A clean approach to water disinfection using catalytic in situ generation of reactive oxygen species.

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Undoubtedly some of the greatest challenges of this century will revolve around the adequate provision of clean water. With an estimated 5.7 billion people living under the threat of water-scarcity by 2050,1 driven largely by increasing urbanisation, rapid population growth and climate change, it is essential that water sanitation infrastructure and services are adapted to ensure sustainability and resilience. This is of utmost importance in communities that have no or limited access to traditional means of water decontamination. Clearly, approaches that promote a localised circular water economy will be favoured, minimising financial and environmental costs.2,3

Indeed, the growing health concerns associated with chlorination by-products will likely lead to a major overhaul in existing water infrastructure and a shift towards approaches that avoid the formation of harmful chemical residues. Theoretically H2O2 would be an attractive alternative to chlorination, however in practice the use of toxic stabilizing agents to prolong shelf-life would prevent the application of commercially generated H2O2 in water treatment.   

In this work we demonstrate that the generation of H2O2, through the combination of dilute streams of H2 and O2 over AuPd alloyed catalysts, and more importantly surface bound intermediate species such as OH and OOH, whose desorption are promoted by the presence of Au are able to achieve bactericidal and virucidal efficacy several orders of magnitude greater than that observed when using chlorination or commercial H2O2. Furthermore, the low levels of residual H2O2 generated via our in situ approach also offers the opportunity for prolonged disinfection and inhibits the formation of biofilms, which are at the core of many pathogens persistence and propagation.

While this technology is in its infancy, we are excited by its potential to revolutionise water disinfection and with a highly motivated, multi-disciplined team that involves chemists, microbiologist, surface scientists and microscopists in addition to process engineers and industrialists we are confident that future hurdles can be overcome.

 Further details can be found at https://www.nature.com/articles/s41929-021-00642-w

 References.

  1. Climate Change and Water, United Nations Water Policy Brief available from https://www.unwater.org/publications/un-water-policy-brief-on-climate-change-and-water/
  2. Larsen, T.A., Hoffmann, S., Luthi, C., Truffer, B., & Maurer M., Emerging solutions to the water challenges of an urbanizing world. Science, 352, 928-933, (2016).
  3. Grant S.B. et al., Taking the “waste” out of “wastewater” for human water security and ecosystem sustainability. Science, 337, 681-686 (2012).

Richard Lewis

PDRA, Cardiff University

Comments

Go to the profile of Isatou Sarr
3 months ago

Hi, great technique. Just a question, how stable is the end product over time when continually exposed to changes in atmospheric/environmental composition? I am assuming there are cleaving catalyst of the reactive oxygen specie, if so are they naturally naturally occurring?  Thank you.

Go to the profile of Richard Lewis
3 months ago

Hi Isatou,

Many thanks for the question. The reactive oxygen species (ROS) are highly energetic and will individually have a lifetime on the order of nanoseconds. The lifetime of any residual H2O2, which has some (limited) anti-microbial properties will last somewhat longer, no longer than a few minutes, depending on environmental conditions (pH / temperature / presence of salts in the water etc ). This is one of the major advantages of this approach compared to chlorination, no toxic chemical residues!

The ROS are generated over the catalyst through reaction between very dilute streams of H2 and O2, rather than being cleaved from the catalyst surface, so as long as both gases are supplied constantly, under ideal conditions, the catalyst will continually generate ROS. 

Go to the profile of Isatou Sarr
3 months ago
Thanks Richard, You're right, chemical residues are a downside of chlorination and its about time to have a more robust water purification system with lesser chances of residues. Beautiful technique!!!!! Just a quick question: How applicable is the technique in resource limited settings where the environmental and atmospheric confounding factors are usually not robustly monitored or documented? It would be great to have internally built monitoring systems for timely flagging of changes in the water prior to large scale production. Moving on, most ROS are formed by the partial reduction of molecular oxygen forming different species of which superoxides  is one of them.  Current data has highlighted it as a potential model for biotherapy and metabolic reactions in bio-organic systems thus it will be wonderful if superoxides can be harvested using the technique highlighted in the paper for therapeutic use.  Kind regards.
Go to the profile of Richard Lewis
3 months ago

Hi Isatou, 

Thanks for these comments. 

Theoretically the resources required to generate the ROS should not be prohibitive and would consist of air (to provide O2), water and electricity, with H2 generated from water splitting. This technology really could use water to treat water! The concentration of H2 used by our system is comparable to that generated by any commercially available electrolyser, run from a generator or even renewable sources. 

Your point about changes in water quality and the need for continual monitoring, for example after a storm event or an accidental spill,  is something we have considered and indeed is an area that many water treatment companies are pursuing.  Thankfully there seem to be a number of affordable, remote water quality management systems available commercially.

The use of superoxide in biotherapy is definitely an interesting topic and there is currently a wide field of research investigating the use of superoxide for the safe treatment of tumours. Our catalytic materials can definitely be modified to deliver tumour targeting species in situ, at a desirable rate. 

Best wishes, 

Rich