Performance of Denitrifying Methanotrophic Bacteria of the NC10 Phylum in Sequencing Batch Reactor

Abstract

Anaerobic treatment processes in wastewater treatment industries discharge methane in gaseous as well as in aqueous form. Methane is considered a powerful greenhouse gas that has a global warming potential 25 times greater than carbon dioxide over a 100-year period. While methane in the gaseous phase can be easily collected and purified, dissolved methane is difficult to recover. Therefore, a post-treatment process is needed in anaerobic systems to oxidize dissolved methane, thereby reducing greenhouse gas emissions and making anaerobic wastewater treatment a more eco-friendly technology. Nitrite dependent denitrifying anaerobic methane oxidation (N-DAMO) is a novel process for simultaneous carbon and nitrogen removal. This process is assigned to a methanotroph that has been identified as a member of the phylum NC 10 and named “Candidatus Methylomirabilis oxyfera (M. oxyfera)”. This bacterium utilizes methane as electron donor as well as carbon source and nitrite as electron acceptor to oxidize methane into carbon dioxide. In this study, cultivation of the denitrifying methanotrophic bacteria of the NC10 Phylum (‘M. oxyfera’) by using activated sludge from Xin-Feng wastewater treatment plant, Taiwan as an inoculum as well as the performance of the N-DAMO process in sequencing batch reactor was investigated. A 3.3 L bioreactor (working volume 2.5 L) was setup and has been in operation in sequencing batch mode for better biomass retention with a hydraulic retention time (HRT) of 10 days. Temperature, pH, alkalinity, oxidation-reduction potential (ORP) and dissolved oxygen (DO) are continuously monitored. Nitrite loading rate is increased slowly. From day 65, modified medium (increased concentration of Cu+2 and Fe+2 ) was provided, which also caused turbulence in removal efficiency. Maximum nitrogen loading rate was 2.23 g N m-3 d-1. Activity experiments were performed to confirm the activity of N-DAMO bacteria.

Anaerobic treatment processes in wastewater treatment industries discharge methane in gaseous as well as in aqueous form. Methane is considered a powerful greenhouse gas that has a global warming potential 25 times greater than carbon dioxide over a 100-year period. While methane in the gaseous phase can be easily collected and purified, dissolved methane is difficult to recover. Therefore, a post-treatment process is needed in anaerobic systems to oxidize dissolved methane, thereby reducing greenhouse gas emissions and making anaerobic wastewater treatment a more eco-friendly technology. Nitrite dependent denitrifying anaerobic methane oxidation (N-DAMO) is a novel process for simultaneous carbon and nitrogen removal. This process is assigned to a methanotroph that has been identified as a member of the phylum NC 10 and named “Candidatus Methylomirabilis oxyfera (M. oxyfera)”. This bacterium utilizes methane as electron donor as well as carbon source and nitrite as electron acceptor to oxidize methane into carbon dioxide. In this study, cultivation of the denitrifying methanotrophic bacteria of the NC10 Phylum (‘M. oxyfera’) by using activated sludge from Xin-Feng wastewater treatment plant, Taiwan as an inoculum as well as the performance of the N-DAMO process in sequencing batch reactor was investigated. A 3.3 L bioreactor (working volume 2.5 L) was setup and has been in operation in sequencing batch mode for better biomass retention with a hydraulic retention time (HRT) of 10 days. Temperature, pH, alkalinity, oxidation-reduction potential (ORP) and dissolved oxygen (DO) are continuously monitored. Nitrite loading rate is increased slowly. From day 65, modified medium (increased concentration of Cu+2 and Fe+2 ) was provided, which also caused turbulence in removal efficiency. Maximum nitrogen loading rate was 2.23 g N m-3 d-1. Activity experiments were performed to confirm the activity of N-DAMO bacteria.