Aeration Pattern Research Articles

Prioritize effluent quality, operational costs or global warming? – Using predictive control of wastewater aeration for flexible management of objectives in WRRFs

This study presents a general model predictive control (MPC) algorithm for optimizing wastewater aeration in Water Resource Recovery Facilities (WRRF) under different management objectives. The flexibility of the MPC is demonstrated by controlling a WRRF under four management objectives, aiming at minimizing: (A) effluent concentrations, (B) electricity consumption, (C) total operations costs (sum electricity costs and discharge effluent tax) or (D) global warming potential (direct and indirect nitrous oxide emissions, and indirect from electricity production) . The MPC is tested with data from the alternating WRRF in Nørre Snede (Denmark) and from the Danish electricity grid. Results showed how the four control objectives resulted in important differences in aeration patterns and in the concentration dynamics over a day. Controls B and C showed similarities when looking at total costs, while similarities in global warming potential for controls A and D suggest that improving effluent quality also reduced greenhouse gasses emissions. The MPC flexibility in handling different objectives is shown by using a combined objective function, optimizing both cost and greenhouse emissions. This shows the trade-off between the two objectives, enabling the calculation of marginal costs and thus allowing WRRF operators to carefully evaluate prioritization of management objectives. The long-term MPC performance is evaluated over 51 days covering seasonal and inter-weekly variations. On a daily basis, control A was 9–30% cheaper on average compared to controls A, D and to the current rule-based control. Similarly, control D resulted on average in 35–43% lower greenhouse gasses daily emission compared to the other controls. Difference between control performance increased for days with greater inter-diurnal variations in electricity price or greenhouse emissions from electricity production, i.e. when MPC has greater possibilities for exploiting input variations. The flexibility of the proposed MPC can easily accommodate for additional control objectives, allowing WRRF operators to quickly adapt the plant operation to new management objectives and to face new performance requirements.

Imaging the Respiratory Transition at Birth: Unraveling the Complexities of the First Breaths of Life.

Rationale: The transition to air breathing at birth is a seminal respiratory event common to all humans, but the intrathoracic processes remain poorly understood. Objectives: The objectives of this prospective, observational study were to describe the spatiotemporal gas flow, aeration, and ventilation patterns within the lung in term neonates undergoing successful respiratory transition. Methods: Electrical impedance tomography was used to image intrathoracic volume patterns for every breath until 6 minutes from birth in neonates born by elective cesearean section and not needing resuscitation. Breaths were classified by video data, and measures of lung aeration, tidal flow conditions, and intrathoracic volume distribution calculated for each inflation. Measurements and Main Results: A total of 1,401 breaths from 17 neonates metall eligibility and data analysis criteria. Stable FRC was obtained by median (interquartile range) 43 (21-77) breaths. Breathing patterns changed from predominantly crying (80.9% first min) to tidal breathing (65.3% sixth min). From birth, tidal ventilation was not uniform within the lung, favoring the right and nondependent regions; P < 0.001 versus left and dependent regions (mixed-effects model). Initial crying created a unique volumetric pattern with delayed midexpiratory gas flow associated with intrathoracic volume redistribution (pendelluft flow) within the lung. This preserved FRC, especially within the dorsal and right regions. Conclusions: The commencement of air breathing at birth generates unique flow and volume states associated with marked spatiotemporal ventilation inhomogeneity not seen elsewhere in respiratory physiology. At birth, neonates innately brake expiratory flow to defend FRC gains and redistribute gas to less aerated regions.

