Aggregate Size and Architecture Determine Microbial Activity Balance for One-Stage Partial Nitritation and Anammox

Abstract

Aerobic ammonium-oxidizing bacteria (AerAOB) and anoxic ammonium-oxidizing bacteria (AnAOB) cooperate in partial nitritation/anammox systems to remove ammonium from wastewater. In this process, large granular microbial aggregates enhance the performance, but little is known about granulation so far. In this study, three suspended-growth oxygen-limited autotrophic nitrification-denitrification (OLAND) reactors with different inoculation and operation (mixing and aeration) conditions, designated reactors A, B, and C, were used. The test objectives were (i) to quantify the AerAOB and AnAOB abundance and the activity balance for the different aggregate sizes and (ii) to relate aggregate morphology, size distribution, and architecture putatively to the inoculation and operation of the three reactors. A nitrite accumulation rate ratio (NARR) was defined as the net aerobic nitrite production rate divided by the anoxic nitrite consumption rate. The smallest reactor A, B, and C aggregates were nitrite sources (NARR, >1.7). Large reactor A and C aggregates were granules capable of autonomous nitrogen removal (NARR, 0.6 to 1.1) with internal AnAOB zones surrounded by an AerAOB rim. Around 50% of the autotrophic space in these granules consisted of AerAOB-and AnAOB-specific extracellular polymeric substances. Large reactor B aggregates were thin film-like nitrite sinks (NARR, <0.5) in which AnAOB were not shielded by an AerAOB layer. Voids and channels occupied 13 to 17% of the anoxic zone of AnAOB-rich aggregates (reactors B and C). The hypothesized granulation pathways include granule replication by division and budding and are driven by growth and/or decay based on speciesspecific physiology and by hydrodynamic shear and mixing.In the last few years, autotrophic nitrogen removal via partial nitritation and anoxic ammonium oxidation (anammox) has evolved from lab-to full-scale treatment of nitrogenous wastewaters with a low biodegradable organic compound content, and this evolution has been driven mainly by a significant decrease in the operational costs compared to the costs of conventional nitrification and heterotrophic denitrification (11,23). Oxygen-limited autotrophic nitrification and denitrification (OLAND) is one of the autotrophic processes used and is a one-stage procedure; i.e., partial nitritation and anammox occur in the same reactor (30). The "functional" autotrophic microorganisms in OLAND include aerobic ammonium-oxidizing bacteria (AerAOB) and anoxic ammonium-oxidizing bacteria (AnAOB). With oxygen, AerAOB oxidize ammonium to nitrite (nitritation), and with the nitrite AnAOB oxidize the residual ammonium to form dinitrogen gas and some nitrate (anammox). Additional aerobic nitrite oxidation to nitrate (nitratation) by nitrite-oxidizing bacteria (NOB) lowers the nitrogen removal efficiency, but it can, for instance, be prevented at low dissolved oxygen (DO) levels because the oxygen affinity of AerAOB is higher than that of NOB (16). Reactor configurations for the OLAND process can be based on suspended b...

Microbial Population Dynamics and Community Structure during the Formation of Nitrifying Granules to Treat Ammonia-Rich Inorganic Wastewater

“…Although there is a report that AOB associated with the N. mobilis lineage synthesize EPS in excessive amounts (39), it is unclear whether the EPS was excreted by N. mobilis or heterotrophic bacteria in the present study. Taking account of a report that EPS contributed to maintaining the structure of aggregates (1), the elasticity of EPS would support granule mechanical stability and contribute to granulation (44).…”

ZeroWasteWater: short-cycling of wastewater resources for sustainable cities of the future

“…Although the OLAND technology has been mainly used for treatment of highly nitrogenous waste streams so far, this technology can also treat low nitrogen concentrations (30-60 mg N L −1 ) at low hydraulic retention time (1-2 h) and high rates (400 mg N L −1 d −1 ) (De Clippeleir et al, in press). Besides high removal efficiencies, a high solids retention time and easy biomass retention are needed, rendering well-settling granular biomass as an appealing option (De Clippeleir et al, 2009;Vlaeminck et al, 2009a;Vlaeminck et al, 2010). Following OLAND, usable heat will be recovered with two sequential heat pumps, and this recovered energy represents about half of the fossil-fuel equivalent energy and of the CO 2 footprint advantages of ZeroWasteWater compared to CAS ( Table 2).…”

Increased salinity improves the thermotolerance of mesophilic nitrification

“…distinguish between Nitrobacter and Nitrospira, as a supporting analysis for the NOB target choice in the following quantitative polymerase chain reaction (qPCR) analysis. Inoculum and endpoint samples were examined by FISH as described by Vlaeminck et al (2010). qPCR was used to quantify the abundance of AOA, AerAOB, NOB and AnAOB over time.…”