**2. Desalinization**

Desalination is a process of removing dissolved salts and other minerals from seawater or brackish water, resulting in freshwater and a subproduct called brine [21, 22]. Seawater desalination is an alternative that can extend water supplies beyond what is available in the hydrological cycle, with a constant and climate-independent supply [23]. The main desalination technologies include thermal methods such as multistage flash distillation (MSF) and multi-effect distillation (MED) and within membrane methods, reverse osmosis (RO). These desalination technologies commercially cover almost 90% of the world market. RO processes lead with a 53% share, followed by thermal technologies with 33% [24], and RO is a technology that has lower energy requirements, low complexity and, therefore, lower economic cost [25]. This technique requires electrical energy to activate a high-pressure pump, whereby the saline water is forced through semipermeable membranes to separate the freshwater (or product) from the saltwater (brine) [26]. However, despite the benefits offered by desalination, it is still an environmental challenge to consider the disposal of coproduced brine to mitigate the environmental impacts attributed to discharges into the environment. Generally, brine is discharged to the sewer or to the sea [27]. Currently, desalination technologies are also applied to treat the large amount of brine generated in these processes, which can be by electrodialysis [28] or by membrane distillation crystallization (MDC) [29], among other alternatives, in order to recover a greater volume of product water.

On the other part, being RO the most widely used technology, its performance depends largely on the type of membrane, which have a pore size <1 nm, allowing the passage of small molecules such as water and rejecting larger species such as Na<sup>+</sup> , K<sup>+</sup> , Cl, or dissolved organic compounds. In that sense, there are several studies that seek to improve and optimize the membrane material to generate higher permeability, better selectivity, and anti-incrustant properties [30].

### **2.1 Brine disposal methods**

The most commonly used methods of brine disposal are i) discharge to the sea (surface and through multiport diffusers installed on the deep sea floor), ii) disposal in sewers (wastewater collection system, low cost and energy), iii) injections into deep wells (injected into porous subsurface rock formations), iv) injections into deep wells (injected into porous subsurface rock formations) (v) sewage disposal

(wastewater collection system, low cost and energy), (vi) deep well injections (injected into porous subsoil rock formations), (vii) land applications (irrigation of salt-tolerant crops and grasses), and (viii) evaporation ponds (evaporation of brine in ponds, salts accumulate at the base of the pond) [7]. In addition, when selecting the disposal technology, it is important to consider the location, quality, and volume of the brines [31].

### *2.1.1 Land applications*

Among these applications, irrigation of crops with a concentrated solution of salts is a great solution in these times, considering that currently there is low-quality water available and that there is an increase in temperature worldwide, which is causing a greater demand for irrigation water [32], which is why having water, even if it is saline (brine), is a benefit to be considered.

Generally, the use of brine in sprinkler irrigation is common in parks, lawns, and golf courses, and also, in the cultivation of forage plants, which require low volumes of this solution. However, its use is limited for large volumes due to climatic conditions, plant size, seasonal demand, and depending on the stratigraphic and structural conditions where the subway aquifer is formed [33].

There are studies of halophyte plants such as *Arthrocnemum macrostachyum*, which indicate that this plant has a high capacity to desalinate soils. To this end, through an experimental analysis and under non-leaching conditions, soil salinity was reduced after 30 days of treatment by 31% (from 10.94 to 7.5 dS m <sup>1</sup> ), regardless of whether the plant had been previously grown in the presence or absence of salt [34].

The means by which halophytes sequester salts and the degree of salt absorption differs according to plant species affect the efficiency of their use for remediation of affected soils. Halophytes have many productive applications: rehabilitating degraded lands, preventing desertification, providing firewood and timber, creating shade and shelter, and producing industrial crops and animal fodder. Halophytes can be grown on soils too saline for normal crops and pastures, from inland soils to soils near the sea, and thus can make a significant contribution to food security for living things [35].

Considering the above, it can be evaluated that this type of brine from desalination plants, when used in irrigation, presents advantages and disadvantages, which are described as follows:

### **Advantages**


*Use of Saline Waste from a Desalination Plant under the Principles of the Circular… DOI: http://dx.doi.org/10.5772/intechopen.105409*


### **Disadvantages**


### **2.2 Brine disposal cost**

One of the main problems in the installation of desalination plants is the cost of brine disposal, which is usually very high, ranging from 5 to 33% of the total cost of the desalination plant [7].

In addition, this cost depends on factors such as concentrate characteristics, treatment prior to disposal, disposal method, environmental regulations, location, concentrate volume, among others. It is also important to consider that the economic and environmental risks would be reduced if there is good management of brine use and final disposal. Así como también, es importante considerar que los riesgos económicos y ambientales se reducirían si existe una buena gestión del uso y disposición final de la salmuera [31].

### **2.3 Regulations applicable to brines**

It is worth mentioning that among the few existing regulations worldwide, the Mexican regulation is a good option to start controlling the start-up of desalination plants and their waste. In this regulation called "PROY-NOM-013-CON AGUA/ SEMARNAT-2015: that establishes specifications and requirements for intake and discharge works to be complied with in desalination plants or processes that generate brackish or saline rejection water," it indicates that it has 11 parameters and whose maximum limits include temperature, pH, total dissolved solids, turbidity, aluminum, copper, cadmium, among others. However, it does not refer to the main compound within the brine, NaCl [36].

Currently in Chile, there are no specific regulations related to desalination plants, as well as no regulatory system that considers the maximum concentration of brine expressed in NaCl, (mg L<sup>1</sup> ) or salinity (dimensionless), or for the temperature (°C) for its final disposal, there is only a guide with minimum technical guidelines for desalination projects related to the jurisdiction of the maritime authority prepared by DIRECTEMAR [37] which includes desalination projects that may or may not be submitted to the Evaluación de Impacto Ambiental (SEIA) [38]. Cornejo-Ponce, et al. 2020 [7] proposed that both salinity and temperature, which are essential parameters, should have their upper limits expressed as follows: for salinity, the concentration should be less than or equal to that of the receiving mass. For example, if discharged into the sea, it should be lower than the salinity of the sea (35 mg L<sup>1</sup> ), and for temperature, it should be considered approximately 2°C higher than that of the


### **Table 1.**

*Calculations involved in the desalination process [39, 40].*

receiving mass, respecting the 2015 Paris agreement. In addition, once these parameters have been established, the different alternatives for their elimination can be evaluated.

### **2.4 Brine concentrate calculation**

The calculations involved in the desalination process (**Table 1**) and specifically for obtaining the amount of brine produced consider a concentration of feedwater Ca (Kg m<sup>3</sup> ), product water Cp (Kg m<sup>3</sup> ), and brine Cs (Kg m<sup>3</sup> ), as well as a flow rate of feedwater Qa (m<sup>3</sup> h<sup>1</sup> ), product Qp (m<sup>3</sup> h<sup>1</sup> ), and brine Qs (m<sup>3</sup> h<sup>1</sup> ) [39, 40].
