This paper describes the vertical profile of adhered suspended matter on the filter sand and its composition in the upper column of a slow sand filter. The water source of the studied slow sand filter is a surface water of a stream. An active growth of algal mat of filamentous diatom and the floating algal mat peeled off from the bottom were commonly observed during the study period in summer. The upper sand column was taken when the supernatant water drained off for the filter cleaning after the long filter run.
The majority of suspended matter was adhered on the filter sand in the upper 1cm of the sand column. The amount of adhered matter was quickly decreased with the depth. The order in the decreasing rate of suspended matter with the depth was: Chlorophyll a > Pheophytin a > Consumption of KMnO4 > Ignition loss > Mud (adhered suspended matter). These results show the biological degradation is active in the surface sand column. And almost all the suspended matters penetrated into the sand are easily trapped and are decomposed within the surface sand layer.
