**2. Methodology**

when demand exceeds freshwater supply in a given area [2]. The three main features that characterize water scarcity are: the physical shortage of available water to meet demand; the level of infrastructure development that controls storage, distribution and access; and the institutional capacity to provide the required water services [3]. In Mexico, there is a chronic shortage of water, especially in the northern part of the country, where precipitation volumes

Considering that 97% of the water available on Earth has a salinity level exceeding 35 g/L, the desalination process is a viable option in the short term, which has had a significant growth in the recent past [2]. At the beginning of the modern development of desalination, before the 1970s, desalination methods consisted of thermal processes and their operation was such that they evaporated the fluid and collected the condensate. Known thermal processes include thermal vapor compression (TVC), multi-stage flash (MSF) and multi-effect distillation (MED) [5]. However, because evaporation processes require large amounts of energy for their operation, the use of semi-permeable membranes through reverse osmosis (RO) has become the main technology in use, accounting for 65% of the installed capacity of desalination plants.

The use of desalination to produce clean water as well as industrial and agricultural water has gained popularity among the sectors that require this resource [3]. The agricultural sector is the most important consumer of water resources, so RO desalination technology for crop irrigation has been successfully implemented in several countries, mainly in arid regions such as Israel [6] and Spain, where more desalinated water is currently provided for agricultural use than for domestic use [7, 8]. Likewise, several nations such as China, Chile and Australia offer specialized advice on the different techniques and technologies of desalination focused on agricultural crops [1], making the RO process the most used to tackle water scarcity in that sector [1, 2]. Therefore, desalination technologies enable the possibility to make optimal use of hydrological resources, both of the product (permeate) water and the retentate (brine).

The characteristics of irrigation water are directly linked to the quality of the crops harvested, as high salinity is intolerable for most crops established for food production. The agricultural sector benefits from the supply of higher volumes of better quality water [7]. However, the volume of global desalinated water currently accounts for only 1% of the world's supply. Of

The state of Sonora, located in northwestern Mexico, ranks second in irrigation crops in the country. About 95% of the state is considered semi-arid and is characterized by a climate of high temperatures and low rainfall per year. Those conditions, combined with the overexploitation and lack of recharge into aquifers, have led to a decrease in the levels of available water [3], especially for agriculture. Several regions in the state present high salinity in well water, ranging from 2000 to 9000 mg/L of total dissolved solids (TDS), which are attributed to saline intrusion effects, causing soil salinization and decreasing the yields of vegetable and grain crops [8]. In this context, the objective of this study is to evaluate the performance of two typical crops (Sorghum and Tomatillo) under brackish water irrigation, by comparing their yield using water with different salinity levels, in order to determine the salinity-yield effect.

this value, only 2% of desalinated water is used for agricultural purposes [9, 10].

/d each year [4].

are notably lower than the potential evapotranspiration [4].

4 Desalination and Water Treatment

This installed RO capacity grows at a rate of 4 million m<sup>3</sup>

#### **2.1. Location of the study area**

This study took place near Cd. Obregon, Sonora, Mexico, in field 1814 (**Figure 1**), located in the Yaqui Valley, with geographic coordinates 27° 11′ 21.7″ N, 109° 52′ 15.6″ W [8].

#### **2.2. Configuration of the desalinization process**

A 150 m<sup>3</sup> /d capacity RO desalination plant was used, consisting of 12 Hydranautics 8 × 40″ SWC4 membrane modules with a permeate flow rate of 27.3 m<sup>3</sup> /d, 99.8% salt rejection, spiral wound configuration, polyamide composite membrane and 440 ft<sup>2</sup> active membrane area. The plant uses a 40 hp high pressure pump (Grundfos). The pressure levels in the membrane modules and cartridge filters, as well as the process flow rates, were all monitored. In determining the water production cost of the RO process, the costs of electricity, labor, chemicals and maintenance were considered.

#### **2.3. Brackish well pump**

The water supplied to the desalination process was sourced from a brackish well adjacent to the study area, with an average salinity of 4000 mg/L TDS. The brackish water was pumped from the well by a 3 hp triphasic pump (Grundfos).

