Intermittent Aeration Research Articles

Enhancing nitrogen removal performance through intermittent aeration in continuous plug-flow anaerobic/aerobic/anoxic process treating low-strength municipal sewage

Advanced nitrogen removal cannot be achieved through the conventional biological nitrogen removal process, which requires higher carbon sources and aeration energy. The proposal of intermittent aeration in the aerobic chambers offered an innovative approach to enhance nitrogen removal in low carbon-to-nitrogen ratio (C/N) municipal sewage, using a plug-flow reactor with anaerobic/aerobic/anoxic (AOA) process. Due to the effective utilization of internal carbon sources through the intermittent aeration, the total inorganic nitrogen removal efficiency (NRE) increased to 77.9 ± 3.2 % with the mean aerobic hydraulic retention time of only 3.2 h and a low C/N of 3.3 during the operation of 210 days. Polyhydroxyalkanoates dominated the nitrogen removal in this AOA system, accounting for 48.0 %, primarily occurring in the alternant aerobic/anoxic chambers. Moreover, the microbial community structure remained unchanged while the NRE increased to 77.9 %. This study provided an efficient and economic strategy for the continuous plug-flow AOA process.

Stimulating extracellular polymeric substances production in integrated fixed-film activated sludge reactor for advanced nitrogen removal from mature landfill leachate via one-stage double anammox

Introducing carbon sources to achieve nitrogen removal from mature landfill leachate not only increases the costs and carbon emissions but also inhibits the activity of autotrophic bacteria. Thus, this study constructed a double anammox system that combines partial nitrification-anammox (PNA) and endogenous partial denitrification-anammox (EPDA) within an integrated fixed-film activated sludge (IFAS) reactor. In this system, PNA primarily contributes to nitrogen removal pathways, achieving a nitrite accumulation rate of 98.23%. The production of extracellular polymer substances (EPS) in the IFAS reactor is stimulated by introducing co-fermentation liquid. Through the utilization of EPS, the system effectively achieves EPDA with the nitrite transformation rate of 97.20%. Under the intermittent aeration operation strategy, EPDA combined with PNA and anammox in the oxic and anoxic stages enhanced the nitrogen removal efficiency of the system to 99.70 ± 0.12%. The functional genus Candidatus kuenenia became enriched in biofilm sludge, while Thauera and Nitrosomonas predominated in floc sludge.

Performance of Hybrid Mesh Filter Bioreactor For Textile Wastewater Treatment

The rapid growth of the textile industry, while bringing positive impacts, also brings negative effects related to the increasing amount of wastewater generated. Poorly managed wastewater can potentially create adverse effects on human health and the environment. This study evaluates the hybrid mesh filter bioreactor (MFBR) performance for textile wastewater treatment. The bioreactor was operated with a nylon mesh filter having 37 µm pore size under intermittent aeration with aeration on/off durations of 1/1 hour. Wastewater influent was degraded by microorganisms attached to biofilm carriers and filtered by an external filtration tank. The process performance was evaluated under varying concentrations of COD (600–1200 mg/L). The stable operation was achieved for around 60 days with 88.4-94.8% turbidity removal and a flux value of 102±15 L/m2·hour. Although high COD removal was observed (89.4-92.1%), only 14.3-25.2% color removal was achieved in hybrid MFBR under hydraulic retention time (HRT) of 4-8 hours.

Achieving partial nitrification: A strategy for washing NOB out under high DO condition

This study investigated the effect of high DO concentrations on PN. The experimental setup involved operating at high DO concentrations (1.5–2.5 mg/L) and environmental temperatures (15–20 °C) over a period of 180 days. Through a sludge enrichment process, the kinetic parameters of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were determined. Surprisingly, contrary to conventional reports, it was observed that NOB exhibited a stronger affinity for DO compared to AOB. As a result, high DO concentrations were necessary to provide favorable conditions for the growth of AOB. In order to establish PN, strategies including intermittent aeration, free ammonia (FA), and controlled sludge retention time (SRT) were employed. The successful PN was achieved with a specific ammonia oxidation rate of 24 mg N/g MLVSS/h and a specific nitrite oxidation rate below 0.10 mg N/g MLVSS/h. The nitrite accumulation rate (NAR) was maintained at 100% during stable operation. The abundance of Nitrosomonas, a typical genus of AOB, was found to be 68.62%, which surpasses previous studies in similar research. A slightly higher DO concentrations may increase energy consumption, but achieve higher efficiency and stability in PN. This study provided new insights into the application of PN in wastewater treatment.

