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Safe Water with the Power of Sunlight: Photocatalytic Water Purification Technology

Across the world, 750 million people lack access to safe drinking water in their daily lives. (WHO, [http://apps.who.int/iris/bitstream/10665/112727/1/9789241507240_eng.pdf?ua=1]). Further, in India, approximately 70% of the population uses groundwater for drinking water – the groundwater which contains toxic substances such as arsenic, hexavalent chromium from factories, and agrichemical runoff. This contaminated groundwater is directly responsible for health problems impacting as many as 50 million people. Photocatalytic water purification technology is expected to provide safe water at a low cost, anywhere in the world.

Gentle on the environment; detoxify harmful substances in drinking water

 Photocatalytic water purification technology creates safe water by utilizing sun’s ultraviolet rays and photocatalysts to react with harmful substances in the water, rendering them harmless. Compared to chlorination or chemical purification, the impact on the environment is minimal, and it provides the advantage of detoxifying the remained harmful substances after chlorination.

Titanium dioxide (TiO2) is one of the most well-known superior photocatalyst. When it is placed in water and exposed to ultraviolet light, the energy of that light is transmitted to the electrons in the titanium dioxide particles, and high-energy electrons (electron excitation) are generated on the surface of particles In addition to purifying toxic metals like arsenic and hexavalent chromium, these high-energy electrons react with oxygen in the water to generate reactive oxygen, purifying bacteria and organic substances. Reactive oxygen is also generated when the surface of photocatalytic particles from which electrons have already been ejected come in contact with water, contributing to the efficiency of the water purifying effect.

Developed new structure particles enabling a high processing speed and easy recovery

 In order to purify water quickly and efficiently, it is necessary to increase area of contact between  the surface of the titanium dioxide particle and water. Mixing the particle into the water was the most effective way, but the 25 nanometer diameter of the particle is too small to separate and recover the photocatalyst from the water after purifycation and it requires a large-scale equipment for practical use. On the other hand, conventional water purification using “fixed photocatalysis” required building  itanium dioxide particles to a flat surface such as a tile. This eliminated the need for separation and collection, but led to a slower processing speed, due to its inability to efficiently promote contact between the photocatalysts and the water. In order to achieve both high processing speed and easy separation and recovery, Panasonic has developed a new photocatalytic particle, composed of titanium dioxide bonded to the surface of another particle called zeolite.

Zeolite’s surface has many microscopic pores, giving it a large surface-to-volume ratio. The new particle developed by Panasonic bonds titanium dioxide particles to the surface of zeolite using static electricity. The titanium dioxide is bonded without interference of other materials, so it doesn’t decrease its reactivity. Furthermore, there is no need for chemical substances like bonding agents.

When water containing this new photocatalytic particle is agitated, the titanium dioxide separates from the surface of the zeolite, spreading throughout the water to react with toxic substances. When agitation is discontinued, the titanium dioxide is adsorbed back into the surface of the zeolite, and the photocatalytic particles return to their original state. The size of these particles are microns scale, so they are easily removed from water after the purification process by filtration or sedimentation. The photocatalytic particles can be reused after collection.

50-100 times faster than conventional process, as much as 99.9% of toxic substances removed

 The new photocatalytic particle greatly enlarges the surface area of the photocatalysts, allowing for major acceleration of the purification speed, as compared to fixed photocatalysis: 100 times faster for the processing of non-biodegradable organic ssubstances, and 50 times faster for arsenic. In addition, this technology not only eliminates organic substances and microorganisms, but also detoxify as much as 99.99% of toxic metals, which had previously been difficult to eliminate from groundwater. This makes it possible for problematic sources of groundwater to be renewed as sources for drinking water.

The latest information

 Water purification equipment utilizing this technology is based on the simple process of mixing the photocatalytic particles into the water, applying sunlight to purify it, and then removing the particles afterward, so it is possible to create a small-scale, recycling-oriented water purification system at a community scale. Panasonic’s technology will contribute to the realization of a world in which people can find clean water to drink anywhere.

Aug., 2013 Panasonic Develops Highly Effective Water Purification System
Using New Unique Photocatalyst

Dec., 2014 Panasonic Proposals for “A Better Life” at Eco-Products 2014

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