Coupling anammox and heterotrophic denitrification activity at mainstream conditions in a single reactor unit

Altres ajuts: Acord transformatiu CRUE-CSICMainstream partial nitritation/anammox (PN/AMX) has attracted large attention in the last decade. Two-stage configurations have been pointed out as an appealing technology for the application of the PN/AMX process at mainstream conditions. However, the process requires of an efficiency improvement by designing a new technology to remove the nitrate produced by anammox bacteria. A new reactor configuration was developed by coupling anammox to heterotrophic denitrification in a single reactor unit while avoiding competition between both processes. The addition of acetate as an external C-source allowed the removal of nitrate by heterotrophic microorganisms without hampering the anammox process by maintaining high nitrogen removal rates (0.16 ± 0.03 g N L-1 d-1) and nitrogen removal efficiencies (91 ± 8 %) (on average from acetate addition periods). Further, a proper organic load management showed to be effective to face the drawbacks derived from previous mainstream treatment stages (i.e. undesired nitrate production), without compromising effluent COD concentrations. By withdrawing samples along the sludge bed, nitrogen compounds and COD concentrations were determined at different reactor heights. This set of experimental data demonstrated that the combination of anammox and heterotrophic denitrification in a single reactor unit was possible as anammox activity dominated within bottom sludge bed sections, while heterotrophic denitrification occurred within middle and upper sludge sections. Microbial diversity results of 16S rRNA gene-targeted sequencing analyses confirmed that anammox and heterotrophic denitrifiers communities occupied two differentiated sludge bed sections along the reactor being dominated by Candidatus Brocadia (30 %) and Thauera (33 to 46 %), respectively. When heterotrophic denitrification occurred, the average N2O emissions with COD addition was ca. 50 % lower than that in periods without COD addition

Ammonium oxidation activity promotes stable nitritation and granulation of ammonium oxidizing bacteria

Two-stage partial nitritation/anammox (PN/AMX) processes have been pointed out as a feasible configuration for achieving mainstream anammox. For two-stage configurations, stable partial nitritation has been reported feasible in granular sludge reactors. This study aimed to explore the operating conditions involved in the development of an autotrophic aerobic granular sludge using floccular sludge as inoculum. The influence of different parameters such as free ammonia concentration, settling time, superficial gas flow velocity and ammonium oxidation rate was investigated. Enhancing ammonium oxidation activity since the early phase of the operation (i.e. using conventional activated sludge as inoculum enriched with a fraction of a floccular nitrifying biomass) promoted a fast development (ca. 30 days) of an autotrophic aerobic granular sludge performing stable nitritation. When the seeded sludge presented a low nitrifying activity (lower than 0.1 g N L−1 d−1), the increase of the air-flow rate triggered the formation of an autotrophic aerobic granular sludge since ammonium oxidation activity was promoted. Contrarily, imposing low settling times (10 min) or strong free ammonia inhibitory conditions (FA concentrations higher than 50 mg N L−1) were shown to negatively influence the achievement of high ammonium oxidation rates, hampering the development of an autotrophic aerobic granular sludge. This study demonstrated the importance of ensuring high ammonium oxidation rates (higher than 0.2 g N L−1 d−1) for the proper development of an autotrophic partial nitritation granular sludge

Stable partial nitritation for low-strength wastewater at low temperature in an aerobic granular reactor