**Figure 1.** Study area, Sonora, Mexico.

#### **2.4. Physical and chemical pretreatment system**

The desalination plant has a physical pretreatment system consisting of a multimedia filter and 6 cartridge filters. The multimedia filter (63″ × 90″) has a capacity of 100 ft<sup>3</sup> and consists of anthracite, turbidex, zeolite, and gravel. This filter removes suspended particles up to 50 μm in diameter. Subsequently, the cartridge filters remove particles of up to 5 μm in size.

For chemical pretreatment, a 0.25 hp diaphragm pump was used for the supply of antiscalant. In order to prevent salt precipitation on the surface of the membranes and, thus, prevent an increase in operating pressure. A 0.20 hp diaphragm pump was also used for the supply of H2 SO<sup>4</sup> at 30%, to regulate pH at the inlet of the RO membrane modules, maintaining a value of 7.0 ± 0.1.

#### **2.5. Water and soil quality**

Water quality was measured using a multiparametric measuring device (YSI 556 MPS). The concentration of salts in the feed, product and retentate of the RO process were determined. In addition, electrical conductivity (μS/cm), TDS (mg/L), pH and temperature (°C) were also measured. A visible spectrophotometer (SPECTRUM PROVE 300) was used to determine the concentration of different minerals in the water.

Soil quality was determined via pH and electrical conductivity (μS/cm) measurements. The damage caused by salinity in the agricultural soil was assessed at the beginning, during and at the end of the project, by determining parameters such as Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP). These parameters measure soil damage caused by sodium buildup.

#### **2.6. Experimental design**

To assess the effect of salt concentration in irrigation water on crop yield, two different experiments were conducted with sorghum and tomatillo (*Physalis philadelphica*). The experiments occurred in different agricultural cycles and different years (2014 and 2016). The first crop was chosen because it has a high tolerance to salt concentration in water. The second crop was chosen because it is not very tolerant to salinity in water. An experimental planting area of 1 ha was used. The field was divided into two sections of 0.5 ha each (**Figure 2**). The first section was irrigated with well water containing 4000 mg/L TDS on average. The second section was irrigated with treated water from the desalination process, with an average of 200 mg/L TDS.

A drip irrigation system was used with a flow rate of 1 L/h, using 16 mm diameter irrigation belts. The treated water for irrigation was generated by mixing the permeate from the RO plant with raw well water, in order to reach an average salinity of 200–285 mg/L TDS. The following formula was used to calculate the mixtures:

$$
\mathbb{C}\_1 V\_1 + \mathbb{C}\_2 V\_2 = \mathbb{C}\_3 V\_3 \tag{1}
$$

where:

*C*<sup>1</sup> = salt concentration in the feed water from the well, in mg/L of TDS.

The water mixtures were stored in three tanks, each being 5000 L in size. The water was

Using Desalination to Improve Agricultural Yields: Success Cases in Mexico

http://dx.doi.org/10.5772/intechopen.76847

7

Electronic sensors (Watermak 200) and manual tensiometers were installed to monitor soil moisture (matric potential), in order to determine the optimal moment to water the soil. The matric potential is a measure of the force or tension of soil moisture with which water is retained. It is the product of adhesion or attraction between the surface of soil particles and water; and cohesion or attraction between water molecules. The water retention process, which depends on the surface tension characteristics of the water in the soil, as well as on the

*C*<sup>2</sup> = salt concentration in the permeate water, in mg/L of TDS.

**Figure 2.** Satellite photograph of the study area and experimental sections.

*C*<sup>3</sup> = required salt concentration for irrigation, in mg/L of TDS.

homogenized by an electric stirrer that was placed in the tank hatch.

*V*<sup>3</sup> = volume of required irrigation water in liters (L).

*V*<sup>1</sup> = volume of well feed water, in liters (L).

*V*<sup>2</sup> = volume of permeate water, in liters (L).

