desalination by the numbers · web viewthe issue: the water crisis increasing water scarcity in...
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1. THE ISSUE: THE WATER CRISIS
Increasing water scarcity in many regions
Around 700 million people in 43 countries suffer from water scarcity today.
2.1 billion people do not have water in their homes.
3.4 million people die every year from water-born and water related diseases.
By 2025 two-thirds of the world’s population could be living under water stressed conditions.
Given that only 2.5 % of the earth’s water is fresh and the other 97.5 % of our water is salty ocean or brackish
groundwater, scientists are turning to examine the applications of desalination.
CREDIT: wwww.arts2science.org
2. CURRENT METHODS: DESALINATION
Current desalination processes have high energy, construction, and operating costs, requiring enormous water pressures and constant maintenance and monitoring of filters.
Primarily REVERSE OSMOSIS using filters / membranes
High ENERGY use
High CONSTRUCTION COSTS
High OPERATING COSTS constant MAINTENENCE & FILTER CLEANING
Other options include:
DISTILLATION (stills) not scale-able
FORWARD OSMOSIS – high costs
ELECTRICALLY CHARGED OSMOSIS -high costs
NEW MEMBRANES – developing
Desalination by the Numbers
18,426 The total number of desalination plants worldwide (as of June 30, 2015)
More than 86.8 million cubic meters per day The global capacity of commissioned desalination plants (as of June 30, 2015)
22.9 billion US gallons The equivalent of 86.8 million cubic meters per day (as of June 30, 2015)
150 The number of countries where desalination is practiced
More than 300 million The number of people around the world who rely on desalinated water for some or all their daily needs
3. GRAPHENEAdvances in nanoscale technology suggest that a much more cost effective and environmentally friendly desalination process using graphene is possible. Graphene’s structure and innate properties make it an ideal candidate to improve the process. Graphene consists of a single atom thick layer of carbon atoms bonded in a honeycomb structure. This allows for high water permeability. Its strength allows it to withstand high water pressures.
WHAT IS GRAPHENE?
GRAPHENE IS A 2-DIMENSIONAL NETWORK OF CARBON ATOMS IN A SINGLE LAYER
THESE CARBON ATOMS ARE BOUND WITHIN THE PLANE BY 3 STRONG ATOMIC BONDS
INTO A HEXAGONAL STRUCTURE (RESEMBLING A HONEYCOMB)
IT IS A BASIC BUILDING BLOCK FOR GRAPHITIC MATERIALS OF ALL OTHER DIMENSIONALITIES.
IT CAN BE WRAPPED UP IN TO FULLERENES, ROLLED INTO NANOTUBES OR STACKED INTO 3D GRAPHITE.
CREDIT: www.hindawi.com
PROPERTIES OF GRAPHENE:
STRENGTH: 200-300 times stronger than steel
TENSILE STRENGTH: > 1 TPa
HARDER than diamond
ELECTRICAL CONDUCTIVITY: 100 times higher than copper wire
>2000S/m
FLEXIBILITY: Stretchable up to 20% of original length
DURABLE: under prolonged contact with salt water
RESISTANT: to fouling by biological materials
THE TENSILE STRENGTH OF GRAPHENE EXCEEDS 1 TPA
1 Tera pascal (TPa) = 1012 pascals (Pa)
The pascal (Pa) is the SI unit of pressure, equivalent to one newton per square meter.
CREDIT: https://twitter.com/generalelectric/status/446333123635052544?lang=en
WHO DISCOVERED GRAPHENE?
ANDRE GEIM & KONSTANTIN NOVOSELOV of UNIVERSITY OF MANCHESTER, ENGLAND discovered graphene in 2004. They essentially used scotch tape to peel layers of graphene off graphite!
IN 2010 THEY WON THE NOBEL PRIZE IN PHYSICS for ground breaking experiments with graphene.
TYPES OF GRAPHENE:
SINGLE LAYERED GRAPHENEA single atom sheet of bonded carbon atoms freely suspended or adhered to substrate.
FEW LAYER GRAPHENE / MULTILAYER GRAPHENEStacked layers of graphene
GRAPHENE OXIDEChemically modified graphene prepared by oxidation and exfoliation
GRAPHIC CREDIT: www.tiochemicals.com
4. POTENTIAL SOLUTIONS
Benefits of using graphene membranes in place of current filters include decreased energy costs (up to 50%) due to greater water flow and permeability, decreased cost of construction and less maintenance. Additionally, the flexibility graphene and graphene oxide suggest improvements and simplifications to desalination and purification processes, such as graphene oxide sieves, and single step filters that can make clean water accessible to the broader population, including areas of poverty.
LATEST RESEARCH & TECHNOLOGIES
Scientists at MIT have developed a new way to produce graphene using a chemical technique that breaks graphite into graphene sheets, optimizing the quality of graphene for desalination while decreasing the time, money, and labor involved in production. They have engineered pores of 0.8-1.6nm in the sheets to allow water molecules to pass through while stopping the passage of salt molecules. (1)
Scientists at the University of Manchester in England are developing a graphene-oxide membrane that works as a sieve. (2)
Australian scientists of the Commonwealth Scientific and Industrial Research Organization (CSIRO) have made a
new filter made from soybean-based graphene film. The filter is called Graphair and is made from a graphene film
with microscopic channels that trap pollutants while letting clean water through. The Graphair technology can grow
graphene film in regular air, making its production faster, simpler and cheaper. It transforms soybean oil, a renewable,
natural material, into graphene films in one step. (3)
Graphic representation of GRAPHENE OR GRAPHENE OXIDE MEMBRANE
POLLUTED/ SALT WATER CLEAN/ DESALINATED WATERCREDIT: https://www.sciencedirect.com/science/article/pii/S0008622317301045
BARRIERS
COST OF PRODUCTION $
This is now decreasing significantly with new production methods
NANOTECHNOLOGY CHALLENGES
Hard to create pores of less than 1nanometer in graphene sheets
It can be done (MIT, 2017)
Graphene oxide membranes swelled in salt water.Applying epoxy resin prevents this (University of Manchester, 2017)
CREDIT: www.bbc.com/news/science-environment-39482342
Forecast of Desalination Costs for Medium and Large Size Projects
Source: International Desalination Association http://www.iwa-network.org/desalination-past-present-future/
Year 2016 Within 5 Years Within 20 Years
Cost of Water
(US$/m3)
0.8 – 1.2
0.6 – 1.0
0.3 – 0.5
Construction Cost
(US$/MLD)
1.2 – 2.2
1.0 – 1.8
0.5 – 0.9
Electrical Energy Use (kWh/m3)
3.5 – 4.0
2.8 – 3.2
2.1 – 2.4