Maximizing the Benefit of Desalination Brine: Guidance and Awareness for Transitioning from Waste to Valuable Resources

1. Introduction

The impending freshwater shortage is a serious issue that requires immediate attention. Scientific studies predict that this crisis is becoming increasingly likely, and its impacts would be far-reaching and devastating. Mass migrations towards the north [1], escalating conflicts between neighboring countries over scarce resources [2], and a sharp decline in the GDP of many nations [3,4] are just some of the potential consequences.

To address this issue, several projects need to be explored urgently. One promising solution is the establishment of water highways connecting southern and northern countries [5], while also transmitting clean energy from the south to the north via cables. This would allow northern countries to tap into the abundant solar and wind resources available in the southern regions [6]. However, such ambitious projects come with a hefty price tag and require extensive feasibility studies and international cooperation.

To safeguard their water security and maintain control over their water supplies for drinking, agriculture, and certain industries, desalination of seawater is a viable, albeit costly, option [7]. The desalination process involves extracting seawater, desalinating it to the maximum extent possible, and then returning the remaining water to the sea. However, environmentalists have raised concerns about the impact of desalination on marine biodiversity [8,9]. The discharged brine, which has a high salinity level, can harm marine ecosystems. This highly saline water, known as brine, is a crucial component of the proposed solution. Instead of being disposed of in the sea, it will be repurposed from an unwanted waste product into a valuable asset for this project.

This article targets two primary audiences: biologists concerned about the impact of underutilized marine waters on sea life, and institutions in countries currently or soon-to-be affected by rain scarcity due to global warming. The aim is to innovatively address this modern challenge by proposing a compromise or effective solution. To maximize the project’s performance and generate more drinking water, electricity, and overall affordability, a comprehensive set of measures is required. Essentially, this work offers a ready-to-implement solution for interested parties, with only the scaling aspects left to be tailored by relevant stakeholders.

2. Shedding Light on the Matter: A Clear Exposition of the Problem

In order to promote this indispensable freshwater resource, this study should focus on the most advanced seawater desalination technologies. Currently, three types of desalination technologies exist, as summarized in the table below, highlighting the two factors most relevant to this study: energy consumption and brine-to-freshwater ratio.

Table 1. Energy consumption and brine-to-freshwater ratio for each desalination technology.

Table 1. Energy consumption and brine-to-freshwater ratio for each desalination technology.

Reverse osmosis, with its outstanding brine-to-freshwater ratio and minimal energy consumption, stands as the most favorable technology [10], thus taking center stage in this study.

Irrespective of the desalination technology used, be it reverse osmosis or any other technique, the end objective is consistent: to generate drinkable water while disposing of the resulting brine in an environmentally responsible way. The central focus of this study is the acknowledgment that the primary hurdle is energy-related, particularly, securing ample energy for both the reverse osmosis process and the disposal of brine. This study offers a potential solution among others to tackle this challenge.

3. Fundamental Principle Guiding the Promised Valorization Process

To address the environmentally responsible disposal of brine derived from seawater desalination, and given that soil injection is not a viable alternative [11], the most practical solution appears to be evaporation. One technique employs natural evaporation through solar radiation [12], a virtually cost-free approach, but unfortunately, it is rather slow, as even in the best-case scenario, only one-fifth of the daily brine production can be evaporated. The other equally evident method is assisted evaporation, which entails dedicating a certain amount of energy to accelerate the evaporation process. This study, however, aims to highlight another method that involves utilizing the water vapor destined to be lost to the atmosphere to generate electricity, which will then be reinjected to facilitate further brine evaporation. The figure n°1 below is dedicated to setting ideas and having a clear vision of the entire process implemented.

Table 2. Figure 1 legend.

Table 2. Figure 1 legend.

Figure 1. Description of the entire process.

Figure 1. Description of the entire process.

4. Situational Analysis and Identification of Paramount Challenges to Surmount

Notwithstanding the somewhat elevated expense of the infrastructure integral to this programme in its entirety, a cost that is nonetheless substantiated by the intricate and potentially precarious circumstances faced by numerous nations consequent to a sequence of arid years [13], another factor that could potentially impede the transition to seawater desalination, should penalties associated with the hazardous nature of brine discharge be imposed subsequently, is indubitably the expenditure incurred in the disposal of this very same highly saline water. The key environmental concern involves successfully recovering all the extracted water, both as filtered drinkable water and as a considerable quantity of solid sea salt, which holds value in various fields. Figure 2 below outlines the challenges that need to be tackled to advance the application of this method.