Air variability in maxillary sinus during radiotherapy for sinonasal carcinoma

IntroductionThe aim was to characterise patterns and predictability of aeration changes in the ipsilateral maxillary sinus during intensity-modulated radiotherapy (IMRT) for sinonasal cancer (SNC), and in a sample evaluate the dosimetric effects of aeration changes for both photon and proton therapy. Materials and methodsThe study included patients treated withIMRT for SNC in a single institution in 2009–2017. The volume of air in the ipsilateral maxillary sinus was recorded in1578 daily cone beam computer tomography (CBCT) from 53 patients.Patterns of changing air volumes were categorised as ‘stable’,increasing’, ‘decreasing’, or ‘erratic’. For the prediction analysis, categorisation was performed based both on the entire treatment course and the first five fractions (F1–5).Photon and proton therapy plans were generated for four patients, the one from each category with the largest aeration variation. Synthetic CT images were generated for each CBCT and all plans were recalculated on the daily synthetic CTs. ResultsThe absolute volume of air varied considerably during the treatment course, ranging from 0 to 25.9 cm3. Changes within a single participant varied in the range of 0–18.7 cm3. In the categorisation of patterns, most patients hadincreasingaeration of the sinus. Generally, patterns of aeration could not be predicted from F1–5. Patients categorised asincreasingin F1–5 had the best prediction, with 78% predicted correctly as increasing for the entire treatment course. The numeric correlation coefficients for target coverage and air volumewere low for 3/4scenarios(photons 0.03–0.23, protons 0.26–0.48). No straightforward correlation between the dosimetric effect and the volume changes could be detected in the sample test of four patients for neither photon nor proton therapy. ConclusionThe variation of aeration was large and unpredictable. No clear dosimetric consequences of the aerationvariation were evident for neither IMRT nor proton therapyfor the patients investigated.

Effect of aeration intensity and aeration pattern on a compact biofilm reactor for rural domestic sewage treatment in China: pollutant removal performance and hydrodynamic behavior

Effect of aeration intensity and aeration pattern on a compact biofilm reactor for rural domestic sewage treatment in China: pollutant removal performance and hydrodynamic behavior

Composting of Night Soil and Horse Manure with Leaves as Organic Substrate

This study aims to investigate the characteristics of night soil/horse manure with leaf co-composting using aerobic static composting method. Two influencing factors, including composting materials and aeration pattern, were investigated by determining the change in the principal physicochemical properties, i.e. temperature, volatile solid, carbon, nitrogen, hydrogen, carbon-to-nitrogen ratio, heavy metals, ammonia nitrogen, nitrate nitrogen, and germination index (GI). The mixture of horse manure and leaf can achieve high composting temperature, long retention time of high temperature (55 °C), fast organic matter degradation, and high GI under the same aeration pattern. Under the same composting materials, the intermittent aeration pattern during composting was superior to the continuous aeration pattern because the former promoted the composting process.

Comparison of Linear and Sector Array Probe for Handheld Lung Ultrasound in Invasively Ventilated ICU Patients

International guidelines do not recommend a specific probe for assessment of lung aeration using lung ultrasound (LUS). The aim of this study was to assess the concordance between linear and sector array probes of a handheld ultrasound device in assessment of lung aeration in invasively ventilated intensive care unit patients. This study included intensive care unit patients who were expected to be ventilated for longer than 24 h. A 12-region LUS exam was performed with a linear and a sector array probe. In each image, the LUS aeration score and number of B-lines were determined. Adding the LUS aeration scores of all regions resulted in a global LUS aeration score. Agreement between the two probes was calculated using intra-class correlation coefficients (ICCs). A total of 30 LUS exams were performed in 19 patients, resulting in a total of 328 pairs of images. Twenty-nine pairs of images were excluded from analysis because the images from the linear probe could not be scored. ICCs calculated for the remaining images revealed good concordance the LUS aeration scores for individual images (ICC = 0.73, 95% confidence interval 0.67–0.78), number of B-lines (ICC = 0.79, 95% confidence interval 0.72–0.83) and global LUS aeration score (ICC = 0.74, 95% confidence interval 0.52–0.87). In conclusion, there is good concordance between linear and sector array probes of a handheld ultrasound device in assessment of lung aeration patterns in mechanically ventilated intensive care unit patients. However, in roughly 10% of the images acquired using the linear probe, the aeration pattern could not be scored.

