This got me thinking about what we could and could not do if we had a magical a energy-unbottlenecker, say an infinite capacity battery with arbitrary power output.
These become much cheaper:
- Transport: synthesise fuel from CO2 + seawater. Or charge a battery.
- Water: electrolysis of seawater.
- Food grown anywhere: Light + water + fertiliser can be made from commonly available materials. Soil is a bit trickier, but I think you could bootstrap up with composting.
- Global warming: pull CO2 out of the air.
- Raw materials (concrete, metals): all cheaper to extract with free energy.
- producing medicine
Still really hard:
- making new treatments
- inflation of housing prices
- escaping earth's gravity (need bounce per ounce)
- world peace
- writing books
- politics
I don't think its fair to say they are "energy" issues, or that they are bottlenecked by a lack of energy.
When building the desalination plant, we can build a solar farm right next door.
The problems are political. Nobody is willing to go out and spend the money.
My hope is that when automation starts taking peoples jobs, governments will employ and train people to build these big infrastructure projects. Desalination, Green Energy, Reforestation, better Agriculture and Land Management.
I feel that, once you have reduced the consumables of something to energy, that doesn't tend to make it energy limited. Instead, it becomes capital limited. You need to be able to pay for the upfront capital costs of installing the thing.
Add to that the fact that, once these developments have happened, they tend to improve a lot, quickly. That means anything you build will, soon, be outdated and stop producing as much yield. Hence, you don't want to invest too much.
Wow, that’s incredible. Since it uses electricity for it’s energy input, this could be readily adapted for use in remote areas powered by solar plus battery. Even in Western nations this is a boon to treat well water sources instead of shock chlorination.
This combined with GAC filtration can produce very clean water anywhere you can get sunlight.
The amount of electricity required wasn't mentioned, so while I'm hopeful that you're right I'm worried that the energy requirements will be prohibitive to adoption in many areas.
It needs gold and platinum catalyst. The trouble would be there would be no catalyst in the plant to process water, the day after it is deployed in a remote area.
Anytime you read things like 100,000,000 times more effective - you should be asking, what was the numerator or denominator in this. Or are they just describing some tiny part of the system.
For example, normally you need to filter, do settling for sediment etc - how did they solve all this?
Given the orders of magnitude involved here a 5 MGD plant could produce 500 trillion gallons per day of "commercial approach" water cleaning. The water handling issues alone in doing 500 trillion GPD seem large. Am I missing something?
The specific measure appears to be in CFU/mL of E. Coli in their test sample before and after. As you suspected, this does not include filtering or settling, just clearing out bacterial contamination.
I haven't read the paper yet (paywall)- just looked at their supplementary data.
The increased effectiveness appears (guessing here a bit) to be in terms of bacteria load reduction given similar concentration of bacteriacidal agents in same volume of liquid.
Right, I don't think these they were really gunning for developed commercial systems for this. Their pitch would be this would be more useful for situations where we might not want to be tied to a chemical supply line. Thanks to fellow poster, I have now started reading the paper. The last sentence of their intro reads:
> This approach offers the potential for in situ water purification that could, we propose, be suitable for decentralized applications.
Part of what will prevent mass adoption is it ignores distribution, which will still require chemical residual treatment, like chlorination.
If you have to install chlorinating equipment and operate it, then it becomes a matter of if the marginal savings in chlorine is worth it.
However there's also a good chance that chlorine concentration is controlled by downstream factors more than initial treatment- which is basically the case at every well/spring that produces drinkable water out of the ground, yet still needs residual treatment.
So there might not be any reduction in the required amount of chlorine.
I'm not very familiar with this field, why is chlorination required in addition to peroxide? Is it because it's pretty stable and so provides protection after the water has left the treatment plant?
If that's the case, I suspect that the type of decentralized system the authors think that this is useful for would be a nature where that's less of a concern. Smaller system leading to decreased time/distance between processing and use.
I'm REALLY going out on a limb here, but we hear about people who have to go and fetch their water supplies every day (perhaps multiple trips per day). I suspect that sources on that scale are where this might be useful.
>provides protection after the water has left the treatment plant?
Yes, that is what residual treatment is.
I'm not familiar with peroxide systems, but for this industry, you don't change things without a very good reason. If we're talking about new niche uses, then that's a different story, but still merits caution.
Related story:
Washington DC tried to "upgrade" from a chlorine system to another chlorine derivative that was supposed to have some marginal EPA benefits, and on paper it was a great design.
In practice (and many tens/hundreds of millions of dollars later), the water quality had a sharp decline, with all sorts of unexpected chemicals showing up. It turns out the old system had the unintentional side effect of "filtering" out all kinds of nasty reactive stuff (including lead), and the new chemical balance reversed the process. All the chemicals that had been sequestered in the pipe walls for decades or longer, were now getting pulled back into the water. Oops.
Then there was the initiative in India where thousands of water wells were drilled, only to discover the water contained arsenic.
>I suspect that the type of decentralized system the authors think that this is useful for would be a nature where that's less of a concern. Smaller system leading to decreased time/distance between processing and use.
It may, but UV disinfection has similar properties and has been available for a while now, probably at a lower price.
Also, if water's getting transported in personal containers, chances are they're dirtier than any water main. It's easy to draw the limits of the system at a convenient point, but these are the situations that probably need residual treatment more than than we do.
Of course reality dictates what's feasible, especially in the 3rd world, and "exciting" new tech like this might get funding that boring old school solutions won't.
This is the trouble with most academic research which focuses on trying to maximize one aspect of the problem while a useful commercial application needs to simultaneously optimize multiple conflicting aspects. A similar stream of useless papers also are published in energy storage (beyond Li-ion batteries) which are not likely to be ever commercialized.
The researcher himself is directly quoted saying things like “revolutionising water disinfection technologies around the world”. If that’s not backed up by it being feasible or valuable commercially, then the criticism is spot on.
I think the point is the science can be useful in that endeavor by demonstrating a new approach one can take. That’s not to say it’s all that would be required. It’s unreasonable and incorrect to expect a full commercial solution to come directly out of a set of lab experiments.
I do not understand why this could be regarded as a relevant response to the post you are replying to. You say "it’s unreasonable and incorrect to expect a full commercial solution to come directly out of a set of lab experiments", but the post you are replying to did little else but point out that this is essentially what the article is claiming. If you do not think the article was making such a claim, then that is a point you could have disputed, but so far have not.
That’s not what the article says. It says the new method “shows the POTENTIAL for revolutionising water disinfection technologies around the world” (emphasis mine). It’s talking about a method of creating disinfectants at the source rather than using chemicals. How to scale this up, deal with degrading catalysts, handle electrical demand, etc are all beyond the scope of an academic lab inventing a new method. They just demonstrated the potential.
If you read the entire thread from the top, you will see that you are making a point that has already been acknowledged by everyone contributing to it. Bringing it up again merely loops the discussion back to a point where it has been before.
The fact that they are making bold claims about potential applications is sufficient to justify Kaibeezy's reply to riddly.
Yeah the researcher is already pretty far into the commercial realm with that kind of statement. I'm just saying, the point of science is to find out stuff or increase certainty about stuff. So even an experiment that finds another way to disinfect water that doesn't work, has scientific value because now we know that doesn't work.
I don't see the problem. Isolating one variable per experiment is helpful to ensure you are appropriately testing your thesis. It makes sense to me that not all science is immediately commercializable and that many of the papers never directly contribute to commercial application. It seems to me that commercialization is a distinct step in the process of discovery and production, which must often come after the initial process of scientific exploration.
