Method of biological purification of sewage

Claim 1

A PROCESS FOR PURIFYING WASTE WATER CONTAINING ORGANIC POLLUTION, SAID PROCESS COMPRISING: INTRODUCING SAID WASTE WATER INTO A FLOCCULATION TANK, INTRODUCING INTO SAID FLOCCULATION TANK AS FLOCCULATION REAGENTS AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM SALTS AND IRON SALTS IN AMOUNTS WHICH ARE NONTOXIC TO PROTOZOA AND BACTERIA, AND SUBJECTING SAID WASTE WATER TO THE ACTION OF SAID FLOCCULATION REAGENTS TO ELIMINATE FROM SAID WASTE WATER MATERIAL IN SUSPENSION AND COLLOIDAL MATERIAL, THUS FORMING FLOCCULATED WATER HAVING DISSOLVED POLLUTANTS THEREIN; PROVIDING A BIOLOGICAL FILTER COMPRISING A FILTER BED FORMED OF A POROUS MASS OF GRANULAR MATERIAL HAVING ON THE SURFACES THEREON SMOOTH ZONES CAPABLE OF SUPPORTING A BACTERIAL FILM AND LIMITED HOLLOW ZONES CAPABLE OF SUPPORTING A BACTERICAL FILM AND RETAINING SUCH BACTERIAL FILM EVEN WHEN SAID FILTER IS SUBJECTED TO SEVERE BACKWASHING, SAID STEP OF PROVIDING SAID POROUS MASS OF GRANULAR MATERIAL COMPRISING BURNING CLAY WITH DEXTRIN THEREIN AT APPROXIMATELY 900*C TO FORM FRAGMENTS HAVING SAID SURFACES OF SMOOTH AND HOLOW ZONES AND HAVING A GRAIN SIZE OF FROM 0.5 TO 10 MM; PROVIDING A RESERVOIR AREA ON THE TOP SURFACE OF SAID FILTER; SUPPLYING SAID FLOCCULATED WATER INTO SAID RESERVOIR AREA TO IMMERSE SAID FILTER IN SAID FLOCCULATED WATER; INTRODUCING AIR INTO SAID FLOCCULATED WATER IN SAID RESERVOIR AREA AND THUS AERATING SAID FLOCCULATED WATER; PASSING SAID FLOCCULATED WATER DOWNWARDLY FROM SAID RESERVOIR AREA INTO SAID FILTER TO FORM A BACTERIAL FILM ON SAID SMOOTH ZONES AND HOLLOW ZONES OF SAID SURFACES OF SAID GRANULAR MATERIAL, AND THEREBY BIOLOGICALLY PURIFYING SAID FLOCCULATED WATER TO FORM PURIFIED WATER; REMOVING SAID PURIFIED WATER FROM SAID FILTER; AND PERIODICALLY PERFORMING A BACKWASHING OPERATION ON SAID FILTER INCLUDING: INJECTING A WASHING LIQUID INTO SAID FILTER IN A DIRECTION OPPOSITE TO THE DIRECTION OF PASSAGE THERETHROUGH OF SAID FLOCCULATED WATER; REMOVING SAID BACTERIAL FILM FROM SAID SMOOTH ZONES OF SAID SURFACES OF GRANULAR MATERIAL; RETAINING SAID BACTERIAL FILM IN SAID HOLLOW ZONES OF SAID SURFACES OF SAID GRANULAR MATERIAL; COLLECTING SAID WASHING LIQUID AND THUS REMOVED BACTERIAL FILM; AND RECYCLING SAID THUS COLLECTED WASHING LIQUID AND REMOVED BACTERIAL FILM INTO SAID WASTE WATER AT A POSITION UPSTREAM OF SAID FLOCCULATION TANK.