RESUMEN
The treatment of wastewater is highly challenging due to large fluctuations in flowrates, pollutants, and variable influent water compositions. A sequencing batch reactor (SBR) and modified SBR cycle-step-feed process (SSBR) configuration are studied in this work to effectively treat municipal wastewater while simultaneously removing nitrogen and phosphorus. To control the amount of dissolved oxygen in an SBR, three axiomatic control strategies (proportional integral (PI), fractional proportional integral (FPI), and fuzzy logic controllers) are presented. Relevant control algorithms have been designed using plant data with the models of SBR and SSBR based on ASM2d framework. On comparison, FPI showed a significant reduction in nutrient levels and added an improvement in effluent quality. The overall effluent quality is improved by 0.86% in FPI in comparison with PI controller. The SSBR, which was improved by precisely optimizing nutrient supply and aeration, establishes a delicate equilibrium. This refined method reduces oxygen requirements while reliably sustaining important biological functions. Focusing solely on the FPI controller's performance in terms of total air volume consumption, the step-feed SBR mechanism achieves an excellent 11.04% reduction in consumption.
Asunto(s)
Reactores Biológicos , Eliminación de Residuos Líquidos , Eliminación de Residuos Líquidos/métodos , Aguas Residuales , Fósforo/análisis , Purificación del Agua/métodos , Nitrógeno/análisis , Contaminantes Químicos del Agua/análisis , Oxígeno/análisisRESUMEN
The hybrid membrane aerated biofilm reactor (MABR) process represents a full-scale solution for sustainable municipal wastewater treatment. However, most of the existing hybrid MABR processes retain large aerobic bioreactor volumes for nitrification, which is undesirable for energy and carbon savings. In this study, we used the plant-wide modeling approach with dynamic simulations to examine a novel hybrid MABR configuration with aeration controls that change the anoxic and aerobic fractions of the bioreactor volume. Result showed that the novel hybrid MABR showed "swinging" nitrification and denitrification capacities in response to diurnal loadings, achieving intensified nitrogen removal performance under both warm and cold temperature scenarios. N2O emissions from the hybrid MABR were only 1/5 of the emissions from the conventional activated sludge. The model predicted higher CH4 emissions from the hybrid MABR than the activated sludge process due to the methanogen growth in the oxygen-depleted MABR biofilm layer. Future measurements for CH4 emission are needed to obtain a holistic picture of the carbon footprint of the hybrid MABR process.
Asunto(s)
Desnitrificación , Aguas del Alcantarillado , Nitrógeno , Nitrificación , Biopelículas , Reactores BiológicosRESUMEN
To enhance nutrient removal from low-strength municipal wastewater in a continuous-flow activated sludge (CFAS) process using aerobic granular sludge (AGS) augmentation strategy, a pilot-scale demonstration was configured with a mainstream reactor (anaerobic/aerobic process) and a sidestream sequencing batch reactor for AGS production. The aeration of the mainstream reactor was controlled based on dissolved oxygen (DO) and ammonium concentrations during Phases I and II-III, respectively. During Phase III, an anoxic zone was created in the mainstream aerobic tank. Throughout the demonstration period, excellent sludge settleability in the mainstream reactor (SVI30 ≤ 80 mL g-1) under long sludge retention time conditions (≥12 d) allowed the maintenance of a high mixed liquor suspended solids concentration (≥3000 mg L-1). The total nitrogen (TN) removal ratio improved significantly during Phases II and III (49.3 ± 4.1% and 50.1 ± 10.2%, respectively) compared to Phase I (43.2 ± 5.5%). Low DO concentration (< 0.5 mg L-1) by the ammonium-based aeration tended to increase the simultaneous nitrification and denitrification efficiency (> 40%), enhancing TN removal (> 50%). The reduction of DO and nitrate concentrations in the returning sludge liquor can stabilize phosphorus removal (approximately 80% of the 25th percentile). In addition, the aeration efficiency during Phase III decreased by 26-29% compared to Phase I. These results suggest that the introduction of ammonium-based aeration control to the CFAS using the AGS augmentation strategy could contribute to superior sewerage treatment, including nutrient removal and a low carbon footprint.
