The researchers studied how to remove dirt from water using roughing filters before slow sand filtration. They found that adding alum and using specific mixing conditions helped reduce turbidity in the water. Different filter media and filtration velocities affected the effectiveness of the process. At lower velocities, the roughing filters removed most of the dirt particles, but at higher velocities, some particles still passed through. Overall, the study showed that the right combination of alum, mixing, and filter media can significantly improve water clarity before it goes through the main filtration process.