The most limiting factor for the agricultural sector in the Sultanate of Oman is a lack of water, and security of supply in terms of both quantity and quality. Salinization of both soils and groundwater systems along the coastal strip of Al-Batinah has placed a substantial burden on farmers regarding crop selection and, therefore, farm profitability. Desalination of brackish and seawaters might be an attractive option to sustain salt-affected lands in the Sultanate, particularly given that recent advances in desalination technologies have reduced energy and running cost requirements. This review is a summary of the international experience on desalination for irrigation water; the opportunities and challenges of the use of this technology for sustaining agriculture in arid environments; and the outcome of a survey that explores the extent of the use of desalination for providing irrigation water on the Al-Batinah coast, Oman. The main challenges for adopting this technology for agriculture are the initial cost of desalination units and the cost of environmentally sustainable disposal of reject water. However, there is a need for more applied research efforts to minimize the detrimental impact of disposal of reject water on the environment, long-term impact of desalinated water on agricultural soils as well as cost and benefit analysis of the technology.

INTRODUCTION

The Sultanate of Oman is an arid country with a mean annual precipitation of only 100 mm (MRMWR 2015). In the last three decades, Oman has experienced a dramatic increase in population, expansion of economic development, and increase in per capita water consumption. Increased water demand compared to the availability of good quality water is one of the main challenges for continued rapid development in the country. Globally, agriculture typically consumes between 70 and 80% of available water resources (Vorosmarty et al. 2005; Zarzo et al. 2012). However, in the Sultanate of Oman the agricultural sector is the main consumer of water, with requirements exceeding 90% of available groundwater resources (MAF 2012). The coastal strip of Al-Batinah governorate (Figure 1) has both the highest population and the largest agricultural activity in the country. Rapid development of the sector in the 1980s in conjunction with unwise use of the finite groundwater has placed a significant burden on coastal aquifers, with irrigation requirements in Al-Batinah now exceeding groundwater renewal by 42% (2010 data; MAF 2012). Overexploitation of the coastal aquifers has also allowed seawater to contaminate the aquifers, resulting in further degradation of groundwater quality and salinization of soil systems.

Figure 1

Location map of Al-Batinah region, Sultanate of Oman.

Figure 1

Location map of Al-Batinah region, Sultanate of Oman.

The impact of salinity on agriculture in Oman is well documented (Al-Belushi 2003; Bajjali 2003; Al Barwani & Helmi 2006; Choudri et al. 2013, 2015). Detrimental levels of salts in irrigation water have drastically affected growth of crops along the Al-Batinah coast, with affected farmers now having shifted production from growing vegetables and fruits to less profitable forages and less productive date palms. The current situation suggests that agricultural production is not sustainable, and requires the finding of another water resource to be so. Prathapar et al. (2006) have suggested the use of graywater (domestic wastewater without fecal matter) to reduce the pressure on groundwater resources. However, the lack of easy access to, and the limited volume of graywater produced do not make this a viable option as a source of water for irrigation in Oman. Al Khamisi et al. (2013) showed that it may be feasible to reuse treated wastewater along the Batinah coast in conjunction with some groundwater to minimize the pressure on groundwater aquifers, subject to the availability of economic transportation options. Elimelech & Philip (2011) consider that desalination of brackish and/or seawaters is probably the only feasible option to provide substantial amounts of water beyond the hydrologic cycle in arid environments. However, although desalination technology offers the potential to cover the freshwater demand deficit, it may not remove key contaminants, such as boron (B) and chloride from irrigation water, and is also commonly considered to be an expensive technology (Shaffer et al. 2012).

The objectives of this paper are to reflect the worldwide experience on the use of desalination technology as an option for providing irrigation water for agriculture, to highlight the benefits and challenges of the technology for providing irrigation water, and to present the extent of use of desalination units in farms in the Sultanate of Oman. The discussion also highlights the environmental aspects associated with the use of this technology at the farm scale. Finally, we present an economic analysis for the adaptation of the technology for agriculture in the Sultanate and suggest future research opportunities of this topic in arid environments.

