Research On Enrichment Of Denitrifying Anaerobic Methane Oxidizing Microorganisms

Denitrifying anaerobic methane oxidation (DAMO) is a newly discovered microbial reaction which catalyzed by NC10bacteria. Several aspects makes the research on the DAMO process and relevant microorganisms meaningful. First, the DAMO process is a new pathway of biogeochemistry for its link of carbon and nitrogen cycles. Second, the finding of NC10bacteria expands the knowledge of microbiology for its unique physiological and biochemical properties. Third, the DAMO process offers option to develop new wastewater treatment technology for its simultaneous removal of methane and nitrate/nitrite. However, the extremely slow growth rate of DAMO microorganisms seriously limited to get the enrichment culture. In consideration of this bottleneck, we investigated the influence of three key factors, inoculum, medium and reactor configuration, on the enrichment of DAMO microorganisms. The major conclusions are as follows:1) The differences to enrich DAMO microorganisms using three distinct inocula were compared and the optimal inoculum was obtained.①The feasibility of the three inocula, methanogenic granular sludge, paddy soil and freshwater river sediment, to enrich NC10bacteria was verified, and the differences of NC10bacteria numbers and specific DAMO activities among the cultures were compared. The NC10bacteria numbers in these three cultures were63,2909and198times higher than that in the inocula, respectively. Specific DAMO activities of the three cultures were0.06mgN·g-1VSS·h-1,0.15mgN·g-1VSS·h-1and0.11mgN·g-1VSS·h-1, respectively. These results revealed that the three inocula were all suitable for the enrichment of DAMO microorganisms, which provided more choices to select DAMO inocula.②It was first proved the feasibility of paddy soil for the enrichment of DAMO culture, and the paddy soil was proved the best inoculum in these three inocula.2) The cultivation effects of the cultures enriched using natural medium and artificial medium were compared and the optimal medium was obtained. ①The differences of DAMO microorganisms enrichment using natural medium and artificial medium were tested. Specific DAMO activities of these two cultures were0.02mgN·g-1VSS·h-1and0.11mgN·g-1VSS·h-1, respectively. The NC10bacteria numbers were1.01×108copies·g-1(dry weight) and2.01×108copies·g-1(dry weight). These results indicated that better enrichment effect could be achieved with artificial medium.②NC10bacteria belonging to group B were successfully enriched using paddy soil as inoculum with artificial medium. This is the first evidence to confirm NC10bacteria belonging to group B are capable of catalyzing the DAMO process.3) The ability of the reactors with different configurations to enrich DAMO microorganisms were compared, and the reactor with optimal configuration was obtained.①The differences of enrichment process and the DAMO cultures using reactors with different configurations were compared. The volume nitrogen removal rate of the three reactors (Magnetic stirred air lift reactor, MSALR; Biofilm reactor, BR; Sequencing batch reactor, SBR) at last obtained an increase of827.10%,302.92%and154.09%compared to that in the initial period, respectively. Specific DAMO activities of the enrichment cultures were0.52mgN·g-1VSS·h-1,0.23mgN·g-1VSS·h-1and0.26mgN·g-1VSS·h-1, respectively. These results showed that the three reactors with different configurations were all proper to enrich DAMO microorganisms.②The culture in MSALR contains the highest volume nitrogen removal rate and specific DAMO activities among the three cultures, which demonstrated that MSALR is the best reactor to enrich DAMO microorganisms.③The transfer of methane is more important than the retention of biomass during the enrichment period.