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Initial rainfall runoff, the non-point source of pollution, causes the quality public waters to deteriorate, and it is urgent to control this. The study is directed toward developing the facility for treating the pollutants contained in the initial rainfall runoff. Used for the facility was the carbide pellet, among other sewage sludge carbides, which has high SS removal ratio. The replacement period of the filtering mediums were decided by seeing the changes of filter pressure according to the clogging of filtering medium layer. For the change value of filter pressure, the differential pressure was used between the pressure of the lower part of the filtering medium carbide pellet(Pa) and that of the filtering medium zeolite pellet(Pb). The differential pressure(Pa-Pb) increased from 110kgf/㎠ in the initial stage to 190kgf/㎠, and then decreased to 85kgf/㎠ as the load of the solids increased. The outflow showed a tendency to decrease with the differential pressure lowering, and it decreased up to 40% of the inflow. It was considered that these phenomena resulted from the clogging of the filtering medium container. As a result of continuous operation under conditions of 68L/min of flow and 4,360㎎/L of SS concentration, it was concluded that the filtering mediums need to be replaced at a point when the outflow decreases from 61.8L/min in the early stage to 34.4L/min, and at a filtering time of 90min when overflow occurs, or at a point when the initial differential pressure increases from 110kgf/㎠ to 190kgf/㎠, decreasing to 150kgf/㎠.