Unfortunately scientific research at this point is not trying to solve difficult problems but just do a small step change improvement that can be published. Most of the kinetics and thermodynamics of these catalyst behaviors have been well understood for decades. The logical next step in scientific exploration would have been to untangle and understand the interactions of the different processes of interest and how they impact one another. Instead most of the research in these areas are to use fancy tools to create patterns like nanostructures that can never be done at scale and create a contest to show delta improvement in the reactivity while providing minimal fundamental insights to either understanding, explaining or solving the problem.
If I've understood correctly, the denominator being compared against isn't a "best available alternative" treatment solution of H2O2. It's against the concentration that's an "equivalent amount"-- which is actually a pretty dilute concentration (for H2O2), that *isn't* effectively bactericidal.
>"...are over 10^7 times more potent than an equivalent amount of preformed hydrogen peroxide..."
Per fig. 2(c,d), the "commercial H2O2" items are solutions of 100 and 200 ppm (0.01% / 0.02%), and have nearly zero effect (less than 1 order-of-magnitude reduction in bacterial/viral viability).
([edit]: or quoting the paper itself: "These standardized preformed H2O2 samples, produced either commercially or catalytically (100–200ppm), exhibited limited bactericidal activity [my emphasis] against...")
Their actual point is that this H2O2+ROS is highly effective at a concentration at which H2O2 alone is not effective.
[edit]: In attempt to find further context, here's some data about disinfection with H2O2 solutions (in entirely different experimental setups which probably have important caveats I don't know):
>"...organisms with high cellular catalase activity (e.g., S. aureus, S. marcescens, and Proteus mirabilis) required 30–60 minutes of exposure to 0.6% hydrogen peroxide for a 10^8 reduction in cell counts, whereas organisms with lower catalase activity (e.g., E. coli, Streptococcus species, and Pseudomonas species) required only 15 minutes’ exposure [657]..."
So, as a hand-waving non-expert: it looks like you can get the same order of magnitude of effect (factor of 10^8 bacterial reduction) as the stuff in the OP paper, at a hydrogen peroxide concentration that's ~60 times higher than what OP uses (0.6% = 6000 ppm). (?)
> The team showed that as the catalyst brought the hydrogen and oxygen together to form hydrogen peroxide, it simultaneously produced a number of highly reactive compounds, known as reactive oxygen species (ROS), which the team demonstrated were responsible for the antibacterial and antiviral effect, and not the hydrogen peroxide itself.
> The catalyst-based method was shown to be 10,000,000 times more potent at killing the bacteria than an equivalent amount of the industrial hydrogen peroxide, and over 100,000,000 times more effective than chlorination, under equivalent conditions.
Basically, I'm getting the highly reactive ROS are the key point here, they're creating them in situ so they're able to be exploited where as standing h2o2 is likely much less reactive.
The order of magnitude gains are easy to grasp if you take into consideration the literal hours you need to wait for chlorine or similar to sterilize water. If there is a way to speed that up to near instant your gains are going to be relatively immeasurable.
This is actually my point exactly. This may not be 100,000,000x better in a practical sense. It is maybe 60x better but because they are doing math with something that is a zero (or close too it) they get to report an insane increase in effectiveness.
It's actually a great tell for what is often garbage analysis when you have this level of a multiple.
"millions of times more effective at killing viruses and bacteria than traditional commercial methods.." "..revolutionise water disinfection technologies"
I don't think this is comparable to a water treatment plant. No sediment settling, biofiltration etc. It's comparable to sterilising water using hydrogen peroxide or boiling it, in a camping context.
I'm curious how well it does with dirty water, one of the big issues in the camping context is sediment in the water ruin the efficacy of all forms of water treatment.
Like your parent post suggests, it's not really for that step -- you'd still need a filter for that. That said, in the context of camping.. because the need for sanitization is offloaded away from the filter, you're able to get away with a filter that has a much higher flow rate. Hand-powered sanitizing filters are an absolute pain to use and getting enough water for a meal is a.. process. So, it would be a welcome addition to camping setups.
> For example, normally you need to filter, do settling for sediment etc - how did they solve all this?
The key sentence should be this:
> In their study, the team tested the disinfection efficacy of commercially available hydrogen peroxide and chlorine compared to their new catalytic method.
In other words, no, this doesn't replace coagulation+flocculation, sedimentation, and filtration; it's only replacing the specific disinfectant in use.
I just hope the Reactive Oxygen Species that are 10M times more lethal to bacteria aren’t equally more lethal to humans. Also, if this requires electrolysis-level power, it might still not be worth it in most cases.
How much gold and palladium are required? Those are massively expensive catalysts and it feels borderline disingenuous to talk about how this will bring clean drinking water to the masses without so much as mentioning cost.
> The catalyst-based method was shown to be 10,000,000 times more potent at killing the bacteria than an equivalent amount of the industrial hydrogen peroxide
Even if it required a fair bit, 10M is a really big number. Long term savings would be huge since the catalysts aren’t consumed in the reactions
Is hydrogen peroxide "good enough" such that it doesn't matter? Like saying I'm 10 million times less likely to drown watering a lawn than I am washing a car isn't important, because the odds of either happening is vanishingly small.
The "equivalent amount" of H2O2 is actually a really pathetic amount (0,01%) and potency is not linear with concentration. Actual concentration of H2O2 that's used for these purposes is only 60 times higher (0,6%) and achieves similar 10^8 times better results as 0,01%.
Plus they only tested vs E. Coli which is not very durable as far as nasty microbes in your water go.
In the real world, catalysts do in fact get used up, usually due to fouling from side reactions and that kind of thing. That's why you often need to replace a catalytic converter within the lifetime of a vehicle.
Though I wish this article addressed some of the questions I had around commercialization, namely the cost of the gold + palladium, the expected lifecycle, and the expected maintenance routine (e.g. do they have to be regularly removed and cleaned?).
The article makes great arguments for why this should work (i.e. hydrogen peroxide is already being used, this just short-circuits how we get a known effective cleaning agent, reducing/removing logistics inefficiencies). So a lot of the question is: Is this cheaper/less hassle than buying stabilized hydrogen peroxide commercially?
A lot of these fantastic advances often end up in the black hole, wherein they work as advertised, but the financials/logistics never line up and therefore nobody uses them in anger.
> So a lot of the question is: Is this cheaper/less hassle than buying stabilized hydrogen peroxide commercially?
From the article: "The team showed that as the catalyst brought the hydrogen and oxygen together to form hydrogen peroxide, it simultaneously produced a number of highly reactive compounds, known as reactive oxygen species (ROS), which the team demonstrated were responsible for the antibacterial and antiviral effect, and not the hydrogen peroxide itself."
Yeah, the use of "millions of times better" just doesn't pass the sniff test. Given that current commercial methods kill 90%+ bacteria in water, thus, nothing can be even 2x better...and makes me suspicious of any claim in the article. Hopefully it can help people in areas that are currently without clean water, but I'm not holding my breath.
(CFU/mL of E. Coli with stored H2O2) / (CFU/mL of E. Coli with catalysts) = 10M
With that in mind "millions of times better" isn't necessarily a disingenuous description. Though you might say it's somewhat misleading, since as the denominator goes to zero, the fraction goes to infinity :)
It's the equivalent of saying 99.99999999% uptime is "ten million times more available" than 99.9% uptime - um, just give me the number of nines please!
If you're measuring in (1-n) terms, you can be 2x better. 95% is 2x as good as 90% and 99.9% is 100x better. Not at all clear at first glance or sure that it's what they're doing here, but just something to keep in mind.
> Given that current commercial methods kill 90%+ bacteria in water, thus, nothing can be even 2x better
That depends how you look at it. Is it 90% killed, or is it 10% survived? If it's 10% survived, then 100m times better is a system where 10/100m % survived instead.
