Intermittent Aeration Research Articles

Improving the removal efficiency of nitrogen and organics in vertical-flow constructed wetlands: the correlation of substrate, aeration and microbial activity.

Four vertical-flow CWs (VFCWs) with different substrates and aeration conditions were studied on nutrient-removal capacity from synthetic wastewater. Zeolite substrate VFCWs (none-aerated: VFCW-1, aerated: VFCW-3) paralleled with ceramsite (none-aerated:VFCW-2, aerated: VFCW-4) were used to study the removal efficiencies of N and organics, the bacterial community, and the related functional genes. The results indicated that the pollutant removal efficiency was significantly enhanced by intermittent aeration. VFCW-4 (ceramsite with aeration) demonstrated a significant potential to remove NH4+-N (89%), NO3--N (78%), TN (71%), and COD (65%). VFCW-3 and VFCW-4 had high abundances of Amx, amoA, and nirK genes, which was related to NH4+-N and NO2--N removal. The microbial diversity and structure varied with aeration and substrate conditions. Proteobacteria, Actinobacteria, Candidatus, and Acidobacteria were the main bacteria phyla, with the average proportion of 38%, 21%, 19%, and 7% in the VFCWs. Intermittent aeration increased the abundance of Acidobacteria, which was conducive to the removal of organic matters. Overall, ceramsite substrate combined with intermittent aeration has a great potential in removing pollutants in VFCWs.

Characteristics of rural sewage discharge and a case study on optimal operation of rural sewage treatment plant in Shaanxi, China

Rural wastewater treatment has become an important issue in China. This study investigated 76 rural wastewater treatment plants (WWTPs) in Shaanxi over a one-year period. We found that although rural sewage is suitable for biological treatment (BOD5/COD = 0.38–0.41), it has an obvious intermittent flow cutoff (5–19 h/d) characteristic, resulting in low sewage loading and poor pollutant removal in rural WWTPs. In order to improve operation efficiency and increase economic benefits of the existing rural WWTPs, a pilot-scale A2/O bioreactor was established, and the effect of rural sewage discontinuity (cutoff duration 10 h/d) on A2/O process was studied. An intermittent aeration and dissolved oxygen (DO) regulation operation strategy was developed. The results demonstrated that ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB), and polyphosphate accumulating bacteria (PAOs) were all enriched when Taeration:Tstop = 5 h:5h and DO = 2.0–3.0 mg/L. During the subsequent process of reducing DO concentration to 0.5–1.0 mg/L, AOBs (2.43 %) and PAOs (1.91 %) were enriched and NOBs (1.61 %) were panned. The transformation of functional bacteria in the system stimulated partial nitrification and denitrification phosphorus removal (DPR) (nitrite accumulation rate = 46.56 ± 6.88 %, DPR rate = 43.15 ± 3.54 %), which improved the nutrient removal rates. Finally, the optimal operation strategy was applied to a typical town-level WWTP in Ankang, China. The removal rates of NH4+-N, TN, and TP increased from 85.85 ± 1.31 %, 59.77 ± 2.86 %, and 23.91 ± 1.77 % to 94.17 ± 2.02 %, 65.32 ± 4.75 % and 61.05 ± 2.34 %, respectively, and the operating cost was reduced by 118,600 CNY (17,541 USD) per year.

Improved nitrogen removal efficiency by implementation of intermittent aeration.

The aim of the paper was to verify the possibility of using intermittent aeration to decrease outflow total nitrogen concentrations in municipal WWTPs of different capacities (15,780, 23,000 and 806,250 PE). A simple time-based intermittent aeration control was used in the experimental work. The results of WWTPs are compared with each other and with literature sources. The use of intermittent aeration led to a significant decrease of outflow total nitrogen concentration by up to 57% without the need of additional investment costs or the increase of operating costs. Nitrification kinetic tests and fluorescence in-situ hybridization observations proved that intermittent aeration has no negative impact on nitrifiers. The results proved that it is possible to utilize intermittent aeration for treatment plants initially designed with permanent aeration of nitrification sections if the current load is lower than the designed capacity. A necessary prerequisite for successful implementation of intermittent aeration is sufficient blower power. Although the time-based control is very simple and inexpensive to implement, the results are comparable to more complex systems such as systems based on rule-based systems for N-NH4+ and N-NO3- concentrations, on fuzzy logic or on mathematical models.

