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Forward Osmosis – Solving Tomorrow’s Water Challenges Using Nature’s Remedy

Nature has an ingenious way of extracting water, but does it have the potential to solve many of today’s global water challenges? Before going into more details on how nature’s way of extracting water can help cut energy usage in water treatment processes, an appreciation is needed of why energy reduction in water treatment is an essential prerequisite for continued global development.

Since water is used in all energy production processes and energy is used to generate fresh, potable water from impaired sources, water and energy are two sides of the same coin. Factor in that global fresh water resources are rapidly declining and energy prices are one the rise due to over-utilization of fossil fuels, you quickly realize that energy reduction in water treatment processes will make a tremendous positive impact on the challenges faced in this water-energy nexus.

Moving back to nature’s way of extracting water, you may have wondered how trees are able to extract water from the soil in which they grow to the leaves in the treetops? Or how mangroves are able to extract fresh water from the seawater surrounding their roots? Given the obvious lack of electrically powered high pressure pumps, nature has come up with it’s own way of generating the pressure needed to transport water in trees and to extract fresh water from seawater in mangroves. It turns out that nature extracts water by utilizing the principle of forward osmosis in which water diffuses spontaneously (and without the input of energy) across a semi-permeable membrane from a low concentration solution on one side of the membrane to a high concentration solution on the other side of the membrane. The driving force for forward osmosis processes being the difference in osmotic pressure between the aqueous streams on either side of the forward osmosis membrane.

Coming back to the trees and mangroves mentioned earlier, the intracellular solution of root cells contains high concentrations of sugars and other dissolved molecules, which in turn generate a large enough osmotic pressure to extract water from soil and seawater respectively and transport this water throughout the stems and leaves of these amazing biological systems.

Now, how can water transport in trees help solve the looming water challenges facing our world today? Well, fortunately scientists have been able to develop artificial forward osmosis membranes and systems for industrial water treatment applications. And since forward osmosis systems do not require electrical energy inputs other than the energy needed to pump solutions across its membranes, it is potentially possible to reduce the overall energy consumption of water extraction by 90% compared to traditional pressure driven technologies such as reverse osmosis and nano-filtration.

Wide-spread adoption of forward osmosis systems in industry is still limited due to lack of high-performing, large-scale system capacity as well as industry preference towards proven technologies with long-term operational track records.

A number of startups and tech companies are working in the area.

 

Oasys Water 

Porifera

HTI Water

As well as ongoing research projects at a number of universities and labs around the world are working hard to commercialize forward osmosis technologies, so don’t be surprised if you – in the near future – start running into examples of forward osmosis being used to treat water in industries or even households.

Reinventing Desalination

by Richard T. Stuebi

Many informed observers consider the inadequacy of clean drinking water to be one of the world’s most serious problems. By some estimates, 20% of the human population lacks access to good water supplies.

That’s not to say that these people live nowhere near water: indeed, most of humankind lives fairly close to an ocean. However, seawater is saline, and desalination is required to render it usable as drinking water.

Desalination is no theoretical pipe-dream: two desalination approaches have long existed to remove salt from water, distillation and reverse-osmosis. Regrettably, both are rather energy-intensive. No problem for the wealthy, but the world’s ultra-poor populations typically cannot afford either the construction or the operation of such desalination technology. And, so they go without good drinking water.

As reported in an article entitled “Current Thinking” in the October 31 issue of The Economist, a pair of entrepreneur/inventors (Ben Sparrow and Joshua Zoshi) from Vancouver BC has launched a company called Saltworks Technologies that to commercialize a completely novel “thermo-ionic” approach for desalination, based on evaporation and ionic conduction, powered mainly by sunlight.

There are three beauties of this new approach concocted by Saltworks:

1. It is based primarily on solar thermal energy sources – and sunlight is often plentiful in some of the world’s poorest and most remote corners.
2. It theoretically requires only about 30% of the electricity requirement of the most efficient reverse-osmosis approaches now available for desalination.
3. It should be upward- and downward-scalable, making it a plausible solution for megacities and tiny villages alike.

All three of these factors imply that the Saltworks technology could dramatically reduce the cost of desalination and bring it into economic reach for the untold billions of the world’s thirsty poor.

This is yet another shining example of how high-tech innovators are solving the world’s biggest problems. The future health of our planet and success of our species demands more people like Mssrs. Sparrow and Zoshi. And, political, corporate, financial, academic and civic leaders around the globe would be well-advised to keep improving the environments within which those like Sparrow and Zoshi come up with and pursue unconventional and sometimes brilliant ideas.


Richard T. Stuebi is a founding principal of the advanced energy initiative at
NorTech, where he is on loan from The Cleveland Foundation as its Fellow of Energy and Environmental Advancement. He is also a Managing Director in charge of cleantech investment activities at Early Stage Partners, a Cleveland-based venture capital firm.

