Methanol-linked synergy between aerobic methanotrophs and denitrifiers enhanced nitrate removal efficiency in a membrane biofilm reactor under a low O2:CH4 ratio. (1st May 2020)

• Record Type: Journal Article
• Authors: Xu, Xingkun; Zhu, Jing; Thies, Janice E.; Wu, Weixiang
• Is Part Of: Water research. Volume 174(2020)
• Publication Date: 2020-05-01
• Subjects: Aerobic methane oxidation coupled to denitrification -- Nitrate removal efficiency -- Membrane biofilm reactor -- O2:CH4 ratio -- Methanol-linked synergy; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2020.115595
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Nitrate removal efficiency of aerobic methane oxidation coupled with denitrification (AME-D) process was elevated by enhancing the methanol-linked synergy in a membrane biofilm reactor (MBfR) under a low O2 :CH4 ratio. After 140 days' enrichment, the nitrate removal rate increased significantly from 3 to 4 mg-N L −1 d −1 to 22.09 ± 1.21 mg-N L −1 d −1 and the indicator, mol CH4 consumed/mol reduced NO3 − -N (C/N ratio), decreased to 1.79 which was very close to the theoretical minimum value (1.27–1.39). The increased nitrate removal efficiency was largely related to the enhanced relationship between aerobic methanotrophs and methanol-utilizing denitrifiers. Type I methanotrophs and some denitrifiers, especially those potential methanol-utilizing denitrifiers from Methylobacillus, Methylotenera, Methylophilus and Methyloversatilis, were abundant in the MBfR sludge. Aerobic methanotrophs and potential methanol-utilizing denitrifiers were closely associated in many globular aggregates (5–10 μm diameter) in the MBfR sludge, which may have promoted the denitrifiers to capture methanol released by methanotrophs efficiently. If we assume methanol is the only cross-feeding intermediate in the MBfR, about 38–60% of the CH4 supplied would be converted to methanol and secreted rather than continuing to be oxidized. At least 63% of this secreted methanol should be utilized for denitrification instead of being oxidized by oxygen in the MBfR. These findings suggest that the nitrate removal efficiency of the AME-D process could be significantly improved. Graphical abstract: Image 1 Highlights: Methanol-linked synergy of AME-D was enhanced in an MBfR under a low O2 :CH4 ratio. The enhanced methanol-linked synergy improved nitrate removal efficiency of AME-D. The C/N value of AME-D was 1.79 ± 0.197 and very close to the theoretical minimum.