Biomass retention and microbial segregation to offset the impacts of seasonal temperatures for a pilot-scale integrated fixed-film activated sludge partial nitritation-anammox (IFAS-PN/A) treating anaerobically pretreated municipal wastewater

Partial nitritation-anammox (PN/A) is a promising deammonification process to develop energy-neutral wastewater treatment plants. However, the mainstream application of PN/A still faces the challenges of low nitrogen concentration and low temperatures, and has not been studied under a realistic condition of large-scale reactor (kiloliter level), real municipal wastewater (MWW) and seasonal temperatures. In this research, a pilot-scale one-stage PN/A, with integrated fixed-film activated sludge (IFAS) configuration, was operated to treat the real MWW pretreated by anaerobic membrane bioreactor. The removal efficiency of total nitrogen (TN) was 79.4%, 75.7% and 65.9% at 25, 20 and 15°C, corresponding to the effluent TN of 7.3, 9.7 and 12.0 mg/L, respectively. The suppression of ammonium-oxidizing bacteria (AOB) and anammox bacteria (AnAOB) occurred at lower temperatures, and the significant decrease in AOB treatment capacity was the reason for the poorer nitrogen removal at 15°C. Biomass retention and microbial segregation were successfully achieved. Specifically, Candidatus_Brocadia and Candidatus_Kuenenia were main AnAOB genera and mainly enriched on carriers, Nitrosomonas and uncultured f_Chitinophagaceae were main AOB genera and mainly distributed in suspended sludge and retained by sedimentation tank. Moreover, nitrite-oxidizing bacteria (NOB) were sufficiently suppressed by intermittent aeration and low dissolved oxygen, the presence of heterotrophic bacteria upgraded the PN/A to a simultaneous partial nitritation, anammox, denitrification, and COD oxidation (SNADCO) system, which improved the overall removal of TN and COD. The results of this investigation clearly evidence the strong feasibility of PN/A as a mainstream nitrogen removal process in temperate climates.

Biodrying with the hot-air aeration system for kitchen food waste.

Biodrying is a promising method that produces bio-stabilized output with minimum pretreatment requirements. In this study, a hot-air supply system was added to the traditional biodrying process for kitchen waste, which showed significant reduction in moisture content in 5 days (maximum reduction of 37.45%). A series of experiments was conducted to optimize the hot-air biodrying system utilizing different aeration rates, temperatures, and mixing ratios of feedstock to bulking agents. The results showed that a 65°C aeration temperature led to the highest water removal rate and low volatile solids consumption rate, with the biodrying index reaching 4.9g water per gram of volatile solids. On the other hand, evaluation of the overall biodrying efficiency based on the weight loss and bio-stabilization showed that intermittent aeration temperature at 55°C performed best, offering suitable conditions for water evaporation and bio-degradation. In combination with a flow rate of 0.8L/kg*min and 1:1 mixing ratio, these conditions resulted in the maximum volatile solids consumption of 26.26% in 5 days. The volatile solids consumption and 34.47% water removal rate of the trial had contributed to a total of 64.13% weight loss. The weight loss was even higher than that of a conventional biodrying system which was conducted for more than 14 days.

Techno-economic feasibility of “membrane-based pre-concentration + post-treatment” systems for municipal wastewater treatment and resource recovery

