| Summary: | Nitrous oxide (N2O) is a potent greenhouse gas that is emitted from wastewater treatment plants. To reduce emissions of N2O from swine wastewater treatment plants, we constructed an experimental aerobic bioreactor packed with carbon fibres (ca. 1 m3 bioreactor) as an alternative to conventional activated sludge treatment. The N2O emission factor for the aerobic bioreactor packed with carbon fibres (CF) was 0.002 g N2O-N/g TN-load and the value for the typical activated sludge (AS) reactor was 0.013 g N2O-N/g TN-load. The CF treatment method achieved more than 80% reduction of N2O emissions, compared with the AS treatment method. The experimental introduction of a CF carrier into an actual wastewater treatment plant also resulted in a large reduction in N2O generation. Specifically, the N2O emission factors decreased from 0.040 to 0.005 g N2O-N/g TN-load following application of the carrier. This shows that it is possible to reduce N2O generation by more than 80% by using a CF carrier during the operation of an actual wastewater treatment plant. Some bacteria from the phylum Chloroflexi, which are capable of reducing N2O emissions, were detected at a higher frequency in the biofilm on the CF carrier than in the biofilm formed on the AS reactor.
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