Extracellular polymeric substances and microbial community shift during the start-up of a single-stage partial nitritation/anammox process.

A sequencing batch reactor (SBR) was operated to investigate variations of extracellular polymeric substances (EPS) and microbial community during the start-up of the single-stage partial nitritation/anammox (SPN/A) process at intermittent aeration mode. The SPN/A system was successfully started on day 34, and the nitrogen removal efficiency and total nitrogen loading rate were 82.29% and 0.31 kg N/(m3 ·d), respectively. Furthermore, the relationship between the protein secondary structures and microbial aggregation was strongly related. The α-helix/ (β-sheet + random coil) ratios increased obviously from 0.20 ± 0.03 to 0.23 ± 0.01, with the sludge aggregation mean size increased from 56 to 107 μm during the start-up of SPN/A. During the start-up of SPN/A, Candidatus Kuenenia was the primary anammox bacteria, whereas Nitrospira was the main functional bacteria of nitrite-oxidizing bacteria. Correlation between the microbial community and EPS components was performed. The EPS and microbial community played important roles in keeping stable nitrogen removal and the formation of sludge granules.

Coupling Iron Sludge Addition and Intermittent Aeration for Achieving Simultaneous Methanogenesis, Feammox, and Denitrification in a Single Reactor Treating Fish Sludge.

An integrated anaerobic digestion system for the simultaneous removal of carbon and nitrogen from fish sludge was developed by coupling iron sludge supplementation with intermittent aeration. In terms of nitrogen removal, Fe(III) in iron sludge could trigger Feammox reactions and intermittent aeration could drive the Fe(II)/Fe(III) cycle to sustain continuous ammonia removal. Mass balance analysis suggested that nitrate was the main product of Feammox, which was subsequently removed through heterotrophic denitrification. In terms of carbon removal, the Fe(III)-induced dissimilatory iron reduction (DIR) process significantly promoted fish sludge hydrolysis and provided more simple organics for methanogens and denitrifiers, but aeration showed a negative impact on methanogenesis. To promote nitrogen removal and avoid serious methanogenesis inhibition, different aeration intensities were studied. Results showed that compared with the control without aeration or iron sludge addition, aeration for 5 min every 3 days (150 mL/min) contributed to a 29.0% lower NH4+-N concentration and a 12.1% lower total chemical oxygen demand level on day 28, and the decline in methane yield was acceptable (only 13.5% lower). Simultaneous methanogenesis, Feammox, and denitrification in a single reactor treating fish sludge were achieved, which provides a simple and low-cost strategy for the treatment of organic wastewater.

The response rule of wetland microorganisms by coupling of partial nitrification process and constructed wetland

In this study, the response rule of wetland microorganisms by coupling of partial nitrification (PN) process and vertical flow constructed wetland (VFCW) were determined. Coupling of PN effluent and exhaust gas positively affected microbial abundance and community. Results revealed that the microbial community structure in the VFCW was changed. The nitrification and denitrification intensities were promoted and the abundance of functional bacteria related to nitrogen and organic matter removal were increased. In addition, the removal efficiencies of pollutants of VFCW have been significantly improved. The results showed that the System II coupling the PN effluent and intermittent aeration with exhaust gas achieved better removal of NH4+-N (92.61 ± 2.25 %) and TN (70.33 ± 3.61 %) than the System I that only fed PN effluent without exhaust aeration. NO2−-N pollution in PN effluent was eliminated with a removal efficiency of 97.58 ± 1.08 %.