Membrane-based pre-concentration (MPC) process has been regarded as an attractive approach to sustainable municipal wastewater (MW) treatment. The aim of this study is to verify the techno-economic feasibility of pilot-scale MPC demonstrations and to design a complete technical route for MPC-based MW treatment and resource recovery. Three pilot MPC demonstrations (50–500 t/d) were operated for several months with different strategy combinations of chemicals and aeration. The filtration performance, pollutant removal performance, and concentrate characteristics were investigated and a techno-economic assessment was conducted. Based on the characteristics of each MPC effluent, biofilters, reverse osmosis (RO) and membrane capacitive deionization (MCDI) were selected as post-treatment units. Comparisons were carried out from 6 perspectives, including effluent quality, energy consumption, capital investment, operating cost, by-products, and recovery potential. In MPC_C, the combination of intermittent aeration and “50 mg/L Polyaluminium chloride +25 mg/L activated carbon” ensured a stable filtration (flux >10 LMH over 3 months) and an exceptional pollutant removal (soluble organics removal rate >75%) performance. The highest energy recovery potential (0.35 kWh/m3) was also achieved in MPC_C with the lowest energy consumption (0.12 kWh/m3) and an acceptable operating cost (0.53 CNY/m3). As for post-treatment units, RO showed advantages in effluent quality, technological maturity, and economic cost. An “MPC (intermittent aeration + high strength dosage) + RO + anaerobic digestion” system was proposed for synchronous water-energy reclamation. The net energy consumption and operating cost were estimated as 0.273 kWh/m3 and CNY 1.132/m3, respectively. This study will open new possibilities for the establishment of revolutionary wastewater treatment routes for carbon neutrality and sustainable development.

A quantified nitrogen metabolic network by reaction kinetics and mathematical model in a single-stage microaerobic system treating low COD/TN wastewater

A single-stage intermittent aeration microaerobic reactor (IAMR) has been developed for the cost-effective nitrogen removal from piggery wastewater with a low ratio of chemical oxygen demand (COD) to total nitrogen (TN). In this study, a quantified nitrogen metabolic network was constructed based on the metagenomics, reaction kinetics and mathematical model to provide a revealing insight into the nitrogen removal mechanism in the IAMR. Metagenomics revealed that a complex nitrogen metabolic network, including aerobic ammonia and nitrite oxidation, anammox, denitrification via nitrate and nitrite, and nitrate respiration, existed in the IAMR. A novel method for solving kinetic parameters with high stability was developed based on a genetic algorithm. Use this method to calculate the kinetics of various reactions involved in nitrogen metabolism. Kinetics revealed that simultaneous partial nitritation-anammox (PN/A) and partial denitrification-anammox (PDN/A) were the dominant approaches to nitrogen removal in the IAMR. Finally, a kinetics-based model was proposed for quantitatively describing the nitrogen metabolic network under the limitation of COD. 58% ∼ 67% of nitrogen was removed via the anammox-based processes (PN/A and PDN/A), but only 7% ∼ 12% and 1% ∼ 2% of nitrogen were removed via heterotrophic denitrification of nitrite and nitrate, respectively. The half-inhibition constant of dissolved oxygen (DO) on anammox was simulated as 0.37 ∼ 0.60 mg L−1, filling the gap in quantifying DO inhibition on anammox. High-frequency intermittent aeration was identified as the crucial measure to suppress nitrite-oxidizing bacteria, although it has a high affinity for DO and NO2−-N. In continuous aeration mode, the simulated NO3−-N in the IAMR would rise by 39.6%. The research provides a novel insight into the nitrogen removal mechanism in single-stage microaerobic systems and provides a reliable approach to practicing PN/A and PDN/A for cost-effective nitrogen removal.

Enhanced nitrogen removal from municipal wastewater via a novel combined process driven by partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A) with an ultra-low hydraulic retention time (HRT)

Anaerobic ammonia oxidation (Anammox) is a highly productive research area in municipal wastewater treatment. A novel combined process driven by partial nitrification/anammox (PN/A) and partial denitrification/anammox (PD/A) was established in this paper using a sequencing batch reactor (SBR) and two up-flow sludge beds (USBs). Municipal wastewater after carbon removal pretreatment in SBR entered PN/A-USB. PN/A process was initiated and enhanced by optimizing the intermittent aeration mode under low dissolved oxygen (DO). After enhancing and stabilizing the PD/A process, PN/A effluent entered the PD/A-USB along with raw municipal wastewater at a ratio of 4:1 and the combined system was established. Through this, this study achieved a nitrogen removal efficiency (NRE) of 84.9 % from municipal wastewater at an ultra-low total hydraulic residence time (HRT) of 3.9 h. Candidatus Brocadia (1.8 % in PN/A, 1.0 % in PD/A) was the only functional anammox bacterium in the combined process.

