Pilot-scale structured bed reactor with intermittent aeration: a novel strategy for simultaneous nitrogen and carbon removal from domestic sewage with industrial contribution

This study outlines the development of an effective pilot-scale simultaneous denitrification and nitrification (SDN) system using intermittent aeration for the removal of carbon and nitrogen from real domestic sewage. Given the limited research in this area, the main objective was to evaluate the overall performance of the SBRIA system on a pilot scale and show its benefits in domestic wastewater treatment. The structured bed reactor with intermittent aeration (SBRIA) notably achieved 57% efficiency in removing total nitrogen without requiring external carbon sources. It also demonstrated impressive removal rates of 56% for total chemical oxygen demand (CODT) and 82% for biochemical oxygen demand (BOD5), indicating its effectiveness in degrading organic matter. In addition, the SBRIA showed high pH control and managed the consumption of alkalinity without the need for an alkalizer, maintaining consistent mean values of 7.7 ± 0.8 for pH and 166.8 ± 79.8 mg·L-1 for alkalinity. The system also proved resilient against toxic shocks caused by significant variations in influent characteristics. This study offers valuable insights and compelling results into a cost-effective and efficient treatment approach using an innovative technology not previously applied at the pilot scale. Its potential to remediate polluted water is substantial.

Carbon-nitrogen removal in a structured-bed reactor (SBRRIA) treating sewage: Operating conditions and metabolic perspectives

Simultaneous nitrification and denitrification (SND) is a process that can remove both nitrogen and organic matter in a single unit. Several bench-scale studies show that the structured bed reactors (STBR) subjected to recirculation and intermittent aeration have achieved a good performance for SND treating different types of wastewater. Thus, this study took a step forward and evaluated the efficiency and stability of treating domestic sewage in a pilot-scale STBR. COD removal efficiencies higher than 87% were achieved in the whole experimental period. The highest Total-N removal efficiency was approximately 74 ± 7% by adopting a hydraulic retention time (HRT) of 47.2 h and intermittent aeration (2 h aerated and 1 h non-aerated). The setup of the aeration system was an important mechanism to ensure the optimal balance between nitrification and denitrification in a pilot-scale system.

Nitrogen and carbon removal from synthetic wastewater in a vertical structured-bed reactor under intermittent aeration

This study evaluated the removal of nitrogen and organic matter in a membrane bioreactor system operating in a condition of simultaneous nitrification and denitrification controlled by intermittent aeration. A submerged-membrane system in a bioreactor was used in a pilot scale to treat domestic wastewater. The dissolved oxygen concentration was maintained between 0.5 and 0.8 mg L-1. The concentration of the mixed liquor suspended solids (MLSS) in the system ranged from 1 to 6 g L-1. The system efficiency was evaluated by the removal efficiency of organic matter, quantified by Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5) and Total Organic Carbon (TOC). Nitrogen removal was assessed by quantifying Total Kjeldahl Nitrogen (TKN) and ammonia nitrogen. During the system start-up, the removal efficiencies of COD and NTK were around 90% and 80%, respectively. After the simultaneous nitrification and denitrification (SND) conditions were established, the removal efficiencies of COD and NTK were 70% and 99%, respectively. These results showed that sewage treatment with the membrane bioreactor (MBR) system, operating with simultaneous nitrification and denitrification conditions, was able to remove organic matter and promote nitrification and denitrification in a single reactor, producing a high-quality permeate.

Controlling factors for simultaneous nitrification and denitrification in a two-stage intermittent aeration process treating domestic sewage

The Structured Bed Reactor with Recirculation and Intermittent Aeration (SBRRIA) is a reactor configuration that presents high efficiency of organic matter and nitrogen removal, besides low sludge production. However, operational parameters, as the recirculation rate, aeration time, and airflow, are not fully established. A bench-scale structured bed reactor with intermittent aeration was fed with synthetic effluent simulating the characteristics of sanitary sewage. The reactor was operated for 280 days with an operational hydraulic retention time (HRT) of 10 h. The reactor was operated without effluent recirculation for the first time since this approach was not yet reported, and was named Structured Bed Reactor with Intermittent Aeration (SBRIA). The COD removal was higher than 81% for all operational conditions, and the total nitrogen removal ranged from 10 to 80%. The highest efficiencies were obtained with an aeration time of 1 h 45 min (total cycle of 3 h) and an airflow rate of 4.5 L.min−1. Different nitrification and denitrification behaviours were observed, resulting in nitrification efficiencies over 90% when the reactor was submitted to higher aeration times and denitrification efficiencies above 90% when the reactor was submitted to low aeration times. The airflow ranges tested in this study affected the nitrification and the total nitrogen efficiencies. Even without effluent recirculation, the temporal profile showed that there were no peaks in the concentration of the nitrogen forms in the reactor effluent, saving electrical energy up to 75% due to pumping.