Asunto(s)
Compuestos de Amonio , Aguas del Alcantarillado , Reactores Biológicos , Aguas Residuales , Nitrificación , Fósforo , Nitrógeno , Desnitrificación , Eliminación de Residuos Líquidos/métodosRESUMEN
Water resource recovery facilities (WRRFs) increasingly must maximize nitrogen and phosphorus removal, but concurrently face challenges to reduce their energy usage and environmental footprint. In particular, biological nutrient removal (BNR), which targets removal of phosphorus and nitrogen, exhibits a large energy demand. However, a BNR process achieving partial oxidation of NH3 to NO2 (nitritation) could reduce energy demands, with secondary environmental emission benefits. Research was conducted on bench-scale systems performing nitritation and nitrification to better understand how mixed microbial consortia, cultured on real wastewater, can sustain nitritation. BNR configurations achieved nitrite accumulation ratios of 64-82%, with excellent overall effluent quality. Applying phylogenetic, transcriptomic, and metabolomic methods, coupled with process monitoring, results indicate that partial nitritation may be induced through a combination of: (1) Employing ammonia-based aeration control, with an ammonia setpoint of 2, 3 mgN/L; (2) Maintaining an aerobic period DO of 1.0-2.0 mg/L; and (3) Operating BNR post-anoxically, integrated within enhanced biological phosphorus removal (EBPR). Significant nitritation was achieved despite the presence Nitrobacter spp., but nitrite oxidoreductase must be functionally impaired or structurally incomplete. Overall, this research demonstrated the value of interrogating a mixed microbial consortia at a macro and molecular level to explore unique metabolic responses such as nitritation.
Asunto(s)
Nitrobacter , Aguas Residuales , Amoníaco/metabolismo , Reactores Biológicos , Nitritos/metabolismo , Nitrógeno/metabolismo , Dióxido de Nitrógeno/metabolismo , Oxidación-Reducción , Oxidorreductasas , Fósforo/metabolismo , Filogenia , Aguas del AlcantarilladoRESUMEN
The start-up of a stable mainstream deammonification requires sufficient anaerobic ammonia-oxidizing bacteria (AnAOB). This study used a plug-flow fixed-bed reactor (PFBR) to verify the feasibility of establishing the mainstream deammonification system by inoculating the sidestream sludge after long-term refrigeration. A rapid resuscitation of the mainstream deammonification system was accomplished by controlling the front-end aeration rate of the PFBR. Results showed that the system was rapidly resuscitated in 44 days eventually with the nitrogen removal rate and nitrogen removal efficiency of 0.1 kg N·(m3·d)-1 and 79.1%, respectively. Also, the efficient performance was secured by the proportionate approaching equilibrium of AnAOB and ammonia-oxidizing bacteria (AOB) activity of 2.35 ± 0.40 and 2.60 ± 0.29 mg N·(g VSS·h)-1, respectively. In addition, Pearson correlation analysis revealed that AnAOB abundance (detected Candidatus Kuenenia) negatively correlated with the AOB (mainly Nitrosomonas)/AnAOB abundance ratio, while correlated positively with the residual ammonium concentration of a region. Furthermore, long-term refrigeration probably reduced the cross-feed relationship between AnAOB and other symbiotic organisms (Armatimonadetes and Chloroflexi) to maintain the basic metabolism. Meanwhile, extracellular polymeric substances produced by other genera (order Xanthomonadales and Pseudomonadales) decreased the mass transfer, protecting AnAOB from unfavorable conditions, thereby facilitating high AnAOB abundance during refrigeration. Thus, this study provides a promising perspective towards the practical applications of mainstream process.
Asunto(s)
Compuestos de Amonio , Aguas del Alcantarillado , Biopelículas , Reactores Biológicos , Nitrógeno , Oxidación-ReducciónRESUMEN
This study deals with the effect of aeration control strategies on the nitrogen removal efficiency and nitrous oxide (N2O) emissions in a partial nitritation-anammox reactor with granular sludge. More specifically, dissolved oxygen (DO) control, constant airflow and effluent ammonium (NH4+) control strategies were compared through a simulation study. Particular attention was paid to the effect of flocs, which are deliberately or unavoidable present besides granules in this type of reactor. When applying DO control, DO setpoints had to be adjusted to the amount of flocs present in the reactor to maintain high nitrogen removal and reduce N2O emissions, which is difficult to realize in practice because of variable floc fractions. Constant airflow rate control could maintain a good nitrogen removal efficiency independent of the floc fraction in the reactor, but failed in N2O mitigation. Controlling aeration based on the effluent ammonium concentration results in both high nitrogen removal and relatively low N2O emissions, also in the presence of flocs. Fluctuations in floc fractions caused significant upsets in nitrogen removal and N2O emissions under DO control but had less effect at constant airflow and effluent ammonium control. Still, rapid and sharp drops in flocs led to a peak in N2O emissions at constant airflow and effluent ammonium control. Overall, effluent ammonium control reached the highest average nitrogen removal and lowest N2O emissions and consumed the lowest aeration energy under fluctuating floc concentrations.