MABR process development downstream of a carbon redirection unit: opportunities and challenges in nitrogen removal processes

ABSTRACT Carbon redirection has become the desired option for sustainable and energy-efficient wastewater treatment due to its contribution to a circular economy. However, its impact on downstream processes such as nitrification and denitrification requires further investigation. This research characterizes the nitrogen removal performance, footprint, aeration mode, and microbial composition of a flow-through membrane aerated biofilm reactor (MABR) downstream of a chemically enhanced primary treatment (CEPT) carbon redirection unit. The batch and long-term studies demonstrated relatively higher nitrification rates than those reported using conventional primary treated wastewaters. The results indicated that reducing carbon in the liquid train positively impacted nitrification by achieving 87 ± 12% (1.4 ± 0.4 g/m2.d) ammonia removal with an effluent 2.5 ± 2.8 mg/L ammonia concentration at a short hydraulic retention time (HRT) of 2.5 h. Despite the lower (1.9 ± 1) soluble COD:N, up to 75 ± 25% (0.6 ± 0.4 g/m2.d) total nitrogen removal was achieved at 4 h HRT by implementing intermittent aeration. The batch tests using the developed biofilms showed nitrification (denitrification) capacity up to 11 ± 1.7 gNH4-N/m2.d (8.5 ± 0.5 gNO3-N/m2.d) and 2.7 ± 0.6 gNH4-N/m2.d (2 ± 0.3 gNO3-N/m2.d) corresponding to ammonia and nitrate concentrations ranging from 10–30 mg/L and 2–10 mg/L, respectively. Microbial analysis indicated that the nitrifiers such as Nitrosomonas and Nitrospira were the dominant species. The ammonia-oxidizing, nitrite-oxidizing, and denitrifying bacteria relative abundances were 10.3 ± 1.5%, 20.7 ± 1.7%, and 20.0 ± 2.8% under continuous aeration and 1.3 ± 0.07%, 1.8 ± 0.09%, and 40.5 ± 3.1% under intermittent aeration, supporting the observed ammonia and total nitrogen removal processes, respectively. Overall, the results demonstrated that MABR downstream of the CEPT behave differently; thus, design guides should be updated accordingly.

A comparative evaluation of the sustainability of alternative aeration strategies in biological wastewater treatment to support net-zero future

In the plight for sustainable development and to support net zero ambitions for climate change mitigation, a broad range of aeration strategies have been developed with the hope of improving efficiency to minimize environmental and economic costs associated with the wastewater treatment processes. However, a balance is levied between reducing oxygen availability and hindering aerobic processes thus compromising performance. In the present work, we evaluate and compare the sustainability of a range of investigated strategies including continuous aeration (CA) at different dissolved oxygen (DO) setpoints (0.5 mg/L, 2.5 mg/L, 4.5 mg/L) and intermittent aeration (IA) at different oxic-anoxic portions (2.5 h on/0.5 h off, 2.0 h on/1.0 h off, 1.5 h on/1.0 h off). To achieve this, an eco-efficiency assessment is performed based on the results of previous life cycle impact and costing analyses for each strategy, while also incorporating a third factor to account for their respective treatment performance. The results demonstrate a clear pattern of increased sustainability for the IA strategies (0.54–0.56 Pt/m3), compared to the CA strategies (0.76–0.77 Pt/m3). While only negligible difference was observed within each aeration type, the trade-off between environmental and economic efficiency and treatment performance was distinct in CA strategies. At the individual pollutant level, IA strategies demonstrated decreasing sustainability for total phosphorous (TP) removal as the anoxic cycle portion increased, while CA at 0.5 mg/L was shown to be the most sustainable strategy for the removal of this pollutant (0.61 Pt/m3). Further work is suggested to incorporate the relative N2O emissions generated by each strategy and to investigate other strategies based on automated control.