5. Investigation of the Multifaceted Dimensions (Technical, Ecological, and Economic) Subsequent to the Deployment of Such a Solution for a Real-World Scenario

In this section, we will delve into the technical characteristics and features of this process, with the goal of illustrating its truly revolutionary nature and the significant impact it could have on two critical areas: the energy sector and the field of water stress management. By exploring these technical aspects in detail, we aim to highlight how this process stands to disrupt and innovate within these industries. Furthermore, other practices and approaches described within this same paragraph are designed to complement and augment this method, making it an even more attractive and impressive proposition in the eyes of potential future investors. By combining these additional practices with the core technical features, the overall appeal and potential of this process are substantially enhanced. With that in mind, here are some key points to consider:

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At 20 °C and standard atmospheric pressure, it takes roughly 0.65 kWh of electricity to evaporate a liter of water.

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The energy demand to reach this temperature target could be substantially reduced if the project leverages deep geothermal energy. This approach would involve maintaining moderate temperatures and employing appropriate materials, as it requires managing water with a high salinity content.

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Alternatively, it is estimated that approximately 2 liters of water are required to produce 1 kWh of electricity using turbines specifically designed for this purpose [14].

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By employing well-designed heat exchangers that involve steam from the thermal power plant and brine from the desalination plant [15], it is possible to:

• On the one hand, it is possible to significantly increase the treated water from 50% using reverse osmosis to theoretically more than 90% by recovering the steam at the turbine outlet.
• In addition, by incorporating the heat exchangers into the system as suggested in the study, it is possible to produce water at a much higher temperature than the ambient temperature. In fact, depending on the efficiency of the exchangers, this water could reach temperatures close to 70 °C, and as a result significantly decrease the energy required for its evaporation.

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Regarding the residual sea salt, it is used in various domains, including culinary, food preservation, cosmetics, health, industrial, agricultural, water treatment, and de-icing. It enhances the flavor of dishes, inhibits the growth of bacteria, exfoliates and softens the skin, improves circulation, and reduces inflammation. It is also used in the production of chemicals, textiles, and paper, as a natural fertilizer, and for water treatment and de-icing. This amount of salt is not insignificant, as it is 35 g/L.

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Beyond the undeniable advantages of such an approach in tackling the challenges faced by the agricultural sector, particularly those related to drought, these initiatives can also contribute to combating global warming in multiple ways. Firstly, by implementing extensive afforestation efforts, these projects can help absorb CO2 from the atmosphere. Tree species such as Eucalyptus and Oaks are particularly effective carbon sinks, capable of storing up to 50 tons of carbon per hectare per year. Moreover, forests play a crucial role in mitigating the greenhouse effect, a phenomenon that has been extensively studied and documented by scientists. Forests emit significantly less infrared radiation compared to bare soil. In fact, implementing widespread afforestation can reduce infrared radiation emissions from 500 W/m² to a mere 200 W/m².

Based on the same dataset and performing simple calculations, the efficacy of this device is clear and aligns with the intended objectives. Therefore, by combining established technologies and techniques, while still expecting some technical innovations, it is quite possible to meet the growing need for water [16] while respecting current environmental standards or potential future standards.

6. Conclusion

The optimal outcome for this research would be for engineering consulting firms to adopt it and provide clarification on various points and technical aspects, transforming it from a purely theoretical study into a practical one. Energy and water are more crucial than ever before and will undoubtedly continue to be the cornerstones of human life on Earth. While it is true that the costs associated with such projects are enormous, gaining control over these two elements, water & energy, would enable us to approach the upcoming decades or even centuries with confidence. With that being said, if there are any areas that unquestionably merit investments from all parties, including private, state, or others, it is undoubtedly the aforementioned two elements. At the time this research was conducted, several major dams in Morocco, a country with a population of nearly 42 million people and whose economy heavily relies on water resources, were less than 10% full.