Compositions of bacteria which are effective for the nitrification of wastewater, particularly at low temperatures, are described. The compositions are comprised of 35 strains or populations of at least partially characterized isolated bacteria. These compositions may be used to treat wastewater contaminated with animal fecal waste and/or ammonia. In use, wastewater is contacted with the bacterial composition of the invention under aerobic conditions and for a period of time effective to oxidize ammonia therein.
