A robust nitrifying community in a bioreactor at 50 °C opens up the path for thermophilic nitrogen removal

Abstract

The increasing production of nitrogen-containing fertilizers is crucial to meet the global food demand, yet high losses of reactive nitrogen associated with the food production/consumption chain progressively deteriorate the natural environment. Currently, mesophilic nitrogen-removing microbes eliminate nitrogen from wastewaters. Although thermophilic nitrifiers have been separately enriched from natural environments, no bioreactors are described that couple these processes for the treatment of nitrogen in hot wastewaters. Samples from composting facilities were used as inoculum for the batch-wise enrichment of thermophilic nitrifiers (350 days). Subsequently, the enrichments were transferred to a bioreactor to obtain a stable, high-rate nitrifying process (560 days). The community contained up to 17% ammonia-oxidizing archaea (AOAs) closely related to 'Candidatus Nitrososphaera gargensis', and 25% nitrite-oxidizing bacteria (NOBs) related to Nitrospira calida. Incorporation of 13 C-derived bicarbonate into the respective characteristic membrane lipids during nitrification supported their activity as autotrophs. Specific activities up to 198 ± 10 and 894 ± 81 mg N g − 1 VSS per day for AOAs and NOBs were measured, where NOBs were 33% more sensitive to free ammonia. The NOBs were extremely sensitive to free nitrous acid, whereas the AOAs could only be inhibited by high nitrite concentrations, independent of the free nitrous acid concentration. The observed difference in product/substrate inhibition could facilitate the development of NOB inhibition strategies to achieve more cost-effective processes such as deammonification. This study describes the enrichment of autotrophic thermophilic nitrifiers from a nutrient-rich environment and the successful operation of a thermophilic nitrifying bioreactor for the first time, facilitating opportunities for thermophilic nitrogen removal biotechnology.

Low Temperature and Neutral pH Define “ Candidatus Nitrotoga sp.” as a Competitive Nitrite Oxidizer in Coculture with Nitrospira defluvii

“…BS was quite high, because growth continued in the presence of 30 mM ammonium chloride at neutral pH (Table S2). In contrast to NH 4 ϩ , free ammonia (NH 3 ) is inhibitory for most NOB (25, 31) but not for relatives of Nitrospira calida (37). In accordance with results for Nt.…”

Enrichment and Physiological Characterization of a Cold-Adapted Nitrite-Oxidizing Nitrotoga sp. from an Eelgrass Sediment

“…Furthermore, a recent study based on Nitrospira isolates demonstrated that the nitrite oxidation activity of Nitrospira strains ND1 and NJ1 was inhibited at concentrations above 0.85 and 4.3 mg of NH 3 -N · liter Ϫ1 , respectively (42). With respect to thermophilic NOB related to Nitrospira calida derived from a nutrient-rich composting fertilizer, its sensitivity for free ammonia was lower than those of other reported Nitrospira spp., characterized by half-maximal inhibition of 5.0 mg of NH 3 -N · liter Ϫ1 (43). In this study, the presence of free ammonia at 0.04 to 1.30 mg of NH 3 -N · liter Ϫ1 (1 to 30 mM NH 4 Cl [pH 8.1]) prompted the nitrite oxidation by AM1.…”

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

“…Similar to the irradiance, microalgae and bacteria growth increases with increasing temperature up to their optimum growth temperature, to rapidly decrease beyond this value. The optimal growth temperature is speciesspecific and typically ranges from 10 to 35°C (Markou and Georgakakis, 2011;Breuer et al, 2013;Courtens et al, 2016). Turbulence in the aquatic medium promotes mass exchange and biomass production, but the shear stress induced by water flow may promote the detachment of attached microalgae from the solid substrate (Ahn et al, 2013).…”

“…3, reaction 5A) and then to N 2 or N 2 O (Fig. 3, reaction 5B) by denitrifying bacteria in the absence of O 2 in the aquatic environment (Fitzgerald et al, 2015;Courtens et al, 2016). Traditionally, it was assumed that ammonium is oxidized into nitrite and then nitrate under aerobic conditions, and nitrate is transformed into N 2 or N 2 O through denitrification anaerobically (Strohm et al, 2007).…”

“…However, most of the currently studied attached microalgae-bacteria consortia form via natural colonization, which may bring undesired microbial species (Adey et al, 2013;Shangguan et al, 2015). In recent decades, the rapid development in genetic engineering has greatly helped to identify and select the functional genes and strains for nutrient transform (Herrero and Stuckey, 2015;van Kessel et al, 2015;Courtens et al, 2016). Genetic and metabolic engineering offer the possibility for strain improvement (Lindemann et al, 2016) and synthetic biology provides innovative approaches for designing microorganisms or communities with superior catalytic abilities on recalcitrant pollutants, but with potential risks to the ecological safety (Karig, 2017).…”