Enhanced nitrogen removal from micro-polluted water by Fe (II)/Fe (III) cycling under intermittent aeration

The potential of iron-carbon materials (FeC) as inorganic electron donors for aerobic denitrification of micro-polluted source water was explored. For this purpose, a raw water denitrification experiment was conducted using FeC under intermittent aeration condition. Then, magnetite was added as a biological carrier to construct another system, FeC and magnetite intermittent aeration reaction system, (FCMI). The findings revealed that FCMI notably removed the pollutants with the removal efficiencies of nitrate, total nitrogen, total phosphorus, and chemical oxygen demand reaching 95.63%, 88.62%, 90.48%, and 61.46%, respectively. Cycling between aerobic and anaerobic environments facilitated the formation of Fe (II)/Fe (III) cycle within FeC materials. Microbial profiling revealed that Proteobacteria and Actinobacteria comprised 97.14% of the total abundance in FCMI. Iron-reducing bacteria and aerobic denitrifying bacteria were found to thrive on the surface of magnetite materials. The abundance of enzymes related to denitrification under intermittent aeration exceeded those under continuous aeration levels by 8–19%. This study verifies the ability of iron electrons to cycle under intermittent aeration condition and proposes a novel strategy for in-situ denitrification of micro-polluted source water.

Insights of microalgal municipal wastewater treatment at low temperatures: Performance, microbiota patterns, and cold-adaptation of tubular and aeration column photobioreactors

In order to refine the treatment of microalgae consortium (MC) for municipal wastewater (MWW) during the winter, this study investigated the effectiveness of tubular and aeration column photobioreactors (TPBR and APBR) in wastewater treatment plant (WWTP) during winter by two start-up modes: microalgae/microalgae-activated sludge (AS). The operation results showed that under 5.7–13.1 °C, TPBR enhanced the assimilation of N and P pollutant by microalgal accumulation, meeting the Chinese discharge standard within 24 h (NH4+-N, TP, and COD ≤8.0, 0.5, and 50 mg·L−1). The microbial community profiles were identified and showed that inoculating AS under low-temperature still promoted bacterial interspecific association, but influenced by the inhibition of microbial diversity by the homogeneous circulation of TPBR, the nitrogen transfer function of MC was lower than that of APBR at low temperatures, except nitrogen fixation (K02588), nitrosification (K10944, K10945, and K10946), assimilatory nitrate reduction (K00366), and ammonification (K01915 and K05601). And the intermittent aeration in the APBR was still beneficial in increasing microbial diversity, which was more beneficial for reducing COD through microbial collaboration. In the treatment, the cryotolerant MGPM were Delftia, Romboutsia, Rhizobiales, and Bacillus, and the cold stress-related genes that were highly up-regulated were defense signaling molecules (K03671 and K00384), cold shock protein gene (K03704), and cellular protector (K01784) were present in both PBRs. This study provided a reference for the feasibility of the low temperature treatment of MC with the different types of PBR, which improved the application of wastewater treatment in more climatic environments.

Effects of different aeration strategies and ammonia-nitrogen loads on nitrification performance and microbial community succession of mangrove constructed wetlands for saline wastewater treatment

In highly salinized environments, nitrification is the process that limits the rate of nitrogen transformation and removal. Therefore, this study concentrated on the impacts of different aeration strategies and NH4+–N loads on the nitrification performance of mangrove constructed wetlands (CWs), as well as investigating the succession mechanism of ammonia-oxidizing microorganisms (AOMs). The results showed that both the CW with continuous aeration (CA-CW) and intermittent aeration (IA-CW) achieved a nitrification efficiency of more than 98% under an NH4+–N loading of 1.25–4.7 g/(m2·d). However, the total nitrogen removal rates of IA-CW under low and high ammonia-nitrogen loads (LAL, 20.09 ± 4.4% and HAL, 8.77 ± 1.35%, respectively) were higher than those of CA-CW (16.11 ± 4.7% and 3.32 ± 2.3%, respectively), especially under HAL (p < 0.05). Pearson correlation analysis showed that under different operating conditions, the differential secretion of Kandelia candel rhizosphere organic matter had a certain regulatory effect on nitrification and denitrification groups such as Candidatus Nitrocosmicus, Nitrancea, Truepera, Pontibacter, Halomonas, and Sulfurovum in the wetland root layer. The quantitative polymerase chain reaction revealed that the NH4+–N load rate was the primary factor driving the succession of the AOMs, with different aeration strategies exacerbating this process. Overall, this study revealed that the dominant AOMs in mangrove CWs could be significantly altered by regulating the aeration modes and pollution loads to adjust the rhizosphere organic matter in situ, thereby resulting in more efficient nitrification.

