There are different ways to generate water for human consumption, and one of the most efficient is through desalination. This process is carried out in desalination plants, whose main objective is to convert salt or brackish water into water suitable for human consumption, agricultural irrigation or industrial use. Thanks to technological advances, this process has improved considerably, allowing more water to be captured and greater volumes of desalinated water to be generated efficiently. This has been fundamental in solving water scarcity problems in various parts of the world.
In this article, we will explain in detail all the phases that make up the desalination process. In addition, we will discuss the characteristics of modern desalination plants, their main advantages and disadvantages, as well as the fundamental role they play in water management at a global level.
Phases of the desalination process in a desalination plant
The desalination process is complex and is divided into several phases, designed to ensure that the result is water of optimum quality for use. Each phase is crucial to ensure that the water is drinkable or usable in other areas. Below we break down each of these phases.
1. Seawater capture
The first step in the desalination process is seawater intake . Depending on the method used, intake can be open (using marine outfalls) or closed (through deep wells). The choice between these methods will depend on factors such as water quality and the desired environmental impact.
- Open recruitment: This method involves the use of marine outfalls that take water directly from the ocean. Although it is a simple procedure, it can result in the capture of marine life, causing possible damage to the marine ecosystem.
- Recruitment closed: This system uses deep wells, allowing natural filtration of water through the soil. As a result, the collected water contains fewer impurities and requires fewer chemicals for further treatment.
Furthermore, to avoid a negative impact on the ecosystem, each water intake is designed to be as non-invasive as possible, minimising damage to species and the marine environment.
2. Pretreatment
After intake, the water undergoes a pretreatment process designed to remove impurities and particles that could interfere with the subsequent desalination stage. This process helps prevent corrosion and clogging of the membranes and other equipment.
Pretreatment can be divided into several sub-phases:
- Physiochemical: These include processes such as flocculation, coagulation and sedimentation. These steps remove suspended particles and solids. For example, the water is acidified and chemicals are added to prevent scale formation on the membranes.
- Membrane filtration: At this stage, particles of a much smaller size are removed through processes such as microfiltration or ultrafiltration. This ensures that particles causing blockage are removed.
- Pretreatment for evaporation: In certain plants that use thermal evaporation, it is essential to remove non-condensable gases and certain insoluble salts that can reduce the efficiency of the heat transfer process.
3. Desalination process
Next, the pre-treated water undergoes the desalination process . The most widely used method is reverse osmosis , although others such as distillation and freezing also exist . Reverse osmosis has proven to be the most efficient and common method due to its balance between cost and performance.
In reverse osmosis , seawater is subjected to high pressure to force it through a semipermeable membrane that retains salts and other impurities. This process produces two streams: one of fresh water and another of concentrated wastewater, known as brine. On average, a desalination plant can process approximately 45 liters of fresh water for every 100 liters of seawater.
In addition, technology has improved significantly in recent decades. Today, higher yields can be achieved with reduced energy consumption of approximately 2.3 kWh per cubic metre of water, a significant decrease from the 8 kWh/m³ consumed by the first plants in the XNUMXs.
4. Post-treatment in the desalination plant
Post -treatment takes place after desalination, once the water has been separated from the salts. This process is designed to optimize the water according to its final use, whether for human consumption, agriculture, or industry.
- Alkalinity correction: It is vital to add certain minerals to desalinated water to balance its pH and improve its taste.
- Boron control: In water intended for agriculture, it is crucial to control boron levels, as high concentrations can damage sensitive crops.
5. Brine management
An unavoidable byproduct of the desalination process is brine . Its management is crucial to avoid negative environmental impacts on the marine environment. In most cases, the brine is pre-diluted before being returned to the ocean. This method minimizes damage to the marine ecosystem, as increased salinity in coastal waters can affect marine life, especially sensitive species such as Posidonia oceanica seagrass.
Advantages and disadvantages of a desalination plant
Desalination plants offer valuable solutions to water scarcity, but they also have certain drawbacks that must be taken into account. Below, we review the benefits and challenges of their implementation.
Advantages
- Inexhaustible source of water: Desalination uses seawater, a source that is, in principle, inexhaustible.
- Reducing dependence on aquifers: By obtaining water from the sea, the overexploitation of aquifers, rivers and lakes is reduced.
- Easy integration with renewable energies: Desalination plants can be combined with renewable energy sources, such as solar or wind, reducing their carbon footprint.
- Effective solution in arid areas: It is essential in regions with a shortage of fresh water, such as the Middle East or the Mediterranean.
Disadvantages
- High initial cost: Desalination plants require a high capital investment both in their construction and in their operation and maintenance.
- Significant energy consumption: Although it has improved, desalination remains an energy-intensive process.
- Environmental impact: Improper brine management can harm nearby marine ecosystems.
- Problems with certain agricultural crops: The use of desalinated water in agriculture can be problematic if the levels of certain minerals, such as boron, are not controlled.
Desalination plants in Spain
Spain is one of the leading countries in terms of desalination, both in Europe and worldwide. Currently, the country has more than 900 desalination plants, many of which are located on the Mediterranean coast and on the islands. These plants produce a significant amount of water suitable for human consumption and other uses.
One of the main desalination plants is the Torrevieja Desalination Plant in Alicante, which has the capacity to produce up to 80 cubic hectometers of water per year. This plant supplies water to more than 440,000 people and irrigates around 8,000 hectares of crops. Also noteworthy is the El Prat desalination plant in Catalonia, which can supply up to 4,5 million people during periods of drought.
Overall, desalination plants represent a viable, long-term solution to mitigate the effects of water scarcity. Despite their challenges, Spain continues to invest in improving the efficiency and sustainability of these plants, integrating them with renewable energy and reducing their environmental impact.