WORLDWIDE USE OF DESALINATED WATER FOR IRRIGATION WATER

Desalination of seawater is becoming the sole source of drinking water in some Gulf Cooperation Council (GCC) countries with an estimated total of about 5,000 million m3/year by 2015 (Dawoud & Al Mulla 2012). Desalination plants across the world provide about 66 million cubic meters (Mm3) per day, of which agriculture's share is about 1.9% (Desalination Yearbook 2012). According to FAO (2004), 4% of desalinated water worldwide goes to the agricultural sector. Countries whose economies depend on agriculture are using desalination technology as a source for irrigation water and include Jordan, Saudi Arabia, United Arab Emirates, Egypt, Spain, and Chile. Australia is considering this option in the near future. Despite Australia's limited water resources, its water price is relatively low and it was deemed unlikely that farmers are willing to pay more than AU$1.2/m3 (Barron et al. 2013). Sometimes farmers pay an extra or premium price for a water supply which has greater reliability, therefore, more-reliable water through desalination can increase its value by providing both a risk-buffering value as well as an additional water supply value in Australia (Barron et al. 2014).

Spain is the leading country in the use of desalinated water for irrigation (FAO 2004) with about 22% of desalination capacity diverted to irrigate commercial farms (Zarzo et al. 2012). The technologies used for desalinating brackish waters and seawater in Spain are reverse osmosis (RO) and electro-dialysis reversal. The use of desalination technology for agriculture in Spain goes back to the 1970s, when a small unit was installed (wind/RO system) in Fuerteventura with a capacity of 80 m3/day. The first large RO desalination plant was built in 1990 in the Canary Islands with a capacity of 36,000 m3/day (recently expanded to 80,000 m3/day). Table 1 provide details on capacities of the Canary Islands’ RO plants (FAO 2004). In 1999, the Spanish authorities in the Canary Islands realized that they needed to minimize abstraction of brackish water to allow groundwater replenishment and, therefore, maintain water balance. Consequently, farmers have turned to seawater desalination for their irrigation purposes. The first seawater reverse osmosis (SWRO) plant for irrigation was built in 1987 with a capacity of 6,900 m3/day, and then extended by another 500 m3/day for purposes of research and development. Silica is present in high amounts in brackish water in the Canary Islands, so switching from desalination of brackish to seawater was a plus for the farmers.

Table 1

Breakdown of brackish water RO plant capacities, Canary Islands (FAO 2004)

Plant capacity < 500 500–1,000 1,000–2,000 > 2,000 Total 
Capacity m3/d 15,198 16,799 14,480 16,300 72,777 
No. of plants 54 90 102 252 
Plant capacity < 500 500–1,000 1,000–2,000 > 2,000 Total 
Capacity m3/d 15,198 16,799 14,480 16,300 72,777 
No. of plants 54 90 102 252 

Source: Foundation Centro Canario del Agua, data online.

Spain adopted desalination not just for agriculture, but also for tourism purposes, e.g., the use of water to sustain golf courses. In the 1990s, many farmers and agricultural businessmen in the Mediterranean coastal areas of southeast Spain adopted the use of small desalination units to solve problems with local water shortages. Zarzo et al. (2012) noted that between 1995 and 2000, more than 200 desalination plants were installed in this coastal zone with typical capacities between 100 and 5,000 m3/day. These units were built with the government's approval and subsidies. In 2001, the Spanish government built the biggest desalination SWRO plant in Spain with a capacity of 120 Mm3/year for agricultural supply. In 2004, the Spanish government started a program called AGUA, which considers desalination as the strategic option for solving water scarcity. The program is designed to produce 693 Mm3/year with partial production utilized for irrigation.