Removal of organic matter and nitrogen from dairy effluents in a structured bed reactor operated with intermittent aeration.

The objective of this research was to evaluate the performance of a structured bed reactor (SBRIA), carried out with intermittent aeration (IA), in the removal of organic matter and nitrogen from dairy effluent, when run with different organic loading rates (OLR). The SBRIA was operated for 227 days, with 2:1 AI cycles (2 h with aeration on and 1 h off) and Hydraulic Retention Time (HRT) of 16 h. Three phases, with different OLR, were evaluated: phases A (1000 gCOD m-3 day-1 - 63 days), B (1400 gCOD m-3 day-1 - 94 days), and C (1800 gCOD m-3 day-1 - 70 days). The percentage of COD, NH4+-N removal, and nitrogen removal, respectively, were above 85 ± 7%, 73 ± 27%, and 83 ± 5, in all phases. There was no accumulation of the oxidized forms of nitrogen in the reactor. The kinetic test, performed to evaluate the nitrification and denitrification in the system, indicated that even in dissolved oxygen concentrations of 4.5 mg L-1, it was possible to obtain the denitrification process in the system. The results demonstrate that the reactor under study has positive characteristics to be used as an alternative for removing the removal of organic material and nitrogen in the biological treatment of dairy effluents.

Machine learning methods for anomaly classification in wastewater treatment plants

Modern wastewater treatment plants base their biological processes on advanced control systems which ensure compliance with discharge limits and minimize energy consumption responding to information from on-line probes. The correct readings of probes are particularly crucial for intermittent aeration controllers, which rely on real-time measurements of ammonia and oxygen in biological tanks. These data are also an important resource for developing artificial intelligence algorithms that can identify process or sensor anomalies, thus guiding the choices of plant operators and automatic process controllers. However, using anomaly detection and classification algorithms in real-time wastewater treatment is challenging because of the noisy nature of sensor measurements, the difficulty of obtaining labeled real-plant data, and the complex and interdependent mechanisms that govern biological processes. This work aims at thoroughly exploring the performance of machine learning methods in detecting and classifying the main anomalies in plants operating with intermittent aeration. Using oxygen, ammonia and aeration power measurements from a set of plants in Italy, we perform both binary and multiclass classification, and we compare them through a rigorous validation procedure that includes a test on an unknown dataset, proposing a new evaluation protocol. The classification methods explored are support vector machine, multilayer perceptron, random forest, and two gradient boosting methods (LightGBM and XGBoost). The best performance was achieved using the gradient boosting ensemble algorithms, with up to 96% of anomalies detected and up to 84% and 62% of anomalies classified correctly on the first and second datasets respectively.

Impact of aeration on/off duration on the performance of an intermittently aerated MBR treating real textile wastewater

Uncontrolled discharge of textile industry wastewater, defined by its highly toxic content, causes serious problems in receiving environment. Especially nitrogen-derived pollutants in wastewater threaten the ecosystem and aquatic life. Separate or simultaneous nitrification/denitrification is the preferred biological processes for removing nitrogen-based pollutants from wastewater. This study aimed to evaluate the impact of aeration on/off cycle durations on organic matter, color, and nitrogen removal performances in an intermittently aerated membrane bioreactor (MBR) receiving real textile wastewater. For this purpose, the MBR was operated under different dissolved oxygen concentrations (6 and 3 mg/L) and the aeration on/off cycle durations (from 2 min/2 min to 90 min/360 min) at a constant flux of 10 L/(m2.h). While the chemical oxygen demand (COD) removal performance ranged from 84 to 91 %, the color removal efficiencies were highly variable. Nitrification performance of ≥89 % was achieved with a minimum of 30 min aeration cycles. The highest denitrification efficiency was obtained in the cycle with 360 min aeration-off duration. Intermittent aeration provided higher TN removal, less sludge generation, and lower energy requirements for aeration. The impacts of aeration cycle duration on membrane filtration performance and foulant characterization were also investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), gel-permeation chromatography (GPC), SEM coupled with energy dispersive spectroscopy (SEM-EDS), particle size distribution (PSD) analyses.

