Reducing Cost and Environmental Impact of Wastewater Treatment with Denitrifying Methanotrophs, Anammox, and Mainstream Anaerobic Treatment.

In water resource recovery facilities, sidestream biological nitrogen removal via anaerobic ammonium oxidation (anammox) is more energy and cost efficient than conventional nitrification-denitrification. However, under mainstream conditions, nitrite oxidizing bacteria (NOB) out-select anammox bacteria for nitrite produced by ammonium oxidizing bacteria (AOB). Therefore, nitrite production is the bottleneck in mainstream anammox nitrogen removal. Nitrate-dependent denitrifying anaerobic methane oxidizing archaea (n-damo) oxidize methane and reduce nitrate to nitrite. The nitrite supply challenge in mainstream anammox implementation could be solved with a microbial community of AOB, NOB, n-damo, and anammox with methane from anaerobic sludge digestion or a mainstream anaerobic membrane bioreactor (AnMBR). The cost and environmental impact of traditional nitrification/dentrification relative to AOB/anammox and AOB/anammox/n-damo systems, with and without an AnMBR, were compared with a stoichiometric model. AnMBR implementation reduced costs and emission rates at moderate to high nutrient loading by lowering aeration and sludge handling demands while increasing methane available for cogeneration. AnMBR/AOB/anammox systems reduced cost and GHG emission by up to $0.303/d/m3 and 1.72 kg equiv. CO2/d/m3, respectively, while AnMBR/AOB/anammox/n-damo systems saw a similar reduction of at least $0.300/d/m3 and 1.65 kg equiv. CO2/d/m3 in addition to alleviating the necessity to stop nitrification at nitrate, allowing easier aeration control.

Sustained nitrogen loss in a symbiotic association of Comammox Nitrospira and Anammox bacteria.

The discovery of anaerobic ammonia-oxidizing bacteria (Anammox) and, more recently, aerobic bacteria common in many natural and engineered systems that oxidize ammonia completely to nitrate (Comammox) have significantly altered our understanding of the global nitrogen cycle. A high affinity for ammonia (Km(app),NH3 ≈ 63nM) and oxygen place Comammox Nitrospira inopinata, the first described isolate, in the same trophic category as organisms such as some ammonia-oxidizing archaea. However, N. inopinata has a relatively low affinity for nitrite (Km,NO2 ≈ 449.2µM) suggesting it would be less competitive for nitrite than other nitrite-consuming aerobes and anaerobes. We examined the ecological relevance of the disparate substrate affinities by coupling it with the Anammox bacterium Candidatus Brocadia anammoxidans. Synthetic communities of the two were established in hydrogel granules in which Comammox grew in the aerobic outer layer to provide Anammox with nitrite in the inner anoxic core to form dinitrogen gas. This spatial organization was confirmed with FISH imaging, supporting a mutualistic or commensal relationship. The functional significance of interspecies spatial organization was informed by the hydrogel encapsulation format, broadening our limited understanding of the interplay between these two species. The resulting low nitrate formation and the competitiveness of Comammox over other aerobic ammonia- and nitrite-oxidizers sets this ecological cooperation apart and points to potential biotechnological applications. Since nitrate is an undesirable product of wastewater treatment effluents, the Comammox-Anammox symbiosis may be of economic and ecological importance to reduce nitrogen contamination of receiving waters.