seawater greenhouse-a restorative approach to agriculture gwf 1220

Suggested Citation: Paton, C. 2012, ‘Seawater Greenhouse: A restorative approach to agriculture’, GWF Discussion Paper 1220, Global

Seawater Greenhouse: A restorative approach to agriculture

Charlie Paton Managing Director of Seawater Greenhouse Ltd., United Kingdom

Discussion Paper 1220 May 2012

This article provides an overview of two seemingly intractable problems – freshwater shortages and brine discharge from desalination. The author describes an innovative new technology which attempts to resolve these problems and provide a solution for crop cultivation, reforestation and realising the value chain of salt, minerals and nutrients from seawater

The Global Water Forum publishes a series of discussion papers to share the insights and knowledge contained within our online articles. The articles are contributed by experts in the field and provide original academic research; unique, informed insights and arguments; evaluations of water policies and projects; as well as concise overviews and explanations of complex topics. We encourage our readers to engage in discussion with our contributing authors through the GWF website.

Keywords: Seawater Greenhouse, desalination, brine discharge, reforestation, water shortage, agriculture.

In arid and semi-arid areas such as around the

Arabian Gulf, the Red Sea, and the

Mediterranean Sea, the scarcity of freshwater

resources has led to increasing use of

desalination plants to produce water.

However, all conventional desalination

techniques reject concentrated brine back into

the sea at roughly double the salinity of the

intake. As a consequence, the salinity in these

semi-enclosed seas rises. Increased salinity

has an adverse effect on all marine life and

there are very few plants or fish that can

survive a doubling of salinity from 3.4% to 6%.

In 2008 about 18.4 million m3/day was

discharged into the Arabian Gulf, 9.8 million

m3/day into the Mediterranean Sea, and 6.8

million m3/day into the Red Sea. That is a

total of 35 million tons/day and the volume is

expected to grow1. This effect is made worse

by reduced inflow from rivers such as the

Euphrates and Tigris, and high rates of

evaporation2.


Figure 1. Salinity in Arabian Gulf. Source:

Allsop & Yao (2010).

For a number of technical reasons,

conventional desalination techniques have to

discharge concentrated brine as their

processes cannot function with high salinity.

However, at Seawater Greenhouse, we have

developed a technology that can. The idea of

the Seawater Greenhouse is to convert these

two seemingly intractable problems – a

shortage of fresh water and brine discharge

from desalination – into an elegant solution

for crop cultivation, reforestation and

realising the value chain of salt, minerals and

nutrients from seawater.

Seawater Greenhouse

Just as with desalination, the last few decades

have seen tremendous growth in conventional

greenhouses around the world. There are now

some 200,000 hectares of greenhouses

around the Mediterranean, and over 1 million

in China, where 30 years ago, there were

almost none. This is because yields that are

achieved in greenhouses can be 10 to 100

times greater than yields achieved outside.

They also enable high value crops to be grown

‘out of season’.

The Seawater Greenhouse enables year-round

crop production in some of the world’s hottest

and driest regions. It does this using seawater

and sunlight. The technology imitates natural

processes, helping to restore the environment

while significantly reducing the operating

costs of greenhouse horticulture. In addition

to not having to discharge concentrated brine,

it also benefits from the fact that high salinity

water has a powerful biocidal or sterilising

effect on the air that passes through it. This

reduces or eliminates airborne pests.

The most important benefit of the Seawater

Greenhouse is that it cools and humidifies

large volumes of air at very low cost, and to do

this, it must evaporate large volumes of

seawater, thereby dealing with the discharge

from desalination. One hectare of Seawater

Greenhouse near the coast will typically

evaporate 50 tons of water/day, but this will

increase 2-3 fold in regions of low humidity.

The effect is illustrated in Figure 2.


Figure 2. Evaporative cooling properties of

air at 30ºC.

With reduced humidity, lower temperatures

(the wet bulb temperature) are achieved and

larger volumes of water are evaporated. For

example, if we pass air at a temperature of

30ºC and a relative humidity of 70% into a

nominal 500m2 Seawater Greenhouse, the air

will be cooled down to 26ºC and two tonnes of

water will be evaporated in 24 hours. If the

incoming air has a relative humidity of 20%,

the air will be cooled down to 17ºC and nearly

three times as much water is evaporated.

Figure 3. Seawater Greenhouse, Tenerife.

The most significant benefit of the process is

that the combination of lower temperature

and higher humidity reduces plant

transpiration up to 10-fold and enables

delicate crops such as lettuce and French

beans to grow in a hot, arid location.

Further, the beneficial effect of the humid

exhaust air creates a zone of locally higher

humidity which encourages vegetation. The

photographs in Figure 4 were taken two years

apart in Oman.

Figure 4. Seawater Greenhouse, Oman.

