Disinfection by Candle Light

I'm not sure whether the light from a candle is sufficient to disinfect any significant amount of water via this new photocatalyst, but the implications of such a material could revolutionise household water filtration. 

Today, many people have simple carbon-based water filters in their homes.  These are fairly effective against heavy metals, certain chemicals, and some microorganisms.  To be sure that your water is completely free from bacteria and viruses, however, reverse osmosis or UV disinfection are necessary.  But these systems tend to be bulky, energy intensive, and expensive. 

A photocatalyst that works under normal visible light would mean that you could just leave a jug of water with the filter submerged on a table in the open, and voila, bacteria-free water! What's more, the photocatalyst is said to be able to retain its disinfecting abilities for up to 24 hours after being exposed to light.  So if you've left said jug of water exposed to light for a short while, you can stuff it in the fridge and it'll continue the disinfection process. 

That said, I'm not convinced that all this purification is truly necessary.  Perhaps in certain rural or developing countries where water is sourced directly from rivers and wells, which could be contaminated.  Or in old houses where water pipes may not have been used in a long time, resulting in the growth of bacteria.  But for the most part, if those glowing water quality reports from our utilities are to be believed, I'm not sure what else our small little home systems hope to achieve.  If you must, do at least try to get a sample of the water from your tap analysed by a certified laboratory before investing heavily in some expensive water treatment system that the friendly saleslady insists is vital for your health. 

 Above: Visible Light Photocatalyst by Professor Jian Ku Shang

Source: University of Illinois, Urbana-Champaign, News Bureau

Main source:
New Visible Light Photocatalyst

Micro Desalination Units

Yesterday, I mentioned that Siemens was fast tracking its desalination system.  And I guess I now know why.  It seems there're a whole lot of promising desalination technologies hot on its tail.  Just over a month ago, I saw an exciting demonstration of a suitcase unit from Canadian Saltworks Technologies (though their low energy requirements are largely a result of tapping waste heat and solar energy).  And now, there is this -- a desalination device that could fit in my handbag!

MIT scientists have come up with a new method of desalination, known as ion concentration polarization.  Basically, an ion-selective membrane that repels all salts and microbes is placed in the salt water so water that does flow through is clean.  This means no high energy costs of forcing water through membranes like in reverse osmosis, and no membrane fouling since the salts are repelled from the membrane. 

And it gets even better.  A 20cm diameter wafer can hold enough of these units so that 360L/day of water can be produced.  Here in Singapore, people use about 155L of water everyday for all their daily needs including showering and cooking, so this would comfortably provide 2 people's supply of water in a handy portable device! 

Nevertheless, there are some downsides to this system.  Uncharged contaminants, mostly industrial pollutants, can't be removed by this method, so the unit has to be connected to some other filtration system.  The scientists think a simple charcoal filter would work too.  And the energy consumed, while definitely lower than a reverse osmosis system of the same capacity, would still be higher than the unit production cost of a full scale plant. 

The scientists estimate it'll be another 2 years before this little unit hits the shelves.  They're thinking of disaster relief applications.  I think it might actually be a huge hit for beach events.  No more cartons and cartons of mineral water bottles.  Just a few of these nifty desalination units. 

Above: A single unit of the desalination device.

Photo from MIT News Office.

Main Source:

A System that's Worth its Salt

Queensland and Coal-Seam Gas Water

Over the last two years, Queensland, Australia's water situation seems to have been growing from strength to strength. Abundant rainfalls have helped to bring reservoir levels up from a low of 16% in 2007 to more than 90%. And now, there is the strong possibility of a new water source: coal-seam gas water.

Coal-seam gas, also known as coalbed methane, is natural gas that is found in the cracks in coal. Water is a by-product of coal-seam gas extraction, and in Queensland, up to 420megalitres per day (approx 90mgd) of brackish water is expected to be produced if proposed coal-seam gas operations go ahead. The Queensland government has reportedly legislated against simple evaporation of this water, so companies have been looking into various methods of treating it.

One option has been to treat the water to potable standards by reverse osmosis. This could contribute close to 15% of Queensland's daily water needs. However, there have been strong protests from farmers concerned that the extraction of water could draw down the water table and pollute the underground aquifers that they currently get their water from. With the 2008 demise of water reuse plans due to strong public opposition still fresh on people's minds, one cannot help but wonder how this will pan out.

Perhaps in anticipation of the public outcry, Santos, one of the coal-seam gas companies, is going in a slightly different direction. They are spending A$50mil to plant 2 million Chinchilla hardwood gum trees on a piece of land close to the gas site. These trees are particularly tolerant to the brackish water, and could later be harvested or used for carbon sequestration. More importantly, Santos estimates that this will cost about half that of an equivalent reverse osmosis plant.


Main Source:
Gas Boom's Watery Legacy

GWI Newsletter -- Siemens' Silver Bullet (Part 4)

Siemens' target of 10% growth in water, twice the rate at which the market is expected to grow, made headlines in this article.  What interested me more, however, was the update from Chuck Gordon (CEO of Siemens Water Technologies) himself that Siemens intended to have a demonstration unit of its revolutionary desalination plant ready by next fall.  Seeing as he comes from the Northern hemisphere, I suppose that means September 2011, which is really really soon!

In 2008, Siemens won a challenge call by Singapore's Environment and Water Industry Development Council, to develop a system that would half the energy requirements for desalination.  Desalination is notoriously energy intensive which means high costs and poor environmental image, hence most countries see it as an option of last resort.  Today's energy solutions for desalination are largely centred about the effective harnessing of alternative energy sources and clever ways of configuring the system so energy usage is optimised.  Using electro-deionisation (EDI), Siemens believe they have a truly disruptive technology on hand that will reduce the gross energy consumption. 

I'm not very sure what exactly this game changing technology of Siemens' is, since EDI in and of itself is not unfamiliar to the water industry.  I understand that lab tests have gone very well to show that the technology works, though costs are still a slight challenge. That could be a real problem especially if all the energy savings just end up paying off the high cost of the system.  On the plus side, Siemens is certainly well ahead of schedule -- they were only due to finish their lab tests by mid 2011, but I hear they intend to wrap that all up by SIWW 2010.  Just two years to develop a disruptive technology?? I thought that was only in the digital media industry.  Maybe those water innovators are finally rousing from their slumber. 

Main sources:
Siemens Targets 10% Growth in Water
Siemens to Develop Innovative Seawater Desalination Technology