Understanding complete ammonium removal mechanism in single-chamber microbial fuel cells based on microbial ecology

• Published in: The Science of the total environment 2021-04, Vol.764, p.144231, Article 144231
• Main Authors: Park, Younghyun, Yu, Jaecheul, Nguyen, Van Khanh, Park, Seonghwan, Kim, Jeongmi, Lee, Taeho
• Format: Article
• Language: English
• Subjects: Ammonium Compounds; Ammonium removal; Bioelectric Energy Sources; Biofilms; Bioreactors; Domestic wastewater; High-throughput sequencing; Humans; Microbial ecology; Microbial fuel cell; Nitrites; Nitrogen; Waste Water
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.144231

The removal of organics and ammonium from domestic wastewater was successfully achieved by a flat-panel air-cathode microbial fuel cell (FA-MFC). To elucidate the reason for complete ammonium removal in the single-chamber MFCs, microbial communities were analyzed in biofilms on the surface of each anode, separator, and cathode of separator-electrode assemblies (SEAs). The spatial distribution of bacterial families related to the nitrogen cycle varied based on local conditions. Since oxygen diffusing from the air-cathode created a locally aerobic condition, ammonia-oxidizing bacteria (AOB) Nitrosomonadacea and nitrite-oxidizing bacteria (NOB) Nitrospiraceae were present near the cathode. NOB (~12.1%) was more abundant than AOB (~4.4%), suggesting that the nitrate produced by NOB may be reduced back to nitrite by heterotrophic denitrifiers such as Rhodocyclaceae (~21.7%) and Comamonadaceae (~5%) in the anoxic zone close to the NOB layer. Near that zone, the “nitrite loop” also substantially enriched two nitrite-reducing bacterial families: Ignavibacteriaceae (~18.1%), facultative heterotrophs, and Brocadiaceae (~11.2%), anaerobic ammonium oxidizing autotrophs. A larger inner area of biofilm contained abundant heterotrophic denitrifiers and fermentation bacteria. These results indicate that the large-surface SEA of FA-MFC allows counter-diffusion between substrates and oxygen, resulting in interactions of bacteria involved in the nitrogen cycle for complete ammonium removal. [Display omitted] •FA-MFC could completely remove nitrogen and organic compounds in domestic wastewater.•Nitrospiraceae near the air-cathode were more abundant than Nitrosomonadacea.•Heterotrophic denitrifiers were present in the anoxic zone close to the NOB layer.•Nitrite-reducing bacteria were abundant near the anoxic zone.•Oxygen diffusion allows bacterial interactions for nitrogen removal.