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Microplastics analytics in municipal wastewater: EU plans are not enough
Untreated municipal wastewater is a major source of water pollution; it must be treated efficiently to prevent the release of bacteria, viruses, nitrogen, phosphorus, and other pollutants. Therefore, most modern wastewater treatment plants (WWTPs) are equipped with three treatment stages to respond to current and future pollution and adhere to regulations, such as the EU Water Framework Directive (Directive 2000/60/EC) and EU Urban Wastewater Treatment Directive (Council Directive 91/271/EEC). However, the release of microplastics (MP) has received little attention in policy and regulations for wastewater treatment, although it has been strongly discussed in MP research since 2011.
Where does all the microplastic pollution come from? © Wasser 3.0
With data transparency and long-term data collection to sensible laws
Wastewater treatment plants (WWTPs) have been identified as important point sources for microplastics in the environment; monitoring MP emissions in the WWTP effluent is therefore essential for contamination control. The aim of the study was to acquire a large number of samples (320) over a period of more than two years to determine the temporal variations in microplastic contamination in the outlet of the municipal WWTP Landau-Mörlheim.
More than 24 months of data collection with standardized sampling, sample preparation and analytics
Using our standardized sample collection and detection methods, we monitored the microplastic levels in the WWTP effluent over 2 years. The MP levels showed high temporal variations, with an average concentration of ~28 MP/L. The yearly discharge was extrapolated by multiplying the average microplastic concentration with the yearly discharge.
The yearly discharge accounted for 5.8 million m³/year in 2022 and 5.0 million m³/year in 2023. As the catchment area has 55,000 inhabitants, this results in an average discharge of 420 million MP/day and 150 billion MP/year into the receiving river.
This amounts to 7614 MP/inhabitant per day and 2.8 million MP/inhabitant per year.
Note: This interpolation does not consider that the microplastics do not only originate from households, but also from industries and surface-runoff. Nevertheless, it makes it clear that measures are necessary to prevent microplastic pollution.
Results in a nutshell
- The data shows high fluctuations in the microplastic concentrations in the effluent of the WWTP. To capture these fluctuations and obtain a representative evaluation of the microplastic contamination, a high number of samples is necessary. Single samples are not representative.
- The minimum MP sampling interval to capture the yearly emissions is recommended to be between two to four samplings per month. To capture both seasonal and monthly variations, higher numbers of samples are needed
- Based on the results, longer sampling intervals do not provide meaningful results; thus, the sampling period outlined in the revised EU Urban Wastewater Treatment Directive will not adequately capture the temporal variations in MP contamination levels and may be misrepresentative of actual pollution loads.
- The average microplastic concentration was 27.8 ± 29.8 MP/L, ranging from 0.6 MP/L to 194 MP/L. In 2023, a lower MP contamination of 19.7 ± 17.9 MP/L was detected than in 2022 with 33.0 ± 33.6. This may be caused by increased awareness of the problems associated with MP in the environment resulting in reduced emission by industries and households, regulations on MP in products, or a change in the industries present and contributing to the influent of the WWTP.
- Clear seasonal variations could not be statistically proven, but there is a trend towards lower MP concentrations and lower fluctuations of the concentrations in summer, which was visible in the data.
- The correlation analysis showed that MPs are not correlated with the investigated wastewater and weather parameters. It should therefore be measured separately as the contamination appears to be driven by other unrelated factors.
- Further, the data show that WWTPs are clear point sources for MP into the environment and appropriate measures should be taken to prevent this contamination. Advanced treatment stages targeting MP removal at both upstream sources and at WWTPs should be investigated intensively. New technology setups should always be tested in comparable process set-ups – bottom-up, data-driven.
On our own behalf
If you would like to read the complete study, you can do so here: MDPI Microplastics.
We received partial support from foundations and the EU to carry out the study. There is no question that these financial injections help, but they are not enough to do more. They are tied to specific studies and clear tasks. Doing more and, above all, continuing in the long term is absolutely necessary to create more pressure for action. We all need clean water. We all need water without microplastics.
Without sponsorship, donations and a maximum degree of self-interest, we would not have been able to test so extensively. We need your help to ensure that this continues to be possible in the future. Help us to further expand our research and develop it internationally. Every euro goes towards research and education for more water without microplastics and accelerates our action for clean water - worldwide.
