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ACO: Interview with Moritz Gesterding
“We are protecting our drinking water resources for tomorrow.”
We spoke with Moritz Gesterding, Head of Research & Development at ACO Beton GmbH, about microplastics in water. Moritz is the perfect conversation partner for the interviewer, who wasn't exactly the brightest bulb in the box when it came to physics. Moritz's recipe: He goes from tire abrasion on the road to cooking pasta in the kitchen, from there to density differences, sedimentation, flotation, and filtration – to arrive at his favorite paragraph of the Water Resources Act and make the leap to cycling.
Moritz Gesterding
Head of Research & Development
Plastic is everywhere. Even some organic cucumbers are wrapped in plastic. A basic distinction is made between visible plastic waste and microplastics, i.e., particles smaller than five millimeters. Moritz, do you remember the moment when you realized how ubiquitous microplastics are?
I have been working on the topic of water for over 15 years. The issue of microplastics has simply become more and more prominent, as we all know from the increasing amount of waste. When I was studying in Malaysia in 2008, you could already see lots of plastic bags blowing around. That's the most visible thing we see in Germany, too. We “cover it up” a little here because we export most of our waste to other countries and pretend that plastic waste is not an issue for us. Over the last five or six years, I have been looking closely at the fact that microplastics are a major issue when it comes to rainwater. A real eye-opener for me was the issue of tire abrasion and the realization that this is the largest emitter of microplastics in Germany.
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It's hard to believe that tire abrasion from cars causes the largest amount of microplastics in the environment in Germany, isn't it?
Exactly. Tire abrasion accounts for the largest share. It's very diffuse, spreading across highways, roads, and large squares into our waters and from there into the sea. The extent of it all is truly extreme.
© J.M Read / Unsplash
Here in Kiel, internist Dr. Wolfgang Kroll recently gave an exciting keynote speech on the topic of microplastics at Sealevel. He reported that, relative to the total world population, we humans consume around five grams of microplastics per week, which is roughly equivalent to a credit card.
I'm familiar with those figures too. As someone who works in research and development, I am sometimes a little critical because I am not familiar with the underlying study. Nevertheless, it is of course good to present the problem in a striking way. The fundamental problem that we ingest microplastics through the food chain definitely exists. With regard to microplastics in drinking water, it is important to look closely at exactly what kind of water is involved. Is it drinking water resources or drinking water itself? Our drinking water is treated so thoroughly that even the smallest particles are filtered out. This means that microplastics end up in our water resources, but not in our drinking water. Of course, that's not much better, because microplastics have many effects and we end up ingesting them again through fish, at the latest. That's why I don't want to downplay the issue. I just think it's important to be precise and maintain clarity in how the problem is described. Nevertheless, it's a huge issue.
In the Ocean Race Europe, all racing yachts are equipped with various measuring devices that regularly take water samples and send the data directly to scientists. Depending on the sensor technology, microplastic content can also be measured. How important is substantial data for sound work, especially since we live in a world of uncertain facts and fake news?
That's why it's important to be familiar with the research situation in order to understand whether something is being dramatized or downplayed. There are interest groups that downplay certain findings so as not to present them as a problem.
© Cherie Bridges / The Ocean Race
The OceanPack, developed by GEOMAR and SubCtech in Kiel, is a specialised instrument with multiple sensors that measure a range of types of data about the ocean. It operates automatically and continuously, taking around 25,000 measurements per day.
© Antoine Auriol / Team Malizia / The Ocean Race
© Antoine Auriol / Team Malizia / The Ocean Race
“To protect our rivers and the sea, we should treat rainwater from the road directly.”
Moritz Gesterding
Another study states that ten million tons of plastic waste are washed into the sea every year – that's equivalent to one truckload per minute. Huge carpets of plastic waste float on the oceans, known as the Great Garbage Patches. And that's just the visible plastic, not the plastic that has sunk or broken down into microplastics. What is the better approach? Avoiding plastic or developing improved methods to filter out microplastics?
Of course, prevention is always better. In environmental science, we talk about the hierarchy of “reduce, reuse, recycle.” Prevention is the most important thing, but we also have to remain realistic. For example, you can't prevent tire wear. You can consider whether to take the car or the much lighter bicycle, which I am a big fan of. That way, I have less abrasion, not to mention the other positive climate effects. When it comes to water management and water treatment, “point of source” treatment is usually better than “end of pipe” treatment. Wastewater should be treated where it is produced and where the pollutants are more concentrated, rather than at the end, where many different types of water with different pollutants have converged.
