Quantification of microplastics in wastewater systems of German industrial parks and their wastewater treatment plants.

Microplastics (MP) enter the aquatic environment via several pathways. Many research groups have focused on municipal discharge, while research on industrial sources is rare. This study provides one of the first insights into MP occurrence and distribution in the wastewater systems of industrial parks (IPs) and their wastewater treatment plants (IPWWTPs). The effluents from production plants as well as influent, effluent, and internal samples from the IPWWTPs were assessed. Sampling methods for parallel MP mass and number analyses were developed for varying conditions. The total item emissions of MP (≥10 µm) into the environment were analyzed using µ-Raman spectroscopy and ranged from 3 · 102 to 8 · 104 MP m-3, with a median of 6 · 103 MP m-3 per IPWWTP. Masses analyzed using differential scanning calorimetry showed an MP mass discharge into the environment of 0.2 to 11 mg m-3 with a median of 3.7 mg m-3 per IPWWTP. MP item concentrations within an IPWWTP varied by two to three log levels over several days. Fibers were rare in all samples. Polymer types varied depending on the types of industrial sites and the production plants discharging into the IPWWTP. Within an IP, MP could be allocated to its dischargers, which could be useful for future regulatory requirements. Further research is needed to include different types of IPs producing various polymers and additional processing plants to expand this data set.

Underestimating microplastics? Quantification of the recovery rate of microplastic particles including sampling, sample preparation, subsampling, and detection using µ-Ramanspectroscopy.

This study is one of the first to investigate the recovery rate of high- and low-density microplastic particles (polyvinyl chloride and polypropylene) from wastewater treatment plant effluents or comparable technical facilities under nearly realistic experimental conditions. For this purpose, a method of continuous dosing of microplastic particles into an experimental flume for open-channel flow was developed. Subsequently, 12 samples were taken using volume-reduced sampling and the entire sample purification process including oxidative treatment (with hydrogen peroxide and sodium hypochlorite), density separation (with sodium polytungstate), and subsampling was carried out. Detection was conducted using automatic particle recognition and µ-Ramanspectroscopy. An average recovery rate of 27 ± 10% was determined for polypropylene microplastic particles (d = 53 ± 29 µm), decreasing with the particle size, and 78 ± 14% for polyvinyl chloride microplastic particles (d = 151 ± 37 µm). The results suggest that microplastic emissions from wastewater treatment plants are underestimated, particularly because the recovery rate of small microplastic particles < 50 µm is only 9%.

Investigation of microplastics contamination in drinking water of a German city.

The drinking water of a German city was investigated for microplastics. Random samples were taken from three house connections, one transfer station, and five consumption taps in an educational institution, an apartment, a single-family house, a residential building, and a commercial enterprise. The sample volumes ranged from 0.25-1.3 m3. A stainless-steel membrane served as a sampling filter. HCl was used for the acidic digestion of the inorganic precipitates. Raman micro spectroscopy was used for the analysis of microplastic particles. The detection limit was 10 µm. Particles and fibers ≥100 µm were measured on 100% of the filter area, while particles and fibers <100 µm were measured on 50% of the filter area. The analytical procedure was validated by determining recovery rates and analyses of blanks. In addition to microplastics, pigmented particles and fibers were also analyzed. Neither microplastic particles and fibers nor pigmented particles and fibers were detected at house connections and the transfer station. No microplastics were detected in any sample at consumption taps. At one tap, 113 ± 83 copper phthalocyanine particles m-3 were detected.

Determination of the microplastics emission in the effluent of a municipal waste water treatment plant using Raman microspectroscopy.

Samples from the secondary clarifier effluent of a waste water treatment plant (serving 98500 inhabitants) were analyzed to determine the microplastics (MP) emission. The samples were collected using a stainless steel centrifugal pump and filtered through a 10 µm stainless steel cartridge filter. Microplastics particles (MPPs) and microplastics fibers (MPFs) were recovered by chemical and physical sample purification. To remove natural organic matter, the samples were first subjected to oxidative treatment with H2O2 and NaClO. Inorganic materials were subsequently removed by density separation in ZnCl2 (ρ = 1.9 g/cm3) using a centrifuge. Special centrifuge tubes were developed for this purpose. Sample analysis was performed on a Si filter by Raman micro-spectroscopy. Particles with a diameter (dp) ≥ 10 µm were analyzed. The results were differentiated by dry and wet weather samples. On average, 5900 MPPs m-3 were identified in the effluent on wet weather days compared to 3000 MPPs m-3 on dry weather days. Most of the MPPs detected were in the 30 µm < dp < 100 µm size range. The MPFs ranged between 100 µm and 1000 µm in length. While most of the MPFs were of PET origin, the MPPs consisted mainly of PET, PP, PE and PS.