*5.4.2 Effect of brine infiltration on soils*

Each plant has a certain tolerance to salinity, depending on the plant species, the soil, and the characteristics of the brine. In general, some plants can tolerate TDS concentrations of 500 mgL�<sup>1</sup> , and this is the case of halophytes that can be irrigated with a brine concentration higher than 2000 mgL�<sup>1</sup> of TDS [58]. In general, soil texture is the main factor affecting the infiltration rate of soils, as well as soil depth, which makes the permeability characteristics of these different [59]. The soil under study has a sandy loam texture, whose infiltration rate is 0.8 to 1.2 cm h�<sup>1</sup> (**Table 6**). This characteristic allows inferring that the soil for cultivation has a moderate infiltration rate, being optimal for drip irrigation [60].

On the other side, the capacity of the soil to retain water, called soil ponding capacity (PC), is another factor that influences infiltration, and in irrigation, it is always limited to a given depth (normally to the depth of roots). For the calculation of the ponding capacity (Ec. (7)), [61] was used, according to the data obtained in **Table 7** at a depth of 40 cm, obtaining a value of 48 mm. It is important to mention that the field capacity (FC) is the water content of a soil after having been abundantly irrigated and having drained freely for 24 to 48 hours, and the permanent wilting point (PWP) is the soil moisture condition in which the plants are unable to absorb water or do so with extreme difficulty, experiencing irreversible wilting:


### **Table 6.**

*Basic infiltration rate according to soil texture class [60].*


### **Table 7.**

*Physical properties for different textures [61].*


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

### **Table 8.**

*Principles and strategies of the circular economy applied to the cultivation of halophytes with brine obtained from the RO plant [44] (proper elaboration).*

$$PC = \left(\frac{FC - PWP}{100}\right) \times Ad \propto Sd \tag{2}$$

The PC value obtained indicates that the soil can store in a depth of 40 cm a height of water equivalent to 48 mm. However, not all of this water is available to the crop, since crops have different minimum water balances, for example, like halophyte, in the case of alfalfa, and in general, they require approximately 60% of the available water capacity to maintain evapotranspiration and avoid water stress.

### **5.5 Circular economy**

This proposal was applied to the present work (**Table 8**), mentioning that strategies R1 to R3 are relevant for the optimal performance and utilization of the RO plant energetically sustained with solar energy, and that its resulting by-products are used for irrigation. From strategy R5 to R8, the products can be maximized through valorization, considering that the "brines" are allowed to produce "food" for other species such as "cattle or goats." In addition, membranes can be reused either by regenerating them or by using them to produce another type of membrane. As for strategies R10 and R11, they allow improving and preserving the natural ecosystem through the use of renewable energies, using the brine for irrigation, and reducing the use of conventional water.

**Figure 5** is a proposal that considers three important components: 1. desalination plant, 2. photovoltaic system, and 3. halophyte cultivation. This integrated proposal

**Figure 5.** *Diagram of brine utilization in the cultivation of forage plants considering the principles of circular economy (proper elaboration).*

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

would allow mainly rural communities to opt for the sustainable development of their products considering the circular economy in their processes.

Although, generally what is sought when implementing desalination plants is to obtain water for irrigation or human consumption; in this case, it is observed that the use of brine from this type of process serves for the cultivation of fodder plants. Therefore, environmental circularity would be achieved from the desalination plant by applying the different strategies of the circular economy.

Initially, the brine (R1) can be used for the cultivation of halophytes, reducing the consumption of irrigation water (R3 and R7). Subsequently, the fodder plant is used as feed for cattle and goats (R10 and R11), preserving the natural resource and reducing environmental pollution. It is worth mentioning that the valorization and consumption of animals fed with halophytes irrigated with brine should reduce production costs due to the water savings generated and the solar energy used as energy support for the system (R2).

Moreover, the desalination plant has parts that can be repaired (R5) or remanufactured (R6) or reevaluated (R7).