OPPORTUNITIES AND CHALLENGES ON USE OF DESALINATION TECHNOLOGY FOR IRRIGATION WATER

According to Desaldata (2012), many countries including GCC countries are beginning to use desalinated water in agriculture, albeit at varying rates. Kuwait's current installed capacity is in excess of 1 million m3/day and 13% is used for agriculture. Saudi Arabia, the world's largest single producer of desalinated water, accounting for about 30% of global capacity, uses only 0.5% of its desalination capacity for agricultural purposes. Other countries which use desalinated water for food production are Italy (desalination capacity 64.5 Mm3/day and uses 1.5% for agriculture), Bahrain (620 Mm3/day, uses 0.4%), Qatar (0.1%), and the USA (1.3%).

Depending upon the desired quality of desalinated water, the running cost of chemicals and membranes is relatively low and costs of desalination can be regulated with the optimization of the seasonal crop water requirements. Moreover, inland desalination usually uses brackish water where salinity level (about 10,000 mg/L) is much lower than that of seawater; hence the cost of desalinating brackish water will be lower than that of seawater. Ayers & Westcot (1994) noted that the FAO irrigation water standards allow salinities up to 2,000 mg/L depending on soil and crop considerations, which has a positive impact on the cost of desalination for irrigation water. However, it should be noted that, unlike seawater, the quality of brackish water is not stable over time and tends to increase with time and, therefore, the quality must be considered (Missimer 1994).

One of the main challenges for adopting this technology for agriculture is the cost of energy. With the advancement of desalination technologies, the energy requirements and the costs are being reduced dramatically (FAO 2003; Elsaid et al. 2012). According to FAO (2003), desalination energy requirements have been reduced to about one-sixth from the 1970s with seawater desalination costs about 0.428 Euro/m3 (about 0.25 Omani Rial) in 2002. The technology provides a positive social impact in that farmers are able to reclaim and recover their salt-affected farms. Other challenges are the cost of the desalination unit and the land occupied by the facilities. However, desalination units and their accessories, such as chemical supplements, are not much larger than any other water treatment facility.

The major environmental impact of desalination technology is the amount and quality of the brine discharge. Desalination units produce brine at about 60% of feed water volume at almost twice the salinity level of the intake water (FAO 2003). Brine production can be highly variable depending on the size of the plant and method used. Disposal of such brine in agricultural lands is associated with major environmental concerns and adds to the overall cost of the technology. Where the desalination technology is located inland, extra efforts must be made for either pumping brines to the coast or drying (Elsaid et al. 2012). In 1997, the Spanish government established a network of pipelines to collect the brines from various desalination units and dispose of them in a protected estuary. Brine disposal from inland desalination plants in Oman has been extensively discussed, but no such studies have been conducted for the desalination plants used for agriculture (Ahmed et al. 2000, 2001a, b, 2002). Brine disposal into the sea requires dilution of the brine first because of its hyper salinity.

Produced water from desalination units has an electrical conductivity (EC) of about 0.2–0.3 dS/m. This is within the recommended level for the use of irrigation water. However, desalination for agriculture requires extra efforts to remove boron (B) and total dissolved salts (TDS). Recommendations for irrigation water include a B concentration of less than 0.50 mg/L, TDS less than 450 mg/L and chloride concentration of less than 105 mg/L (Shaffer et al. 2012). Boron in neutral and acidic environments passes through the RO filters, and without any additional filtration, B in produced water is about 2 mg/L, which is toxic to many fruit crops. It should be noted that some crops that are grown in Oman are ‘semi-tolerant’ to B at about 1.0 mg/L (Zarzo et al. 2012), therefore such extra restriction on water quality for agriculture requires additional costs for the SWRO technology. Another issue is that desalination removes important ions such as calcium (Ca2+), magnesium (Mg2+), and sulfates (SO42−) that maintain the structure of the soil and serve as plant nutrients. Further re-mineralization is thus required to supplement such ions for the plants and soils, which adds additional costs to the process.

