Significant Desalination Project in Mexico
Mexico is set to host one of the largest desalination plants in Latin America, employing reverse osmosis technology to convert substantial quantities of seawater into potable water. With a production capacity of up to 380,000 cubic metres per day, this facility is poised to make a significant impact on local water supply.
The construction contract has been awarded to the Spanish company Grupo Cox by the National Water Commission (Conagua) following a public tender. The project is scheduled to be established in the community of Rosarito, Baja California, over the next three years, with a total investment of $304 million aimed at enhancing water security for the municipality of Playas de Rosarito and the southwestern region of Tijuana.
Officials estimate that the operations of the plant could benefit approximately two million residents, providing an independent and supplementary source of water alongside the Colorado River, which currently serves the area. This innovative technology, which has been employed globally over the past few decades to tackle water scarcity, also presents challenges related to energy costs and environmental considerations.
Understanding Reverse Osmosis Technology
For around three decades, reverse osmosis has been a primary method for desalinating seawater. Unlike the natural process of osmosis, this technology involves applying pressure to seawater, which has a high salt concentration, forcing H2O molecules through an artificial membrane. This process effectively separates salts, ions, and other dissolved substances from the water.
The most commonly used membranes are made from polyamide and thin-film composite structures. However, the efficiency of separation relies heavily on the membrane characteristics and the physical and chemical properties of the elements being separated. Therefore, large-scale installations necessitate a pre-treatment phase to remove suspended particles, organic matter, microorganisms, and other compounds that could impair membrane function.
Subsequently, high-pressure pumps propel the water towards membrane modules, resulting in two liquid streams. The first, known as permeate, is the water that successfully passes through the membrane, exhibiting a lower concentration of salts and other compounds. The second stream, referred to as brine, contains the concentrated salts and residuals that remain after the process, which are unsuitable for human consumption.
It is noteworthy that in a desalination facility, the pressure applied to the water is dictated by its salinity concentration. For seawater desalination, pressures can exceed 1,000 pounds per square inch (PSI). The United States Environmental Protection Agency (EPA) indicates that reverse osmosis not only removes salts from seawater and brackish water but can also eliminate dissolved solids, various inorganic substances, radionuclides, and certain synthetic organic compounds.
Energy Consumption and Waste Management Challenges
It is crucial to acknowledge the high energy consumption associated with various stages of the desalination process. Industrial plants that employ reverse osmosis for seawater desalination typically consume between 2.5 and 4.0 kilowatt-hours per cubic metre (kWh/m³) of produced water. When factoring in processes such as pre-treatment and post-treatment (when necessary), along with other plant equipment, the total energy consumption can range from approximately 3.5 to 4.5 kWh/m³.
This total energy consumption can be mitigated through energy recovery systems, which utilise the pressure from the brine flow to reduce the electricity needed for operations. Furthermore, the brine generated requires specialised handling. Due to its high salt concentration and the presence of potentially harmful compounds, proper management of this waste is essential prior to its discharge into the environment to minimise adverse effects.
Grupo Cox asserts that the technology employed in the upcoming plant in Mexico is distinguished by its high operational efficiency, the quality of the produced water, and a lower energy intensity compared to other desalination solutions. However, the company has not detailed measures aimed at mitigating potential environmental impacts from the plant’s operation or specified the mechanisms to ensure reduced energy consumption. Nevertheless, existing scientific evidence suggests that advancements in reverse osmosis processes have led to reduced environmental and energy impacts, keeping this technology at the forefront of solutions to address the water scarcity affecting over 25% of the global population.