Comparison of AOP, GAC, and Novel Organosilane-Based Process for the Removal of Microplastics at a Municipal Wastewater Treatment Plant

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.