Asunto(s)
Compuestos de Amonio , Nitrógeno , Reactores Biológicos , Desnitrificación , Nitrógeno/análisis , Óxido Nitroso/análisis , Oxidación-Reducción , Aguas del AlcantarilladoRESUMEN
A pilot scale process was operated with A-stage effluent (ASE) and primary clarifier effluent (PCE) in MLE, all tanks aerated, A/O, and A2O configurations. Continuous DO control at high DO (2 mg/L), low DO (0.1-0.3 mg/L), ammonia-based aeration control (ABAC), and ammonia versus NOx (AvN) control (both continuous and intermittent operation) were compared on the basis of total inorganic nitrogen (TIN) removal, and simultaneous nitrification-denitrification (SND). The highly loaded adsorption/bio-oxidation (A/B) process configuration (4 hr HRT) with intermittent aeration was capable of achieving a maximum TIN removal of 80%, while the A2O process with PCE feed, an 11 hr HRT, and 0.2-0.3 mg/L DO continuous aeration achieved a maximum of 88% TIN removal. ABAC and AvN control did not always result in DO setpoints low enough to achieve SND, and even if setpoints were low enough to achieve SND that did not always result in increased overall TIN removal over continuous DO control of 2 mg/L. While there are other benefits to transitioning to sensor driven aeration control strategies such as ABAC and AvN, increased TIN removal during continuous aeration is not guaranteed. Results suggest that although low DO is a prerequisite for SND, carbon availability for denitrification in the aerobic zone is more likely to be the limiting factor once low DO conditions are met. PRACTITIONER POINTS: Intermittent aeration control results in higher TIN removal than continuous aeration at the same total SRT Continuous aeration AvN control is not likely to result in more TIN removal than continuous aeration ABAC for a given COD and nitrogen load Configurations that are designed to maximize predenitrification (e.g., MLE and A2O) are less likely to achieve increased SND in the aerobic zone from low DO operation than configurations that are not (e.g., A/O).
Asunto(s)
Desnitrificación , Nitrificación , Reactores Biológicos , Nitrógeno , Eliminación de Residuos LíquidosRESUMEN
A sensor-mediated strategy was applied to a laboratory-scale granular sludge reactor (GSR) to demonstrate that energy-efficient inorganic nitrogen removal is possible with a dilute mainstream wastewater. The GSR was fed a dilute wastewater designed to simulate an A-stage mainstream anaerobic treatment process. DO, pH, and ammonia/nitrate sensors measured water quality as part of a real-time control strategy that resulted in low-energy nitrogen removal. At a low COD (0.2 kg m-3 day-1 ) and ammonia (0.1 kg-N m-3 day-1 ) load, the average degree of ammonia oxidation was 86.2 ± 3.2% and total inorganic nitrogen removal was 56.7 ± 2.9% over the entire reactor operation. Aeration was controlled using a DO setpoint, with and without residual ammonia control. Under both strategies, maintaining a low bulk oxygen level (0.5 mg/L) and alternating aerobic/anoxic cycles resulted in a higher level of nitrite accumulation and supported shortcut inorganic nitrogen removal by suppressing nitrite oxidizing bacteria. Furthermore, coupling a DO setpoint aeration strategy with residual ammonia control resulted in more stable nitritation and improved aeration efficiency. The results show that sensor-mediated controls, especially coupled with a DO setpoint and residual ammonia controls, are beneficial for maintaining stable aerobic granular sludge. PRACTITIONER POINTS: Tight sensor-mediated aeration control is need for better PN/A. Low DO intermittent aeration with minimum ammonium residual results in a stable N removal. Low DO aeration results in a stable NOB suppression. Using sensor-mediated aeration control in a granular sludge reactor reduces aeration cost.