Aerobic granular sludge (AGS) has been considered a breakthrough in the wastewater treatment sector given its key characteristics, such as excellent settleability, simultaneous removal of organic and nutrient pollutants, and compactness. However, the formation of granules often delays the start-up of granular-based systems, especially in large-scale settings. This study addressed the start-up of a pilot-scale AGS sequencing batch reactor (SBR) treating domestic sewage, monitored for over 280days. The challenges faced during aerobic granulation using a mixture of activated sludge and anaerobic granular sludge as inoculum and the performance of the reactor on organic matter, nitrogen, and phosphorus removal were discussed. Results showed that robust and stable granules were formed after an initial period of around six months, with the settling time playing a key role on granules development. At least 80% of granules had a diameter greater than 0.2mm and 60% >1mm. In general, the reactor achieved high nitrogen removal efficiency, as well as satisfactory removal of soluble COD. However, total COD abatement was impaired by the various episodes of suspended solids loss with the effluent. Overall, this study demonstrated that the reactor was efficient in the treatment of domestic sewage, but its performance was adversely affected from sudden changes in the influent quality. PRACTITIONER POINTS: Aerobic granular sludge (AGS) applied to small-scale domestic sewage treatment. The control of sludge age in AGS can be a problem due to short sedimentation times. High DO to maintain aerobic granulation can economically make the process economically unfeasible in tropical countries. A sludge with excellent sedimentation properties was obtained. However, maintaining the granule over time is a challenge.

Reduction in VOC emissions by intermittent aeration in bioreactor landfills with gas-water joint regulation

Purifying tank as a compact biofilm reactor has been widely used to remove organic matter in rural sewage, but its potential for nitrogen removal is rare to be discussed. This study developed a lab-scale compact biofilm reactor to realize an efficient nitrogen removal performance by step-feed, intermittent aeration, and immobilization technique. The results show that an efficient simultaneous nitrification and denitrification (SND) process took place by feeding with synthetic wastewater under high C/N ratio of 2 and with real sewage as well, mainly due to the step-feed. The average removal efficiency of total inorganic nitrogen arrived at 72.7 and 63.3% for synthetic wastewater and real sewage, respectively. Besides the step-feed operation, the intermittent aeration was adopted to enhance SND, which allowed hydraulic behavior of compact biofilm reactor following the model of completely stirred tank reactor. The high-throughput sequencing analysis indicates that Sphaerotilus became the dominant genera with relative abundance of 30.29% under high C/N ratio, and the nitrifiers were not greatly inhibited. Moreover, the immobilization technique helped restore microbial activity under low temperature, promoting the satisfactory nitrogen removal performance of recovered microorganism to be rebuilt by feeding nutrient solution. Overall, the long-term SND process and maintaining effective biofilm activity can be established in the compact biofilm reactor through several improving alternatives.

