In this work we evaluated biological deammonification process to more economically remove ammonia from livestock wastewater. The process combines partial nitritation (PN) and anammox. The anammox is a biologically mediated reaction that oxidizes ammonia (NH4+) and releases di-nitrogen gas (N2) under anaerobic conditions using nitrite (NO2-) as the electron acceptor. We tested two deammonification configurations: 1) a two-stage process (PN in one tank and anammox in another), and 2) a one-stage deammonification process (PN and anammox in a single tank). In both cases, a high performance nitrifying sludge, HPNS (NRRL B-50298) was used for PN and Brocadia caroliniensis (NRRL B-50286) was used for the anammox reaction. The two-tank process was carried out using sequencing batch reactors (SBR), one aerated and the other anaerobic, at 32ºC water temperature. The single-tank process was carried out in an aerated vessel operated under continuous flow. It contained biofilm plastic carriers at 30% v/v packing ratio that were fluidized by the aeration. The process water temperature was 22oC and DO generally below 0.5 mg/L. In the PN-SBR reactor, the NO2- production rate obtained at was 0.91 g NO2--N/L-reactor/d. The PN effluent contained 1.38 g NO2--N/g NH4+-N, which was within 5% of the target oxidation of ammonium to nitrite of 57%, which corresponds with the reaction ratio of anammox. In the second SBR, the anammox process was effectively applied to the PN effluent, attaining a nitrogen conversion rate of 0.36 g N/L-reactor/day (14.3 mg N/g VSS/ h) and anammox stoichiometric ratios of 1.00:1.32:0.15. For the single-tank deammonification, total N removal rates of 0.75 to 1.0 g N/L-reactor/day were obtained for both synthetic and swine wastewater. The stoichiometry of the reaction obtained in the single-tank process was consistent with deammonification process theory combining partial nitritation and anammox: NH4+ + 0.88 O2 ¿ 0.44 N2 + 0.11 NO3- + 1.43 H2O + 1.14 H+. Compared to conventional nitrification/denitrification, a partial nitritation/anammox pathway (deammonification process) can reduce 58% of the oxygen requirement to biologically eliminate the ammonia from wastewater. Thus, it offers the potential to reduce the cost of treatment of ammonia in livestock wastewaters and other effluents containing high ammonia nitrogen.