Asunto(s)
Aguas del Alcantarillado , Aguas Residuales , Reactores Biológicos , Desnitrificación , Nitritos , Nitrógeno , Oxidación-ReducciónRESUMEN
Sewage nitritation is a promising process for nitrogen removal, but its practical application is limited by long start-up period and unstable operation. In this study, hydroxylamine (NH2OH) addition and real-time aeration control strategies were adopted for the promotion of sewage nitritation in a sequencing batch reactor. Initially, 4.5â¯mg/L NH2OH was added into reactor every 24â¯h to establish nitritation, increasing the nitrite accumulation ratio (NAR) from 1.7% to 93% in 19 d. In the following period, NH2OH addition was stopped and nitritation remained stable over 55 d, with NAR of 97% by real-time aeration control. The aeration duration was determined by characteristic points on pH curve. The main genera of nitrite oxidizing bacteria, Nitrobacter and Nitrospira, were both eliminated from the system, supporting the long-term stability of nitritation. Overall, NH2OH addition and real-time aeration control is an excellent strategy for establishing and maintaining effective sewage nitritation.
Asunto(s)
Reactores Biológicos , Aguas del Alcantarillado , Hidroxilamina , Hidroxilaminas , Nitritos , Nitrógeno , Oxidación-ReducciónRESUMEN
The low ammonium concentration, low temperature, presence of organic matter, and large variation of influent ammonium load pose serious challenges for the application of PN/AMX (partial nitrification-anammox) reactor in the mainstream wastewater treatment. Previous mathematical simulation studies of PN/AMX granule reactor mainly concentrated on the steady-state modeling. The steady-state simulation cannot be used for developing control strategies under dynamic condition. In this study, four control strategies were evaluated on their abilities to minimize the impact of feed disturbances on autotrophic nitrogen removal in mainstream wastewater. The four control strategies included are the following: (A) direct airflow adjustment to maintain the fixed NH4+ set point, (B) fixed NH4+ set point control manipulated by DO concentration with DO limit, (C) constant DO control strategy, and (D) adaptive change of NH4+ set point control based on the feed disturbance (NH4+ set point value achieved by DO concentration manipulation with DO limit). The results indicated that the control strategy A successfully implemented for high NH4+ strength wastewater treatment cannot be directly transferred into the mainstream wastewater treatment, in which high NO2- accumulation was resulted during the NH4+ peaks at the low-temperature period. Satisfactory TN removal could be achieved by maintaining either fixed or variable bulk NH4+ set point values calculated based on the feed disturbances (control strategies B and D). The DO limit imposed on the DO concentration manipulation to derive the desired NH4+ set point values was essential for the successful implementation of control strategies B and D. The control strategy C with constant DO concentration was not feasible for the PN/AMX process under dynamic feed disturbances. The control simulation results and the control variable sensitivity analysis indicated that the NH4+ concentration was a better control variable than the DO concentration.
Asunto(s)
Compuestos de Amonio/análisis , Reactores Biológicos , Nitrógeno/análisis , Aguas del Alcantarillado/análisis , Eliminación de Residuos Líquidos/métodos , Aguas Residuales/análisis , Nitrificación , Eliminación de Residuos Líquidos/instrumentaciónRESUMEN
In this study, a sequencing batch reactor (SBR), treating synthetic wastewater (COD/N = 5), was operated in two stages. During stage I, an aeration control strategy based on oxygen uptake rate (OUR) was applied, to accomplish nitrogen removal via nitrite >80%. In stage II, the development of aerobic granular sludge (AGS) was examined while two aeration control strategies (OUR and pH slope) maintained the nitrite pathway and optimized the simultaneous nitrification-denitrification (SND) performance. Stimulation of slow-growing organisms, (denitrifying) polyphosphate-accumulating organisms (D)PAO and (denitrifying) glycogen-accumulating organisms (D)GAO leads to full granulation (at day 200, SVI10 = 47.0 mL/g and SVI30 = 43.1 mL/g). The average biological nutrient removal efficiencies, for nitrogen and phosphorus, were 94.6 and 83.7%, respectively. Furthermore, the benefits of an increased dissolved oxygen concentration (1.0-2.0 mg O2/L) were shown as biomass concentrations increased with approximately 2 g/L, and specific ammonium removal rate and phosphorus uptake rate increased with 33 and 44%, respectively. It was shown that the combination of both aeration phase-length control strategies provided an innovative method to achieve SND via nitrite in AGS.