Relative humidity almost invariably falls with

increasing distance from the coast. Lower

humidity means that lower temperatures are

achieved and more water is evaporated. The

map below illustrates typical daytime

humidity across the UAE, with relative

humidity at the coast above 70% yet falling to

15% further inland.


Figure 5. UAE relative humidity chart.

Evaporating large volumes of water in the

GCC region could have many environmental

benefits and the Seawater Greenhouse has a

similar effect on the local environment to an

area of forest in terms of the amount of water

vapour it produces and the consequent cooling

achieved. For example, one hectare of

greenhouse will evaporate ~ 100 tons of

water/day, consuming 60MWh of heat in the

process. Effectively, it reduces the

temperature of air from the dry bulb to the

wet bulb temperature.

If implemented on a large scale, it makes

sense to evaporate the water some distance

from the coast. It may also be beneficial to

evaporate it at the base of a mountain, as air

cools with increasing height, typically by 1ºC

for every 100m of elevation, so there is a

greater chance of contributing to rain or dew

by increasing the humidity of air that blows up

a mountain.

Figure 6. Locating at the base of mountains

increases the humidity of air blowing up

thereby encouraging rain.

Just add water

Drought, desertification, food shortages,

famine, energy security, land use conflict,

mass migration and economic collapse,

climate change and CO2 sequestration are all

issues that can be overcome by increasing the

supply of water. Present methods of supply in

arid regions include; over-abstraction from

groundwater reserves, diverting water from

other regions, and energy-intensive

desalination. None of these are sustainable in

the long term and inequitable distribution can

lead to conflict.

The growth in demand for water and

increasing shortages are two of the most

predictable scenarios of the 21st century.

Agriculture is the primary pressure point3 (see

The state of the world’s land and water

resources). A shortage of water will also affect

the carbon cycle as shrinking forests reduce


the rate of carbon capture, and will disrupt the

regulating influence that trees and vegetation

have on our climate. Fortunately, the world is

not short of water, it is just in the wrong place

and too salty. Converting seawater to fresh

water and water vapour in the right places

offers the potential to help solve all these

problems.

References

1. Al Barwani, H.H. and Purnama, A. (2008), ‘Evaluating the Effect of Producing Desalinated Seawater on Hypersaline Arabian Gulf’, European Journal of Scientific Research, Vol. 22, No. 2, pp. 279-285. 2. Bashitialshaaer, R., Persson, K.M. and Aljaradin, M. (2011), ‘Estimated Future Salinity in the Arabian Gulf, the Mediterranean Sea and the Red Sea Consequences of Brine Discharge from Desalination’, International Journal of Academic Research, Vol. 3, No. 1, pp. 133-140. 3. FAO (2011), ‘The State of the World’s Land and Water Resources’, United Nations Food and Agriculture Organisation, Rome. 4. Allsop, N.K. and Yao. F (2010), ‘Experiences of hybrid Ocean modelling of the Persian Gulf on the Blue Gene/P’, Available at http://www.hpc.kaust.edu.sa/events/Supercomputing__44___November_2010/posters/KAUST_NKA_SC10.pdf.

About the author(s)

Charlie Paton studied at the Central School of Art and Design in London. Working his way through College as an electrician – starting his career with ITN as a studio assistant on the Apollo 11 moon landing (1969), he went on to become a lighting designer and maker of special effects. Charlie’s fascination with light and plant growth led to the concept for the Seawater Greenhouse. Starting with an experimental pilot in Tenerife, he has designed and built further Seawater Greenhouses in Abu Dhabi, Oman and Australia. For more information see the Seawater Greenhouse website.

About the Global Water Forum

The Global Water Forum (GWF) is an initiative of the UNESCO Chair in Water Economics and Transboundary Governance at the Australian National University. The GWF presents knowledge and insights from some of the world’s leading water researchers and practitioners. The contributions generate accessible and evidence-based insights towards understanding and addressing local, regional, and global water challenges. The principal objectives of the site are to: support capacity building through knowledge sharing; provide a means for informed, unbiased discussion of potentially contentious issues; and, provide a means for discussion of important issues that receive less attention than they deserve. To reach these goals, the GWF seeks to: present fact and evidence-based insights; make the results of academic research freely available to those outside of academia; investigate a broad range of issues within water management; and, provide a more in-depth analysis than is commonly found in public media.

If you are interested in learning more about the GWF or wish to make a contribution, please visit the site at www.globalwaterforum.org or contact the editors at [email protected].

The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance,


UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.

Copyright 2012 Global Water Forum.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivative Works 3.0 License. See http://creativecommons.org/licenses/by-nc-nd/3.0/ to view a copy of the license.

seawater greenhouse-a restorative approach to agriculture gwf 1220

Documents