[Rapid Start-up of a Nitrite-Dependent Methane Anaerobic Oxidation Reaction Under Static Pressure Conditions]

The present study explores the effect of static pressure on the rapid start-up of a nitrite-dependent anaerobic methane oxidation (N-DAMO) process in lab-scale sequencing batch reactors (SBR). A mixture of anaerobic sludge and deep paddy soil with a volume ratio of 1:1 was used as inoculum and the influent of the nitrite (NO₂^--N) concentration was gradually increased to avoid a toxicity shock. The variation of the NO₂^--N removal performance and corresponding microbial characteristics were analyzed to evaluate the development of the N-DAMO process. After 120 days of operation, significant N-DAMO phenomena were observed in both the control SBR (R1) with normal pressure and pressurized SBR (R2) with a static pressure of 0.3 MPa. The NO₂^--N removal rate (measured by NO₂^--N) of R2 (36.90 mg·(L·d)^-1) was 24% higher than that of R1, while the average NO₂^--N removal rate in the first 4 h of the batch cycle in R2 (0.10 mmol·(L·h)^-1) was 186% higher than that of R1. The mean sludge size of R2 was~2-fold larger than that of R1. Sludge in R2 also has a bigger specific surface area, which improves the mass transfer rate of methane and the N-DAMO performance. The specific activity of N-DAMO (measured by N/VSS) reached 0.29 mg·(g·h)^-1 in the study period, which is approximately 2 times higher than that of R1. Moreover, the abundance of N-DAMO functional microbes Candidatus Methylomirabilish oxyfera (M. oxyfera) in R2 was 10-fold higher than that of R1. These results indicate that static pressure effectively accelerates the start-up of the N-DAMO process.