The principle aim of this study was to gain an understanding of the conditions and processes governing the occurrence of simultaneous nitrification and denitrification (SND). SND is the process that combines nitrification and denitrification in the same reactor (at the same time) under fully aerobic conditions. From various studies, two main hypotheses, one physical and one biological, have been proposed to explain SND (Simultaneous Nitrification and Denitrification). Significant research has been performed on the biological aspects, whereas relatively little is known about the physical explanation. Therefore, further investigations of physical explanation on SND (Simultaneous Nitrification and Denitrification) are carried out in this thesis. To fulfill this principal objective, two major tasks were preformed: experimental studies and model development. The experimental investigation was conducted using lab scale sequencing batch reactors (SBR). The operating conditions of the reactors were varied corresponding to the aim of each experiment. The influent wastewater was collected from the effluent of an anaerobic pond at an abattoir wastewater treatment plant. The main experimental studies focused on three factors, the effect of soluble organic carbon, floc size and dissolved oxygen (DO) concentrations, on the SND activity. The results revealed that all these factors had a significant influence on the degree of SND achieved. Almost 50% of inorganic nitrogen lost by SND (Simultaneous Nitrification and Denitrification) could be achieved when operating at a soluble COD:TKN ratio of 6. A dramatic increase in SND activity to 85% was found when this ratio reached 10. With a soluble COD:TKN ratio of 15, complete nitrogen removal by SND could be achieved. The effect of dissolved oxygen (DO) was equally strong. SND could completely occur at very low DO concentrations (0.2 mg/L). However, the nitrogen removal in this range was substantially limited by the low nitrification rate. To improve the nitrification rate but still achieve effective denitrification, a DO concentration of around 0.4-0.5 mg/L seems to be an optimal value to maintain a significant degree of SND. In this range, the nitrification rate reached 50% of the rate found at DO of 1.1 mg/L and 60% SND activity was achieved. The effect of bacterial floc size on SND was also quite remarkable. It was found that an SBR operating with a median floc size of 80 mm could achieve 80% SND, whereas the SND activity decreased to only 50% after the median floc size was reduced to 40 mm in the following treatment cycle. A complete nitrogen balance over the whole process was performed to confirm the occurrence of SND in such systems. Under typical operating conditions, it was found that the nitrogen gas was the major nitrogen product of the treatment process (approximately 58% of the total output). 14% of nitrogen was assimilated to biomass whereas 23 % of nitrogen at the end of the process was in the soluble form (organic nitrogen, nitrite, nitrate and ammonium). The mathematical dynamic model was developed to gain a better understanding of SND in the situation that is difficult to investigate experimentally. The overall model structure can be divided into 4 main areas : 1. a ‘micro’ level model for a single floc 2. the reaction rates for a single floc size 3. the reaction rates for the entire reactor considering the floc size distribution 4. a ‘macro’ model for the whole reactor including the operational changes throughout the cycle. It was found that the model can predict the SND behavior well for the system operating under typical influent characteristics (SCOD:TKN of 10). However, poor predictions were found at different levels of SCOD:TKN. Two crucial reasons can be given. Firstly, this model did not include intracellular carbon storage by bacteria. Secondly, many parameters, especially floc and microorganism characteristics (i.e. intra floc biomass distribution, growth and decay of the microorganism, etc.) could not be determined or estimated accurately. However, under normal operating conditions of this study, the model advances the fundamental understanding of SND process in activated sludge system. The simulation results showed that both floc diameter and liquid phase concentration are important factors influencing the internal floc concentrations. It was also predicted that an anoxic microzone, caused by oxygen diffusion limitation, potentially occurs in the floc center. This microzone therefore enhances denitrification activity inside the floc. A number of major conclusions can be drawn from this thesis: 1. SND potentially occurs as a result of physical phenomenon 2. high soluble COD is beneficial to SND activity 3. suitable floc size distribution (with more large flocs) can enhance SND 4. major nitrogenous product of the treatment process is nitrogen gas 5. dissolved oxygen optimization is critical to get good nitrification rate and SND.

This paper reports on a possible technique to determine specific nitrification and denitrification rates (SNR and SDNR) in an oxidation-reduction potential (ORP) controlled, intermittent aeration (IA) tank, in which simultaneous nitrification and denitrification (SND) occurred. In addition, SNRs in a three-stage Bardenpho aerobic zone and SDNRs in its anoxic zone were determined. This research was done at bench scale. The technique involves a steady-state run and two additional transient-state tests (created by either ammonia or nitrate shock loading). The rates obtained, using this technique, are the maximum rates possible in a continuous process under certain, improvised conditions. The technique is extremely flexible and generates data relating the rate to substrate concentration in one steady-state run. Data analysis was performed using the integral method; an excellent agreement between predicted and experimental data was found. Zero-order kinetics could describe nitrification in an ammonia concentration range of 1–30 mg/L and denitrification in a nitrate concentration range of 10–30 mg/L. The SNRs in the intermittently aerated, complete-mix (IACM) tank (0.39–1.69 mg g–1 h–1) were considerably lower than those in the 3-stage Bardenpho aerobic zone (3.4–3.81 mg g–1 h–1) due mainly to imposed dissolved oxygen limitations. The SDNRs in the IACM tank were in a range of 0.16–1.26 mg g–1 h–1, which were also considerably lower than that in the 3-stage Bardenpho anoxic zone (2.0–2.5 mg g–1 h–1). Key words: acetate, denitrification, intermittent aeration, kinetics, methanol, nitrification, ORP control, simultaneous nitrification and denitrification.

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.

