Nitrogen removal from wastewater by coupling anammox and methane-dependent denitrification in a membrane biofilm reactor

This work demonstrates, for the first time, the feasibility of nitrogen removal by using the synergy of anammox and denitrifying anaerobic methane oxidation (DAMO) microorganisms in a membrane biofilm reactor (MBfR). The reactor was fed with synthetic wastewater containing nitrate and ammonium. Methane was delivered from the interior of hollow fibres in the MBfR to the biofilm that grew on the fiber's outer wall. After 24 months of operation, the system achieved a nitrate and an ammonium removal rate of about 190 mgN L -1 d-1 (or 86 mgN m-2 d-1, with m2 referring to biofilm surface area) and 60 mgN L-1 d-1 (27 mgN m-2 d-1), respectively. No nitrite accumulation was observed. Fluorescence in situ hybridization (FISH) analysis indicated that DAMO bacteria (20-30%), DAMO archaea (20-30%) and anammox bacteria (20-30%) jointly dominated the microbial community. Based on the known metabolism of these microorganisms, mass balance, and isotope studies, we hypothesize that DAMO archaea converted nitrate, both externally fed and produced by anammox, to nitrite, with methane as the electron donor. Anammox and DAMO bacteria jointly removed the nitrite produced, with ammonium and methane as the electron donor, respectively. The process could potentially be used for anaerobic nitrogen removal from wastewater streams containing ammonium and nitrate/nitrite

Active pathways of anaerobic methane oxidation across contrasting riverbeds.

Anaerobic oxidation of methane (AOM) reduces methane emissions from marine ecosystems but we know little about AOM in rivers, whose role in the global carbon cycle is increasingly recognized. We measured AOM potentials driven by different electron acceptors, including nitrite, nitrate, sulfate, and ferric iron, and identified microorganisms involved across contrasting riverbeds. AOM activity was confined to the more reduced, sandy riverbeds, whereas no activity was measured in the less reduced, gravel riverbeds where there were few anaerobic methanotrophs. Nitrite-dependent and nitrate-dependent AOM occurred in all sandy riverbeds, with the maximum rates of 61.0 and 20.0 nmol CO2 g-1 (dry sediment) d-1, respectively, while sulfate-dependent and ferric iron-dependent AOM occurred only where methane concentration was highest and the diversity of AOM pathways greatest. Diverse Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria and Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like archaea were detected in the sandy riverbeds (16S rRNA gene abundance of 9.3 × 105 to 1.5 × 107 and 2.1 × 104 to 2.5 × 105 copies g-1 dry sediment, respectively) but no other known anaerobic methanotrophs. Further, we found M. oxyfera-like bacteria and M. nitroreducens-like archaea to be actively involved in nitrite- and nitrate/ferric iron-dependent AOM, respectively. Hence, we demonstrate multiple pathways of AOM in relation to methane, though the activities of M. oxyfera-like bacteria and M. nitroreducens-like archaea are dominant

Complete nitrification by a single microorganism

Contains fulltext : 151073.pdf (publisher's version ) (Closed access

Catabolic Pathways and Enzymes Involved in Anaerobic Methane Oxidation

Microbes use two distinct catabolic pathways for life with the fuel methane: aerobic methane oxidation carried out by bacteria and anaerobic methane oxidation carried out by archaea. The archaea capable of anaerobic oxidation of methane, anaerobic methanotrophs (ANME), are phylogenetically related to methanogens. While the carbon metabolism in ANME follows the pathway of reverse methanogenesis, the mode of electron transfer from methane oxidation to the terminal oxidant is remarkably versatile. This chapter discusses the catabolic pathways of methane oxidation coupled to the reduction of nitrate, sulfate, and metal oxides. Methane oxidation with sulfate and metal oxides are hypothesized to involve direct interspecies electron transfer and extracellular electron transfer. Cultivation of ANME, their mechanisms of energy conservation, and details about the electron transfer pathways to the ultimate oxidants are rather new and quickly developing research fields, which may reveal novel metabolisms and redox reactions. The second section focuses on the carbon catabolism from methane to CO2 and the biochemistry in ANME with its unique enzymes containing Fe, Ni, Co, Mo, and W that are compared with their homologues found in methanogens

Methane as a resource: can the methanotrophs add value?

Methane is an abundant gas used in energy recovery systems, heating, and transport. Methanotrophs are bacteria capable of using methane as their sole carbon source. Although intensively researched, the myriad of potential biotechnological applications of methanotrophic bacteria has not been comprehensively discussed in a single review. Methanotrophs can generate single-cell protein, biopolymers, components for nanotechnology applications (surface layers), soluble metabolites (methanol, formaldehyde, organic acids, and ectoine), lipids (biodiesel and health supplements), growth media, and vitamin B12 using methane as their carbon source. They may be genetically engineered to produce new compounds such as carotenoids or farnesene. Some enzymes (dehydrogenases, oxidase, and catalase) are valuable products with high conversion efficiencies and can generate methanol or sequester CO2 as formic acid ex vivo. Live cultures can be used for bioremediation, chemical transformation (propene to propylene oxide), wastewater denitrification, as components of biosensors, or possibly for directly generating electricity. This review demonstrates the potential for methanotrophs and their consortia to generate value while using methane as a carbon source. While there are notable challenges using a low solubility gas as a carbon source, the massive methane resource, and the potential cost savings while sequestering a greenhouse gas, keeps interest piqued in these unique bacteria