I don't think this is basic statistics. I think it the correct way of reporting the improvement, but it may be confusing for someone that does not understand the usual notation in the field. Moreover, I had to look at the paper to be sure what they were reporting. (Actually, they report the log of the improvement, i.e. something like "8" that is better to put in graph to compare different methods.)
If you take your 90%+ as a baseline (ie zero) then you can fiddle with the stats to get a massive number.
Let's say the best effort is 91.001% and our smart new process is 92.001%. Now set the baseline at 91.000% This is the sleight of hand bit: If we say that "normal" is 91.000, we now set the best effort as 0.001 and our effort as 1.001. That can seem quite reasonable when trotted out by a news reader or reporter.
So we are (1.001/0.001) x 100 = 100,100% better than the previous best!
The real improvement is more like: 92.001/91.001 x 100 = 101.098% which is a bit obvious when you look at the numbers involved.
With a single quite clumsy move and a bit of misdirection you can turn 101 into 100,100 and sound quite convincing. Now that's only using the very basic arithmetic operations and a bit of bullshit. The clever kids can really go to town.
We need some sort of laws about the presentation of statistics because it really is getting out of hand. The nonsense I've just presented isn't fiction. I saw something similar recently, can't remember what for but it took a while for me to calm down afterwards 8)
But in your example it's more sane if you flip it.
Survival rate from a new medicine may be 99.99% and only allows 1.0001 multiple of improvement. For severe outcomes, not allowing expansive language to describe improvements is a legitimate problem. i.e. if we insisted on this, it would be hard to motivate improvements in safety from 99% to 99.999% since they are "only <1% improvements".
So in cases like this I think of it in reverse: the death rate of 0.01% can be improved by 90% (or 10x) to 0.001%. This does run the risk of inflating the importance of the fix when the base rate is extremely low.
My rule is: articles which use multiples or percentages must give enough detail to exactly reconstruct the calculation method used.
And don't even get started on "Improved by 40%" (1.4x) being occasionally referred to as "Improved to 140%" (1.4x), which then is backported "Improved by 140%" (to 2.4x).
The real problem is percentages; people also intuitively assume "50% less than (50% more than X) is X"
this is poor logic. imagine two disinfectants, A and B, both kill 90%+ of known bacteria. imagine that you need 1 part per billion for A to be effective and 10 million parts per billion for B to be effective.
“Better” does not necessarily mean “kills a higher percentage of bacteria”
By the way, this isn’t a comment on the article itself in any way, simply a comment on the logic of your comment
A tangentially related development recently has been peroxide generators to put inside buildings to generate enough hydrogen peroxide to sterilize the air/surfaces without being a health hazard. I've recently had a local school district request that we analyze these devices as an option for COVID mitigation: https://synexis.com/science/reports-data/
Nice, but it seems the method is not exactly new. Here's a short nature article from the 2nd of March 2016 talking about the same research programme on catalysts at Cardiff University.
WOW, is this thread treading on thin ice in July? Uh, it is apparently well established that public commentary, e.g., in the mainstream media (MSM), 100% must NOT include chemical formulas or meaningful uses of ratios, proportions, percentages, or scientific, chemical, or microbiological terminology, yet post after post in this thread are in flagrant violation! As I recall, ratios and proportions are from somewhere above the third grade and some of the rest of the topics go up even to, horrors, high school science courses!
To add to the transgressions, this thread is discussing the content of a peer-reviewed paper of original research about some tricky, detailed parts of chemistry and microbiology.
Intelligent discussion and content? Horrors!!
Stand aside as 99 44/100% of media comes tumbling down like that condo recently did in Florida? Maybe!
Ah, that's Hacker News for you; no chance of seeing such content, such flagrant transgressions, in the MSM!
Uh, I'm not complaining, you understand! Not complaining at all!
[edit: commenter is right, the paper abstract rendered as "107" not "10^7" in browser, will leave followup question]
Since it's a challenge to separate the products/byproducts in catalytic reactions that are homogenous/liquid phases, how would this setup achieve separation post reaction exactly? Anyone know?
Oh dear. After reading the notes in the study itself about the scale this was done at, scaling up might be an issue:
> A typical H₂O₂ synthesis reaction was carried out using 120 mg of 1% AuPd/TiO₂ [...] The reactor system was then pressurized, typically to 10 bar. The reactor was then cooled by a water bath to 2 °C. When the reactor had reached the required pressure and the flow through the system had stabilized, the solvent (H²O, HPLC grade), typically at a flow of 0.2 ml min¯¹, was introduced into the system.
Oh hey, 0.2 mL/min of water. In Virginia, the lowest flow cutoff for waterworks is 0.5 MGD (or 5000 people), the border between Class 3 and Class 4. That flow rate is 6.5 million times that done in the tests here. The large water treatment plant I worked at is another 400 times that, and there are plants that would be another 5 or 6 times that. So the necessary scaling factor is going to be measured in the billions.
So what about those reagants? This uses about 0.6 mg of gold to process 0.2 mL/min of water (if I'm reading the notation of 1% AuPd/TiO₂ correctly). Scale that to our small plant, and that's about $225,000 of gold and $350,000 of palladium. Go to the scale I worked at, and that's $190 million of catalyst in terms of raw metal worth alone. That's comparable to the cost of a regular treatment plant of that scale--just on the catalyst. This assumes that there's a neat linear scaling, which I doubt is going to be the case (square-cube law!).
Thanks for the insights, though let's remember that research is just a first step. This isn't a product being announced for the market. If we looked at the original research behind a lot of mature technology, we'd find the state of the technology to be similarly far from from production.
Now others can try to reproduce it, refine it, find other methods of producing the same reactive oxygen species, find substitutes that are more effective or cheaper, etc.
It doesn't have to be panacea either. Maybe it will fill a niche. It could save some lives.
It wouldn't be a university press release if it didn't make a specialized laboratory experiment sound like something that is about to revolutionize life as we know it.
Maybe they can use metallic foam to increase the surface area of the catalyst and increase the flow rate without scaling the noble metal usage at the same rate as the flow!
If its effectiveness is as good as they say, seems like you could just use 1,000,000x less catalyst and end up with something as effective as current technology.
$190 million -> 190 bucks ;)
Seriously though, couldn't they just use far less catalyst and not have to deal with the prices you've calculated?
would it still work though? Like if the mechanism is a relation between surface area and the water, you might not have a choice to just use less material? Unless your "strategy" is to, like.... just have a tiny flow of super pure water and then mixing it into untreated water.
(Your strategy might totally work of course, just might not be a given)
> Seriously though, couldn't they just use far less catalyst and not have to deal with the prices you've calculated?
The flow rate is likely positively correlated with catalyst loading (in the part that we care about) and the calculation is already based on the flow rate of 0.2 ml min¯¹ they reported in the paper. The reported flow rate is also likely already optimised for the Nature Communications paper.
It is very unlikely that they could have even explored the full parameter space if they wanted to, it's such a huge undertaking. It's probably optimized under some constraints, but there's a huge number of things involved -- support material, surface area, catalyst metal, alloying, promoters, pretreatment, temperature, pressure, flow rate -- my experience has been that you can take any catalyst and make it work a lot better by just picking an understudied parameter and optimizing it.
My guess is that you could drop the catalyst noble metal content by 10-100x or even substitute an alternative catalyst and find a combination of conditions and catalyst that works. It's not a sure thing, but it's not unlikely. Sometimes it's as simple as swapping one support for another and the performance goes up 100x, it's just a lot of tests to run that don't even apply to both lab and commercial scales anyway (so a lot of the tests are never practical to run anyway).
I think it'd be a bigger deal if it didn't require pressurization to 10 bar personally, pumps are expensive to operate and catalysts are a one-time-cost (if you're lucky).