Asunto(s)
Desnitrificación , Nitrificación , Nitritos/metabolismo , Aguas del Alcantarillado/microbiología , Eliminación de Residuos Líquidos/métodos , Bacterias/metabolismo , Fenómenos Fisiológicos Bacterianos , Biodegradación Ambiental , Reactores Biológicos , Redes y Vías Metabólicas , Nitrógeno/análisis , Nitrógeno/metabolismo , Fósforo/análisis , Fósforo/metabolismo , Aguas del Alcantarillado/química , Aguas Residuales/química , Aguas Residuales/microbiologíaRESUMEN
This study aim to enhance nitrogen removal performance via shifting nitrogen removal pathway from nitrate to nitrite pathway. It was demonstrated that nitrite pathway was successfully and stably achieved in CWs by using modified intermittent aeration control with aeration 20min/non-aeration 100min and reducing DO concentration during aeration, nitrite in the effluent could accumulate to over 70% of the total oxidized nitrogen. Q-PCR analysis showed that nitrifying microbial communities were optimized under the alternating anoxic and aerobic conditions, ammonia oxidizing bacteria increased from 7.15×106 to 8.99×106copies/g, while nitrite oxidizing bacteria decreased approximately threefold after 234days operation. Most importantly, high nitrogen removal efficiency with ammonium removal efficiency of 94.6%, and total nitrogen removal efficiency of 82.6% could be achieved via nitrite pathway even under carbon limiting conditions. In comparison to the nitrate pathway, the nitrite pathway could improve the TN removal by about 55%.
Asunto(s)
Desnitrificación , Nitrificación , Humedales , Aerobiosis , Compuestos de Amonio/metabolismo , Bacterias/metabolismo , Análisis de la Demanda Biológica de Oxígeno , Reactores Biológicos/microbiología , Ambiente , Nitratos/metabolismo , Nitritos/metabolismo , Nitrógeno/metabolismo , Oxidación-Reducción , Reacción en Cadena de la PolimerasaRESUMEN
Reducing the energy consumption of membrane bioreactors (MBRs) is highly important for their wider application in wastewater treatment engineering. Of particular significance is reducing aeration in aerobic tanks to reduce the overall energy consumption. This study proposed an in situ ammonia-N-based feedback control strategy for aeration in aerobic tanks; this was tested via model simulation and through a large-scale (50,000 m(3)/d) engineering application. A full-scale MBR model was developed based on the activated sludge model (ASM) and was calibrated to the actual MBR. The aeration control strategy took the form of a two-step cascaded proportion-integration (PI) feedback algorithm. Algorithmic parameters were optimized via model simulation. The strategy achieved real-time adjustment of aeration amounts based on feedback from effluent quality (i.e., ammonia-N). The effectiveness of the strategy was evaluated through both the model platform and the full-scale engineering application. In the former, the aeration flow rate was reduced by 15-20%. In the engineering application, the aeration flow rate was reduced by 20%, and overall specific energy consumption correspondingly reduced by 4% to 0.45 kWh/m(3)-effluent, using the present practice of regulating the angle of guide vanes of fixed-frequency blowers. Potential energy savings are expected to be higher for MBRs with variable-frequency blowers. This study indicated that the ammonia-N-based aeration control strategy holds promise for application in full-scale MBRs.
