Sewage delivery for an activated sludge process

An arrangement for purifying waste water by an activated sludge process having intermittent batchwise sewage supply in an urban waste water treatment plant, said arrangement comprising:

• (a) a plurality of separate aeration tanks adapted for the purification of waste water by activated sludge under aeration;
• (b) a delivery means common to all of said tanks, in the shape of a first ring main located horizontally above the maximum liquid level which is attained in said tanks during the sludge purification process, said ring main having a volume of about 5 to 40% that of each tank;
• (c) means for emptying the sewage contents of said ring main into said tanks one at a time at predetermined time intervals and in pulses of predetermined duration;
• and
• (d) common discharge means in the shape of a second ring main which is located horizontally below the minimum liquid level which is attained in the tanks during the sludge purification process;
• wherein said first ring main and said second ring main comprise a single, double-channel ring main having an upper channel for delivery of sewage and a lower channel for discharge of same after processing, said double channel ring main being located so as to pass through said tanks horizontally and in such a way as to maintain said upper channel above the maximum liquid level attained in said tanks during said process, and said lower channel below the minimum liquid level obtained in said tanks during said process, said upper and lower channels being connected to one another by means of a discontinuous beam which allows the sewage to circulate freely between said upper and lower channels and which facilitates attachment of auxiliary devices within the tank.

An activated sludge process for waste water purification by an activated sludge process having intermittent batchwise sewage supply in an urban waste processing installation, said process comprising the steps of:

• a) aerating waste water and activated sludge contained in at least one of a plurality of separate activated sludge tanks;
• b) monitoring the nitrate level within said activated sludge tanks;
• c) introducing sewage into a delivery means, common to all of said tanks, comprising one or more elongated channels for selectively and alternately introducing sewage into each one of said tanks, wherein said common delivery means is arranged in an essentially horizontally extending manner essentially above a portion of each of said tanks and above the maximum liquid level which is attained in the tanks during said activated sludge process, and wherein said delivery means has a holding space for the sewage feed comprising an amount equal to about 5 to about 40% of the volume of one said tanks;
• d) performing an intermittent denitrification process in a selected one of said tanks when said nitrate level increases in said selected tank above a first predetermined level, said denitrification processing comprising the steps of:
• d1) discontinuing aeration within said selected tank;
• and
• d2) intermittently emptying sewage from said delivery means directly into said selected one of said tanks by gravity when said nitrate level in said tank reaches a predetermined level, wherein said sewage is discharged directly into said tank in an amount equal to about 5% to 40% of the volume of one of said tanks over a period of a few minutes by means of a valve on said delivery means and located above said selected tank;
• e) continuing said denitrification process until the nitrate level of said selected tank decreases below a second predetermined level;
• f) resuming aeration in said selected tank;
• and
• g) repeating steps (b) through (f).