> It is very unlikely that they could have even explored the full parameter space if they wanted to, it's such a huge undertaking...
Absolutely agree and no arguments whatsoever. In fact, one of the first things that I joked to myself was that we will soon see papers on MOF-suppoorted version of the catalyst -- well before we see any DoE.
In any case, I just want to note that I made the comment in response to the following:
> $190 million -> 190 bucks ;)
Which appears to be a misunderstanding, as the calculation in question has implicitly taken into account the "millions of times" increase in disinfection efficacy.
> I think it'd be a bigger deal if it didn't require pressurization to 10 bar personally, pumps are expensive to operate and catalysts are a one-time-cost (if you're lucky).
I felt uncomfortable about the pressure, too, but it was just a hunch. Thank you for putting this into context. :)
Chlorine in the water provides disinfection all throughout the pool, this is very desirable when you have a pool. Imagine you see someone's bandage floating next to you in the water! Do you want to wait for the water to be pulled through the filtration system to get cleaned up? It typically takes a pool pump many hours to bring the full volume of the pool through the filtration system.
By having the disinfection agent spread through the pool, any bacteria or other contaminant will be acted on immediately. Algae is another big problem in many pools. Oftentimes there is some corner of the pool (or ladder, etc) that will harbor a little bit of algae that is waiting to take over the rest of the pool. Having chlorine dispersed through the water is very effective at preventing algae. Also, shocking the pool water with high levels of chlorine is oftentimes needed to keep the algae under control.
The common approach for making a pool need less daily maintenance is to get a salt water chlorine generator. A small amount of chlorine is generated by running an electrical current through electrodes. The electrodes need to be replaced every so often. Liquid chlorine is generally considered to be cheaper, but requires a lot of diligence because the chlorine dissipates pretty quickly.
I've seen hot tubs that use ozone for disinfection but not pools. I'm not sure what makes it a reasonable choice for hot tubs but not pools. Ozone would disperse through the water like chlorine, but it dissipates even more quickly.
One more interesting tidbit I picked up alone the way: the chlorine smell in a pool is not from the free chlorine. Free chlorine is what's available for disinfection. After a free chlorine molecule bonds to it's target, it's called combined chlorine. Combined chlorine is what is responsible for the nasty smell in pools. The solution for combined chlorine is to add dd more free chlorine!
What does MGD mean, and what is it in SI units? Million gallons per day? US gal or Imperial ones? (I'm not being facetious -- I genuinely don't know and it's my understanding that the US mix parts of the old British Imperial system, e.g. BTU, together with their own)
Yes, MGD means million gallons / day, and this is US gallons not Imperial (you should have been able to guess that from my reference to Virginia's standards--Virginia being a US state).
“When the reactor had reached the required pressure and the flow through the system had stabilized, the solvent (H²O, HPLC grade), typically at a flow of 0.2 ml min¯¹, was introduced into the system.“
You’re making such a big deal of the 0.2 ml/min that you didn’t stop to read that it’s talking about the amount of solvent… you’re just stirring up drama for the sake of drama
(I should preface this by saying that, unlike you, I have no real water disinfection expertise, so I may be overlooking significant fundamentals in what follows.)
Those costs sound reasonable for niche uses (though I do think they would prevent it from "revolutionizing water disinfection technologies" as they claim in the Conclusions), and being able to operate in practical terms at a very small scale seems to me like an advantage rather than a disadvantage. It clearly is more expensive than conventional water treatment and would have difficulty scaling to replace it for reasons of material availability. Other alternative very-small-scale disinfection approaches are probably cheaper than their process in its current form; they mention ozonation, UV irradiation with germicidal lamps, photocatalytic disinfection, and the Fenton process in the paper and supplement.
I don't see how the square-cube law plays into it; the reason they're supporting the catalyst on rutile (anatase?) instead of just using solid bars of metal alloy is precisely to ensure neat linear scaling, and the reason it's 1% metal instead of 0.1% or 0.001% is that the rutile is in the form of 1–100 nm particles. (See p. 8/12 in the article and Fig. 4 on p. 7/12). The only square-cube thing that occurs to me is that a large ice bath requires much less ice input than a small ice bath, but that favors scaling the process up, not down.
A couple of other points:
⓪ Your calculations seem to be correct.
① People's drinking water needs are lower than you suggest by a factor of about 65, although conventional surface-water treatment plants cannot take advantage of this.
② You're not taking into account the supply-chain issues that plague smaller-scale treatment facilities.
③ The cost of consumables that this process would eliminate would still be lower than the cost of the catalyst.
④ There are plausible ways the process might be improved that could make it economic.
Here are the calculations in more detail, since I misread yours badly at least twice.
You say 0.5 MGD is 6.5 million times higher than the 0.2 mℓ/min (3.3 μℓ/s) in the experiment. 0.5 MGD is 21.9 ℓ/s, which is 6.6 million times higher than 3.3 μℓ/s.
I think you are reading it correctly; they do say their catalyst is 0.5% Au and 0.5% Pd on a TiO₂ support: 0.6 mg of gold and 0.6 mg of palladium to process 0.2 mℓ/min of water. The supplementary material has a plot of different catalyst mixes they tried (Sup. Fig. 14, p. 12, 13/32).
If we normalize that amount of catalyst metal to SI units, that's 180 gram seconds per liter (g·s/ℓ) each of gold and palladium. Your 0.5 MGD (22 ℓ/s) for 5000 people is 4.4 mℓ/s per person, which works out to 790 mg per person each of gold and palladium. Palladium at US$2800 per troy ounce (https://www.kitco.com/charts/livepalladium.html — that is per troy ounce, isn't it?) is US...
This is mentioned in the Conclusions section of the paper.
Conventional surface-water treatment facilities involve treatment with hypochlorite, permanganate, chloramine, and whatnot. These pose some safety concerns (especially at small scales) and in many places are subject to legal reporting requirements. Occasionally there are industrial accidents because a truck driver pumped ammonia into the hypochlorite tank or vice versa; when people try to use the same materials at the household scale, sometimes you get medical problems because somebody put 1000 ppm of hypochlorite into their drinking water instead of 3 ppm. And, especially for individual households in middle-income and poor countries, there are often supply-chain issues with these materials; sometimes shipments don't arrive, or the household doesn't have enough money to buy a new bottle of bleach when they run out, or the products are falsely labeled, or have degraded before delivery—a particular problem with sodium hypochlorite.
For example, the cleaning-products store down the street from me here in Argentina advertises that they sell "100% chlorine", which I found pretty alarming until I saw that they are unpressurized bottles of liquid, not pressurized gas cylinders. Probably it's mostly aqueous sodium hypochlorite, but who the hell knows what the concentration is, and what else they put in it? The supermarket has jugs of sodium hypochlorite solution stabilized with sodium hydroxide, and the label tells you the nominal concentration (usually 66 g Cl/ℓ) but of course the bottles aren't hermetically sealed, may be exposed to sunlight, and may not have been properly quality-controlled at the factory in the first place.
If you're running an 0.5 mgd water treatment plant, you can presumably just measure the concentration in your hypochlorite tank, and have someone assigned to do this. And since they replaced the water main last year, we finally do have a reliable water supply 24/7, instead of only at night when the neighbors aren't pumping so much water. Still, the water from the mains has to be pumped up to the rooftop tank, where the chlorine concentration falls before we use it; maybe the water plant is putting way too much chlorine in the water to compensate for that, because it smells pretty strongly of bleach when it comes out of the tap.
If, by contrast, you have a durable catalyst that fulfills the same microbicidal function without needing constant reliable shipments of bleach, all of these concerns go away. It's like the difference between photovoltaic panels and the electric grid: even if a reliable electric grid might give you energy at a lower cost than having your own solar panels, that doesn't help if you don't have a reliable electric grid. It might be worth spending US$10-US$200 per person for an autonomous germicidal appliance; it might be cheaper than a refrigerator or washing machine.
