WT Interview with Ralf Kaegi, Ph.D., Institute of Aquatic Science and Technology, Switzerland

WT: I have on the phone Ralf Kaegi, he is a Ph.D. and Process Engineer from the Swiss Federal Institute of Aquatic Science and Technology. Thanks for doing this. Can you tell us about your research project about the removal of nano-plastics and micro-plastics from drinking water using old technology? What did you find?

Ralf Kaegi: We ran pilot studies with drinking water treatment plants using the conventional low-flow sand filters, testing for the removal of nano-plastics. We found that nano-plastics and other particles will be removed or retained by the conventional water filter plant, to a level of 99.9% or more.

If you go back into the theory which has been developed decades ago, you will assume that everything is removed or the majority is removed. We just wanted to make sure that this is actually the case when you do these experiments on a pilot scale.

WT: You are saying that sand filters in wastewater plants would catch 99% of the nano-plastics, is that accurate?

Kaegi: We are not talking about wastewater plants here but drinking water plants. Basically, they are also (using) sand filters. I would assume that if you have the so-called ‘Schmutzdecke’ (German), a bio-layer that develops over time on the top layer of the sand filter, then you have a very, very efficient filtration, very efficient retention of any kind of particulate material, including nano-plastics, so 99.9% is certainly true, it may be also 99.99%.

WT: One of the interesting things about this, is I understand this process should be relatively easy for water plants to do, and the process is not expensive. Is that accurate?

Kaegi: Easy for sure. If you have space and you do have space in Canada, then low-flow sand filtration will do it. In Switzerland, where we have restricted space, we increasingly use membrane filtration. There you have pore spaces of the membranes in the order of 10 nanometres, so (those) will have higher retention, probably have removal of 99.999%.

"Sand filtration is very old technology. It’s a very simple technology but it is also a very efficient technology to remove all kinds of particulate materials, including micro-plastics and nano-plastics." Ralf Kaegi

WT: Ralf, I am just not understanding something. If it’s that easy to put a sand filter in front of the drinking water treatment plant, what would someone’s logic be for not doing this, if it is a proven technology and it does work?

Kaegi: I am not familiar with Canadian drinking water plants, but I would use sand filtration, I would assume this is already installed. In Switzerland when you have the source water which comes directly from the crystalline rocks or whatever, the chances that you have elevated concentrations of nano-plastics is very, very low. In these cases, in your sort of pristine areas, there is probably no need to do sand filtration. However, if you are in urban areas, I would expect that sand filters are also installed in Canada. But I don’t know this.

WT: How long did it take you to do the research to put this paper out? I am trying to give people a timeframe of how long this takes. It seems to me, that this is such a simple thing, most Canadian plants do have sand filters. Have you discussed this with any Canadian plants at all?

Kaegi: The research was interrupted by corona. It took a little longer than we thought, it always takes longer than you think. I think from the original idea to finalizing the final paper, three years. The delays affected the pilot plant experiments, but as a rough number, I would say three years.

No, certainly I didn’t talk to Canadian waterwork. I did my research in Switzerland, so I don’t have any contacts in Canadian waterworks.

WT: If I was to put a Canadian waterwork company on the phone, could I get you to discuss this with them? I think this is a huge problem, and if you have a relatively simple solution, connecting you with a water plant, would that be a good idea? I would love to get a trial test going in Canada.

Kaegi: Sure, but again, sand filtration is nothing new to Canadians. That’s just the earliest technology we’ve developed for purifying the water. I could simply imagine that you have such an enormous amount of space here. I mean, you probably have less plastic pollution than we have, for example, in Switzerland. So, I can imagine that for some waterworks, it’s just probably not needed. In other waterworks, I would certainly be needed, but I would assume that they have already installed (sand filters) because they were invented to remove particulate materials. You don’t have to upgrade or anything, just (use) the standard technique. We just wanted to show that when you use the standard technique, you also get rid of the nano-plastics.

WT: I think that’s just fantastic! After I hang up, I will get in touch with sand filter water plants and ask them, do you know, have you tested for nano-particles? Is that the right question to be asking?

Kaegi: Sure, certainly they have tested for nano-plastics. The theory says it works, but at the moment the topic is so emotionally discussed, that the theory is not enough to convince the public. We wanted to convince the public, so this was also a collaboration with the local waterworks. We did the experiments and, in the end, it came out as the theory predicts.

WT: So you essentially did this as a public relations measure to convince the population with a sand water plant that, “look, you are not drinking as much nano-plastics as you think you are”. Is that a fair statement, Ralf?

Kaegi: That’s a very fair statement. You know, there are many reports about nano-plastics or micro-plastics in bottled water and drinking water, and we were just reaching out to the waterworks, saying this cannot be from the treatment. We cannot imagine that the nano-plastics or the micro-plastics from the source water make it through the drinking water treatment.

There may be nano-plastics and micro-plastics in the drinking water, but this doesn’t come from the treatment process. More likely the distribution system, or if you look at bottled water, when you open and close the bottle, these are the sources we think the plastics come from, but it does not come from the treatment plant itself.

WT: So this would be a bit of good news. I would think the next thing would be if you don’t have sand filtration out in front of your system, you should be quickly working on that, is this right?

Kaegi: I have no idea about the waterworks in Canada. If you have a membrane filtration, sure, it will filter out all the nano-plastics, that’s not an issue then anymore. So, it really depends on the treatment chain that you have in specific waterworks. Having said that, if you look at our experiments, they were done with extremely high concentrations of nano-plastics. At the moment we have no record of nano-plastics in the source water. We don’t think that there is much nano-plastic in ­­­­the source water, but we don’t know this because we can’t measure this reliably. That was another motivation to do the study, to say in the worst case we have, even if we have elevated concentrations of nano-plastics in the source water they will not make it in our drinking water. You are most likely not drinking plastic, if you are drinking plastic, it is not coming from the waterworks.

WT: Can we say to communities with sand filtration, “you can leave the bottled water on the shelf and drink your municipal water” because there are really good odds that there are no nano-plastics or nano-particles in the water from the tap? Is that a fair statement?

Kaegi: I would say so, though I haven’t done the measurements (in Canada).

I really do trust that the treatment works. I drink tap water, yes.

WT: That’s fantastic Ralf. Thanks very much for doing this.

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