ppt - IIHR – Hydroscience & Engineering

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Desalination by pervaporation for subsurface irrigation in arid regions
Dr Michael Templeton
Department of Civil and Environmental Engineering
Imperial College London
What is the problem?
 Clean fresh water is an increasingly scarce resource
 Groundwater supplies are being abstracted faster than they are being
replenished and are becoming salted
 Agricultural land is being polluted by irrigation water itself and by agrichemicals
 There is an increasing demand for food crops to support growing
populations
 There is an increasing demand for non-food crops (e.g. biofuel crops)
What is pervaporation?
 Specially constructed material – non-porous hydrophilic polymer
 Water permeates across the surface and condenses on the opposite
side as moisture
 Virtually all non-water constituents are rejected (e.g. salts, microbes,
organics)
 When partial pressures are balanced, water transfer stops
 The new idea - to construct irrigation piping out of this material
 Partnership with Design Technology & Irrigation Ltd (DTI Group),
based in Brighton
How does it work?
What does a pervaporative material look like?
Does it work?
Does it work?
Does it work?
 Tested in the UK (Eden project), Middle East, USA, and South
America
 Trial crops have included peppers, tomatoes, strawberries, radishes,
beans, lettuce, potatoes, grass, vines, sunflowers, and various types
of trees (cherry, banana, Acacia)
 Major trial in Abu Dhabi currently – 200 Prosopis trees growing in 45
ºC watered with highly saline untreated groundwater (140,000 ppm!)
 Possibly better crop uniformity and yield - i.e. one trial yielded higher
radish biomass
What are the advantages?
 Allows the use of otherwise unusable water resources (e.g. brackish
water, seawater)
 By definition, it is an efficient water delivery process – impossible to
over-water; potential for significant reduction in water use
 Easy to operate and manage
 No requirement for high pressure input (unlike other membrane
filtration processes)
What are the challenges?
 It is not possible to provide nutrients to the plants through this system
 Some plants have shown better aptitude for this method than others
 Currently more expensive than drip irrigation (but it is more efficient
and allows the use of water resources that would be otherwise
unusable)
 Disposal of the reject water must be considered
What are some research questions?
 What are the limits of water quality that are feasible?
 How do different soil characteristics influence water transfer rate?
 How can fouling and salt accumulation best be managed?
 What are the limits of pipe diameter and thickness?
 When is this technology more favourable/appropriate compared to
drip irrigation or other irrigation techniques?
 What is the pattern/rate of crop growth when a new irrigation project is
started with this technology?
 Do water-stressed plant roots develop differently and have different
requirements than plants under un-stressed conditions?
 Are plants grown in this way as healthy / productive as those grown
by alternative irrigation methods?
Interested in collaborating?
 Dr Michael Templeton, Imperial College London
Tel: +44 (0)207 594 6099
Email: [email protected]
Web: www.imperial.ac.uk/people/m.templeton
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