③ Consumables costs.
That brings us to the question of consumables costs. Obviously enough, I've never operated a waterworks, but for example Callie Sue Rogers's 02008 B.S. thesis on conventional surface-water treatment plants https://core.ac.uk/download/pdf/4276743.pdf has a table surveying a number of Texas "conventional surface-water treatment facilities", concluding that they spend between US$20.21 and US$286.14 per million gallons on "chemical costs", depending on the condition of the water they're starting with; I infer "chemical costs" means things like the oxidants mentioned above, flocculants, and precipitants; this works out to 5.3 to 76 microdollars per liter. She estimates that the total production cost ranges from US$0.31/1000 gallons for small 5 mgd plants down to US$0.13/1000 gallons for larger 130 mgd plants (respectively 81 and...
From what I can tell of the paper, this would only replace the disinfectant stage of a waterworks; you'd still need the coagulation, flocculation, sedimentation, and maybe the filtration stages of the treatment plant. I don't know what the breakdowns of the various chemical loads for cost is, although I do know that the sodium hypochlorite for disinfection was by far the most heavily-consumed one. (Although the pH control for coagulation/flocculation was no slouch either, especially when all of the algae were busy having sex in summertime).
> How long would the catalyst last in practice?
That is a very interesting question, and one which immediately came to mind when I read the paper. Which is why I fell over laughing when the paper said something along the lines of "it lasts a long time, we tested it after three runs"--three runs is very far from establishing how long it lasts in an industrial setting.
> you'd still need the coagulation, flocculation, sedimentation, and maybe the filtration stages of the treatment plant.
Agreed, although lots of people have access to well or river water that's already pretty good if it weren't for the fecal coliforms in it.
> Which is why I fell over laughing when the paper said something along the lines of "it lasts a long time, we tested it after three runs"
Yes! It probably doesn't dissolve to any significant extent (though I'd be interested to know what the lower detection limit for their ICP-MS results would have been) but crap might build up on it. Still, it would have to be inorganic, fully oxidized crap that was in solution at the initial filtration stage and then precipitated on the catalyst and withstood continuous 200ppm ROS attack, which narrows down the candidates quite a bit. Maybe some kind of transition metal salt that got further oxidized into insolubility inside the reactor? But it has to be preeetty darn insoluble at the usual dissolved-solids levels, and then you could probably solve that problem with a little bit of carbonate or something upstream from the catalyst.
> ① Potable water needs are 5.7 ℓ/day/person, not 380.
> Your figure of 4.4 mℓ/s/person is 380 liters per day per person (100 gallons per day per person), but Burning Man recommends 1.5 gallons per day per person (5.7 liters/day/person, 0.066 mℓ/s/person), which includes water for showers, for cooking, and for drinking in a very dry environment with extensive physical exertion, though not for bidets. My experience at Burning Man is that you can get by on less.
So the figure of 100 gallons per day per person is the conversion factor literally built into Virginia's waterworks regulations (e.g., you're class 4 if you treat less than 0.5 MGD of water and you service fewer than 5,000 people). From my experience working at a water treatment plant, 100 gallons per day per person is the right order of magnitude for the amount of water that is actually used.
Yes, most of that water does not need to be potable (97% is the statistic I've heard cited). But if you want to supply both potable and non-potable water, you need to duplicate the entire distribution infrastructure; you can't just treat 3% of the water and say "that's good enough, right?"
> Yes, most of that water does not need to be potable (97% is the statistic I've heard cited). But if you want to supply both potable and non-potable water, you need to duplicate the entire distribution infrastructure; you can't just treat 3% of the water and say "that's good enough, right?"
Agreed! To speculate about where the difference between 3% (your figure) and 1.5% (my 65×) comes from; maybe people in Virginia take more showers, take longer showers, and use more water to wash their dishes, than people at Burning Man?
If you're disinfecting water at a household, building, or neighborhood level, though, rather than a town or city, duplicating the entire distribution infrastructure is a totally reasonable thing to do. For example, it might amount to running three water pipes instead of two vertically through the building core, next to the 40 chimneys and the elevator shaft, or having a potable-water faucet next to your sink that's hooked up to a water disinfection filter, or keeping a peroxide-generating water jug in the fridge, next to the potatoes, or having a water sanitizer in the utility closet next to the hot-water heater.
In this sense, centralization of water treatment is imposing a 30× or 60× waste factor, which is just a staggering factor: literally 97%–99% of its output is wasted! What's even more amazing is that, historically anyway, it makes up for it by improving convenience, safety, and reliability by an even greater factor. Except, I guess, in places like Flint.
I still think that, with current technology, an ozone generator or germicidal lamp is probably cheaper than this catalytic ROS generation stuff. But it'll be interesting to see how it develops.
yeah, we will take the catalysts that get donated and buy our way out of the third world!
"heres a solution for limitless free energy! step one, launch a bunch of solar reflectors into space to reflect solar energy at concentrated points on the surface of the earth. Step 2, wait, you don't have a scalable and advanced aerospace industry capable of launching thousands of collectors into orbit? I guess this won't work for you."
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[ 2.9 ms ] story [ 34.5 ms ] threadWhat are some other basic problems (food, water, temperature management, etc.) we're facing that are primarily energy-bottlenecked?
These become much cheaper:
- Transport: synthesise fuel from CO2 + seawater. Or charge a battery. - Water: electrolysis of seawater. - Food grown anywhere: Light + water + fertiliser can be made from commonly available materials. Soil is a bit trickier, but I think you could bootstrap up with composting. - Global warming: pull CO2 out of the air. - Raw materials (concrete, metals): all cheaper to extract with free energy. - producing medicine
Still really hard: - making new treatments - inflation of housing prices - escaping earth's gravity (need bounce per ounce) - world peace - writing books - politics
When building the desalination plant, we can build a solar farm right next door.
The problems are political. Nobody is willing to go out and spend the money.
My hope is that when automation starts taking peoples jobs, governments will employ and train people to build these big infrastructure projects. Desalination, Green Energy, Reforestation, better Agriculture and Land Management.
Everything is energy-bottlenecked.
Add to that the fact that, once these developments have happened, they tend to improve a lot, quickly. That means anything you build will, soon, be outdated and stop producing as much yield. Hence, you don't want to invest too much.
It's the same reason that we're not all driving around in hydrogen powered cars.
This combined with GAC filtration can produce very clean water anywhere you can get sunlight.
Though I guess that is also a precious metal.
For example, normally you need to filter, do settling for sediment etc - how did they solve all this?
Given the orders of magnitude involved here a 5 MGD plant could produce 500 trillion gallons per day of "commercial approach" water cleaning. The water handling issues alone in doing 500 trillion GPD seem large. Am I missing something?
I haven't read the paper yet (paywall)- just looked at their supplementary data.
The increased effectiveness appears (guessing here a bit) to be in terms of bacteria load reduction given similar concentration of bacteriacidal agents in same volume of liquid.
I'd focus on other benefits - ie, removal of other compounds etc.
> This approach offers the potential for in situ water purification that could, we propose, be suitable for decentralized applications.
If you have to install chlorinating equipment and operate it, then it becomes a matter of if the marginal savings in chlorine is worth it.
However there's also a good chance that chlorine concentration is controlled by downstream factors more than initial treatment- which is basically the case at every well/spring that produces drinkable water out of the ground, yet still needs residual treatment.
So there might not be any reduction in the required amount of chlorine.
If that's the case, I suspect that the type of decentralized system the authors think that this is useful for would be a nature where that's less of a concern. Smaller system leading to decreased time/distance between processing and use.