Intermittent cycle extended aeration system pilot scale (ICEAS-PS) for wastewater treatment: experimental results and process simulation

Intermittent cycle extended aeration system is a modification of a conventional sequencing batch reactor system in which the system is operated under continuous feed. The objective of this research is to study the effect of sludge retention time and aeration pattern on the performance of intermittent cycle extended aeration system pilot scale for wastewater treatment. In addition, the process simulation using GPS-X software was conducted. Five different runs of sludge retention times of 10, 15, 20, 25 and 30 days were studied. The optimum sludge retention time for wastewater treatment by intermittent cycle extended aeration system pilot scale was 10 days, and under operating condition of sludge retention time of 10 days, effluent quality was 15.5 ± 3.8, 6.5 ± 1.1, 5.3 ± 1.6, 0.7 ± 0.2, 5.0 ± 1.4 mg/L and 1.4 ± 0.7 mg/L for COD, BOD5, TSS, NH4–N, TN and TP which amply met the local regulation of class A treated wastewater. GPS-X sensitivity analysis tool box was used to determine the most sensitive kinetic parameters affecting the intermittent cycle extended aeration system pilot scale performance. Out of about 50 kinetic parameters, YH, bH, μA, Ko, bA, Ka and μPAO appeared to the most sensitive kinetic parameters. The calibrated GPS-X model proved that the presence of anoxic phase in the cycle has a significant impact on nitrogen and phosphorus removal. In addition, intermittent aeration pattern achieved the highest performance compared with other patterns of aeration only, aeration/anoxic and anoxic/aeration.

Preliminary Research on Synergetic Removal of Phosphorus and Nitrogen by Aeration and Adsorption

Zhao, L.; Gong, D.; Li, L.; Lin, L.; Du, Q.; Qiao, Q.; Guo, W.; Tang, X., and Li, Q., 2019. Preliminary research on synergetic removal of phosphorus and nitrogen by aeration and adsorption. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 291–297. Coconut Creek (Florida), ISSN 0749-0208.Eutrophication of lakes, estuaries and coastal waters is one of the global environmental issues and removal of phosphorus and nitrogen from the water is the most direct way for eutrophication control for those water bodies. The synergistic removal effects of phosphorus and nitrogen by aeration and adsorption in water under different aeration intensities and aeration patterns were investigated in the present research. The results indicated that aeration and adsorption simultaneously used had a synergistic effect on the removal of phosphate in water, over 90% of orthophosphate was removed jointly, which was significantly greater than the summational removal rate (<50%) of aeration and adsorption alone. However, such synergistic effect did not reflect in the removal of ammonia nitrogen. Similar ammonia nitrogen removal efficiency was exhibited in intermittent aeration and continuous aeration group under different aeration patterns. Therefore, intermittent aeration can be utilized for the energy consumption reduction of the further experiment. The combination of aeration and adsorption has definite advantages in the phosphate removal in water. However, further in-depth research is needed in the synergistic removal of ammonia nitrogen by adsorption and aeration. The results of present research can provide some technical references for eutrophication control in lakes, estuaries and coastal waters.

A comprehensive hydrodynamic analysis of a full-scale oxidation ditch using Population Balance Modelling in CFD simulation

This work exhibits the importance of the experimental validation when full-scale computational fluid dynamics (CFD) models are developed to provide a detailed analysis of the spatial variations in 3D of the fluid flow inside aerated tanks. Single-phase and two-phase CFD models were performed to study the fluid behaviour carefully by means of the velocity profiles and the aeration pattern in a full-scale oxidation ditch. Air hold-up, bubble size distribution and interfacial area density were calculated by polydisperse models where Population Balance Model (PBM) was governed by break-up and coalescence; the free-surface approach allowed the CFD model to describe the three-dimensional effect of bubbly plumes in large scales in detail. Tracer tests were carried out to obtain the flow pattern and the hydraulic distribution of the flow into two wastewater treatment lanes in order to define the boundary conditions for the model correctly. Despite the difficulty of performing velocity measurements of the fluid in 3D, with and without air bubbles, these provided essential information to validate the CFD model. From this analysis, several simulations were performed to improve the hydrodynamics and the operation of the process by relocating the propellers.

