**1. Introduction**

Since the 1960s, water treatment and water desalination have been the subject of scientific studies in the USA [1]. Among these studies, water specialists have tried to see the performance of thermal desalination plants with thermodynamic cycle plants to have high energy efficiency, large solar plants called concentrating solar power (CSP) can thus be associated with multi-effect distillation (MED) or multi-stage flash distillation (MSF) desalination stations [2]. These investigations verified the technical feasibility of setting up desalination stations for agricultural purposes. These studies have shown that an irrigated perimeter can have a water supply through desalination plants for sustainable agricultural production. This can help ensure competitive prices on the market for agricultural products [3]. Several successful experiences exist in this area.

In the Bay Lagoon in the Philippines [4], the main challenge for agriculture is the salinity of the water, which exceeds 2 g/L. The establishment of a desalination plant for irrigation has enabled the increase in agricultural production for the water supply of 30,000 ha. In this sense, several countries have chosen desalination for water supply. Arid countries such as Tunisia, Saudi Arabia, and Egypt, and less arid countries such as Nigeria, China, Indonesia, and Cuba have set up drinking water desalination plants [5]. Half of Malta's municipal water quantity comes from seawater desalination [6]. In Kuwait, there have been years of excess desalinated water over requirements [7].

Nowadays, desalination is a method to obtain good quality water. All desalination processes are energy intensive and share the common minimum energy required to cause the saline solution to separate into pure water and concentrated brine. It is dependent on the detailed technology used, the exact mechanism, or the number of process steps. Furthermore, the overall equivalent power consumption of a multi-stage flash (MSF) unit is 20–30 kWhelec/ m3 , the overall equivalent power consumption of the multi-effect desalination (MED) unit also varies from 15 to 22 kWhelec/m3 [8, 9]. These thermal processes are energy intensive because there is a loss of energy efficiency due to phase changes (fossil to thermal or fossil to electric to thermal). According to the same author [10], for the reverse osmosis (RO) membrane process, the overall equivalent power consumption of the SWRO unit (seawater RO) reached the lowest specific energy consumption level of SWRO at 2.00 kWhelec/m3 . The energy consumed by conventional desalination plants usually comes from the combined cycle power plants. They are characterized by the highest efficiency of electricity generation technology from fossil fuels. These units are among the most developed, currently achieving yields above 60%. The CO2 emission is equal to 330 kg—CO2/MWh [11]. Speaking of agricultural water consumption, according to the United Nations report [12], agriculture alone uses 70% of the world's water supply. Besides, global food demand is expected to increase by another 70% by 2050. However, according to the report, the main challenge facing the world today is not so much the increase of food production, but rather to provide good-quality irrigation water to farmers in sufficient quantities. The shortage of water in arid zones has led to the usage of low-quality irrigation water in agriculture in most arid climate areas [13]. The water deficit is a problem present in many parts of the world, with lower rainfall and increased salinity of aquifers [14].

There is another method of desalination that finds success among manufacturers. This is "MEDAD" desalination which is a hybrid of traditional multi-effect distillation (MED) and adsorption cycle (AD) [15]. In general, there are several hybridization trends. In RO processes, intake, pretreatment, and brine disposal cost 25% of total desalination cost at 30–35% recovery. Shahzad and Ng [16] proposed a tri-hybrid system to enhance overall recovery up to 81%. The conditioned brine leaving from RO processes is supplied to proposed multi-evaporator adsorption cycle driven by low-temperature industrial waste heat sources or solar energy. The brine rejection concentration of the tri-hybrid cycle may vary from 166,000 to 222,000 ppm if the concentration of RO retentate varies from 45,000 to 60,000 ppm.

Several coastal countries see water desalination as a solution to water scarcity [17]. In Algeria, a neighboring country of Tunisia, desalination is considered by water experts as the only solution present to avoid a future water shortage [18]. The very specific conditions of the Mediterranean Sea (freshwater at 19°C and a salinity of 38 g/L [19], while the waters of the golf course are at 30°C and a salinity of 40.5 g/L [20]) will result in lower cost per cubic meter of desalinated water Algeria started building large-scale desalination plants after the 2001 water crisis, with a total capacity of over 2 million m3 /d [21].

Also in Libya, which is Tunisia's second neighbor country, a serious effort has been made to develop additional water sources from desalination [22] and the country has about 10 desalination stations.

There are great advances in the field of membrane and thermal desalination in particular the specific energy consumption (**Table 1**). According to Shahzad et al. [8], the performance of desalination plants, conventionally reported based on fossil fuels, can now be transformed fairly on a common platform based on specific energy consumption (SPE). This new factor, called the standard universal performance ratio (SUPR), is calculated on the basis of SPE and presented in **Table 1**. Thermal processes have better efficiency of 2.82 and 2.00 m3 /kWh for

*Desalination and Agriculture DOI: http://dx.doi.org/10.5772/intechopen.100197*


#### **Table 1.**

*SPE and SUPR calculation of major desalination processes.*

MSF and MED respectively with respect to RO. The CSP + MSF or MED configuration should experience a boom in the future.