I'm REALLY going out on a limb here, but we hear about people who have to go and fetch their water supplies every day (perhaps multiple trips per day). I suspect that sources on that scale are where this might be useful.
Yes, that is what residual treatment is.
I'm not familiar with peroxide systems, but for this industry, you don't change things without a very good reason. If we're talking about new niche uses, then that's a different story, but still merits caution.
Related story:
Washington DC tried to "upgrade" from a chlorine system to another chlorine derivative that was supposed to have some marginal EPA benefits, and on paper it was a great design.
In practice (and many tens/hundreds of millions of dollars later), the water quality had a sharp decline, with all sorts of unexpected chemicals showing up. It turns out the old system had the unintentional side effect of "filtering" out all kinds of nasty reactive stuff (including lead), and the new chemical balance reversed the process. All the chemicals that had been sequestered in the pipe walls for decades or longer, were now getting pulled back into the water. Oops.
Then there was the initiative in India where thousands of water wells were drilled, only to discover the water contained arsenic.
>I suspect that the type of decentralized system the authors think that this is useful for would be a nature where that's less of a concern. Smaller system leading to decreased time/distance between processing and use.
It may, but UV disinfection has similar properties and has been available for a while now, probably at a lower price.
Also, if water's getting transported in personal containers, chances are they're dirtier than any water main. It's easy to draw the limits of the system at a convenient point, but these are the situations that probably need residual treatment more than than we do.
Of course reality dictates what's feasible, especially in the 3rd world, and "exciting" new tech like this might get funding that boring old school solutions won't.
The fact that they are making bold claims about potential applications is sufficient to justify Kaibeezy's reply to riddly.
>"...are over 10^7 times more potent than an equivalent amount of preformed hydrogen peroxide..."
Per fig. 2(c,d), the "commercial H2O2" items are solutions of 100 and 200 ppm (0.01% / 0.02%), and have nearly zero effect (less than 1 order-of-magnitude reduction in bacterial/viral viability).
([edit]: or quoting the paper itself: "These standardized preformed H2O2 samples, produced either commercially or catalytically (100–200ppm), exhibited limited bactericidal activity [my emphasis] against...")
Their actual point is that this H2O2+ROS is highly effective at a concentration at which H2O2 alone is not effective.
https://www.researchgate.net/publication/352882305_A_residue...
~~~~~
[edit]: In attempt to find further context, here's some data about disinfection with H2O2 solutions (in entirely different experimental setups which probably have important caveats I don't know):
>"...organisms with high cellular catalase activity (e.g., S. aureus, S. marcescens, and Proteus mirabilis) required 30–60 minutes of exposure to 0.6% hydrogen peroxide for a 10^8 reduction in cell counts, whereas organisms with lower catalase activity (e.g., E. coli, Streptococcus species, and Pseudomonas species) required only 15 minutes’ exposure [657]..."
https://www.cdc.gov/infectioncontrol/pdf/guidelines/disinfec... (page 47)
So, as a hand-waving non-expert: it looks like you can get the same order of magnitude of effect (factor of 10^8 bacterial reduction) as the stuff in the OP paper, at a hydrogen peroxide concentration that's ~60 times higher than what OP uses (0.6% = 6000 ppm). (?)
> The catalyst-based method was shown to be 10,000,000 times more potent at killing the bacteria than an equivalent amount of the industrial hydrogen peroxide, and over 100,000,000 times more effective than chlorination, under equivalent conditions.
Basically, I'm getting the highly reactive ROS are the key point here, they're creating them in situ so they're able to be exploited where as standing h2o2 is likely much less reactive.
The order of magnitude gains are easy to grasp if you take into consideration the literal hours you need to wait for chlorine or similar to sterilize water. If there is a way to speed that up to near instant your gains are going to be relatively immeasurable.
If you are into camping you might be thinking of things like Giardia - much harder to kill.
This is actually my point exactly. This may not be 100,000,000x better in a practical sense. It is maybe 60x better but because they are doing math with something that is a zero (or close too it) they get to report an insane increase in effectiveness.
It's actually a great tell for what is often garbage analysis when you have this level of a multiple.
I don't think this is comparable to a water treatment plant. No sediment settling, biofiltration etc. It's comparable to sterilising water using hydrogen peroxide or boiling it, in a camping context.
Not sure what the "millions of times" measures.
The key sentence should be this:
> In their study, the team tested the disinfection efficacy of commercially available hydrogen peroxide and chlorine compared to their new catalytic method.
In other words, no, this doesn't replace coagulation+flocculation, sedimentation, and filtration; it's only replacing the specific disinfectant in use.
"Let them use palladium."
Even if it required a fair bit, 10M is a really big number. Long term savings would be huge since the catalysts aren’t consumed in the reactions
Plus they only tested vs E. Coli which is not very durable as far as nasty microbes in your water go.
Catalysts don't get used up, and metals of platinum group are 100% recycleable.
[1]: https://en.wikipedia.org/wiki/Catalytic_converter
Probably nobody knows. It's research; it's not a technology or product in development.
Though I wish this article addressed some of the questions I had around commercialization, namely the cost of the gold + palladium, the expected lifecycle, and the expected maintenance routine (e.g. do they have to be regularly removed and cleaned?).
The article makes great arguments for why this should work (i.e. hydrogen peroxide is already being used, this just short-circuits how we get a known effective cleaning agent, reducing/removing logistics inefficiencies). So a lot of the question is: Is this cheaper/less hassle than buying stabilized hydrogen peroxide commercially?
A lot of these fantastic advances often end up in the black hole, wherein they work as advertised, but the financials/logistics never line up and therefore nobody uses them in anger.
From the article: "The team showed that as the catalyst brought the hydrogen and oxygen together to form hydrogen peroxide, it simultaneously produced a number of highly reactive compounds, known as reactive oxygen species (ROS), which the team demonstrated were responsible for the antibacterial and antiviral effect, and not the hydrogen peroxide itself."
https://www.researchgate.net/publication/352882305_A_residue...
With that in mind "millions of times better" isn't necessarily a disingenuous description. Though you might say it's somewhat misleading, since as the denominator goes to zero, the fraction goes to infinity :)
It's the equivalent of saying 99.99999999% uptime is "ten million times more available" than 99.9% uptime - um, just give me the number of nines please!
That depends how you look at it. Is it 90% killed, or is it 10% survived? If it's 10% survived, then 100m times better is a system where 10/100m % survived instead.
Let's say the best effort is 91.001% and our smart new process is 92.001%. Now set the baseline at 91.000% This is the sleight of hand bit: If we say that "normal" is 91.000, we now set the best effort as 0.001 and our effort as 1.001. That can seem quite reasonable when trotted out by a news reader or reporter.
So we are (1.001/0.001) x 100 = 100,100% better than the previous best!
The real improvement is more like: 92.001/91.001 x 100 = 101.098% which is a bit obvious when you look at the numbers involved.
With a single quite clumsy move and a bit of misdirection you can turn 101 into 100,100 and sound quite convincing. Now that's only using the very basic arithmetic operations and a bit of bullshit. The clever kids can really go to town.
We need some sort of laws about the presentation of statistics because it really is getting out of hand. The nonsense I've just presented isn't fiction. I saw something similar recently, can't remember what for but it took a while for me to calm down afterwards 8)
But in your example it's more sane if you flip it.
Survival rate from a new medicine may be 99.99% and only allows 1.0001 multiple of improvement. For severe outcomes, not allowing expansive language to describe improvements is a legitimate problem. i.e. if we insisted on this, it would be hard to motivate improvements in safety from 99% to 99.999% since they are "only <1% improvements".
