Diversity and enrichment of nitrite-dependent anaerobic methane oxidizing bacteria from wastewater sludge.
Bottom Line: This enrichment was monitored using specific pmoA primers and M. oxyfera cells were visualized with fluorescence oligonucleotide probes.After 112 days, the enrichment consumed up to 0.4 mM NO(2)(-) per day.The results of this study show that appropriate sources of biomass, enrichment strategies, and diagnostic tools existed to start and monitor pilot scale tests for the implementation of nitrite-dependent methane oxidation in wastewater treatment at ambient temperature.
Affiliation: Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.Show MeSH
Mentions: A 15-l sequencing batch reactor was inoculated with biomass from the WWTP Lieshout. During the initial trial period, we noticed that the denitrifying activity measured inside the bioreactor gradually decreased. Furthermore, biomass that was not efficiently retained in the reactor accumulated in the external settler. The biomass collected in the external settler (0.7 l liquid culture containing 1.5 g of protein) did show denitrifying activity: NO2− and NO3− were converted at rates of 2.1 and 9.2 nmol h−1 mg protein−1, respectively. Besides the denitrification, anaerobic methane oxidizing activity (1.7 nmol CH4 h−1 mg protein−1) could be measured. In addition to these activity experiments, the biomass in the external settler was analyzed for the presence of NC10 bacteria using a nested PCR approach. M. oxyfera-type bacteria were detected in the settler biomass and were all clustering in group a of the NC10 phylum (Ettwig et al. 2009). The sequences obtained from the external settler were closely related to the 14 sequences found in the inoculum originating from the WWTP in Lieshout (Fig. 1a). Based on these results, the biomass from the external settler was used to inoculate a new 3-l bioreactor (SBR) that was operated at ambient temperature under strict anoxic conditions and a stringent biomass retention regime. At the startup of the 3-l bioreactor, the initial nitrite concentration (1 mM) was diluted to 0.01 mM by pumping fresh medium into the reactor (day 0–50). The activity of the culture till 77 days was low but thereafter the culture showed increasing denitrifying activity up to 0.4 mM of NO2− day−1 on t = 112 days (Fig. 2a). There were a number of technical problems (power failures, interruption of the methane supply) from days 112 to 175 causing fluctuating nitrite and methane consumption activities. However, from day 175, there was an ongoing increasing nitrite reducing activity up to 1.1 mM day−1 (Fig. 2a).Fig. 2
Affiliation: Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.