Biological process for enhanced removal of ammonia, nitrite, nitrate, and phosphate from wastewater

An activated sludge treatment process for removing nitrogen and phosphate from wastewater comprising:

• (a) forming a mixed liquor by mixing wastewater influent with return activated sludge in an initial contact zone, said initial contact zone being maintained under anaerobic conditions;
• (b) transferring the mixed liquor to an aerobic zone;
• (c) aerating the mixed liquor in the aerobic zone to oxidize BOD in the mixed liquor, and to convert ammonia present in the mixed liquor to NO.sub.x, wherein the NO.sub.x so produced is concurrently reduced to N.sub.2 and/or N.sub.2 O;
• (d) transferring the mixed liquor from the aerobic zone to a downstream anoxic zone to effect further denitrification of the mixed liquor;
• (e) transferring the mixed liquor from the anoxic to a settling zone where the activated sludge is separated from the mixed liquor;
• (f) transferring at least a part of the activated sludge to a sludge holding zone where it is maintained under anaerobic conditions;
• (g) holding the activated sludge in the sludge holding zone for approximately 4 to 20 hours after denitrification of the sludge is completed;
• and
• (h) returning at least a portion of the activated sludge from the sludge holding zone to the initial contact zone for mixing with the influent wastewater so that upon aeration of the mixed liquor in the aerobic zone, concurrent nitrification and denitrification in the aerobic zone is obtained.

An activated sludge treatment process for biologically removing phosphorus and concurrently nitrifying and denitrifying wastewater in an aerobic zone of a treatment plant, comprising:

• (a) mixing wastewater influent containing BOD, ammonia, and phosphate with activated sludge in an initial contact zone to form mixed liquor;
• (b) transferring the mixed liquor to an aerobic zone and aerating the mixed liquor to oxidize BOD in the mixed liquor, and to convert ammonia present in the mixed liquor to NO.sub.x, wherein the NO.sub.x so produced is concurrently reduced to N.sub.2 and/or N.sub.2 O;
• (c) transferring the mixed liquor to a separation zone where the activated sludge is separated from the mixed liquor;
• (d) transferring at least a part of the activated sludge to a sludge holding zone maintained under anaerobic conditions and holding the activated sludge in the sludge holding zone for a prolonged period after complete denitrification of the sludge is achieved to effect the selection of microorganisms capable of reducing NO.sub.x and biologically removing phosphorus in the presence of oxygen;
• and
• (e) returning a portion of the activated sludge from the sludge holding tank to the initial contact zone for mixing with the influent wastewater so that upon aeration of the mixed liquor in the aerobic zone the selected microorganisms concurrently reduce NO.sub.x being produced to elemental N.sub.2 and/or N.sub.2 O in the aerobic zone while phosphorus is biologically removed by the process.