We want to avoid sending rainwater to the sewage treatment plant as much as possible so as not to overload it hydraulically. Rainwater should therefore be directed straight into the groundwater or rivers. The water that is discharged into rivers eventually flows into the sea, where the pollutants from the road would naturally end up. To protect our rivers and the sea, we should treat rainwater from the road directly. This “point of source” approach is naturally more difficult on a long road than in a place such as a factory.
“The larger the particles, the better they float or sink. And that brings us to the problem of microplastics.”
Moritz Gesterding
ACO distinguishes between the steps Collect, Clean, Hold, and Reuse in the WaterCycle. What technical options are available for removing microplastics in the “Clean” step during rainwater treatment?
There are two options, two different physical process steps. One is sedimentation, the other is flotation. These involve separation based purely on density differences. Water has a density of almost exactly 1. At a density of 0.9, something floats, and at 1.1 or above, it sinks. To explain it very simply, it works like in the kitchen: when I pour olive oil into my spaghetti pot, it floats on top because its density is lower than that of water. That is flotation. When I was a child and weighed a little more, people would say, “Look, Moritz can swim.” Fat floats to the top, as we all know. And this also applies to other liquids and substances that have a lower density than water, such as all fuels used for cars, such as gasoline and diesel, but also many plastics.
With sedimentation, it's the other way around: the heavier particles sink. We know this principle from muddy water. After a while, the sand sinks to the bottom and clean water remains at the top of the bucket. Sedimentation is useful for substances such as brake dust. The greater the difference in density compared to water, the better it works.
But it's also a question of particle diameter. The larger the particles, the better they float or sink. And that brings us to the problem of microplastics. Imagine you have a stone and styrofoam of the same size. The stone sinks because it is simply heavier, and the styrofoam floats on top because it is relatively lighter than water. But if we go down to the micrometer range, the same thing happens, but it takes much longer. And that is precisely the crucial point: you also have the time component. This means that if I have a treatment plant that works with flotation or sedimentation, i.e., with floating or sinking, I also have to give the water time. If I have large particles with a diameter of about one millimeter, this will happen relatively quickly. But if I go into the micrometer range, I eventually have the problem that my plants would have to be not only two meters in diameter, but 100 meters long to give the particles enough time to really sink and be separated. If the density is then very close to one, it becomes even more difficult, because then the particle almost floats. This brings us to the next step, filtration.
So now we come to the pasta strainer?
Exactly. The water is allowed to run through and the spaghetti is filtered out. Well, some of the spaghetti slips through, so we use spiral pasta (laughs). That's basically what we do on a smaller scale. Of course, it's really micro-small, in the micrometer range, with our rainwater treatment plants.
Is this also used in sewage treatment plants?
Not exactly. In a sewage treatment plant, there is usually a mechanical cleaning process at the beginning. It starts with coarse and fine screens that retain the coarser materials up to a size of about one millimeter. This is followed by treatment steps involving sedimentation and flotation. This is followed by biological cleaning, which produces sewage sludge. Our sewage treatment plants retain up to 95 percent of the microplastics that end up there. And around 80 percent of that accumulates in this sewage sludge. However, this is not currently a dedicated microplastics treatment, but rather, to use marine jargon, a positive bycatch.
© ACO
“I believe that drinking water is a human right. However, it has to be treated, which incurs costs and should therefore also have a price.”
Moritz Gesterding
Ultimately, it is always a social and political issue, because every water treatment process involves weighing up the benefits and costs.
Basically, you always have to say: water quality costs money. That's just a fact. And that's exactly what you're talking about. We have to consider what it's worth to us to treat rainwater appropriately so that we don't continue to pollute our rivers with microplastics and other pollutants. We have to protect our drinking water resources. Personally, I believe that drinking water is a human right. However, it has to be treated, which incurs costs and should therefore also have a price. But drinking water must of course be affordable for everyone! It's not just about microplastics, but also about other contaminants such as heavy metals and copper, which can have a serious impact on the environment and which we have to remove from rainwater. And that simply costs money. As a society, we have to ask ourselves: What is such an investment worth to us? If someone has a parking lot, they don't just have the construction costs. On top of that, there may be another 20,000 Euros for a treatment plant approved by the German Institute for Building Technology. We want to keep the water on site and return it to the groundwater there in order to maintain the local water cycle. To do this, however, it must be cleaned of tire abrasion, oil loss, and other pollutants. To put it bluntly, we are protecting our drinking water resources for tomorrow!
