Enrichment of Nitrogen-Fixing Bacteria in a Nitrogen-Deficient Wastewater Treatment System.

Anthropogenic nitrogen fixation is essential to sustain a global population of 7.7 billion. However, there has been a long-standing desire to find cheaper and more environmentally friendly alternatives to the Haber-Bosch process. In this study, we developed a new strategy of nitrogen fixation by enriching free-living N-fixing bacteria (NFB) in reactors fed with low nitrogen wastewater, analogous to those usually found in certain industrial effluents such as paper mills. Our reactors fixed appreciable quantities of nitrogen with a rate of 11.8 mg N L day. This rate is comparable to recent "breakthrough" nitrogen-fixing technologies and far higher than observed in low C/N reactors (fed with organic matter and nitrogen). NFB were quantified using quantitative polymerase chain reaction (qPCR) of the (marker gene used to identify biological nitrogen fixation) and genes. The gene was enriched by a factor of 10 in the nitrogen-fixing reactors (compared to controls) attaining 13% of the bacterial population (1:4.2 copies of to ). The Illumina MiSeq gene amplicon sequencing of reactors showed that the microbial community was dominated (19%) by . We envisage that nitrogen-enriched biomass could potentially be used as a biofertilizer and that the treated wastewater could be released to the environment with very little post-treatment.