Nontoxic powder uses sunlight to quickly disinfect contaminated drinking water

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Have you ever been camping or survived a natural disaster and needed to sterilize water for drinking? There are filtration methods, or you can use chemicals like iodine or bleach. If all else fails, boiling the water for a sufficient time will kill the bacteria in it. All of these methods have their disadvantages, though. What if you could just sprinkle some powder into the water and wait a very short time? Now, that's possible thanks to scientists at Stanford University.

Image from powderbulksolids.com

The Centers for Disease Control in Atlanta, Georgia, USA describe several ways that people can sterilize drinking water.

• You can boil it for a minute (longer at elevations above 6,500 feet). Being able to make a fire is the key point, though.
• You can add a few drops of household chlorine bleach. How much you add depends on the concentration of the bleach and the volume of water. But, you'll have to wait half an hour for it to take effect. And, it may leave an odor that you don't like.
• You can add tablets of chlorine dioxide or iodine. Chlorine may leave a taste or smell, and iodine will not kill parasites. Iodine is also not recommended for pregnant women.
• Filters with pumps can remove parasites, but most don't remove bacteria and viruses. They are bulky and need cleaning for reuse. You also have to add iodine, chlorine, or chlorine dioxide to the filtered water to kill bacteria.

Methods to kill bacteria in water: boiling, filtering, tablets, iodine drops

About 2 billion people in the world do not have access to clean water on a regular basis, and 80% of them live in rural areas, so this problem is not limited to campers or emergency situations. Contaminated water is responsible for killing millions of people from various illnesses, so it is critical to find ways to clean it up, and the easier and cheaper, the better.

People have introduced cooking methods to Africa that eliminate the need for firewood, just by providing basic materials to make solar ovens. Why not give similar populations a magnet and a bottle of some powder to clean up their drinking water, too? That's all that the Stanford U researchers say may be needed.

From gettyimages.com

It all works on a simple disinfection principle that uses hydrogen peroxide, the stuff in some household cleaners. The chemical formula for water is the familiar H2O, but hydrogen peroxide is a bit unstable because it has an extra oxygen on it to make H2O2. Its instability causes it to react with bacterial cell membranes and DNA to kill the bugs rapidly on surfaces. The instability also gives it a short lifespan of activity when mixed with water, but if the concentration is high enough, that will not matter. The main point is that it leaves behind nothing toxic but oxygen and water.

Stanford scientists found a way to make nano-sized flakes of aluminum oxide, molybdenum sulfide, copper, and iron oxide linked together into a powder. 

Aluminum oxide (left) and molybdenum sulfide (right) nano particles

The aluminum component absorbs sunlight. The molybdenum component takes the sunlight energy from the aluminum to generate hydrogen peroxide in the water. And, the iron oxide component is magnetic, so after the powder has cleaned the water, the entire powder made of these 3 chemicals can be separated with a magnet and reused at least 30 times. 

Top left: add powder to contaminated water

Top right: allow light to activate the powder into H2O2

Bottom right: after disinfection, remove power with a magnet

Bottom left: recovered powder is put into a new beaker with contaminated water for reuse

Diagram from phys.org

They tested this powder with a million E. coli per 20 drops in a container with nearly a cup of water. (Drinking water standards prohibit any E. coli at all, and just 10 cells of some highly infectious strains can cause illness.) In just one minute of exposure to sunlight, it killed 99.999% of the bacteria. See the jagged cell membranes as a result in the pictures below.

Healthy E. coli (left), peroxide-damaged E. coli (right, red circles), from nanotechnologyworld.org

Not only is E. coli a bacteria commonly used in the lab, but certain types can cause severe diarrhea at a drastic level. It is one of four types of bacteria responsible for this life-threatening situation, along with Shigella, Campylobacter, and Salmonella (typhoid fever). But various parasites and viruses can also cause that disease, so the Stanford researchers will test their powder on them in the near future, too.

They also speculated on how this technology might be used in the developed countries by replacing UV light in wastewater treatment plants to disinfect water before it is released into the environment. Since the starting materials for the powder are cheap and commonly found, and the chemical reaction doesn't create any smelly or toxic chemicals, this is a promising step to helping people around the world. 

Here are some tips for using hydrogen peroxide for cleaning surfaces in your home.