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.

Determination of alpha factors for monitoring of aeration systems with the ex situ off-gas method: experience from practical application and estimation of measurement uncertainty.

Performance of aeration systems in wastewater treatment plants (WWTP) under process conditions can be monitored with off-gas tests. The ex situ off-gas method transfers activated sludge from an adjacent aeration tank into aerated columns to determine oxygen transfer parameters (e.g., the α-factor). This method is an alternative to in situ off-gas testing with hoods at the tank surface; however, its application and measurement uncertainty have not been examined yet. We outline our experience from long-term off-gas testing with two pilot-scale test reactors (8.3 m3 volume). Global variance-based sensitivity analysis using Sobol' indices revealed oxygen concentration in off-gas and dissolved oxygen as the most important input quantities to determine α-factors accurately. Measurement uncertainty of other instruments was negligible. These findings are transferable to in situ off-gas hoods because the methods are similar. Random measurement error of α-factors was estimated with uncertainty analysis and comparison measurements to a relative standard deviation of about ± 2.8% for our ex situ pilot setup. Diffuser fouling, biofilm growth, or sensor drift caused systematic errors avoidable by maintenance. Additional mixing of bubble column due to sludge inflow into ex situ tanks led to a systematic overestimation of α-factors at lower airflow rates. Hence, the ex situ off-gas method is not suitable to determine α-factors for the design of aeration systems but offers unique possibilities for research of oxygen transfer dynamics and development of aeration equipment because ex situ columns can be operated independently from a full-scale activated sludge tank.