Continuous anaerobic oxidation of methane: Impact of semi-continuous liquid operation and nitrate load on N2O production and microbial community

• Published in: Chemosphere (Oxford) Vol. 278; p. 130441
• Main Authors: Valenzuela, Edgardo I., Ortiz-Zúñiga, María F., Carrillo-Reyes, Julián, Moreno-Andrade, Iván, Quijano, Guillermo
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2021
• Subjects: Anaerobic oxidation of methane; Greenhouse gas; Microbial community; Nitrate removal; Nitrous oxide production; Nitrate removal; Anaerobic oxidation of methane; Nitrous oxide production; Greenhouse gas; Microbial community
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2021.130441

This work proves the feasibility of employing regular secondary activated sludge for the enrichment of a microbial community able to perform the anaerobic oxidation of methane coupled to nitrate reduction (N-AOM). After 96 days of activated sludge enrichment, a clear N-AOM activity was observed in the resulting microbial community. The methane removal potential of the enriched N-AOM culture was then studied in a stirred tank reactor (STR) operated in continuous mode for methane supply and semi-continuous mode for the liquid phase. The effect of applying nitrate loads of ∼22, 44, 66, and 88 g NO3− m−3 h−1 on (i) STR methane and nitrate removal performance, (ii) N2O emission, and (iii) microbial composition was investigated. Methane elimination capacities from 21 ± 13.3 to 55 ± 12 g CH4 m−3 h−1 were recorded, coupled to nitrate removal rates ranging from 6 ± 3.2 to 43 ± 14.9 g NO3− m−3 h−1. N2O production was not detected under the three nitrate loading rates applied for the assessment of potential N2O emission in the continuous N-AOM process (i.e. ∼22–66 g NO−3 m−3 h−1). The lack of N2O emissions during the process was attributed to the N2O reducing capacity of the bacterial taxa identified and the rigorous control of dissolved O2 and pH implemented (dissolved O2 values ≤ 0.07 g m−3 and pH of 7.6 ± 0.4). Microbial characterization showed that the N-AOM process was performed in absence of putative N-AOM archaea and bacteria (ANME-2d, M. oxyfera). Instead, microbial activity was driven by methane-oxidizing bacteria and denitrifying bacteria (Bacteroidetes, α-, and γ-proteobacteria).
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•Continuous N-AOM was successfully implemented from activated sludge.•N2O was not detected at nitrate loading rates of 22–66 gNO3- m−3 h−1.•A maximum CH4 elimination capacity of ∼55 g m−3 h−1 was recorded.•M. nitroreducens (ANME-2d) and M. oxyfera were absent.