Methanol-linked synergy between aerobic methanotrophs and denitrifiers enhanced nitrate removal efficiency in a membrane biofilm reactor under a low O 2 :CH 4 ratio

• Published in: Water research (Oxford) Vol. 174; p. 115595
• Main Authors: Xu, Xingkun, Zhu, Jing, Thies, Janice E, Wu, Weixiang
• Format: Journal Article
• Language: English
• Published: England 01.05.2020
• Subjects: Biofilms; Bioreactors; Denitrification; Methane; Methanol; Nitrates; Oxidation-Reduction; Methanol-linked synergy; O:CH ratio; Nitrate removal efficiency; Aerobic methane oxidation coupled to denitrification; Membrane biofilm reactor
• ISSN: 1879-2448

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 O :CH ratio. After 140 days' enrichment, the nitrate removal rate increased significantly from 3 to 4 mg-N L d to 22.09 ± 1.21 mg-N L d and the indicator, mol CH consumed/mol reduced NO -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 CH 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.