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Standardized microplastic sampling and detection: From mobile solutions for municipal wastewater treatment plants and standard operating procedure protocols
Wastewater treatment plants are the central point of wastewater treatment and necessary to maintain sufficient water quality of our water bodies. Nevertheless, they are considered hotspots for microplastics. And due to the complexity and concentrations of new mixtures of substances and pollutants, wastewater treatment plants are reaching the limits of wastewater treatment. Although all wastewater from industries and households is still treated within the legally prescribed parameters, most pollutants are not monitored and their removal is not targeted, thus these pollutants enter nearby bodies of water, including microplastics.
Lack of standards and incomplete data - solutions had to be found
During Michael’s doctoral thesis (2018-2021), he noticed that it was not so easy to sample different types of water (e.g. wastewater, rivers, seawater, drinking water) for microplastics. He wanted to validate the process of sampling from wastewater treatment plants and found that there was no standardized procedure for this at the time. In addition, at the time, sample collection alone took two to three hours. Furthermore, with this method there was a constant risk of contamination of the samples and sampling errors could not be ruled out.
This was a highly unsatisfactory situation, not only for Michael, but for the entire Wasser 3.0 team. The scientists have been working intensively on microplastic analysis for more than five years.
In addition to the development of new fluorescent markers that selectively stain microplastics and not natural particles and thus provide quick and easy results using microscopy, they have also been able to develop their own solution for microplastic sampling. This has been used as the standard for microplastic monitoring at the municipal sewage treatment plant in Landau for more than three years.
This special sampling unit (also known as a particle sampling unit, or PSU for short) is being used in the EU REMEDIES and UPSTREAM projects. You can read the first scientific publications on monitoring at wastewater treatment plants in our publications.
How does a Particle Sampling Unit (PSU) work?
In addition to the filter cartridge, the PSU also includes a pump and associated process technology, giving it maximum mobility. This means that representative sample volumes of 100 liters and more can be taken very quickly from the wastewater treatment plant effluent, the receiving water, or adjacent bodies of water. The plug & play principle also means that wastewater treatment plant personnel can take the samples independently following training. It takes less than an hour from set-up to dismantling, and the sampling itself usually takes just a few minutes.
The PSU is made of robust, high-quality materials. Oleg is already experienced in the set up and dismantling. © Wasser 3.0
The filter cartridge catches the microplastics like a sieve. If the water is very dirty, the water flows through slowly. © Wasser 3.0
Standardized sampling: Our offers for municipal wastewater treatment plants and industry
In addition to the all-round carefree package that we offer wastewater treatment plants and interested parties, there is also the option of renting the PSU. Our manuals for standardized microplastic sampling and standardized sample preparation are available to ensure a standardized procedure.
Why are a representative sample volume and a standard protocol so important?
Microplastics are distributed irregularly (heterogeneously) in water. This means that the microplastic load can change every second, ranging from 0 to 1000 particles per liter and more. Many measurements are necessary for a valid measurement result, including so-called blank measurements, to exclude sources of contamination and to constantly scrutinize and control the process.
In addition, a municipal wastewater treatment plant treats large volumes of wastewater and transports this into the environment. If you only fill a 1-liter, 5-liter or 10-liter sample, then extrapolations to the full flow volume are far more prone to error. If you take two samples with a representative quantity of 100 liters and analyze them at least in duplicate and preferably in triplicate, you will obtain meaningful data packages and absolute figures.
And why are smaller sample volumes sufficient for efficiency measurements and water monitoring?
Compared to the sampling of municipal wastewater treatment plants, a smaller volume is required for sampling for the Global Map of Microplastics or for process-related efficiency measurements. These are so-called non-representative samples, which in turn provide a representative statement based on each other. A percentage reduction from “untreated” to “treated” is then obtained for the efficiency measurement of microplastic removal. In our microplastic removal process, we not only separate but also recycle the agglomerates.