Energy saving and rapid establishment of granular microalgae system from tiny microalgae cells: Effect of decrease in upflow air velocity under intermittent aeration condition

The novel type of microalgae granules (MGs) derived from tiny microalgae cells has received extensive attention due to its great potential for nutrient remediation and resource recovery in wastewater treatment whereas the long start-up time with increased labor expenses remains a bottleneck. In this study, an operation strategy at reduced upflow air velocity (UAV = 0.49 cm/s in RA) under intermittent aeration mode was proposed and compared with RB at a higher UAV (0.98 cm/s) in terms of MGs formation, maintenance, and energy consumption. Although the formation of MGs in RA was delayed for 12 days compared to RB, 40.78 % increase in chlorophyll-a content was detected in MGs in RA along with more cost-effective carbon, nitrogen, and phosphorus removals due to efficient microalgae assimilation and energy reduction. Results from this study provide new insight into minimizing energy input for rapid establishment and stable operation of MG systems towards environmentally sustainable wastewater management.

ORGANIC REMOVAL IN DOMESTIC WASTEWATER USING ANAEROBIC TREATMENT SYSTEM-MBBR WITH FLOW RECIRCULATION RATIO AND INTERMITTENT AERATION

Aim: The modified Small-scale Domestic Sewage Treatment Plant (SDSTP) reactor with anaerobic fixed bed- aerobic Moving Bed Biofilm Reactor (MBBR) is implemented to find the optimum condition for organic degradation related to recirculation and intermittent aeration practices with the purpose to comply with the governmental regulation standard. Methodology and Results: This research have been done with the artificial wastewater with characteristic similar to the sewage treatment plant (STP) of Telkom company with ratio C:N:P of characterized domestic wastewater is 252.40:85.42:3.01 that consists of glucose, NH4Cl, potassium dihydrogen phosphate, potassium nitrate, and sodium nitrite (NaNO2). Reactor design related with attached biomass in media until 2478.56 mg MLVSS.L-1 with the growth kinetics rate (μ) of 0.4691 day—1. The artificial wastewater is applied the determine the optimum variation of flow recirculation and periodic aeration in specific Hydraulics Retention Time (HRT) and Organic Loading Rate (OLR). In this research, the optimum recirculation ratio for organic degradation is 26.40 L.h-1 and the optimum aeration frequency variation is 12 hours in intermittent frequency with the maximum efficiency of organic degradation of 76.10% with the degradation efficiency real domestic wastewater application from STP Telkom company is 83.09%. Conclusion, significance and impact study: Stover-Kincannon model is the best model with highest accuracy rate to model the degradation performance of organic compounds by the anaerobic fixed bed- aerobic MBBR SDSTP with determination coefficient 0.8623 and also degradation coefficient 38.121 day-1 compared with other models studied in this research.

Scheduling of Batch Operation for a Wastewater Treatment Plant under Time-of-Use Electricity Pricing.

High operating cost caused by electric energy consumption is a common problem challenging many municipal wastewater treatment plants (WWTPs). Due to the characteristics of intermittent inflow and aeration, WWTPs using sequencing batch reactor technology and its variants can be managed to relieve operating cost through taking advantage of time-of-use electricity pricing. However, little attention has been paid to the scheduling of treatment processes in the context of WWTPs. In this paper, a novel mixed-integer linear programming model is established for scheduling the batch operation of a WWTP under time-of-use electricity pricing, which considers constraints arising from task allocation, processing sequence, and processing duration. The modeling method is developed from the event-based continuous-time approach. The start time and end time of each treatment task are optimized to shift electricity consumption from peak hours to off-peak hours to the greatest extent, thus minimizing electricity cost. A case study demonstrates that the proposed model can quickly generate precise operational plans for the investigated WWTP. By implementing the optimum schedules, the WWTP can save on its electricity bill without changing the treatment capacity or the treatment process. The widening of peak and off-peak electricity pricing gap is favorable for the proposed model to display a more significant effect in reducing electricity cost.

