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: m. templeton@imperial. ac. uk Web: www. imperial. ac. uk/people/m. templeton
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