In the recent years microplastics in the marine environment has been recognized as a potentially important environmental issue. Today there are microplastics spread in the waterbodies all over the world, from the equator to the poles in south and north. In 2016 artificial turf was labeled the second largest source of microplastics to the marine environment in Sweden. Football is the national sport of Sweden and accounts for the majority of the activity hours among the youth in Sweden. The artificial turf has made it possible for more children to play football and for them to get more hours on the field. Today about 90 % of the football players play on artificial turf. The microplastics pathways to the nature and the marine environment were studied and treatment methods were developed. One of these methods is the so called granule trap, a filterbag which is placed in a stormwater drainage well to catch the rubber granulates and the artificial turf fibers which can be spread from the artificial field to the drainage system. The aim of this study was to optimize the granule trap for possible water flows to the stormwater drainage well and its efficiency to catch microplastics. This was researched through field studies of the efficiency of the granule trap at two artificial turfs in Stockholm and the development of a waterflow model of an artificial turf with varying construction.The rainfall which was used in the waterflow model was the 10-year storm with a duration of 10 minutes. This to find the maximum waterflow the granule traps must manage. The waterflows to the stormwater drainage well were dependent on the number of wells placed around the artificial turf, in which area of Sweden the football field was placed, in other words the amount of rain that fell, and the infiltration capacity of the artificial turf. The waterflow model works as a template for possible waterflows at an artificial turf with a certain construction and at a certain location in Sweden.The artificial turfs which were examined in the field studies were Skytteholms IP in Solna andSpånga IP in Stockholm. At each football field 6 granule traps were placed, each loaded with twofilter bags, the inner with larger sized mesh and the outer with smaller sized mesh. The mesh size combinations were 200 μm with 100 μm, 200 μm with 50 μm and 100 μm with 50 μm. atSkytteholms IP a total amount of 10.3 kg microplastics were caught and at Spånga IP a total of 1.5kg microplastics were caught during the 49 days the granule traps were placed at the football fields. Out of the total amount of microplastics in each granule trap at least 99 % by mass was in the inner filter bag and maximum 1 % by mass was in the outer filter bag, in the size fraction between the outer and the inner filter bag.In conclusion this study shows that the waterflow to the stormwater drainage wells placed aroundthe artificial turfs vary a lot depending on the construction of the artificial turf. Foremost it depends on the infiltration capacity of the artificial turf and the number of stormwater drainage wells around the field. With regards to the waterflows from the waterflow model and the results from the field studies the recommended mesh size for the filter bags is 200 μm. This since at least99 % by mass of the microplastics, which were larger than 50 μm, that reached the granule traps were trapped in the inner filter bag and the elevated risk of clogging and biofilm growth on the filter bags with smaller mesh size. Further studies should be conducted on the waterflow through the granule traps over time, microplastics smaller than 50 μm, other pathways for the microplastics away from the artificial turf, improved constructions of artificial turfs and improved maintenance on the artificial turfs to reduce the risk of spreading of microplastics from artificial turfs.