Modeling the relationship of aeration, oxygen transfer and treatment performance in aerated horizontal flow treatment wetlands

Mechanical aeration is commonly used to improve the overall treatment efficacy of constructed wetlands. However, the quantitative relationships of air flow rate (AFR), water temperature, field oxygen transfer and treatment performance have not been analyzed in detail until today. In this study, a reactive transport model based on dual–permeability flow and biokinetic formulations of the Constructed Wetland Model No. 1 (CWM1) was developed and extented to 1) simulate oxygen transfer and treatment performance for organic carbon and nitrogen of two pilot–scale horizontal flow (HF) aerated wetlands (Test and Control) treating domestic sewage, and, 2) to investigate the dependence of oxygen transfer and treatment performance on AFR and water temperature. Both pilot–scale wetlands exhibited preferential flow patters and high treatment performance for chemical oxygen demand (COD) and NH4–N at AFRs of 128–700 L m−2 h−1. A reduction of the AFR in the Test system from 128 to 72 L h−1 m−2 substantially inhibited NH4–N removal. Conservative tracer transport as well as reactive transport of dissolved oxygen (DO), soluble and total chemical oxygen demand (CODs, CODt), NH4–N and NOx–N measured in pilot–scale experiments were simulated with acceptable accuracy (E1¯=0.39±0.26). An equation to estimate the volumetric oxygen transfer coefficient was found to be: kLa,20=0.511ln(AFR). Simulated treatment performance depended on kLa,20 in a non–linear manner. A local sensitivity analysis of the calibrated parameters revealed porosity, hydraulic permeability and dispersion length of the fast flow field as well as kLa,20 as most important. An optimal AFR for a spatially and temporally continuous aeration pattern for treatment wetlands treating similar influent was estimated to 150–200 L h−1 m−2. This study provides insights into aeration mechanisms of aerated treatment wetlands and highlights the benefits of process modeling for in–depth system analysis.

Effect of aeration pattern and gas distribution during scale-up of bubble column reactor for aerobic granulation

This study investigates the influence of aeration pattern and gas bubble distribution on aerobic granulation in pilot bubble columns and advances the understanding on crucial factors to be considered during scale-up. Experiments were conducted in a pilot scale bubble column of 22-L capacity. A laboratory-scale bubble column of 5-L capacity, which could achieve granulation in a short time, was used as the control reactor. The pilot reactor was operated with optimal operational conditions evaluated for the control reactor, but the granulation was initially inhibited; improper aeration pattern was found as the most significant factor in precluding granulation. Aerobic granulation in the pilot-scale reactor was achieved upon modifying the gas distributor design. The effect of gas distributor characteristics (i.e., pore size, free area φ, and relative surface area of the gas distributor to the cross-section of the column R) on the aeration pattern has been thoroughly discussed. A scale-up ratio (S) for the gas distributor has been proposed. Reliability of aeration intensity in terms of superficial air velocity usg, which has been commonly used as an indicator of prevailing hydrodynamics and shear stress in lab-scale granular bubble columns, has been discussed; it was demonstrated that usg could not realistically represent the aforementioned conditions in a larger module. Instead, it was suggested that a greater attention should be paid to bubble size and bubble ascending velocity and thus to the subsequent aeration pattern. Gas holdup has been eventually introduced as a crucial and easy-to-measure controlling parameter for the scale-up of granularreactors.

Dynamic air supply models add realism to the evaluation of control strategies in water resource recovery facilities.

