Desalination for agriculture: water quality and plant chemistry, technologies and challenges

INTRODUCTION

Seawater desalination is playing an important role in addressing the challenge of global water scarcity. The most important drivers for water scarcity are growing water demands due to population growth and economic development, and increased per capita consumption of goods and services (Vorosmarty et al. 2005). The total global water demand is dominated by agricultural use (70%) followed by industrial use (21%) and domestic use (9%). Limited water resources have enforced the use of low-quality irrigation water. Using low-quality irrigation water may reduce crop yields and damage the environment, soils, and aquifers. Therefore, with increasing water scarcity, development of efficient water sources for agricultural use is the major challenge that the growing population is currently facing.

Seawater, brackish water or wastewater desalination are the only alternatives to increase water supply beyond what is available from the hydrological cycle (Shannon et al. 2008). The climate changes due to global warming are constantly increasing the salinity level of both land and seawater, reducing the availability of existing fresh water for households, agriculture and industry. A study from Diaz et al. (2013) demonstrated that irrigation with desalinated seawater led to a significant increase in salinity and boron in the soils that could affect the yield of moderately tolerant crops. This has made it urgent to invent an appropriate water treatment technology that not only removes macro, micro and nano-pollutants but also desalinates water to a significant extent. Continued research and development of new treatment technologies are essential to improve the availability and quality of water supplies for agricultural use (Shannon et al. 2008). Consequently, thermal and membrane based desalination technologies are playing an important role in solving global water scarcity problems.

Desalination not only separates the undesirable salts from the water, but also removes ions which are essential to plant growth. The desalinated water when applied to agriculture has added advantages as it contains sufficient levels of nutrients such as calcium (Ca²⁺), magnesium (Mg²⁺), and sulfate (SO₄^2–) (Yermiyahu et al. 2007). According to Domingo et al. (2013) the important features of desalination for agriculture are: (a) no requirement for post-treatment since the water produced will be rich in nutrients, (b) the presence of boron above 0.5 ppm is toxic...