So in cases like this I think of it in reverse: the death rate of 0.01% can be improved by 90% (or 10x) to 0.001%. This does run the risk of inflating the importance of the fix when the base rate is extremely low.
My rule is: articles which use multiples or percentages must give enough detail to exactly reconstruct the calculation method used.
The real problem is percentages; people also intuitively assume "50% less than (50% more than X) is X"
“Better” does not necessarily mean “kills a higher percentage of bacteria”
By the way, this isn’t a comment on the article itself in any way, simply a comment on the logic of your comment
How to we get rid of those without needing to rely on expensive multi-stage filters that need to be replaced every 4 months?
https://www.nature.com/articles/531011b
To add to the transgressions, this thread is discussing the content of a peer-reviewed paper of original research about some tricky, detailed parts of chemistry and microbiology.
Intelligent discussion and content? Horrors!!
Stand aside as 99 44/100% of media comes tumbling down like that condo recently did in Florida? Maybe!
Ah, that's Hacker News for you; no chance of seeing such content, such flagrant transgressions, in the MSM!
Uh, I'm not complaining, you understand! Not complaining at all!
Yeah, those are just found lying around wherever people need clean water.
"Cleaning" is much different from "disinfecting", sometimes the opposite.
Since it's a challenge to separate the products/byproducts in catalytic reactions that are homogenous/liquid phases, how would this setup achieve separation post reaction exactly? Anyone know?
> A typical H₂O₂ synthesis reaction was carried out using 120 mg of 1% AuPd/TiO₂ [...] The reactor system was then pressurized, typically to 10 bar. The reactor was then cooled by a water bath to 2 °C. When the reactor had reached the required pressure and the flow through the system had stabilized, the solvent (H²O, HPLC grade), typically at a flow of 0.2 ml min¯¹, was introduced into the system.
Oh hey, 0.2 mL/min of water. In Virginia, the lowest flow cutoff for waterworks is 0.5 MGD (or 5000 people), the border between Class 3 and Class 4. That flow rate is 6.5 million times that done in the tests here. The large water treatment plant I worked at is another 400 times that, and there are plants that would be another 5 or 6 times that. So the necessary scaling factor is going to be measured in the billions.
So what about those reagants? This uses about 0.6 mg of gold to process 0.2 mL/min of water (if I'm reading the notation of 1% AuPd/TiO₂ correctly). Scale that to our small plant, and that's about $225,000 of gold and $350,000 of palladium. Go to the scale I worked at, and that's $190 million of catalyst in terms of raw metal worth alone. That's comparable to the cost of a regular treatment plant of that scale--just on the catalyst. This assumes that there's a neat linear scaling, which I doubt is going to be the case (square-cube law!).
Now others can try to reproduce it, refine it, find other methods of producing the same reactive oxygen species, find substitutes that are more effective or cheaper, etc.
It doesn't have to be panacea either. Maybe it will fill a niche. It could save some lives.
The press release makes bold implications tbh
$190 million -> 190 bucks ;)
Seriously though, couldn't they just use far less catalyst and not have to deal with the prices you've calculated?
(Your strategy might totally work of course, just might not be a given)
The flow rate is likely positively correlated with catalyst loading (in the part that we care about) and the calculation is already based on the flow rate of 0.2 ml min¯¹ they reported in the paper. The reported flow rate is also likely already optimised for the Nature Communications paper.
My guess is that you could drop the catalyst noble metal content by 10-100x or even substitute an alternative catalyst and find a combination of conditions and catalyst that works. It's not a sure thing, but it's not unlikely. Sometimes it's as simple as swapping one support for another and the performance goes up 100x, it's just a lot of tests to run that don't even apply to both lab and commercial scales anyway (so a lot of the tests are never practical to run anyway).
I think it'd be a bigger deal if it didn't require pressurization to 10 bar personally, pumps are expensive to operate and catalysts are a one-time-cost (if you're lucky).
Absolutely agree and no arguments whatsoever. In fact, one of the first things that I joked to myself was that we will soon see papers on MOF-suppoorted version of the catalyst -- well before we see any DoE.
In any case, I just want to note that I made the comment in response to the following:
> $190 million -> 190 bucks ;)
Which appears to be a misunderstanding, as the calculation in question has implicitly taken into account the "millions of times" increase in disinfection efficacy.
> I think it'd be a bigger deal if it didn't require pressurization to 10 bar personally, pumps are expensive to operate and catalysts are a one-time-cost (if you're lucky).
I felt uncomfortable about the pressure, too, but it was just a hunch. Thank you for putting this into context. :)
Edit: clarity, typo.
I'm not sure what the hydrogen peroxide method brings to the table compared with UV/ozone (besides a university press release).
[0]: https://www.espwaterproducts.com/ultraviolet-uv-systems/
[1]: https://www.socotec.co.uk/media/faqs/faqs-ozone-water-treatm...
By having the disinfection agent spread through the pool, any bacteria or other contaminant will be acted on immediately. Algae is another big problem in many pools. Oftentimes there is some corner of the pool (or ladder, etc) that will harbor a little bit of algae that is waiting to take over the rest of the pool. Having chlorine dispersed through the water is very effective at preventing algae. Also, shocking the pool water with high levels of chlorine is oftentimes needed to keep the algae under control.
The common approach for making a pool need less daily maintenance is to get a salt water chlorine generator. A small amount of chlorine is generated by running an electrical current through electrodes. The electrodes need to be replaced every so often. Liquid chlorine is generally considered to be cheaper, but requires a lot of diligence because the chlorine dissipates pretty quickly.
I've seen hot tubs that use ozone for disinfection but not pools. I'm not sure what makes it a reasonable choice for hot tubs but not pools. Ozone would disperse through the water like chlorine, but it dissipates even more quickly.
One more interesting tidbit I picked up alone the way: the chlorine smell in a pool is not from the free chlorine. Free chlorine is what's available for disinfection. After a free chlorine molecule bonds to it's target, it's called combined chlorine. Combined chlorine is what is responsible for the nasty smell in pools. The solution for combined chlorine is to add dd more free chlorine!
You’re making such a big deal of the 0.2 ml/min that you didn’t stop to read that it’s talking about the amount of solvent… you’re just stirring up drama for the sake of drama
Those costs sound reasonable for niche uses (though I do think they would prevent it from "revolutionizing water disinfection technologies" as they claim in the Conclusions), and being able to operate in practical terms at a very small scale seems to me like an advantage rather than a disadvantage. It clearly is more expensive than conventional water treatment and would have difficulty scaling to replace it for reasons of material availability. Other alternative very-small-scale disinfection approaches are probably cheaper than their process in its current form; they mention ozonation, UV irradiation with germicidal lamps, photocatalytic disinfection, and the Fenton process in the paper and supplement.
I don't see how the square-cube law plays into it; the reason they're supporting the catalyst on rutile (anatase?) instead of just using solid bars of metal alloy is precisely to ensure neat linear scaling, and the reason it's 1% metal instead of 0.1% or 0.001% is that the rutile is in the form of 1–100 nm particles. (See p. 8/12 in the article and Fig. 4 on p. 7/12). The only square-cube thing that occurs to me is that a large ice bath requires much less ice input than a small ice bath, but that favors scaling the process up, not down.
A couple of other points:
⓪ Your calculations seem to be correct.
① People's drinking water needs are lower than you suggest by a factor of about 65, although conventional surface-water treatment plants cannot take advantage of this.
② You're not taking into account the supply-chain issues that plague smaller-scale treatment facilities.
③ The cost of consumables that this process would eliminate would still be lower than the cost of the catalyst.
④ There are plausible ways the process might be improved that could make it economic.