Low Cost Desalination – Saltworks Breakthrough

Canadian firm, Saltworks Technologies, just came out of stealth in relation to their desalination technology, which they claim reduce the electrical energy required for desalination by over 70%. They report they can produce 1m3 of water with 1kW hour of electrical energy, compared to the 3.7kWhr per m3, which is what is currently achievable using reverse osmosis with the use of energy recovery devices.
So how to they do it? Well its novel. It appears to be a new approach. And novel and new are two things scarce as hens teeth in relation to desalination technologies.
They use solar heat (or waste heat) to evaporate water and concentrate salt water. They are converting solar energy into osmotic energy by doing this. They then use this osmotic energy to desalinate water.
They then expose the concentrated salt water to two separate solutions of regular salt water via two different ‘bridges’, one which is porous to chloride ions, the second which is porous to sodium ions.

The sodium and chloride ions migrate across the respective bridges into the salt water solutions to equalise the difference in ion concentration between the solutions.
This creates two charged solutions, one enriched with sodium ions (positively charged), the second enriched with chloride ions (negatively charged).
These two solutions are then exposed across two similar bridges to the water to be desalinated. This draws sodium ions into the chloride enriched solution and draws chloride ions into the sodium enriched solution: Net result desalination. Doing this they reckon they can produce 1m3 of water using 1kWh of electrical energy, which is used to pump fluids around the pipework.
Because the system is not under pressure, they can use plastic pipes instead of steel pipes, potentially reducing capital costs also.

I met with Saltworks about six months ago in Vancouver and I was impressed by the methodical way they have been going about technology commercialisation. Despite winning a technology innovation award in British Columbia in May 2009, they have kept this remarkably quiet. An article in the Economist provides a good review of this.

Paul O’Callaghan is CEO of Technology Assessment Group, O2 Environmental Inc and author of Water Technology Markets.

There’s water in dem dar clouds!

With seawater covering seventy-one per cent of the Earth’s surface, at an average depth of four kilometers, and another 1,000,000,000,000,000 liters of water in the first kilometer alone of the earth’ atmosphere, water could hardly be described as a rare element. Its more a case of ‘water water everywhere and not a drop to drink‘. I’m going to highlight a few different ways in which renewable energy can be used to produce drinking water.
One of the readers last week commented that use of wind turbines or wave energy to power desalination would be a great idea. Well in Perth Australia they are doing exactly that. Perth Australia has now established one of the largest desalination plants outside of the Middle East and set up a wind farm to power it. Electricity for the desalination plant, which has an overall 24MW requirement, comes from the new 80MW Emu Downs Wind Farm, located 30km east of the town of Cervantes. (anyone else see the irony here… Miguel Cervantes, …Don Quixote, Windmills?)

Speaking of windmills, another Australian, Max Whisson, an energetic septuagenarian inventor, believes he can solve the current water crisis with his Water Windmill invention, a unique technology to extract moisture from the atmosphere. The concept is to use windmills to cool air and extract water directly from the air and was partly inspired from an African beetle, Stenocara, who manages to be completely water sufficient by standing on his head in the desert and using cooling plates on his body to extract water vapor from the air. Here is a link to a video
showing the wind turbine in operation. The “Whisson Windmill” will make it possible to get adequate water anywhere at any time, drought or no drought” says Dr. Whisson. Given that between 1% and 4% of the earths atmosphere is water vapor, he may be onto something.
Max also had another concept he called a ‘Water Road’ which Nick Bruce featured on his podcast, the CleanTech Show. In the “Water Road”, seawater is transported inland in black pipes covered with Perspex; solar energy heats up the water at it travels through the pipes to 70-80 C. Water vapor is produced and condensed several hundred kilometers inland to provide water for irrigation. The genius of both of his ideas is the direct conversion of primary energy to the desired end result which is pure water. They are very early stage, conceptual as far as I can tell.

Another technology being developed by the New Mexico State University uses low grade heat and a vacuum to run a distillation process. The system can convert saltwater to pure drinking water on a round-the-clock basis – and its energy needs are so low it could be powered by the waste heat of an air conditioning system. At the risk of losing you, here’s the 101 of how it works. The system consists of two 30-foot vertical tubes – one rising from a tank of saline water and the other from a tank of pure water – which are connected by a horizontal tube. The natural effect of gravity creates a vacuum in the air space above the water column. The lower pressure in the headspace causes water to evaporate at a lower temperature, (this is why water boils at lower temperatures on top of a mountain). Then they use waste heat, for example from an air conditioning system, to heat up the saline water (e.g. seawater or brackish groundwater) to 10 -150 C more than the freshwater. Water vapor from the salt water column travels across the horizontal bridge and condenses in the freshwater column.
Commenting on its energy efficiency, one of the inventors, Nirmala Khandan, an environmental engineering professor in NMSU’s Department of Civil Engineering said “That’s the trick of this vacuum, we don’t have to boil the water like normal distillation, so you can use low-grade heat like solar energy or waste heat from a diesel engine or some other source of waste heat.”
So there you have it. Both energy and water are present in abundance on the planet and if we can use our ingenuity, we may be able to harness and access both in a sustainable manner.

Paul O’Callaghan is the founding CEO of the Clean Tech development consultancy O2 Environmental. Paul is the author of numerous papers environmental technologies and lectures on Environmental Protection technology at Kwantlen University College. He is chair of a technical committee on decentralized wastewater management in British Columbia, is a Director with Ionic Water Technologies and an industry expert reviewer for Sustainable Development Technology Canada.