Lessons learnt from different inoculation strategies for pilot-scale start-up of partial nitritation for landfill leachate treatment

Conventional biological processes are not enough to achieve desired removal efficiencies from N-rich waste streams such as landfill leachate. In this aspect, start-up phase of a sequencing batch reactor was monitored that treated landfill leachate through a nitritation (LPN) process. The reactor was inoculated from two different sources with distinctive microbial compositions. The acclimatized sludge, taken from a leachate intermittent aeration reactor, failed to establish nitritation but instead developed a nitrification process initially (N-NO3 > 500 mg/l and N-NO2 almost null) and showed no biological activity afterwards. The latter non-acclimatized sludge taken from a conventional activated sludge (CAS) reactor achieved N-NH4 removal up to 96%. Although the nitrite oxidizing genus Nitrospira was abundant in the CAS, it was not further detected in the LPN system. Moreover, the enrichment of ammonia oxidizing genus Nitrosomonas in the LPN was consistent with the establishment of an efficient nitritation process.

Oxygen dynamics, organic matter degradation and main gas emissions during pig manure composting: Effect of intermittent aeration

To investigate the effect of intermittent aeration on oxygen dynamics, organic matter degradation and main gas emissions, a lab-scale pig manure composting experiment was conducted with intermittent aeration (I_A, 30-min on and 30-min off) and continuous aeration (C_A). Although aeration volume and oxygen supply of I_A was only half of C_A, I_A could obviously enhance the oxygen utilization efficiency by 96.67 % and reduce energy dissipation for aeration by 50.87 %. Based on the comprehensive analysis of total organic matter, total carbon, total nitrogen, cellulose, hemicellulose and lignin contents, there was no significant difference in organic matter degradation between I_A and C_A (p > 0.05). Moreover, a reduction of 21.71 %, 38.93 %, 44.40 % and 62.19 % of CH4, N2O and the total GHG emission equivalent as well as NH3 emissions was realized, respectively, in I_A compared with C_A. Therefore, adopting intermittent aeration was a useful strategy and choice for high-efficiency, high-quality and environment-friendly composting.

Exploring GHG emissions in the mainstream SCEPPHAR configuration during wastewater resource recovery

The wastewater sector paradigm is shifting from wastewater treatment to resource recovery. In addition, concerns regarding sustainability during the operation have increased. In this sense, many water utilities have become aware of the potential GHG emissions during the operation of wastewater treatment. This study assesses the nitrous oxide and methane emissions during the long-term operation of a novel wastewater resource recovery facility (WRRF) configuration: the mainstream SCEPPHAR. The long-term N2O and CH4 emission factors calculated were in the low range of the literature, 1 % and 0.1 %, respectively, even with high nitrite accumulation in the case of N2O. The dynamics and possible sources of production of these emissions are discussed. Finally, different aeration strategies were implemented to study the impact on the N2O emissions in the nitrifying reactor. Results showed that operating the pilot-plant under different dissolved oxygen concentrations (between 1 and 3 g O2 m−3) did not have an effect on the N2O emission factor. Intermittent aeration was the aeration strategy that most mitigated the N2O emissions in the nitrifying reactor, obtaining a reduction of 40 % compared to the normal operation of the pilot plant.

Efficient management of the nitritation-anammox microbiome through intermittent aeration: absence of the NOB guild and expansion and diversity of the NOx reducing guild suggests a highly reticulated nitrogen cycle

Obtaining efficient autotrophic ammonia removal (aka partial nitritation-anammox, or PNA) requires a balanced microbiome with abundant aerobic and anaerobic ammonia oxidizing bacteria and scarce nitrite oxidizing bacteria. Here, we analyzed the microbiome of an efficient PNA process that was obtained by sequential feeding and periodic aeration. The genomes of the dominant community members were inferred from metagenomes obtained over a 6 month period. Three Brocadia spp. genomes and three Nitrosomonas spp. genomes dominated the autotrophic community; no NOB genomes were retrieved. Two of the Brocadia spp. genomes lacked the genomic potential for nitrite reduction. A diverse set of heterotrophic genomes was retrieved, each with genomic potential for only a fraction of the denitrification pathway. A mutual dependency in amino acid and vitamin synthesis was noted between autotrophic and heterotrophic community members. Our analysis suggests a highly-reticulated nitrogen cycle in the examined PNA microbiome with nitric oxide exchange between the heterotrophs and the anammox guild.

