Simultaneous autotrophic denitrification and nitrification in a low-oxygen reaction environment.

The occurrence of autotrophic denitrification and nitrification activities by ammonia-oxidising bacteria and nitrite-oxidising bacteria is studied in a bioreactor system operable at low-dissolved oxygen (DO) and at variable oxygen influx rates. At a loading of 3.6 mg NH4(+)-N/h into the bioreactor, simultaneous autotrophic denitrification and nitrification contributed to NH4(+)-N removal over oxygen influxes of 2-14 mg O2/h and DO <0.5 mg/L. The maximum autotrophic denitrification (or total-N removal) rates were achieved in a narrow oxygen influx band of 3-5 mg O2/h, where it accounted for up to 36% of NH4(+)-N removal. At oxygen influx >16 mg O2/h and DO >2 mg/L, autotrophic denitrification ceases and roughly 90% of feed NH4(+)-N is oxidised to NOX(-)-N. The stability of total effluent chemical oxygen demand (COD) over the range of oxygen influxes tested confirms the absence of heterotrophic denitrification in the bioreactor. The long solids residence time of the stable biomass zone (21 days) led to production of effluent COD as a result of cell decay, and thus effluent COD was used to calculate more accurately the mean cell residence time.

Analysis of an upflow bioreactor system for nitrogen removal via autotrophic nitrification and denitrification.

The upflow bioreactor system without biomass-liquid separation unit was evaluated for its efficacy in sustaining autotrophic nitrification and denitrification (AND). The bioreactor system was capable of sustaining AND by means of carefully controlled oxygenation to achieve the maximum NH(4)(+)-N removal rate of 0.054 g N gVSS(-1) day(-1) (38% removal efficiency) at the oxygen influx and nitrogen loading rate of 3.68 mg O(2) h(-1) L-bioreactor(-1) and 182 mg N day(-1) L-bioreactor(-1), respectively. Additional nitrogen removal was achieved in a two-stage bioreactor configuration due to endogenous denitrification under long mean cell residence time. Quiescent conditions maintained in the bioreactor provided stable hydrodynamic environments for the chemoautotrophic biomass matrix, which revealed porous, loosely-structured, and mat-like architecture. More than 95% of the total biomass holdup (1.3-1.5 g VSS) was retained, thereby producing low biomass washout rate ( approximately 40 mg VSS day(-1)) with VSS < 11 mg VSSL(-1) in the effluent.

Performance of an aerobic/anaerobic hybrid bioreactor under the nitrogen deficient and low F/M conditions.

A bioreactor system without a biomass-liquid separation unit is evaluated for its chemical oxygen demand (COD) removal and biomass retention capabilities under the nitrogen deficient and low F/M conditions that are known to produce bulking biomass. A fully oxygenated stream recycled from an external oxygenator delivers the oxygen to an upflow bioreactor in which a biomass zone is formed and maintained in the absence of gas effervescence. COD is removed with up to 90% efficiency by means of aerobic and anaerobic bacterial activities occurring in the biomass zone. The biomass is bulking which is brought about by the extensive filamentous growth caused by the nitrogen deficient and low F/M conditions adopted. However, the biomass zone is undisturbed at superficial upflow velocities as high as 0.66 cm/min, because it has a porous, mat-like matrix that is augmented by the entanglement of filamentous bacteria with the cell clusters. A low-VSS effluent (i.e.,< 10 mg/L) is produced directly from the bioreactor.

A Novel Bioreactor for High Density Cultivation of Diverse Microbial Communities.

A novel reactor design, coined a high density bioreactor (HDBR), is presented for the cultivation and study of high density microbial communities. Past studies have evaluated the performance of the reactor for the removal of COD(1) and nitrogen species(2-4) by heterotrophic and chemoautotrophic bacteria, respectively. The HDBR design eliminates the requirement for external flocculation/sedimentation processes while still yielding effluent containing low suspended solids. In this study, the HDBR is applied as a photobioreactor (PBR) in order to characterize the nitrogen removal characteristics of an algae-based photosynthetic microbial community. As previously reported for this HDBR design, a stable biomass zone was established with a clear delineation between the biologically active portion of the reactor and the recycling reactor fluid, which resulted in a low suspended solid effluent. The algal community in the HDBR was observed to remove 18.4% of total nitrogen species in the influent. Varying NH4(+) and NO3(-) concentrations in the feed did not have an effect on NH4(+) removal (n=44, p=0.993 and n=44, p=0.610 respectively) while NH4(+) feed concentration was found to be negatively related with NO3(-) removal (n=44, p=0.000) and NO3(-) feed concentration was found to be positively correlated with NO3(-) removal (n=44, p=0.000). Consistent removal of NH4(+), combined with the accumulation of oxidized nitrogen species at high NH4(+) fluxes indicates the presence of ammonia- and nitrite-oxidizing bacteria within the microbial community.

Impulse responses of a monoethylamine-fed fluidized bed reactor.

The responses of a steady-state, continuous-flow, completely-mixed fluidized bed reactor (FBR) to a range of monoethylamine (MEA) impulses are analyzed in terms of its combined carbon oxidation and nitrification efficiencies. Immobilized cells are cultivated at a mean cell residence time (MCRT) that exceeds 75 days. Responses due to bacterial activities and physical flows are separately estimated using a methodology based on mass balance calculations. MEA inhibition becomes evident when respective critical impulse loadings are exceeded, i.e., 0.12 mg TOC/mg VS for carbon oxidation and 0.021 mg TOC/mg VS for nitrification (TOC: total organic carbon, VS: volatile solids). Nitrifying cells are shown to be more susceptible to MEA impulses than their heterotrophic counterparts. However, the presence of nitrification activities under the conditions tested demonstrates the advantages of cell immobilization that offer greater flexibility when challenged with suddenly increased MEA loads over a short period of time. Mass balance calculations on nitrogen species confirms that 0.583 mg NH(4)(+)-N is produced per mg MEA-C removed when the assimilatory nitrogen requirements for cell synthesis are negligible.