This study was supported by the AGAUR and ACC1Ó through the ANFIBIO project (2010VALOR0096). J. Pérez acknowledges the mobility fellowship (PRX12/00418, Ministerio de Educación, Cultura y Deporte, through the Programa Nacional de Movilidad de Recursos Humanos del Plan Nacional de I + D + I 2008-2011) provided by the Spanish Government.Partial nitritation for a low-strength wastewater at low temperature was stably achieved in an aerobic granular reactor. A bench-scale granular sludge bioreactor was operated in continuous mode treating an influent of 70 mg N-NH₄⁺ L⁻¹ to mimic pretreated municipal nitrogenous wastewater and the temperature was progressively decreased from 30 to 12.5ºC. A suitable effluent nitrite to ammonium concentrations ratio to a subsequent anammox reactor was maintained stable during 300 days at 12.5ºC. The average applied nitrogen loading rate at 12.5 ºC was 0.7 ± 0.3 g N L⁻¹ d⁻¹, with an effluent nitrate concentration of only 2.5 ± 0.7 mg N--NO₃ L⁻¹. The biomass fraction of nitrite-oxidizing bacteria (NOB) in the granular sludge decreased from 19% to only 1% in 6 months of reactor operation at 12.5ºC. Nitrobacter spp. where found as the dominant NOB population, whereas Nitrospira spp. were not detected. Simulations indicated that: (i) NOB would only be effectively repressed when their oxygen half-saturation coefficient was higher than that of ammonia-oxidizing bacteria; and (ii) a lower specific growth rate of NOB was maintained at any point in the biofilm (even at 12.5ºC) due to the bulk ammonium concentration imposed through the control strategy

Sequentially alternating pollutant scenarios of phenolic compounds in a continuous aerobic granular sludge reactor performing simultaneous partial nitritation and o-cresol biodegradation

Industrial wastewater treatment plants must operate properly during the transient-state conditions often found in the industrial production. This study presents the performance of simultaneous partial nitritation and o-cresol biodegradation in a continuous aerobic granular reactor under sequentially alternating pollutant (SAP) scenarios. Three SAP scenarios were imposed during the operation of the granular reactor. In each one, a secondary recalcitrant compound (either p-nitrophenol (PNP), phenol or 2-chlorophenol (2CP)) were added for a short period of time to the regular influent containing only ammonium and o-cresol. Partial nitritation and o-cresol biodegradation were not inhibited by the presence of PNP or phenol and both compounds were fully biodegraded. On the contrary, the presence of 2CP strongly inhibited both processes within 2 days. However, the reactor was recovered in a few days. These findings demonstrate that treatment of complex industrial wastewaters with variable influent composition is feasible in a continuous aerobic granular reactor

Efficient and automated start-up of a pilot reactor for nitritation of reject water : from batch granulation to high rate continuous operation

An automated sequencing batch reactor operation based on online measurement of the ammonium concentration was investigated as a tool for improving the start-up of a nitrifying granular airlift reactor. The effectiveness of this start-up procedure was verified with the characteristics of the developed granular sludge but also the improvement of the start-up was confirmed when comparing with the results achieved with two continuous-mode start-up strategies. Once a stable granular biomass was obtained, the reactor started to operate in continuous mode during more than 100 days, maintaining the characteristics of the granular biomass and achieving a nitrogen loading rate of 1.75 g N L⁻¹ d⁻¹. The intermittent recirculation of small flocs of nitrifying biomass was explored as an alternative to increase the biomass concentration in the reactor and consequently, to increase the treated loading rate

Simultaneous nitritation and p-nitrophenol removal using aerobic granular biomass in a continuous airlift reactor

The chemical and petrochemical industries produce wastewaters containing ammonium and phenolic compounds. Biological treatment of these wastewaters could be problematic due to the possible inhibitory effects exerted by phenolic compounds. The feasibility of performing simultaneous nitritation and p-nitrophenol (PNP) biodegradation using a continuous aerobic granular reactor was evaluated. A nitrifying granular sludge was bioaugmented with a PNP-degrading floccular sludge, while PNP was progressively added to the feed containing a high ammonium concentration. Nitritation was sustained throughout the operational period with ca. 85% of ammonium oxidation and less than 0.3% of nitrate in the effluent. PNP biodegradation was unstable and the oxygen limiting condition was found to be the main explanation for this unsteadiness. An increase in dissolved oxygen concentration from 2.0 to 4.5 mg O₂ L⁻¹ significantly enhanced PNP removal, achieving total elimination. Acinetobacter genus and ammonia-oxidising bacteria were the predominant bacteria species in the granular biomass