Enhancing nitrogen removal from domestic sewage with low C/N ratio using a biological aerated filter system with internal reflux-coupled intermittent aeration

Biological aerated filter (BAF) systems with internal reflux-coupled intermittent aeration enhance the removal of nitrogen pollutants from low-C/N ratio domestic sewage. Two experimental systems with the same specifications, a BAF system with internal reflux-coupled intermittent aeration (system A) and a traditional BAF system (system B) was constructed to explore the efficiency of nitrogen removal. Overall, the nitrification in system B was higher than that in system A due to the influence of aeration model. Conversely, the system A can use the alternating anoxic (DO<0.5 mg·L−1) and aerobic (DO around 1 mg·L−1) environment to obtain better Total Nitrogen (TN) removal rate of 21.56 mg·(kg·h)−1 in the bottom of 30–70 cm zone of the reactor by combining reflux nitrate with influent COD. This section had a low specific oxygen uptake rate but high triphenyl tetrazolium chloride-dehydrogenase activity, indicating that the system enhanced nitrogen removal by denitrification in this section. The 16 S rDNA high-throughput sequencing analysis showed that the diversity index of system A was higher than that of system B. The abundance of microorganisms involved in denitrification was higher in the 30–50 cm zone of system A, mainly in the phylum (10.63%) and the phylum Bacillus (32.05%), indicating that system A was used for denitrification through nitrate reflux and intermittent aeration.

Development of Single AI-MAS Process for Continuous Removal of Phosphorus, Nitrogen and Organic Compounds from Wastewater

The developed Anaerobic/Intermittent aerobic-Magnetic Activated Sludge (AI-MAS) process was found suitable for the continuous removal of phosphorus, nitrogen and organic compounds simultaneously from wastewater. This AI-MAS process reactor consisted of a small anaerobic compartment (first stage) placed at the corner of the intermittent aeration tank (second stage) with a magnetic separator in the middle. Better sludge separation was observed at 1-6 rpm of the magnetic drum. Using AI-MAS process, continuous removal of about 90% T-P, 96% T-N and 94% soluble CODCr were achieved with the loading rate of 3.5 mg/l T-P, 16 mg/l T-N and 250 mg/l CODCr, for the period of 160 d at the rate of 6 hrs hydraulic retention time (HRT). Simultaneous removal of phosphorus and nitrogen from the wastewater was possible due to coexistence of both phosphorus and nitrogen removal bacteria within the same sludge biomass. Phosphorus removal was performed through phosphate accumulation in aerobic condition and released again in anaerobic condition with the concomitant uptake of organic substances. Nitrification and denitrification occurred simultaneously in non-aeration/aeration (NA/A) cycle of the intermittent aeration. Plant Tissue Cult. &amp; Biotech. 32(1): 21-29, 2022 (June)

Shifts of microbial community structure along substrate concentration gradients in immobilized biomass for nitrogen removal

Immobilized biomass technology has been regarded as an effective strategy to enhance simultaneous nitrification and denitrification (SND) in existing aerobic biological wastewater treatment processes. Nevertheless, the mechanisms of SND in an aerobic immobilized biomass need to be proven. In this study, waste sludge from municipal wastewater treatment plants was immobilized by cellulose triacetate as bioplates, and an immobilized bioplate reactor (IBPR) was successfully established for nitrogen removal tests. The SND efficiency of the IBPR was increased 18% under the intermittent aeration (IA) mode compared with that under the continuous aeration (CA) mode. During IA operation, the IBPR achieved 96% COD removal and 76% NH4+-N removal, with 71% SND. The results of microbial community analysis by high-throughput sequencing showed that nitrogen-related functional bacteria were more abundant in the bioplates than in the attached biofilms. The colocalization of nitrifiers and denitrifiers in the bioplates was observed, and the microbial community of nitrogen-related functional bacteria clearly shifted with the substrate concentration gradients.