This paper introduces the application of a fully dynamic air distribution model integrated with a biokinetic process model and a detailed process control model. By using a fully dynamic air distribution model, it is possible to understand the relationships between aeration equipment, control algorithms, process performance, and energy consumption, thus leading to a significantly more realistic prediction of water resource recovery facility (WRRF) performance. Consequently, this leads to an improved design of aeration control strategies and equipment. A model-based audit has been performed for the Girona WRRF with the goal of providing a more objective evaluation of energy reduction strategies. Currently, the Girona plant uses dissolved oxygen control and has been manually optimised for energy consumption. Results from a detailed integrated model show that the implementation of an ammonia-based aeration controller, a redistribution of the diffusers, and the installation of a smaller blower lead to energy savings between 12 and 21%, depending on wastewater temperature. The model supported the development of control strategies that counter the effects of current equipment limitations, such as tapered diffuser distribution, or over-sized blowers. The latter causes an intermittent aeration pattern with blowers switching on and off, increasing wear of the equipment.

Effects of the aeration pattern, aeration rate, and turning frequency on municipal solid waste biodrying performance

Interactive influences of the aeration pattern, aeration rate, and turning frequency on municipal solid waste biodrying performance were investigated. Energy and water mass balances were used to identify the main water-removal routes and determine the amount of energy used and efficiency. Changing the aeration pattern and turning frequency did not significantly affect biodrying performance when the other conditions and total aeration volume were constant. The total aeration volume controlled the pile temperature and evaporation, making it the main factor affecting water loss during biodrying. A continuous aeration rate of 0.5 L kg−1 dry matter·min−1 gave the best biodrying performance (the highest water-removal rate, biodrying index, and sorting efficiency, 0.5 kg kg−1, 4.12, and 86.87%, respectively, and the highest lower heat value (LHV) and heat utilization rate, 9440 kJ kg−1 and 68.3%, respectively). There was an optimum aeration rate, water loss reaching a maximum at an aeration rate of 0.5 L kg−1 DM·min−1 and not increasing further as the aeration rate increased further. Lower aeration rates gave higher volatile solid degradation rates. The effects of turning could be achieved by increasing the aeration rate. The recommended biodrying parameters are continuous aeration at an aeration rate of 0.5 L kg−1 dry matter min−1 and one turn every 3 d.

Model extension, calibration and validation of partial nitritation–anammox process in moving bed biofilm reactor (MBBR) for reject and mainstream wastewater

ABSTRACTIn the paper, the extension of mathematical model of partial nitritation–anammox process in a moving bed biofilm reactor (MBBR) is presented. The model was calibrated with a set of kinetic, stoichiometric and biofilm parameters, whose values were taken from the literature and batch tests. The model was validated with data obtained from: laboratory batch experiments, pilot-scale MBBR for a reject water deammonification operated at Himmerfjärden wastewater treatment and pilot-scale MBBR for mainstream wastewater deammonification at Hammarby Sjöstadsverk research facility, Sweden. Simulations were conducted in AQUASIM software. The proposed, extended model proved to be useful for simulating of partial nitritation/anammox process in biofilm reactor both for reject water and mainstream wastewater at variable substrate concentrations (influent total ammonium–nitrogen concentration of 530 ± 68; 45 ± 2.6 and 38 ± 3 gN/m3 – for reject water – and two cases of mainstream wastewater treatment, respectively), temperature (24 ± 2.8; 15 ± 1.1 and 18 ± 0.5°C), pH (7.8 ± 0.2; 7.3 ± 0.1 and 7.4 ± 0.1) and aeration patterns (continuous aeration and intermittent aeration with variable dissolved oxygen concentrations and length of aerated and anoxic phases). The model can be utilized for optimizing and testing different operational strategies of deammonification process in biofilm systems.

