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Microfluidics and sunlight combined to purify water

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January 16, 2011

Researchers have created a microreactor that purifies water utilizing sunlight and microfl...

Researchers have created a microreactor that purifies water utilizing sunlight and microfluidics

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It has been known for some time now that sunlight can be used to purify drinking water. The practice of Solar Water Disinfection (SODIS) basically involves just leaving water sitting in direct sunlight, where a combination of heat and UV rays kill off waterborne pathogens – the process is called photocatalysis, and it’s what’s at work behind both the Solaqua water purification device, and a system recently created by students from the University of Washington. Now, researchers from Hong Kong Polytechnic University have taken things a step further, by combining photocatalysis with microfluidics in a microreactor.

The team from Hong Kong Polytechnic created a planar microfluidic reactor, which consists mainly of a rectangular chamber made up of two facing glass plates, each coated with titanium dioxide (Ti02) – this is the active ingredient in many sunscreens. Tainted water passes between the plates via microchannels, to maximize the surface-to-volume ratio. When exposed to sunlight, the Ti02 releases electrons, which in turn break down contaminants in the water.

"These two technologies have been developed in parallel but there have been few efforts to employ the natural synergy between them," said study author Xuming Zhang. "Our results showed a dramatic improvement in the efficiency of the photocatalyst." When compared to a bulk container with the same amount of water, pollutant (methylene blue), and Ti02 surface area – but without the microchannels – they were actually able to improve the photoreaction efficiency by more than 100 times.

Microfluidics and sunlight combined to purify water

While the space between the plates is very small, Zhang intends to increase the reactor’s capacity by scaling the plate size up to two square meters (21.5 square feet), with an ultimate goal of being able to process 1,000 liters (264 US gallons) per hour – the current version has plates that measure just 5 x 1.8 cm (about 2 x 0.7 inches). If the larger version works as well as hoped, he envisions multiple devices being used together in industrial applications. Before that can happen, however, he wants to increase the oxygen availability in the reactor chamber, and boost the light sensitivity of the Ti02.

The research was recently published in the journal Biomicrofluidics.

Images courtesy Xuming Zhang

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
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3 Comments

But i see two problems

1. it will be far more expensive then just leaving watter in a bottle

2. it will be far less available then an empty bottle

(so both will result big problems in emerging countries, where it is mainly focused)

3. it will probably need some cleaning from polutions on that TiO2 plates (btw it is TiO2, not Ti02).

but it can be a good solution for cleaning water in houses, for military etc. travels to emerging countries ...

P.S.: IMO it would be great to try to combine it with electricity/heat generator

a) it would take heat from the water (what is in most cases very welcomen), so it is colder

b) the heat can be used to generate electric or heating a house.

c) both functions will take about the same space as one panel

d) all resulting in higher efectivity (lower price per resulting function)

Tomáš Kapler
17th January, 2011 @ 02:20 am PST

I was under the impression that titanium dioxide, used in sunscreens, was in the form of small white flakes, which merely reflect sunlight back, and do not have any chemical activity.

Presumably, the water would have to be tested for its purity, after passing through the processor? This is one of the problems the water bottle method.

windykites1
17th January, 2011 @ 07:06 am PST

I designed a SOLAR DISINFECTION SYSTEM which is cost effective and can be fabricated locally.

Details:

www.drjagadeeshncda.blogspot.com

Dr.A.Jagadeesh

Nellore(AP),India

E-mail: anumakonda.jagadeesh Nellore(AP),India

Anumakonda Jagadeesh
20th January, 2011 @ 02:28 am PST
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