Method and apparatus for filtration of undigested sludge

Claim 1

IN THE ART OF SEWAGE TREATMENT, WHEREIN SOLIDS ARE PROGRESSIVELY REMOVED FROM THE SEWAGE IN A SERIED OF TREATMENT UNITS IN ACCORDANCE WITH THEIR SIZE AND PHYSICAL AND CHEMICAL CHARACTERISTICS, THE PROCESS WHICH BASICALLY INCLUDES THE SUCCESSIVE STEPS OF CLARIFYING THE SEWAGE TRANSFERRING THE SETTLED SLUDGE FROM THE CLARIFYING PROCESS TO DRUM-TYPE VACUUM FILTER; SAID PROCESS CHARACTERIZED BY THE FACTS: FIRST, THAT THE SLUDGE IS PUMPED TOWARD SAID FILTER WITHOUT SUBJECTING TI TO A DIGESTION PERIOD; SECOND, THAT THE SLUDGE IS PUMPED THROUGH A CLOSED LINE FROM THE CLARIFYING STAGE TOWARD THE FILTER AND DURING ITS PROGRESS THROUGH SAID LINE A QUANTITY OF CALCIUM HYDROXIDE IS INTRODUCED INTO THE FLOW OF SLUDGE IN SAID CLOSED LINE, AND IN QUNATITIES PROPORTIONED TO THE AMOUNT OF DRY SOLIDS IN THE SLUDGE TO CONDITION AND DEODORIZE THE SLUDGE; THIRD, THAT DURING THE PASSAGE OF THE SLUDGE THROUGH THE FILTER THERE IS PROGRESSIVELY CREATED UPON THE SURFACE OF THE FILTER MEDIUM, A FILTERING LAYER CONSISTING OF SOLIDS CONTAINED IN THE SLUDGE, AND THE FURTHER SUBSEQUENT FLOW OF SLUDGE THROUGH THE FILTER IS FILTERED BY MEANS OF SAID FILTER LAYER, THUS ACCUMULATING FURTHER SOLIDS THEREON IN THE FORM OF A FILTER CAKE; FOURTH, THAT THE FILTRATE FROM THE DRUM-TYPE VACUUM FILTER IS RECIRCULATED TO REPEATEDLY PASS THROUGH AT LEAST A PORTION OF THE CALIRIFYING STAGE, WHEREUPON THE SUSPENDED SOLIDS CARRIED THROUGH WITH THE FILTRATE ARE RESETTLED AND REFILTERED, THE PROCESS AS DESCRIBED PERMITTING A LARGER QUANTITY OF SUSPENDED SOLIES TO PASS THROUGH THE FILTER INTO THE FILTRATE THAN IN CONVENTIONAL SEWAGE SLUDGE FILTERING METHODS, BUT WITHOUT DELETERIOUS EFFECT ON THE PROCESS; AND FIFTH, THAT THE FILTER CAKE AND THE EFFIUENT FROM THE CLARIFICATION PROCESS ARE APPROPRIATELY DISPOSED OF.