Elsevier

Desalination

Volume 364, 15 May 2015, Pages 2-16
Desalination

Desalination techniques — A review of the opportunities for desalination in agriculture

https://doi.org/10.1016/j.desal.2015.01.041Get rights and content

Highlights

  • Water from reverse osmosis/electrodialysis technologies is suitable for agriculture.

  • Water from these technologies is more expensive than normal agricultural water.

  • The use of desalination for agriculture may currently be justified for high value crops.

  • Wider technology application is viable where fit for purpose water is limited.

  • Technology development requires cost reduction and improved agricultural practices.

Abstract

The adoption of desalination for agricultural purposes in countries such as Australia has been very limited, with only a small number of cases available to demonstrate its suitability. This can be compared to countries such as Spain where the uptake has been significant. A number of suitable technologies such as reverse osmosis and electrodialysis are available to provide desalinated water, but not at a cost comparable to that for water commonly utilised for agricultural purposes. The use of blended waters, where the quality of the water is tailored to the crop may go part way to addressing this cost differential. However, if the overall efficiency of the combined production of water and food, as well as opportunities for better soil management is considered, then desalination's applicability to agriculture becomes more viable. The use of state of the art technologies for the provision of desalinated water for agriculture is most likely to be cost effective in a tightly controlled environment, using agricultural practices with the most-effective water use and crops with high productivity. Such conditions are often associated with greenhouses and the production of high-value irrigated crops, where the cost of water is small compared to the infrastructure investment.

Introduction

Population growth, food security concerns, climate change impacts on agriculture, freshwater resource overuse and land degradation worldwide are forcing international scientific communities to look for alternative approaches to our current resource management approach for agricultural purposes. This includes all aspects associated with water resources and their availability to support ever-growing demands for both agricultural and potable water demands. Desalination technologies may provide one opportunity for generating cost-effective and potentially climate-independent water resources of controlled quality for agriculture applications.

As shown in Fig. 1, seawater desalination is the most used solution to address water shortage especially for potable water applications. In this respect the number of desalination plants around the world, both planned and under construction, has increased significantly in recent years, as shown in Fig. 2, especially in Australia where they have been targeted for providing additional sources of potable water [25]. It is estimated that about 69% of available water resources around the world are used for irrigation [110] and as water demands increase the number of desalination plants for irrigation for agriculture has also increased. Consequently there is increased emphasis on enabling cost effective desalination technologies to provide water of suitable quantity and quality for agricultural applications.

Drier countries such as Australia and Spain have a long history with desalination technologies. In the past, the high capital and operating costs of desalination and the energy required have been major constraints to large-scale production of freshwater from brackish waters and seawater. However, desalinated water is becoming more competitive for urban use because desalinating costs are declining associated with increasing demand from population growth and reduced security of supply from surface water and usable groundwater and it is expected that these increases in efficiency will flow through to the agricultural sector. However, in spite of these developments, currently the cost of desalinated water is still too high for the use of this resource in broad-scale irrigated agriculture. An exception appears to be intensive horticulture for high-value cash crops, such as vegetables and flowers (mainly in greenhouses) grown in coastal areas where safe disposal of brines is easier than in inland areas [11]. For example Sundrop farms (Sundrop-Farms, Personal communication), uses 860,000 m3 of fresh water yearly to irrigate 2000 m2 of greenhouses. If the costs for providing desalinated water continue to reduce, its use is expected to become more viable because desalination for agricultural purposes has a number of significant advantages including:

  • Tailored conductivity for irrigation water

  • Assured supply

  • Enables agricultural products of consistent quality

  • Production may be increased compared to other water sources.

  • The water may attain a higher resale price due to quality and supply assurance.

  • It allows recovery of saline soils by irrigation with high quality water.

Section snippets

Integrated water and food production: desalination and agriculture

Desalination allows a widening in utilisation of available water resources by producing freshwater from saline or brackish natural water sources. Over the past decade conventional water production costs have been rising in many parts of the world and costs for desalination have been declining, consequently desalination has become more economically attractive and competitive. Lattemann et al. [58] estimated that by 2015 the costs of freshwater treatment, wastewater reuse and desalination are

Desalination technologies

There are a significant number of technologies available for desalination of both sea and brackish water supplies. Many of these are commercial, however; there are some that are either approaching commercialisation or are at an advanced stage of development such as membrane distillation; which are not assessed in this analysis. The choice of technology is influenced by the source water quality, energy demand, and most importantly the value placed upon the recovered water. For example the

Other techniques applicable to desalination for agricultural purposes

There are a number of other commercial techniques available that may potentially be suitable for providing desalinated water for agricultural purposes depending on the specific location and water needs. These techniques include multistage flash distillation (MSF), multi effect distillation (MED), capacitive deionization (CDI), vapour compression (VC) and solar humidification and dehumidification (HDH). Emerging technologies which may one day be suitable for providing desalinated water include

Feedwater quality

A summary of the processes for treating a range of feedwater salinities is summarised in Table 3. For low salinity brackish waters of salinity up to 2500–3000 mg/L the processes that are in commercial scale use and that are the most economic for that salt concentration are RO, NF, ED, IX and HDH. RO and ED both have large-scale plants up to hundreds of ML/day capacity running. The rest have smaller but well-tested plants operating and CDI has a 1 ML/day plant at the commercial stage. Distillation

Discussion

Opportunities for applying desalination technologies to agriculture go hand-in-hand with requirements to improve irrigation practices and efficiency, which can achieve significant reductions in water demand and therefore make the application of desalinated technologies more viable, because the cost of the water is not as critical a component.

Gregory [118] summarised the challenges and opportunities in water-use efficiency in irrigated agriculture as “Irrigated crops occupy about 15–20% of the

Conclusions

Suitable technologies such as reverse osmosis and electrodialysis to provide desalinated water for agriculture are currently available and can provide water for agriculture, but at a cost that is currently more expensive than that generally used for agricultural purposes. The adaptation of desalination to supply water for agriculture may be cost effective; especially when applied to high value crops where the cost of the water is not a critical issue. For these applications established

Acknowledgements

The support of the National Centre of Excellence for Desalination and the CSIRO Water for a Healthy Country Flagship is gratefully acknowledged.

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