EXTENT OF USE OF DESALINATION TECHNOLOGY FOR PRODUCTION OF IRRIGATION WATER IN THE SULTANATE OF OMAN

The extent of use of desalination technology within the farms along the Al-Batinah coast was explored by contacting 12 farmers who currently own a small-scale desalination unit; farmers were identified through the help of a local desalination unit supplier. Only 10 farmers agreed to participate in our pilot survey. The pilot survey involved completion of a questionnaire and collection of water samples from intake, produced, and brine. The farms were in the towns of Manouma, Barka, Musanah, and Quraiyat in the Sultanate (Figure 1). The key indicators in the survey were: (i) the cost of the desalination unit, (ii) operation and maintenance costs, (iii) main use of desalinated water, (iv) amounts and quality of production and reject brines, (v) means of disposal of brines, and (vi) type of crops grown.

A summary of costs and energy requirements of the desalination units used along the Al-Batinah coast of the Sultanate of Oman are presented in Table 2; all of the units used by the farmers are based on RO technology. It should be noted here that the units are assembled locally using imported parts from abroad. Operation and maintenance costs include the costs of filters and antiscalents. Energy tariffs are subsidized in the Sultanate and range between Rial Omani (RO) of 0.01 and 0.025 per kWh.

Table 2

Desalination units used for production of irrigation water in the Sultanate of Oman

Model Small Medium Large 
Production capacity (m3/day) 11.5 19.0 38.0 
Cost (RO) 3,000 4,500 6,000 
O&M costs (RO/year) 420 480 600 
Energy requirements (kWh/m32.7 3.0 3.5 
Model Small Medium Large 
Production capacity (m3/day) 11.5 19.0 38.0 
Cost (RO) 3,000 4,500 6,000 
O&M costs (RO/year) 420 480 600 
Energy requirements (kWh/m32.7 3.0 3.5 

Note: 1 Rial Oman (RO) = 2.58 USD.

Water quality (EC, pH) for the intake, production, and brine waters is presented in Table 3. Also, the table summarizes the disposal means of brines. All the farmers’ units are utilized for producing irrigation water except one, where water is used for drinking and household activities. The volume of brine produced is about 55% of the intake (feed) water volume; disposal is into old wells, protected soil pits, soil surface, or simply outside the vicinity of the farm (Table 3 and Figure 2). Three farmers mentioned that they had to stop operating the desalination units periodically to allow time for brine to infiltrate into the soil. Soils with poor structures have very slow infiltration rates and, therefore, farmers must wait a long time until most of the brines infiltrate into subsurface soil layers. One farmer indicated that he reused some of the brines to irrigate his date palms, which are adapted to survive at moderate salinity levels. No farms had greenhouses and produced water was used to irrigate field crops and date palms. All farmers are highly concerned about the amounts of disposal and the means of disposal. They mentioned that their neighbors are willing to own desalination units but do not due to the difficulty of disposing of the brine. None of the farmers had a permit from the Ministry of Environment and Climate Affairs for their means of disposal of brine.

Table 3

Average values of water quality (in terms of EC and pH) of water associated with desalination units in the Sultanate of Oman and overall disposal means of brines

  Intake water Production water Brine Disposal means of brine 
EC (dS/m) 8.09 0.36 25.6 Soil pits, soil surface, old wells, areas outside farm 
pH 7.2 7.1 7.31 
  Intake water Production water Brine Disposal means of brine 
EC (dS/m) 8.09 0.36 25.6 Soil pits, soil surface, old wells, areas outside farm 
pH 7.2 7.1 7.31 
Figure 2

An example of brine disposal and irrigated groves of date palms.

Figure 2

An example of brine disposal and irrigated groves of date palms.

The energy cost currently paid by farmers is 10 Bz/kWh (0.01 RO/kWh) and the cost of electricity generation in Oman is around 25 Bz/kWh. The cost of desalination of brackish water (i.e., water up to 10,000 mg/L TDS) in the Sultanate of Oman for units owned by the farmers was estimated using a 12% interest rate (which is the prevailing interest rate on small loans in Oman) and 10 year life span (Figure 3); the life span was chosen based on personal communication with the local supplier. The total cost of electricity including distribution is estimated at 50 Bz/kWh. The cost of desalination to the farmer varies from 215 to 310 Bz/m3. The difference is an indirect subsidy. Therefore, the farmers can make a profit at the current subsidized energy prices on the conditions of growing high-value crops. The FAO (2008) stated that the economic return: the farmers of Al-Batinah can make a profit if they grow crops such as peppers, eggplants, cucumbers, onions, okra, carrots, cherry tomatoes, strawberry, and capsicums. It should be noted here that FAO (2008) have not included the cost of brine disposal in this analysis.

