NOVELTY - A composition (C1) comprises mixture of 16 isolated bacteria, as given in the specification, e.g. Nitrosomonas species strain high performance nitrifying sludge (HPNS).1, Unclassified species strain HPNS.4, Sejongia species strain HPNS.6, Nitrosomonas species strain HPNS.9, Comamonas species strain HPNS.10, Castellaniella species strain HPNS.13, and Comamonas species strain HPNS.16, of the high performance nitrifying sludge (HPNS) culture, deposited as NRRL deposit accession number no. NRRL B-50298.    USE - For treating wastewater (claimed), which is contaminated with animal waste and having undesirable levels of ammonia, including municipal, industrial or agricultural wastewater; for treatment of wastewater collected from animal rearing or holding facilities; and treatment of animal wastes generated by a variety of livestock, and domestic or wild animals, including zoo animals, sheep, swine, poultry, goats, cattle, dairy cows, horses, ducks, or geese.    ADVANTAGE - The composition of bacteria is effective for the nitrification of wastewater, particularly at low temperatures; is effective to oxidize ammonia under aerobic conditions and for a period of time; reduces high concentrations of ammonia in wastewater under cold weather conditions; and is effective for nitrification of wastewater at cold temperatures, and exhibits excellent flocculation properties.    DETAILED DESCRIPTION - A composition (C1) comprises mixture of isolated bacteria selected from: Nitrosomonas species strain high performance nitrifying sludge (HPNS).1, Mycetocola species strain HPNS.2, Chitinophaga species strain HPNS.3, Unclassified species strain HPNS.4, Castellaniella species strain HPNS.5, Sejongia species strain HPNS.6, Kaistella species strain HPNS.7, Pedobacter species strain HPNS.8, Nitrosomonas species strain HPNS.9, Comamonas species strain HPNS.10, Subtercola species strain HPNS.11, Comamonas species strain HPNS.12, Castellaniella species strain HPNS.13, Thermomonas species strain HPNS.14, Adhaeribacter species strain HPNS.15, and Comamonas species strain HPNS.16, of the high performance nitrifying sludge (HPNS) culture, deposited as NRRL deposit accession number no. NRRL B-50298. An INDEPENDENT CLAIM is included for treating wastewater involving contacting water with the composition (C1) under aerobic conditions and for a period of time effective to oxidize ammonia in it.