Compact pilot-scale aerobic granular sludge system treating real wastewater continuously for over 500 days

This long-term investigation provides a step-wise optimization of a pilot-scale continuous flow reactor (CFR, total volume ∼ 200 L) using aerobic granular sludge (AGS) to treat municipal wastewater (MW) at temperatures of 18.2 ± 1.8 °C and with organic loading rates of 1.39 ± 0.89 kg COD·m−3·d−1. Short settling times of about 10 min which led to a high selection pressure allowed for a complete granulation after day 47 — i.e., >80 % of the mixed liquor suspended solids (MLSS) larger than 200 μm in diameter and sludge volume indexes of ∼40 mL·g−1. Following a start-up and optimization period of 187 days, the system was stably operated with ∼6.1 g MLSS·L−1 over one year. The best-performance was achieved with an aerobic/anaerobic volume ratio of 2/1 and intermittent aeration. Furthermore, for most of the time a NH4+-N removal of 99 % was possible with low oxygen concentrations (2.0 to 2.5 mg·L−1), and despite the high‑nitrogen ratios of CODt:TN:TP (100:15:1.7).

Feasibility of low-intensity ultrasound treatment with hydroxylamine to accelerate the initiation of partial nitrification and allow operation under intermittent aeration

Partial nitrification is a key aspect of efficient nitrogen removal, although practically it suffers from long start-up cycles and unstable long-term operational performance. To address these drawbacks, this study investigated the effect of low intensity ultrasound treatment combined with hydroxylamine (NH2OH) on the performance of partial nitrification. Results show that compared with the control group, low-intensity ultrasound treatment (0.10 W/mL, 15 min) combined with NH2OH (5 mg/L) reduced the time required for partial nitrification initiation by 6 days, increasing the nitrite accumulation rate (NAR) and ammonia nitrogen removal rate (NRR) by 20.4% and 6.7%, respectively, achieving 96.48% NRR. Mechanistic analysis showed that NH2OH enhanced ammonia oxidation, inhibited nitrite-oxidizing bacteria (NOB) activity and shortened the time required for partial nitrification initiation. Furthermore, ultrasonication combined with NH2OH dosing stimulated EPS (extracellular polymeric substances) secretion, increased carbonyl, hydroxyl and amine functional group abundances and enhanced mass transfer. In addition, 16S rRNA gene sequencing results showed that ultrasonication-sensitive Nitrospira disappeared from the ultrasound + NH2OH system, while Nitrosomonas gradually became the dominant group. Collectively, the results of this study provide valuable insight into the enhancement of partial nitrification start-up during the process of wastewater nitrogen removal.

Enhancing nitrite production rate made anammox bacteria have a competitive advantage over nitrite oxidizing bacteria in mainstream anammox system.

Nitrite oxidizing bacteria (NOB) is easy to accumulate in the mainstream anammox process, leading to the decrease of anammox bacterial abundance and deterioration of nitrogen removal. In this study, anammox bacteria was gradually enriched by increasing nitrite production rate under intermittent aeration despite high NOB abundance. With the DO increased from 0.4 to 0.6 mg/L, Nitrosomonas increased from 0.14% to 0.22%, providing more nitrite for anammox bacteria and promoting its enrichment (grew by 77.4%). Adding extra nitrite of 7.14 mg N/(L·h) during the aeration phase to reactor could further increase anammox bacterial abundance by 117.6%, which was higher than the control reactor (40.2%). In contrast, NOB abundance decreased from 1.4 × 1010 to 1.2 × 1010 copies/L. The results suggested that anammox bacteria had a competitive advantage for nitrite over NOB with increasing nitrite production rate. In addition, Thauera and Dechloromonas, which were responsible for reducing nitrate to nitrite, provided additional substrates for anammox bacteria. Overall, this research provides a new idea for mainstream anammox applications. PRACTITIONER POINTS: Inhibiting NOB might be no longer necessary and difficult for mainstream anammox. Anammox bacteria competed for more nitrite with NOB when nitrite production rate increased. Increasing DO from 0.4 to 0.6 mg/L facilitated anammox bacterial growth and nitrogen removal.