Thanks to mkr-hn I found the paper at https://www.researchgate.net/publication/352882305_A_residue... the canonical paper link (unforgivably missing from the original press release) is https://www.nature.com/articles/s41929-021-00642-w, and the supplementary material is at https://static-content.springer.com/esm/art%3A10.1038%2Fs419....
— ⁂ —
⓪ Scaling calculations.
Here are the calculations in more detail, since I misread yours badly at least twice.
You say 0.5 MGD is 6.5 million times higher than the 0.2 mℓ/min (3.3 μℓ/s) in the experiment. 0.5 MGD is 21.9 ℓ/s, which is 6.6 million times higher than 3.3 μℓ/s.
I think you are reading it correctly; they do say their catalyst is 0.5% Au and 0.5% Pd on a TiO₂ support: 0.6 mg of gold and 0.6 mg of palladium to process 0.2 mℓ/min of water. The supplementary material has a plot of different catalyst mixes they tried (Sup. Fig. 14, p. 12, 13/32).
If we normalize that amount of catalyst metal to SI units, that's 180 gram seconds per liter (g·s/ℓ) each of gold and palladium. Your 0.5 MGD (22 ℓ/s) for 5000 people is 4.4 mℓ/s per person, which works out to 790 mg per person each of gold and palladium. Palladium at US$2800 per troy ounce (https://www.kitco.com/charts/livepalladium.html — that is per troy ounce, isn't it?) is US...
This is mentioned in the Conclusions section of the paper.
Conventional surface-water treatment facilities involve treatment with hypochlorite, permanganate, chloramine, and whatnot. These pose some safety concerns (especially at small scales) and in many places are subject to legal reporting requirements. Occasionally there are industrial accidents because a truck driver pumped ammonia into the hypochlorite tank or vice versa; when people try to use the same materials at the household scale, sometimes you get medical problems because somebody put 1000 ppm of hypochlorite into their drinking water instead of 3 ppm. And, especially for individual households in middle-income and poor countries, there are often supply-chain issues with these materials; sometimes shipments don't arrive, or the household doesn't have enough money to buy a new bottle of bleach when they run out, or the products are falsely labeled, or have degraded before delivery—a particular problem with sodium hypochlorite.
For example, the cleaning-products store down the street from me here in Argentina advertises that they sell "100% chlorine", which I found pretty alarming until I saw that they are unpressurized bottles of liquid, not pressurized gas cylinders. Probably it's mostly aqueous sodium hypochlorite, but who the hell knows what the concentration is, and what else they put in it? The supermarket has jugs of sodium hypochlorite solution stabilized with sodium hydroxide, and the label tells you the nominal concentration (usually 66 g Cl/ℓ) but of course the bottles aren't hermetically sealed, may be exposed to sunlight, and may not have been properly quality-controlled at the factory in the first place.
If you're running an 0.5 mgd water treatment plant, you can presumably just measure the concentration in your hypochlorite tank, and have someone assigned to do this. And since they replaced the water main last year, we finally do have a reliable water supply 24/7, instead of only at night when the neighbors aren't pumping so much water. Still, the water from the mains has to be pumped up to the rooftop tank, where the chlorine concentration falls before we use it; maybe the water plant is putting way too much chlorine in the water to compensate for that, because it smells pretty strongly of bleach when it comes out of the tap.
If, by contrast, you have a durable catalyst that fulfills the same microbicidal function without needing constant reliable shipments of bleach, all of these concerns go away. It's like the difference between photovoltaic panels and the electric grid: even if a reliable electric grid might give you energy at a lower cost than having your own solar panels, that doesn't help if you don't have a reliable electric grid. It might be worth spending US$10-US$200 per person for an autonomous germicidal appliance; it might be cheaper than a refrigerator or washing machine.
③ Consumables costs.
That brings us to the question of consumables costs. Obviously enough, I've never operated a waterworks, but for example Callie Sue Rogers's 02008 B.S. thesis on conventional surface-water treatment plants https://core.ac.uk/download/pdf/4276743.pdf has a table surveying a number of Texas "conventional surface-water treatment facilities", concluding that they spend between US$20.21 and US$286.14 per million gallons on "chemical costs", depending on the condition of the water they're starting with; I infer "chemical costs" means things like the oxidants mentioned above, flocculants, and precipitants; this works out to 5.3 to 76 microdollars per liter. She estimates that the total production cost ranges from US$0.31/1000 gallons for small 5 mgd plants down to US$0.13/1000 gallons for larger 130 mgd plants (respectively 81 and...
> How long would the catalyst last in practice?
That is a very interesting question, and one which immediately came to mind when I read the paper. Which is why I fell over laughing when the paper said something along the lines of "it lasts a long time, we tested it after three runs"--three runs is very far from establishing how long it lasts in an industrial setting.
Agreed, although lots of people have access to well or river water that's already pretty good if it weren't for the fecal coliforms in it.
> Which is why I fell over laughing when the paper said something along the lines of "it lasts a long time, we tested it after three runs"
Yes! It probably doesn't dissolve to any significant extent (though I'd be interested to know what the lower detection limit for their ICP-MS results would have been) but crap might build up on it. Still, it would have to be inorganic, fully oxidized crap that was in solution at the initial filtration stage and then precipitated on the catalyst and withstood continuous 200ppm ROS attack, which narrows down the candidates quite a bit. Maybe some kind of transition metal salt that got further oxidized into insolubility inside the reactor? But it has to be preeetty darn insoluble at the usual dissolved-solids levels, and then you could probably solve that problem with a little bit of carbonate or something upstream from the catalyst.
> Your figure of 4.4 mℓ/s/person is 380 liters per day per person (100 gallons per day per person), but Burning Man recommends 1.5 gallons per day per person (5.7 liters/day/person, 0.066 mℓ/s/person), which includes water for showers, for cooking, and for drinking in a very dry environment with extensive physical exertion, though not for bidets. My experience at Burning Man is that you can get by on less.
So the figure of 100 gallons per day per person is the conversion factor literally built into Virginia's waterworks regulations (e.g., you're class 4 if you treat less than 0.5 MGD of water and you service fewer than 5,000 people). From my experience working at a water treatment plant, 100 gallons per day per person is the right order of magnitude for the amount of water that is actually used.
Yes, most of that water does not need to be potable (97% is the statistic I've heard cited). But if you want to supply both potable and non-potable water, you need to duplicate the entire distribution infrastructure; you can't just treat 3% of the water and say "that's good enough, right?"
Agreed! To speculate about where the difference between 3% (your figure) and 1.5% (my 65×) comes from; maybe people in Virginia take more showers, take longer showers, and use more water to wash their dishes, than people at Burning Man?
If you're disinfecting water at a household, building, or neighborhood level, though, rather than a town or city, duplicating the entire distribution infrastructure is a totally reasonable thing to do. For example, it might amount to running three water pipes instead of two vertically through the building core, next to the 40 chimneys and the elevator shaft, or having a potable-water faucet next to your sink that's hooked up to a water disinfection filter, or keeping a peroxide-generating water jug in the fridge, next to the potatoes, or having a water sanitizer in the utility closet next to the hot-water heater.
In this sense, centralization of water treatment is imposing a 30× or 60× waste factor, which is just a staggering factor: literally 97%–99% of its output is wasted! What's even more amazing is that, historically anyway, it makes up for it by improving convenience, safety, and reliability by an even greater factor. Except, I guess, in places like Flint.
I still think that, with current technology, an ozone generator or germicidal lamp is probably cheaper than this catalytic ROS generation stuff. But it'll be interesting to see how it develops.
"heres a solution for limitless free energy! step one, launch a bunch of solar reflectors into space to reflect solar energy at concentrated points on the surface of the earth. Step 2, wait, you don't have a scalable and advanced aerospace industry capable of launching thousands of collectors into orbit? I guess this won't work for you."