This project aims to transform Gibraltar’s future wastewater treatment plant into a benchmark model for advanced and safe water reuse in coastal urban environments. Gibraltar is a territory with unique hydrographic characteristics: it lacks rivers, lakes, or usable aquifers and relies entirely on seawater desalination to supply its population and economic sectors. This dependency entails high energy costs, climate vulnerability, and a significant environmental footprint associated with the desalination process.
Additionally, Gibraltar uses seawater for toilet flushing, resulting in a residual effluent with extremely high salinity (15,000–20,000 mg/l), which has historically hindered the use of conventional biological treatment technologies. This situation has created a structural gap in wastewater management and prevented the development of reuse schemes.
The new plant will include a tertiary treatment system based on advanced technologies, including reverse osmosis (RO) for salt removal, ultraviolet (UV) disinfection to ensure microbiological quality, and an underground storage system. These interventions will enable the production of safe water for non-potable uses such as public space irrigation, street cleaning, or industrial cooling, replacing desalinated water and generating quantifiable volumetric benefits under VWBA 2.0, as well as quality improvements in line with WQBA.
The core issue lies in the historic lack of a wastewater treatment plant capable of operating effectively under high salinity conditions. The use of seawater in toilets leads to an effluent with Total Dissolved Solids (TDS) concentrations between 15,000 and 20,000 mg/l—far above the operational limits of most biological treatment systems. This salinity disrupts the activity of microorganisms responsible for organic matter degradation, drastically reducing the efficiency of aerobic and anaerobic processes.
This technical limitation has, for decades, prevented the implementation of functional treatment and reuse schemes, forcing Gibraltar to rely entirely on desalination for both potable and non-potable demands. The situation is further exacerbated by:
This combination of factors creates a structural vulnerability that hinders the closing of the water cycle and results in high water and energy footprints for a resource-constrained territory.
The project incorporates a modular and technically advanced solution tailored to address the specific challenges of Gibraltar’s hypersaline effluent:
This integrated solution will produce a stable flow of reclaimed water suitable for multiple urban applications, helping to close the local water cycle, reduce dependency on desalination, and avoid discharges into the Mediterranean Sea.
Project execution will take place in five well-defined stages over an estimated 36 to 42 months.
Stage 1 involves the detailed engineering design of the tertiary system, including hydraulic specifications, RO membrane selection, UV system sizing, and the structural design of the underground storage tank. It also includes preparing the tunnel infrastructure to house the equipment.
Stage 2 covers procurement and installation of the technological components: RO racks with high-pressure pumps and CIP systems, medium-pressure UV disinfection modules with automatic cleaners, disc prefilters, and a pumping and recirculation system. All equipment will be factory tested and installed on-site with technical assistance.
Stage 3 focuses on operational integration with the main wastewater treatment plant under construction, ensuring hydraulic compatibility, automation, and traceability across the primary, secondary, and tertiary modules. Flow, conductivity, turbidity, COD, and temperature sensors will be installed for real-time monitoring.
Stage 4 includes training of technical and operational personnel, covering maintenance protocols, fault response, data management, and brine handling. Sensor calibration and validation procedures will also be established.
Stage 5 involves a 12-month period of intensive performance monitoring. Weekly microbiological controls will be conducted on the treated effluent, along with physico-chemical analyses of TDS, COD, and chlorides, and continuous measurement of reused volume. Monthly audits by external entities will validate performance, and digital reports will be generated.
This structured implementation will ensure efficient and safe system operation, generating real, quantifiable, and auditable water benefits both in volume and quality.
This initiative provides a comprehensive response to Gibraltar’s urban water cycle closure needs by installing an advanced tertiary treatment system capable of reusing wastewater to high standards. Its foundation rests on three key principles: water sustainability, energy efficiency, and marine ecosystem protection.
The project’s five implementation phases, design, procurement, integration, training, and monitoring, will enable Gibraltar to reduce desalinated water use, protect marine biodiversity, enhance system resilience, and promote circular water management. Benefits include: (1) reduction of desalinated water consumption for non-potable uses; (2) reduced pollutant discharge into the sea; (3) energy savings from decreased desalination dependency; (4) increased climate resilience; and (5) a reliable source of water for sustainable urban applications.
Potential uses for the treated water include: irrigation of gardens and green areas, street and urban furniture cleaning, industrial system cooling, fire protection system filling, tunnel washing, and eventual use in closed-loop cooling systems. All of these applications will reduce pressure on the desalination plant while improving the operational efficiency of the entire urban water system. Through strict application of methodologies such as VWBA A-2 and WQBA, this project stands as a replicable model for circular water management in densely populated coastal areas.
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