**2.7. Irrigation control sensors**

Using Desalination to Improve Agricultural Yields: Success Cases in Mexico http://dx.doi.org/10.5772/intechopen.76847 7

**Figure 2.** Satellite photograph of the study area and experimental sections.

where:

**2.4. Physical and chemical pretreatment system**

concentration of different minerals in the water.

following formula was used to calculate the mixtures:

H2 SO<sup>4</sup>

of 7.0 ± 0.1.

**2.5. Water and soil quality**

6 Desalination and Water Treatment

by sodium buildup.

200 mg/L TDS.

**2.6. Experimental design**

The desalination plant has a physical pretreatment system consisting of a multimedia filter

anthracite, turbidex, zeolite, and gravel. This filter removes suspended particles up to 50 μm

For chemical pretreatment, a 0.25 hp diaphragm pump was used for the supply of antiscalant. In order to prevent salt precipitation on the surface of the membranes and, thus, prevent an increase in operating pressure. A 0.20 hp diaphragm pump was also used for the supply of

Water quality was measured using a multiparametric measuring device (YSI 556 MPS). The concentration of salts in the feed, product and retentate of the RO process were determined. In addition, electrical conductivity (μS/cm), TDS (mg/L), pH and temperature (°C) were also measured. A visible spectrophotometer (SPECTRUM PROVE 300) was used to determine the

Soil quality was determined via pH and electrical conductivity (μS/cm) measurements. The damage caused by salinity in the agricultural soil was assessed at the beginning, during and at the end of the project, by determining parameters such as Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP). These parameters measure soil damage caused

To assess the effect of salt concentration in irrigation water on crop yield, two different experiments were conducted with sorghum and tomatillo (*Physalis philadelphica*). The experiments occurred in different agricultural cycles and different years (2014 and 2016). The first crop was chosen because it has a high tolerance to salt concentration in water. The second crop was chosen because it is not very tolerant to salinity in water. An experimental planting area of 1 ha was used. The field was divided into two sections of 0.5 ha each (**Figure 2**). The first section was irrigated with well water containing 4000 mg/L TDS on average. The second section was irrigated with treated water from the desalination process, with an average of

A drip irrigation system was used with a flow rate of 1 L/h, using 16 mm diameter irrigation belts. The treated water for irrigation was generated by mixing the permeate from the RO plant with raw well water, in order to reach an average salinity of 200–285 mg/L TDS. The

*C*<sup>1</sup> *V*<sup>1</sup> + *C*<sup>2</sup> *V*<sup>2</sup> = *C*<sup>3</sup> *V*<sup>3</sup> (1)

at 30%, to regulate pH at the inlet of the RO membrane modules, maintaining a value

in diameter. Subsequently, the cartridge filters remove particles of up to 5 μm in size.

and consists of

and 6 cartridge filters. The multimedia filter (63″ × 90″) has a capacity of 100 ft<sup>3</sup>

*C*<sup>1</sup> = salt concentration in the feed water from the well, in mg/L of TDS.

*V*<sup>1</sup> = volume of well feed water, in liters (L).

*C*<sup>2</sup> = salt concentration in the permeate water, in mg/L of TDS.

*V*<sup>2</sup> = volume of permeate water, in liters (L).

*C*<sup>3</sup> = required salt concentration for irrigation, in mg/L of TDS.

*V*<sup>3</sup> = volume of required irrigation water in liters (L).

The water mixtures were stored in three tanks, each being 5000 L in size. The water was homogenized by an electric stirrer that was placed in the tank hatch.

#### **2.7. Irrigation control sensors**

Electronic sensors (Watermak 200) and manual tensiometers were installed to monitor soil moisture (matric potential), in order to determine the optimal moment to water the soil. The matric potential is a measure of the force or tension of soil moisture with which water is retained. It is the product of adhesion or attraction between the surface of soil particles and water; and cohesion or attraction between water molecules. The water retention process, which depends on the surface tension characteristics of the water in the soil, as well as on the contact angle between water and soil particles, is the main mechanism of water retention in light and middle soils within certain moisture intervals, and in heavy soils. In this context, a matric potential between 30 and 40 kPa indicates that the soil needs irrigation, whereas a matric potential between 0 and 10 kPa indicates that the soil is saturated [11].