Figure 3

The cost of desalination of brackish water (10,000 mg/L) in the Sultanate of Oman for the desalination units.

Figure 3

The cost of desalination of brackish water (10,000 mg/L) in the Sultanate of Oman for the desalination units.

CONCLUSION

Water resources must be managed carefully in the Sultanate of Oman, especially along the coastal strip of Al-Batinah because of the chronic shortage of groundwater. In regions where no other sources of water, e.g., treated wastewater, are available, non-conventional sources of water must be considered to sustain the agricultural sector, and desalination can be an attractive option for providing substantial amounts of good quality water beyond the natural hydrologic cycle. Desalination units are simple to operate and involve low operation and maintenance costs and their high initial cost can be recovered by growing and selling high-value crops in properly controlled environments. The main concern of adopting this technology is the means of brine disposal. More than 50% of intake water is returned back with almost twice the salinity level. Other concerns are high boron and chloride levels in the production water and the impact of low nutrients on soil fertility and structure. One positive aspect is the social impact, where farmers can revive their lands.

The survey conducted among farmers showed that some farmers in the Sultanate of Oman are currently using this technology on their farms. All farmers showed concern regarding brine disposal and are keen on environmentally sound options for its disposal. It is worth mentioning that not all impacts must be considered negative. Desalination, in salt-affected areas, provides good quality water that would otherwise be unavailable. However, the technology is rather expensive and still cost-ineffective unless used in conjunction with another source of water, such as treated wastewater. Furthermore, more research needs to be conducted, especially regarding environmentally sound means for brine disposal and the cost/benefit analysis on a farm income basis.

ACKNOWLEDGEMENT

This study is part of an ongoing research project entitled ‘Desalination for Agriculture’ funded by the Agricultural and Fisheries Funds (AFDF), Ministry of Agriculture and Fisheries, Sultanate of Oman.