© Abhishek Tewari / Unsplash
How much do parking lot operators understand these regulations and the additional costs they entail?
It varies greatly, but in general there is growing understanding. In the past, drainage was usually the last thing to be considered. Back then, it was just a matter of installing gutters to drain rainwater. Today, we also have to think about rainwater quality. Some do this on their own initiative, but there are also legal requirements. My favorite legal paragraph is § 54 of the German Water Resources Act. It defines what wastewater is: wastewater is dirty water from households and industry, but also rainwater that hits sealed surfaces, is collected, and drained away. You can't just discharge wastewater into waterways. You have to apply for a permit.
In a small residential street where a few people drive their cars to work in the morning, you could drain the rainwater into the nearby Elbe River – it's big. However, if you have a huge parking lot or logistics center where many cars or trucks drive every day, you cannot discharge the water into the small mountain stream next to it. This would completely overload the stream during a heavy rain shower when all the dirt is washed off the surface. You need a treatment plant for this. This is the tension horizon in which we operate.
“The most important thing is to understand that rainwater is no longer clean once it hits sealed surfaces.”
Moritz Gesterding
... and opinions on rainwater treatment are correspondingly diverse.
The most important thing is to understand that rainwater is no longer clean once it hits sealed surfaces. You mentioned our WaterCycle – “Collect, Clean, Hold, Reuse.” The “clean” part, the purification, is a very, very crucial component.
I come from the Elbe and mountain streams to the Baltic Sea, where Kiel is located. The Baltic Sea is one of the most microplastic-polluted inland waters in the world. The measuring devices of the Ocean Race Europe sailing teams are expected to confirm this again. It is also one of the topics of the Ocean Summit, which will take place on August 5 as part of the race event. How can the influx of microplastics into the Baltic Sea be reduced?
We focus on rainwater management and are not involved in equipping sewage treatment plants. However, we are developing solutions and products to clean the water in the various tributaries of the Baltic Sea. One example is sedimentation plants, which can effectively retain larger and, to a certain extent, smaller particles, depending on how they are designed. Another example is the filtration plants approved by the German Institute for Building Technology (Deutsches Institut für Bautechnik), which bring the water to a quality level that allows it to be discharged into the groundwater in accordance with applicable laws. As already mentioned, this is where we start at the “point of source.”
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The teams are in close contact with scientists and provide them with data. It all started with the collaboration between Boris Herrmann and Team Malizia with GEOMAR in Kiel. Do you also have a connection to science?
We participate in various committees and exchange ideas at conferences, where we also give presentations. We want to actively contribute our knowledge and help shape guidelines. We are also currently part of a research project, but I can't say too much about it yet. All I can say is that it involves testing systems and developing a testing program for the removal of microplastics. We are involved with our systems because it has to be proven that they work. It is an area in which we as manufacturers clearly say: We want to be more regulated. We need strict rules that are comparable for everyone. I always like to refer to it as a Wild West market: whoever shoots the fastest says, “I have the best solution.” But the performance of the systems has never been tested because there are no binding test protocols. As ACO, it is our aim to be at the forefront and to prove conclusively that our systems work appropriately for microplastics. We currently have our own tests that prove this, but of course we also want to prove it officially and in a comparable way.
Given all the technical aspects and the complexity of the issue in economic, social, and political terms, what do you think would be a small step in everyday life that could have a big impact in the fight against microplastics?
At ACO, we use plastic in the right place, in the right quality and with a high recycling rate. In our private lives, we can all try to avoid plastic wherever possible. And as a passionate cyclist, I would say: ride your bike wherever possible to reduce tire abrasion from cars.
*ACO – Ambassador of SDG 6
Water has an enormous impact on the quality of life of the world's population. This is why the United Nations (UN) has defined the improvement of water quality as one of the 17 Sustainable Development Goals in its 2030 Agenda. All UN member states are to achieve the desired changes by 2030.
With its holistic water-related business model, ACO contributes in particular to the realisation of the sixth (Clean Water and Sanitation), ninth (Industry, Innovation and Infrastructure) and eleventh (Sustainable Cities and Communities) UN Sustainable Development Goals.
On the occasion of the UNESCO anniversary year 2025, ACO was selected as an ambassador for the sixth UN Sustainable Development Goal.
© ACO – Interview: Ralf Löwe / sonofasailor.de
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