Swine wastewater treatment technology to reduce nitrous oxide emission by using an aerobic bioreactor packed with carbon fibres

From a global warming perspective it is important to control emissions of methane (CH4) and nitrous oxide (N2O) from excreta and manure management. To mitigate emissions of N2O during swine wastewater treatment, we examined aerobic treatment technologies that use carbon fibre carriers as an alternative to conventional activated sludge treatment. We used scaled-up experiment equipment (water volume, 700 L) to evaluate the treatment performance. The N2O emission factor was 0.008 g N2O-N/g total N load in an aerobic bioreactor packed with carbon fibres (CF reactor), compared with 0.021 gN2O-N/g total N load in an activated sludge reactor (AS reactor). The CF treatment reduced N2O emissions by more than 60% compared with the AS treatment. Combined CH4 and N2O emissions from the CF reactor were 504 g-CO2 eq/m3.day, whereas those from the AS reactor were 1333 g-CO2 eq/m3.day. Interestingly, N2O emissions from the CF reactor were reduced even when nitrate and nitrite accumulated.