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Reactores Biológicos , Membranas Artificiales , Eliminación de Residuos Líquidos/métodos , Purificación del Agua/métodos , Aire , Algoritmos , Amoníaco/química , Amoníaco/metabolismo , Simulación por Computador , Ingeniería/instrumentación , Ingeniería/métodos , Modelos Teóricos , Oxígeno/metabolismo , Eliminación de Residuos Líquidos/instrumentación , Purificación del Agua/instrumentaciónRESUMEN
This work describes the development of an intermittently aerated pilot-scale process (V = 0.45 m(3) ) operated for optimized efficient nitrogen removal in terms of volume, supplemental carbon and alkalinity requirements. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia concentration set-points. The unique feature of the ammonia-based aeration control was that a fixed dissolved oxygen (DO) set-point was used and the length of the aerobic and anoxic time (anoxic time ≥25% of total cycle time) were changed based on the effluent ammonia concentration. Unlike continuously aerated ammonia-based aeration control strategies, this approach offered control over the aerobic solids retention time (SRT) to deal with fluctuating ammonia loading without solely relying on changes to the total SRT. This approach allowed the system to be operated at a total SRT with a small safety factor. The benefits of operating at an aggressive SRT were reduced hydraulic retention time (HRT) for nitrogen removal. As a result of such an operation, nitrite oxidizing bacteria (NOB) out-selection was also obtained (ammonia oxidizing bacteria [AOB] maximum activity: 400 ± 79 mgN/L/d, NOB maximum activity: 257 ± 133 mgN/L/d, P < 0.001) expanding opportunities for short-cut nitrogen removal. The pilot demonstrated a total inorganic nitrogen (TIN) removal rate of 95 ± 30 mgN/L/d at an influent chemical oxygen demand: ammonia (COD/NH4 (+) -N) ratio of 10.2 ± 2.2 at 25°C within the hydraulic retention time (HRT) of 4 h and within a total SRT of 5-10 days. The TIN removal efficiency up to 91% was observed during the study, while effluent TIN was 9.6 ± 4.4 mgN/L. Therefore, this pilot-scale study demonstrates that application of the proposed on-line aeration control is capable of relatively high nitrogen removal without supplemental carbon and alkalinity addition at a low HRT.
Asunto(s)
Amoníaco/metabolismo , Nitrógeno/metabolismo , Aerobiosis , Álcalis/metabolismo , Carbono/metabolismo , Medios de Cultivo/química , Oxígeno/análisis , Temperatura , Purificación del Agua/métodosRESUMEN
In this study, we have evaluated different strategies for the optimization of the aeration during the active thermophilic stage of the composting process of source-selected Organic Fraction of Municipal Solid Waste (or biowaste) using reactors at bench scale (50L). These strategies include: typical cyclic aeration, oxygen feedback controller and a new self-developed controller based on the on-line maximization of the oxygen uptake rate (OUR) during the process. Results highlight differences found in the emission of most representative greenhouse gases (GHG) emitted from composting (methane and nitrous oxide) as well as in gases typically related to composting odor problems (ammonia as typical example). Specifically, the cyclic controller presents emissions that can double that of OUR controller, whereas oxygen feedback controller shows a better performance with respect to the cyclic controller. A new parameter, the respiration index efficiency, is presented to quantitatively evaluate the GHG emissions and, in consequence, the main negative environmental impact of the composting process. Other aspects such as the stability of the compost produced and the consumption of resources are also evaluated for each controller.
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Gases/análisis , Oxígeno/metabolismo , Microbiología del Suelo , Suelo/química , Amoníaco/análisis , Reactores Biológicos , Dióxido de Carbono/análisis , Cromatografía de Gases , Efecto Invernadero , Metano/análisis , Óxido Nitroso/análisis , Oxígeno/química , TemperaturaRESUMEN
This work describes the development of an intermittently aerated pilot-scale process (V = 0.34 m(3)) operated without oxidized nitrogen recycle and supplemental carbon addition optimized for nitrogen removal via nitritation/denitritation. The aeration pattern was controlled using a novel aeration strategy based on set-points for reactor ammonia, nitrite and nitrate concentrations with the aim of maintaining equal effluent ammonia and nitrate + nitrite (NOx) concentrations. Further, unique operational and process control strategies were developed to facilitate the out-selection of nitrite oxidizing bacteria (NOB) based on optimizing the chemical oxygen demand (COD) input, imposing transient anoxia, aggressive solids retention time (SRT) operation towards ammonia oxidizing bacteria (AOB) washout and high dissolved oxygen (DO) (>1.5 mg/L). Sustained nitrite accumulation (NO2-N/NOx-N = 0.36 ± 0.27) was observed while AOB activity was greater than NOB activity (AOB: 391 ± 124 mgN/L/d, NOB: 233 ± 151 mgN/L/d, p < 0.001) during the entire study. The reactor demonstrated total inorganic nitrogen (TIN) removal rate of 151 ± 74 mgN/L/d at an influent COD/ [Formula: see text] -N ratio of 10.4 ± 1.9 at 25 °C. The TIN removal efficiency was 57 ± 25% within the hydraulic retention time (HRT) of 3 h and within an SRT of 4-8 days. Therefore, this pilot-scale study demonstrates that application of the proposed online aeration control is able to out-select NOB in mainstream conditions providing relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.