Evaluation of microplastics removal efficiency at a wastewater treatment plant discharging to the Sea of Marmara

Levels, composition and fate of microplastics (MPs) were investigated along different compartments of a secondary wastewater treatment plant (WWTP) with nutrient removal on the northern Sea of Marmara coast (Istanbul, Turkey). When all samples were combined, fibers were found to be the most dominant particles, followed by hard fragments. 500-1000 mu m and 1000-2000 mu m were the most common size ranges for wastewater and sludge, respectively. Rate of removal differed for sizes and shapes of the particles combined. Hard fragments of <500 mu m and fibers of size ranges 250-500 mu m and 1000-2000 mu m were more successfully removed within the WWTP. Size averages increased throughout the WWTP units. 84.6-93.0% removal was achieved for grab and 3hr composite samples. Despite the high removal rates of the WWTP, 2,934 x 106 microplastic particles/d were released in the effluent to the Sea of Marmara. Our results show that the Ambarli WWTP considerably contributes to microplastics contamination in the Sea of Marmara since the plant has a high operating capacity.

Automated summary

The study investigated the levels, composition, and fate of microplastics at a secondary wastewater treatment plant in Istanbul, Turkey. Fibers were found to be the most dominant particles, followed by hard fragments. The removal efficiency varied for different sizes and shapes of particles, with a considerable amount of microplastics still being released into the Sea of Marmara despite high removal rates at the treatment plant.