Clean, disinfected water is essential for a good life, but millions of people around the world lack access to it. Researchers at the Cardiff University plan to change this state of affairs with an on-site disinfection approach that is massively more efficient than our current disinfection approaches. The method relies only on atmospheric hydrogen, oxygen, and a gold-palladium catalyst.
The new method aims to provide clean, safe water for consumption and hygiene in areas without access to such resources or reliable disinfection methods. All in all, it could help improve life for billions of people who are struggling with lack of water or water insecurity.
"The significantly enhanced [anti-viral and anti-bacterial] activities achieved when reacting hydrogen and oxygen using our catalyst, rather than using commercial hydrogen peroxide or chlorination, shows the potential for revolutionizing water disinfection technologies around the world," says Professor Graham Hutchings, Regius Professor of Chemistry at the Cardiff Catalysis Institute, co-author of the paper.
The gold-palladium catalyst allows for hydrogen and oxygen atoms in the air to merge into hydrogen peroxide. This is a common chemical produced in huge quantities around the world which also sees heavy use as a disinfectant. Over four million tons of the compound are produced globally each year.
Typically, hydrogen peroxide is produced at one site and used (for various purposes, including water disinfection) at another. This means it requires storage and transport before use, so hydrogen peroxide is often mixed with other chemicals that stabilize it and keep it fresh until it's used. While these do perform their intended role, they also cut down its efficiency as a disinfectant (since it's now, essentially, diluted).
One alternative to this approach is to use chlorine as a disinfectant -- add enough of it to water and it'll kill most pathogens swimming their way around in there, just like hydrogen peroxide does. However, chlorine can react with naturally occurring chemicals in the water creating compounds that can be toxic to humans.
The novel approach however works around these issues by producing the disinfecting agent -- hydrogen peroxide -- at the point where it is used. The team first tested the efficiency of commercially-available hydrogen peroxide and chlorine in disinfecting water, and then compared this to the efficiency of their catalytic method. All of them were compared based on their ability to destroy Escherichia coli, a common bacteria species, under identical conditions. After this quantitative step, a qualitative step followed, where the team investigated exactly how each method killed the germs.
First off, their method proved to be the most effective, being 10,000,000 times more potent at killing the bacteria per unit of volume than hydrogen peroxide, and over 100,000,000 times more effective than chlorine per unit of volume. It also killed the bacteria faster than either of the two other methods.
Its secret seems to be that the reaction which creates the hydrogen peroxide also produces reactive oxygen species (ROS), highly-reactive compounds that bind to other chemicals, degrading them in the process. Bacteria are also made of chemicals -- hence, they're also being degraded. This process is the same one that makes us grow 'old' with age.
Interestingly enough, the team found that these ROSs are what's killing the bacteria and other pathogens, not the hydrogen peroxide itself.
The team notes that an estimated 785 million people around the world lack access to water, and around 2.7 billion experience water scarcity for at least one month every year. Inadequate sanitation, which is also powered by lack of clean water, affects a further 2.4 billion people worldwide and can lead to a host of water-borne illnesses.
This on-site disinfection method could help all of those people finally have reliable access to clean water for drinking, washing, and any other need they might have. Hopefully, the team's work will quickly find its way into practice.
"We now have a proven one-step process where, besides the catalyst, inputs of contaminated water and electricity are the only requirements to attain disinfection."Crucially, this process presents the opportunity to rapidly disinfect water over timescales in which conventional methods are ineffective, whilst also preventing the formation of hazardous compounds and biofilms, which can help bacteria and viruses to thrive."
The paper "A residue-free approach to water disinfection using catalytic in situ generation of reactive oxygen species" has been published in the journal Nature Catalysis.