REFERENCES

REFERENCES
Ahmed
M. W.
Shayya
D. H.
Mahendran
A.
Morris
R.
Al-Handhaly
J.
2000
Use of evaporation ponds for brine disposal in desalination plants
.
Desalination
130
,
155
168
.
Ahmed
M.
Shayya
W.
Hoey
D.
Al-Handhaly
J.
2001a
Brine disposal from RO plants in Oman and the United Arab Emirates
.
Desalination
133
,
135
147
.
Ahmed
M.
Arakel
A.
Hoey
D.
Coleman
M.
2001b
Integrated power, water and salt generation: a discussion paper
.
Desalination
134
,
37
45
.
Ahmed
M.
Shayya
W. H.
Hoey
D.
Al-Handaly
J.
2002
Brine disposal from inland desalination plants: research needs assessment
.
Water Int.
27
,
194
201
.
Al Barwani
A.
Helmi
T.
2006
Sea water intrusion in a coastal aquifer: a case study for the area between Seeb and Suwaiq, Sultanate of Oman
.
Agr. Marine Sci. Res. J.
11
,
55
69
.
Al Khamisi
S.
Prathapar
S. A.
Ahmed
M.
2013
Conjunctive use of reclaimed water and groundwater in crop rotations
.
Agr. Water Manage.
116
,
228
234
.
Al-Belushi
A. S.
2003
Desertification in Al-Batinah Plain, Sultanate of Oman. PhD Dissertation, Jordan University, Jordan (in Arabic)
.
Ayers
R. S.
Westcot
D. W.
1994
Water Quality for Agriculture, Irrigation And Drainage, Paper 29, rev. 1
.
Food and Agriculture Organization of the United Nations
,
Rome, Italy
.
Bajjali
W.
2003
Evaluation of the groundwater salinity throughout Sultanate of Oman using GIS
.
Barron
O. V.
Ali
R.
Hodgson
G.
Smith
D.
Qureshi
M. E.
McFarlane
D.
Burn
S.
Kumar
A.
Campos
E.
Olewniak
F.
Zarzo
D.
2013
National and regional assessment of opportunities for desalination in Australian agriculture
.
Technical Report to National Centre of Excellence in Desalination in Australia
,
CSIRO Flagship Water for a Healthy Country
,
Australia
.
Barron
O. V.
Ali
R.
Hodgson
G.
Smith
D.
Qureshi
M. E.
McFarlane
D.
Campos
E.
Zarzo
D.
2014
Feasibility assessment of desalination application in Australian traditional agriculture
.
Available at: http://www.awa.asn.au/htmlemails/Ozwater14/pdf/119barron.pdf (accessed 11 January 2015
).
Choudri
B. S.
Al-Busaidi
A.
Ahmed
M.
2013
Climate change, vulnerability and adaptation experiences of farmers in Al-Suwayq Wilayat, Sultanate of Oman
.
Int. J. Climate Change Strat. Manage
5
(
4
),
445
454
.
Choudri
B. S.
Mahad
B.
Ahmed
M.
Al-Sidairi
A.
Al-Nadabi
H.
2015
Relative vulnerability of coastal Wilayats to development: a study of Al-Batinah North, Oman
.
J. Coast. Conserv.
19
(
1
),
51
57
.
Dawoud
M. A.
Al Mulla
M. M.
2012
Environmental impacts of seawater desalination: Arabian Gulf case study
.
Int. J. Environ. Sustain.
1
(
3
),
22
37
.
Desalination Yearbook
.
2011–2012
Water Desalination Report
,
International Desalination Association (IDA)
,
Topsfield, MA
.
Desaldata
2012
Available at: www.idadesal.org/publications/desaldata-com/ (accessed 10 January 2015
).
Elsaid
K.
Bensalah
N.
Abdel-Wahab
A.
2012
Inland desalination: potentials and challenges
. In:
Advances in Chemical Engineering
(
Nawaz
Z.
Naveed
S.
eds
).
InTech Pub.
, doi: 10.5772/2068.
Food, Agriculture Organization (FAO)
.
2003
Desalination of brackish water and seawater, status in California and the USA by K. Tanji
.
Draft report
,
FAO
,
Rome, Italy
.
Food, Agriculture Organization (FAO)
.
2004
Water desalination for agricultural applications
.
Land and Water Discussion Paper 5
,
FAO
,
Rome, Italy
.
Food, Agriculture Organization (FAO)
.
2008
Policy options and alternatives for the cultivation of fodder crops in Al-Batinah Region. FAO Regional Office for the Near East, Cairo, Egypt.
Ministry of Agriculture, Fisheries (MAF), the International Center for Boisaline Agriculture (ICBA)
.
2012
Oman Salinity Strategy Report
.
Muscat, Sultanate of Oman
.
MRMWR (Ministry of Regional Municipalities and Water Resources)
2015
Water resources in the Sultanate of Oman, Muscat, Sultanate of Oman
.
Prathapar
S. A.
Ahmed
M.
Al-Adawi
S.
Al-Sidiari
S.
2006
Treatment and reuse of ablution water from community mosques in Oman: a case study
.
Int. J. Environ. Stud.
63
(
3
),
283
292
.
Vorosmarty
C. J.
Leveque
C.
Revenga
C.
2005
Fresh water
. In:
Ecosystems and Human Well-Being: Current State and Trends
(
Hassan
R.
Scholes
R.
Ash,
N.
eds
).
Island Press
,
Washington DC
, pp.
165
207
.
Zarzo
D.
Campos
E.
Terrero
P.
2012
Spanish experience in desalination for agriculture
.
Desalin. Water Treat.
51
,
53
66
.