We also have the option of weighing the agglomerates and can therefore describe our removal process both relatively (percentage value) and absolutely (real removal quantities in kilograms and tons). This makes our process unique compared to our competitors and adds value to the circular economy, as we can recycle the microplastic waste. And once the sampling is complete, the sample is sent to the laboratory.
Color comes into play in microplastic analysis
After the sample has been taken, the actual analysis takes place: the filter cartridge is removed and the microplastics are transferred to a glass transport container using a spray can.
Microplastic analysis is carried out in our laboratories and is based on the use of specially developed fluorescent markers. It is difficult to visually distinguish between microplastic particles and natural particles. Instead of counting, we have developed a simple and fast analysis method in which we selectively stain the microplastics with specially developed fluorescent markers, making them visible under a fluorescence microscope. Organic particles do not show a fluorescent signal, so they can be reliably distinguished from natural particles.
Where we are - and where we are going
So far, we have been able to carry out long-term monitoring (more than 6 months of data collection) on microplastics in three wastewater treatment plant effluents. The results have already been published.
These show microplastics in all samples with strong fluctuations. Based on the results, we have formulated a recommendation for action for the EU, as the amendment of the EU Urban Waste Water Directive also addresses the issue of microplastics to a small extent. We point out that sampling twice a year is by no means sufficient to be able to make a reliable statement on microplastic pollution.
Our recommendation for action for microplastic monitoring
For monitoring, we recommend sampling intervals of two to eight samples per month, plus double determination and cross-validation. If samples were taken in this way in the future, it would be possible to learn from the data more quickly and take effective action (i.e. make it mandatory to install removal technologies in the right places or implement avoidance strategies).
With this type of monitoring of wastewater treatment plants and water bodies, environmental and water protection could be implemented much more quickly and effectively. However, politicians would have to recognize more quickly where concrete action makes sense, free themselves from the influence of lobbyists and become more active in supporting society. Valuable support is provided by non-profit companies that act independently, pursue clear value structures and statutory mandates and have implemented real, data-based impact measurements.
And what about microplastics in the expansion of municipal wastewater treatment plants - keyword: 4th purification stage?
With our PSU and the associated standardized microplastics analysis, we have already been able to test and analyze the effectiveness of the 4th purification stage regarding microplastics. And as always, we carried out a comparative analysis of an Advanced Oxidation Process (AOP for short) versus a granulated activated carbon (GAC) process.
We also carried out a sustainability analysis. In addition, we recently took a closer look at the process using powdered activated carbon with a cloth filter. All in all, it can be said that a 4th purification stage or trace substance elimination is not designed for microplastics. If you want to build with the future in mind, then you not only include micropollutants, but also microplastics, and learn from the mistakes of the past. Because back then, people often didn't think things through or think ahead when awarding construction projects in municipal areas.
What else do we recommend?
Microplastics should also be monitored more effectively in general, especially in wastewater and non-domestic wastewater, including industrial wastewater, sewage sludge, urban runoff, and combined sewer overflows. This monitoring, which is standardized and easy to carry out with the help of the PSU, could show across the board how many microplastics are entering wastewater treatment plants and the environment and via which routes. The advantage of this would be that hotspots could be identified and targeted instead of just doing something somewhere.
Michael takes a water sample using the analysis kit to compare the values with those of the PSU © Wasser 3.0
And what's next for us with the PSU?
In addition to the wastewater treatment plant, our mobile sampling unit has also been increasingly used in microplastic water monitoring since this year. In the EU project UPSTREAM, for example, we are investigating the River Queich in Landau, which is the water body adjacent to the wastewater treatment plant. Through the regularity and frequency of sampling, actual dilution factors can be determined in order to be able to make statements on the ecological assessment of water quality in the future.
And because we at Wasser 3.0 want to improve every day and put ourselves to the test, we regularly compare the microplastic concentrations of the sampling unit with those from the microplastic mapping using the analytics kit.
Would you like to get to know the PSU and everything about microplastics analysis live and in action?
Then perhaps our OPEN HOUSE is the place for you. Please read our blog post and register using the links provided. We look forward to your visit.
