrient concentrations generally reflected solution composition, yet NFT systems maintained optimal nutrient levels even when solution concentrations exceeded targets. Preliminary studies on chelate dynamics suggested interactions that could limit micronutrient availability, highlighting the importance of nutrient management under low-input and saline conditions. Fraunhofer research focused on greenhouse energy efficiency and climate control (Figure 2). Thermal screens improved heat retention, LED lighting reduced electrical demand, and partial photovoltaic shading lowered heat gain while allowing recovery of water from condensation. Simulation studies of a fully controlled growing environment (FCGE) indicated potential for year-round cultivation, wastewater elimination, and substantial reduction of external water requirements. FCGE systems demonstrated high yields, significant water savings, and resilience under semi-arid and saline conditions. Collectively, the consortium showed that hydroponic systems with integrated climate and water-recovery technologies could reduce daily water demand by up to 2.25 L m⁻², nearly matching the annual irrigation allocation for protected vegetables in the Jordan Valley. Applied across an estimated 4,000 ha of greenhouse cultivation, these technologies could save roughly 19–22 million m³ of water annually - about 17% of the total supply from the King Abdullah Canal and equivalent to the freshwater needs of several hundred thousand people. At the same time, crop- and genotype-specific salt uptake was shown to enable biological removal of salts through harvested biomass, reducing or eliminating the need for energy-intensive brine management under moderate salinity conditions. Together, these findings demonstrate that closed-loop hydroponic systems can simultaneously address water scarcity and salinity constraints while substantially lowering energy demand and operational costs. Despite geopolitical tensions limiting in-region mobility and field activities, the consortium maintained continuous communication, shared methodologies, and harmonized workflows, reflecting a common understanding of regional water and agricultural challenges. Capacity-building activities included MSc, BSc, and doctoral-level research projects, remote mentoring, and cross-institutional supervision. These efforts strengthened human capital across Israel, Jordan, and Germany, creating a cadre of trained professionals ready to implement water-efficient agricultural technologies and support future science–industry collaboration. Through technical innovation, environmental monitoring, and capacity development, EXALT advanced sustainable greenhouse production, disseminated environmentally innovative technologies, and fostered long-term professional networks. By addressing both water scarcity and salinity, the project contributes to regional water security, demonstrates the value of cross-border cooperation, and provides a replicable model for sustainable agriculture under challenging conditions. Even under restricted mobility and political constraints, the consortium’s integrated approach delivered measurable contributions to technology transfer, capacity building, and resilient agricultural practices.