Partial nitritation and o-cresol removal with aerobic granular biomass in a continuous airlift reactor

Several chemical industries produce wastewaters containing both, ammonium and phenolic compounds. As an alternative to treat this kind of complex industrial wastewaters, this study presents the simultaneous partial nitritation and o-cresol biodegradation in a continuous airlift reactor using aerobic granular biomass. An aerobic granular sludge was developed in the airlift reactor for treating a high-strength ammonium wastewater containing 950+/-25 mg N-NH⁺₄ L⁻¹. Then, the airlift reactor was bioaugmented with a pnitrophenol-degrading activated sludge and o-cresol was added progressively to the ammonium feed to achieve 100 mg L⁻¹. The results showed that stable partial nitritation and full biodegradation of o-cresol were simultaneously maintained obtaining a suitable effluent for a subsequent anammox reactor. Moreover, two o-cresol shock-load events with concentrations of 300 and 1000 mg L⁻¹ were applied to assess the capabilities of the system. Despite these shock load events, the partial nitritation process was kept stable and o-cresol was totally biodegraded. Fluorescence in situ hybridization technique was used to identify the heterotrophic bacteria related to o-cresol biodegradation and the ammonia oxidising bacteria along the granules

Aerobic biodegradation of a mixture of monosubstituted phenols in a sequencing batch reactor

A sequencing batch reactor (SBR) was inoculated with p-nitrophenol-degrading activated sludge to biodegrade a mixture of monosubstituted phenols: p-nitrophenol (PNP), PNP and o-cresol; and PNP, o-cresol and o-chlorophenol. Settling times were progressively decreased to promote biomass granulation. PNP was completely biodegraded. The PNP and o-cresol mixture was also biodegraded although some transitory accumulation of intermediates occurred (mainly hydroquinone and catechol). o-Chlorophenol was not biodegraded and resulted in inhibition of o-cresol and PNP biodegradation and complete failure of the SBR within a few days. The biomass had very good settling properties when a settling time of 1 min was applied: sludge volume index (SVI₅) below 50 mL g⁻¹, SVI₅/SVI₃₀ ratio of 1 and average particle size of 200 μm

Stratification of nitrifier guilds in granular sludge in relation to nitritation

A lab-scale partial nitritation granular sludge air-lift reactor was operated in continuous mode treating low strength synthetic medium (influent ca. 50 mg-N-NH /L). Granules were initially stratified with AOB in the external shell and NOB in the inner core at 20 °C. Once temperature was decreased progressively from 20 °C to 15 °C, nitrate production was initially observed during several weeks. However, by maintaining relatively high ammonium concentrations in the liquid (ca. 28 mg-N-NH /L), effluent nitrate concentrations in the reactor decreased in time and process performance was recovered. Batch tests were performed in the reactor at different conditions. To understand the experimental results an existing one-dimensional biofilm model was used to simulate batch tests and theoretically assess the impact of stratification, dissolved oxygen (DO) and short-term effects of temperature on time course concentrations of ammonium, nitrite and nitrate. This theoretical assessment served to develop an experimental methodology for the evaluation of in-situ batch tests in the partial nitritation reactor. These batch tests proved to be a powerful tool to easily monitor the extent of stratification of nitrifier guilds in granular sludge and to determine the required bulk ammonium concentration to minimize nitrite oxidation. When nitrifier guilds were stratified in the granular sludge, a higher bulk ammonium concentration was required to efficiently repress NOB at lower temperature (ca. 19 versus 7 mg-N-NH /L at 15 and 20 °C, respectively)

Ophrys querciphila Nicole, Hervy & Soca en la península ibérica

Data and pictures of the first Iberian citation of Ophrys querciphila Nicole, Hervy & Soca; as well as data relative to its ecology and phenology, altitudinal range, diagnostic traits for its identification and experiences with possible pollinator