This research aimed the performance evaluation of a structured bed reactor with different cycles of Intermittent Aeration (IA)(SBRRIA) in the municipal sewage treatment and the verification of the effect of IA cycles on the total nitrogen (TN) removal and organic matter (COD). Three IA cycles were evaluated: phase I (4 h AE (aeration on) – 2 h NA (aeration off)); II (2 h AE–1 h NA) and III (2 h AE–2 h NA), with Hydraulic Retention Time of 16 h. The best nitrogen removal was obtained during phase II, with the lowest non-aeration time: efficiency of nitrification, denitrification, TN and COD removal of 80 ± 15%, 82 ± 12%, 67 ± 6% and 94 ± 7%, respectively. The mean cell residence time was 19, 26 and 33 d in phases I, II and III, respectively. The statistical analysis applied to the AE/NA profiles showed that the time of AE and NA in the cycles did not influence nitrogen and organic matter removal. Thus, this indicates the recirculation and the gradient formed in the support material facilitate the process of Simultaneous Nitrification and Denitrification. The lowest concentration of nitrifying and denitrifying microorganisms was obtained in effluent and sludge at the end of phase III. From the TP (Total Proteins)/TPS (Total Polysaccharides) ratio obtained (0.8 ± 0.1, 1.3 ± 0.1 e 1.5 ± 0.1 in phases I, II and III), it was possible to conclude that the biofilm in phase I was more porous, with a thin layer if compared to that in phase II and III.

This study examines the complexities of the integration of different technologies for nutrient removal, investigating parameters like sludge residence time (SRT), carbon-to-nitrogen (C/N) ratio, Anaerobic/Oxic (A/O), and Anaerobic/Oxic/Anoxic (A/O/A) systems, continuous and intermittent aeration regimes, and air OFF/air ON periods ratios for efficient nitrogen and phosphorus removal. Two continuous aeration systems were implemented: The first aimed to carry out a simultaneous nitrification and denitrification (SNdN) process for nitrogen and phosphorus removal under low dissolved oxygen (DO) and C/N ratio conditions. This system operated with 4.5-5-day total sludge age in a single-stage anaerobic/oxic (A/O)-SBR, performing stepwise DO reduction at varying DO setpoints (4.0-5.0, 2.0-2.2, 1.2-1.4, 0.45-0.55, and 0.3-0.4 mgO2/L). The second system combined low DO-enhanced biological phosphorus removal (EBPR) with post-anoxic denitrification in a single-stage setup at a total sludge age of 9-14 days. DO setpoints were 0.8-1.0 mgO2/L for anaerobic/oxic (A/O) phases and 0.5-0.6 mgO2/L for anaerobic/aerobic/anoxic (A/O/A) phases. The third system aimed to investigate the feasibility of applying an intermittent aeration strategy for the simultaneous removal of nitrogen and phosphorus under low dissolved oxygen (DO) conditions of 0.35-0.5 mgO2/L. The system employed varying reduction ratios for air-off to air-on periods, precisely 1.67, 1.25, 1.57, and 2.0. Additionally, C/N ratios were maintained around 6.4, 7.4, and 5.8, aiming to explore the impact of the C/N ratio on nitrogen and phosphorus removal. The obtained results from continuous aeration studies demonstrated robust and consistent removal efficiencies of NH4+ and TIN under low DO conditions (0.3-0.4 mgO2/L) under short SRT reaching 97.1±0.4% and 71.5±2.3%, respectively, with effluent concentrations as low as 1.39±0.19 mg/L for NH4+ and 13.5±1.0 mgN/L for TIN. Similarly, COD and TP removal efficiencies were achieved at low DO levels, measuring 90.1±1.2% and 78.7±3.1%, respectively. Notably, the results showcased the ability to achieve a remarkable SNdN efficiency of 73.64% for wastewater with a C/N ratio of 4.64. Distinguishing from other studies on the SNdN process, this research highlighted its unique capability to reduce the demand for organic carbon for nitrogen removal. Remarkably, under longer SRT and a higher C/N ratio of 6.8, high removal efficiencies were achieved for COD, NH4+, TIN, and TP, measuring 93±0.3%, 94.4±0.5%, 67.9±2.1%, and 95.7±0.6%, respectively. The resulting effluent concentrations were low: 22.7±1.0 mg/L, 2.7±0.2 mg/L, 15.3±0.8 mg/L, and 0.5±0.1 mg/L for COD, NH4+, TIN, TP, respectively. The results highlighted that integrating low DO-A/O/A could be an economical approach for effective TIN and TP removal under low