Performance of Denitrifying Phosphate Removal via Nitrite from Slaughterhouse Wastewater Treatment at Low Temperature

This study aims to investigate the effects of the organic loading rate (OLR) and the aeration rate on denitrifying phosphate removal (DPR) from slaughterhouse wastewater treated at a temperature of 11 °C. Three laboratory-scale intermittently aerated sequencing batch reactors (IASBRs) were set up and three OLRs and five aeration rates were employed in the study. The results indicated that efficient removals of nitrogen (N) and phosphorus (P) from DPR were achieved. Furthermore, the intermittent aeration pattern benefitted both the phosphorus-accumulating organisms (PAOs) and the denitrifying phosphorus-accumulating organisms (DPAOs) that accumulated at 11 °C. The ratio of P uptake in the aeration periods/P release in the non-aeration periods was in the range of 0.94–1.10 in the three stages. The relationship between the specific poly-β-hydroxybutyrate (PHB) degradation rate (z), the specific P removal rate (x), and the specific total oxidized nitrogen(TON) reduction rate (y) can be fitted approximately as a plane ( z = 1.3626 x + 0.2882 y − 0.6722 , R2 = 0.83).

Smart operation of nitritation/denitritation virtually abolishes nitrous oxide emission during treatment of co-digested pig slurry centrate

The implementation of nitritation/denitritation (Nit/DNit) as alternative to nitrification/denitrification (N/DN) is driven by operational cost savings, e.g. 1.0–1.8 EUR/ton slurry treated. However, as for any biological nitrogen removal process, Nit/DNit can emit the potent greenhouse gas nitrous oxide (N2O). Challenges remain in understanding formation mechanisms and in mitigating the emissions, particularly at a low ratio of organic carbon consumption to nitrogen removal (CODrem/Nrem). In this study, the centrate (centrifuge supernatant) from anaerobic co-digestion of pig slurry was treated in a sequencing batch reactor. The process removed approximately 100% of ammonium a satisfactory nitrogen loading rate (0.4 g N/L/d), with minimum nitrite and nitrate in the effluent. Substantial N2O emission (around 17% of the ammonium nitrogen loading) was observed at the baseline operational condition (dissolved oxygen, DO, levels averaged at 0.85 mg O2/L; CODrem/Nrem of 2.8) with ∼68% of the total emission contributed by nitritation. Emissions increased with higher nitrite accumulation and lower organic carbon to nitrogen ratio. Yet, higher DO levels (∼2.2 mg O2/L) lowered the aerobic N2O emission and weakened the dependency on nitrite concentration, suggesting a shift in N2O production pathway. The most effective N2O mitigation strategy combined intermittent patterns of aeration, anoxic feeding and anoxic carbon dosage, decreasing emission by over 99% (down to ∼0.12% of the ammonium nitrogen loading). Without anaerobic digestion, mitigated Nit/DNit decreases the operational carbon footprint with about 80% compared to N/DN. With anaerobic digestion included, about 4 times more carbon is sequestered. In conclusion, the low CODrem/Nrem feature of Nit/DNit no longer offsets its environmental sustainability provided the process is smartly operated.

Increasing economic and environmental benefits of media-based aquaponics through optimizing aeration pattern

Aquaponics is the cultivation form that integrates aquaculture with hydroponics to nurture plants and fish simultaneously. And aeration plays an important role in its sustainable operation, as well as economic and environmental feasibility. In this study, two patterns to reduce aeration intensity, i.e., semi-aeration (SA) and intermittent aeration (IA) were used to improve the economic and environmental benefits of media-based aquaponics. Results showed that SA aquaponics, in which the energy efficiencies on culturing fish and crop were improved respectively by 78.20% and 77.61% compared with Control, had the potential to obtain higher economic benefits. Although both SA and IA could save half of the aeration cost by reducing aeration flux and time respectively, the product yields in SA weren’t impaired seriously while in IA aquaponics they were. And the nitrogen utilization efficiency (NUE) of SA aquaponics was 11.3% higher than that of IA aquaponics, mainly attributed to the more stable dissolved oxygen concentration in SA. Better water quality was obtained in IA aquaponics, however, it was achieved at the cost of higher N loss (mainly in the form of N2), which subsequently reduced the potential for further improvement of NUE. Both SA and IA could considerably reduce GHG emissions from aquaponics, due to lower energy requirement. IA aquaponics showed the lowest N2O emission, but the primary source (over 97%) of greenhouse gases (GHG) emissions from aquaponics was off-site indirect CO2 emission. Taking productivity and environmental impact into consideration, semi-aeration was believed to be a better choice when reducing aeration.

