Mitigation of nitrous oxide (N2O) emission from swine wastewater treatment was demonstrated in an aerobic bioreactor packed with carbon fibers (CF reactor). The CF reactor had a demonstrated advantage in mitigating N2O emission and avoiding NOx (NO3+NO2) accumulation. The N2O emission factor was 0.0003g N2O-N/gTN-load in the CF bioreactor compared to 0.03gN(2)O-N/gTN-load in an activated sludge reactor (AS reactor). N2O and CH4 emissions from the CF reactor were 42g-CO2 eq/m(3)/day, while those from the AS reactor were 725g-CO2 eq/m(3)/day. The dissolved inorganic nitrogen (DIN) in the CF reactor removed an average of 156mg/L of the NH4-N, and accumulated an average of 14mg/L of the NO3-N. In contrast, the DIN in the AS reactor removed an average 144mg/L of the NH4-N and accumulated an average 183mg/L of the NO3-N. NO2-N was almost undetectable in both reactors.