Exploring the effects of intermittent aeration on the performance of nitrifying membrane-aerated biofilm reactors

Membrane-aerated biofilm reactors (MABRs) are an emerging technology for nutrient removal; however, a trade-off remains between their removal rate and oxygen transfer efficiency. This study compares nitrifying flow-through MABRs operated under continuous and intermittent aeration modes at mainstream wastewater ammonia levels. The intermittently-aerated MABRs maintained maximal nitrification rates, including under conditions allowing the oxygen partial pressure on the gas side of the membrane to considerably drop during the no-aeration period. Nitrous oxide emissions of all reactors were comparable and amounted to approximately 20 % of the converted ammonia. Intermittent aeration increased the transformation rate constant of atenolol, yet did not affect the removal of sulfamethoxazole. Seven additional trace organic chemicals were not biodegraded by any of the reactors. The ammonia-oxidizing bacteria in the intermittently-aerated MABRs were dominated by Nitrosospira, previously shown to be abundant at low oxygen concentrations and provide reactor stability under changing conditions. Our findings indicate that intermittently-aerated flow-through MABRs can achieve high nitrification rates and oxygen transfer efficiencies, highlighting the possible implications of air supply discontinuity on nitrous oxide emissions and trace organic chemical biotransformation.

Improve nitrogen removal of the biofilm single-stage PN/A process by optimizing the intermittent aeration strategy

Improve nitrogen removal of the biofilm single-stage PN/A process by optimizing the intermittent aeration strategy

Effect of Anammox Granular Sludge Type on the CANON Process with Immobilized Fillers Treating Domestic Wastewater

Immobilized fillers were prepared using intact and crushed ammonia oxidation granular sludge (AnGS) to compare their effects on the completely autotrophic N-removal over nitrite (CANON) process in domestic sewage. Using pre-aerated domestic sewage as an influent, the effect of granular type on nitrogen removal was investigated under intermittent aeration. The results show that the total nitrogen removal (TNR) of the crushed AnGS immobilized filler was 75.8–80.0% at a dissolved oxygen (DO) concentration of 3 mg/L, while the intact AnGS immobilized filler required a DO of 4 mg/L to achieve the same TNR level. The DO concentration is the key factor affecting the nitrogen removal efficiency, because partial nitrification was affected by the DO concentration. Candidatus Kuenenia was the dominant genus of anaerobic ammonium oxidation (anammox) bacteria, and its relative abundance was higher in the crushed AnGS immobilized filler (21.11%) than in the intact AnGS immobilized filler (9.60%). Furthermore, the immobilized filler could inhibit the growth of nitrite-oxidizing bacteria (NOB), and the relative abundance of Nitrospira, the major NOB genus, decreased after operation. The results of this study indicate that the use of AnGS immobilized filler is a promising strategy to strengthen the CANON process in municipal wastewater treatment.

The rapid start-up of CANON process through adding partial nitration sludge to ANAMMOX system

This study aimed to start up the completely autotrophic nitrogen removal over nitrite (CANON) process after adding partial nitration (PN) sludge to the ANAMMOX reactor, so as to help the rapid start-up and stable operation of the CANON process in practical engineering applications. There were three steps in the research: cultivating the PN sludge, building a reliable ANAMMMOX system, and finally starting and running the CANON process. The PN sludge was successfully cultivated in less than 45 days with around 90% nitrite accumulation rate. The ANAMMOX reactor enriched a significant quantity of red granular sludge within 70 days, achieving the maximum nitrogen removal rate of 1.74 kg/(m3·d). Eventually, the CANON reactor was started up successfully, which achieved 95.08% of average ammonium removal efficiency and 84.51% of average total nitrogen removal efficiency in 60 days. The residual recalcitrant nitrite-oxidizing bacteria in the CANON process was successfully inhibited by intermittent aeration and 12 mg/L free ammonia in UASB reactor. Besides, Candidatus Kuenenia, Candidatus Brocadia and Nitrosomonas were the main functional microorganisms involved in the CANON process.