Fluorescent staining of microplastics as a detection method is consistently gaining importance in microplastics research, as it is fast, easy to use, and requires low technical effort. In this study, a complete procedure was developed, from sample collection to sample processing and detection, to measure microplastics with low cost and time requirements. The developed procedure was tested by measuring the microplastics in the effluent of a German wastewater treatment plant over a period of one year. The results show that the process is especially well suited to investigate temporal variations of microplastic contamination, which requires a large number of samples to be processed. Further, the precision and selectivity of the detection process could be improved by applying newly developed Nile red derivatives for fluorescent staining. A low budget modification of a microscope for fluorescent imaging is compared to a modification with precise optical bandpass filters. A script enabling automated microplastic detection and counting was developed, improving the accuracy and comparability of the process.

Micropollutants have been increasingly detected at low concentrations in surface waters and may have harmful effects on humans, organisms, and the environment. As wastewater treatment plants are one of the main sources of micropollutants, conventional wastewater treatment methods and plants (mainly one to three cleaning stages) must be improved through an advanced (fourth) treatment stage. The optimal fourth treatment stage should be determined based not only on removal efficiencies but also on a holistic sustainability assessment that further considers the process’s adaptability, economic, environmental, and social parameters. The ability of a tertiary wastewater treatment plant to remove organic pollutants was investigated over four months using two different advanced treatment methods: (1) an advanced oxidation process (AOP) (using UV + H₂O₂) and (2) granular activated carbon (GAC). The resulting average micropollutant removal efficiencies were 76.4 ± 6.2% for AOP and 90.0 ± 4.6% for GAC. As the GAC became saturated, it showed a decreasing performance from 97.6% in week one to 80.7% in week 13, after 2184 bed volumes were processed. For the AOP, adjusting the UV and H₂O₂ doses results in higher removal efficiencies. With 40 ppm H₂O₂ and 10 kJ/m² UV, a removal of 97.1% was achieved. Furthermore, the flexibility and adaptability of the AOP process to adjust to real-time water quality, along with a lower resource consumption and waste disposal, make it a more promising technology when comparing the sustainability aspects of the two methods.

Wastewater treatment plants (WWTPs) have been identified as important point sources of micropollutants and microplastics into the environment. Existing fourth cleaning steps are designed to remove dissolved micropollutants, however do not target dispersed solids such as microplastics. Therefore, the ability of an Advanced Oxidation Process (AOP) and Granular Activated Carbon (GAC) in parallel and serial connection to remove microplastics was investigated and determined. The pilot plants were operated at the municipal WWTP Landau, Germany, a three-step biological waste treatment plant with a capacity of 80,000 population equivalents. A Nile red-based detection method was applied to quantify microplastics. Neither method showed a significant removal of microplastics. To achieve a simultaneous removal of microplastics and dissolved micropollutants, a pilot plant using organosilanes for microplastics’ removal was connected in series with the GAC. When added to the water, the organosilanes attach to the microplastics and collect them in agglomerates by chemically binding them in a water-induced sol–gel process. The pilot plant for microplastics’ removal was operated with a flow rate of 12 m³/h and a retention time of 10 min; the GAC with 2 m³/h and a retention time of 1 h. An average reduction in micropollutants by 86.2 ± 2.0% and a reduction in microplastics by 60.9 ± 27.5% was reached. Thus, there is an effective reduction in micropollutants and a significant reduction in microplastics. Further optimizations of the pilot plant are expected to result in a more stable and higher removal performance.

Wastewater from plastic manufacturing or processing industries is often highly polluted with microplastics (MPs) and high levels of oxidizable organic matter, which results in a high chemical oxygen demand (COD). When industrial wastewater enters wastewater streams, the high microplastic load is a high burden for municipal wastewater treatment plants (WWTPs), as they are not sufficiently removed. To prevent MP from entering the WWTPs, an upstream prevention method is essential. This paper presents a pilot-scale plant study for the removal of MP and COD from industrial wastewater that was tested on-site at a plastic manufacturer in Germany. Eight test phases were performed over 3 months, with each test phase processing 1 m³ wastewater and four treatments. Per test phase, 12 samples were analyzed for 5 parameters: COD, total suspended solids (TSSs), particle count, pH, and turbidity. The results showed an average decrease in MP by 98.26 ± 2.15% measured by TSSs and 97.92 ± 2.31% measured by particle count. This prevents the emission of 1.1 kg MP/m³ water and an estimated 2.7 t MP/year. The COD was reduced efficiently by 94.3 ± 8.9%. Besides MP and COD, this treatment allows reuse of water and agglomerates, resulting in a reduction in the CO₂ footprint.

The fast, affordable, and standardized detection of microplastics (MP) remains one of the biggest challenges in MP research. Comparable data are essential for appropriate risk assessments and the implementation of laws and limit values. The fluorescent staining of MP in environmental samples is a possible solution to this problem. This study investigates the optimization of a sample preparation process (hydrogen peroxide digestion) and the staining process (temperature, concentration, time, surfactants as staining aids) for using a specifically developed fluorescent dye for MP detection. The optimization is performed by comparing the sample preparation process and staining of MP from different polymers and natural particles. Further, the suitability of the optimized process for the detection of fluoropolymers and tire abrasion was tested. The results show that the optimized method (increased temperature and optimized stain concentration) can detect microplastics reliably with a total sample preparation and measurement time of 2.5–3 h per sample, reaching recovery rates of 93.3% (polypropylene) to 101.7% (polyester). Moreover, two of the three tested fluoropolymers could be detected reliably. Tire abrasion could not be detected with the here presented method, as the black color leads to strong quenching. A long-term study measuring the MP pollution in the effluent of a municipal wastewater treatment plant compared the optimized and original processes and confirmed the stability of the improved method for routine measurements and contamination control.

Wastewater treatment plants (WWTPs) have been identified as important point sources for microplastics (MPs) in the environment; monitoring MP emissions in the WWTP effluent is therefore essential for contamination control. The aim of this study is to acquire a large number of samples (320) over a period of two years and three months to determine the temporal variations in microplastic contamination in the outlet of the municipal WWTP Landau-Mörlheim. The effluent of the third cleaning stage is sampled with a 10 µm filter cartridge, processed in the laboratory using a hydrogen peroxide treatment, and MPs are then detected by fluorescence staining. The results show high temporal variations in the microplastic concentrations in the effluent of the WWTP. This indicates that high numbers of samples are necessary to obtain a representative assessment of the microplastic emissions; single samples are not representative. The average microplastic concentration in the effluent was 27.8 ± 29.8 MP/L, ranging from 0.6 MP/L to 194.0 MP/L. This leads to a yearly emission of 1.5 × 10¹¹ MP for the WWTP Landau-Mörlheim, corresponding to an emission of 2.8 × 10⁶ MP/inhabitant and year. Statistically significant seasonal variations could not be observed, although there is a trend towards lower MP concentrations in summer. Further, no correlations with other wastewater or weather parameters could be found.