The researchers studied how to clean groundwater with iron, manganese, ammonium, and organics for drinking water. They tested three types of water and found that removing iron and manganese was hard when all pollutants were present. Ammonium made it harder to remove iron, while manganese removal was affected a lot. When all pollutants were together, the filter could slowly clean the water. Overall, polluted groundwater with ammonium and organics makes it tough to treat with a contact oxidation filter for drinking water.