BIOLOGICAL MEMBRANE FILTER APPARATUS USING FOLDABLE FILTER MATERIAL

PROBLEM TO BE SOLVED: To enable efficient backwashing and to obtain good treated water, in an apparatus passing raw water through the floatable filter material housed in a filter tank in an ascending flow state, by connecting the liquid suction pipe fitted to the lower part of the filter tank and the liquid jet pipe fitted to the upper part of the filter tank to circulate the liquid in the tank. SOLUTION: At a time of the operation of a sewage treatment apparatus, oxygen- containing gas is diffused to propagate aerobic biological membranes on the surfaces of particles of a floatable filter material. Raw water is supplied into a raw water inflow part 20 and coarse granular sedimentary SS(suspended substance) in raw water is sedimented on the bottom part of the inflow part 20 to be separated and the seconding streams of raw water from the inflow part 20 are allowed to flow in a floatable filter material bed 11 to remove BOD and fine SS. At a time of backwashing, raw water is sent to the liquid jet pipe 18 in a filter tank 10 from the liquid section pipe 17 in the tank by a circulating pump 23 to generate descending streams within the filter tank 10 to develop the floatable filter material bet 11 downwardly and air is diffused from an air diffusion pipe 14. By this constitution, SS and excessive biological membranes on the filter material are peeled and the used liquid in the tank is discharged from a backwashing water discharge part 24.