Control of nitrification/denitrification in an onsite two-chamber intermittently aerated membrane bioreactor with alkalinity and carbon addition: Model and experiment

Denitrifying membrane bioreactors (MBRs) are being found useful in water reuse treatment systems, including net-zero water (nearly closed-loop), non-reverse osmosis-based, direct potable reuse (DPR) systems. In such systems nitrogen may need to be controlled in the MBR to meet the nitrate drinking water standard in the finished water. To achieve efficient nitrification and denitrification, the addition of alkalinity and external carbon may be required, and control of the carbon feed rate is then important. In this work, an onsite, two-chamber aerobic nitrifying/denitrifying MBR, representing one unit process of a net-zero water, non-reverse osmosis-based DPR system, was modeled as a basis for control of the MBR internal recycling rate, aeration rate, and external carbon feed rate. Specifically, a modification of the activated sludge model ASM2dSMP was modified further to represent the rate of recycling between separate aerobic and anoxic chambers, rates of carbon and alkalinity feed, and variable aeration schedule, and was demonstrated versus field data. The optimal aeration pattern for the modeled reactor configuration and influent matrix was found to be 30 min of aeration in a 2 h cycle (104 m3 air/d per 1 m3/d average influent), to ultimately meet the nitrate drinking water standard. Optimal recycling ratios (inter-chamber flow to average daily flow) were found to be 1.5 and 3 during rest and mixing periods, respectively. The model can be used to optimize aeration pattern and recycling ratio in such MBRs, with slight modifications to reflect reactor configuration, influent matrix, and target nitrogen species concentrations, though some recalibration may be required.

Seasonal effects of pre-aeration on microbial processes for nitrogen removal in constructed wetlands.

Seasonal effects of pre-aeration on microbial nitrogen performance in constructed wetlands (CWs) involved with anaerobic ammonium oxidation (anammox) process were investigated in this study. Slow natural re-aeration rate was the inhibiting factor for total nitrogen removal in CW without pre-aeration, and partial nitrification was the main way for nitrite generation. Besides partial nitrification, pre-aeration provided nitrite generation in CWs with an alternative way: nitrate reduction. Advantage of pre-aeration of influent was much different under various temperature ranges. Mean temperature of 15°C seemed to be the turning point. With a mean temperature of or higher than 15°C, nitrate in the influent effectively improved nitrogen removal in CWs. With a mean temperature lower than 15°C, the nitrate reduction process in CWs was greatly inhibited. The benefit of pre-aeration was weak under this temperature range. Seasonal aeration pattern for the pre-treatment of HSSF CWs might be a more energy-saving alternative in in-suit domestic sewage treatment.

Numerical simulations of impact of membrane module design variables on aeration patterns in membrane bioreactors

Computational Fluid Dynamics (CFD) models incorporating sludge rheology model and porous media sub-models were used to simulate the impact of eight design variables, including fibre orientation, filtration tank geometry and aeration design, on the hydrodynamics and aeration patterns in a pilot scale membrane bioreactor (MBR) fitted with commercially available membrane modules. Comparison of simulated with experimental grid averaged flow velocities measured using Particle Image Velocimetry (PIV) in an aerated bench scale MBR differed by approximately 6%. The assessment of different turbulence models revealed that it was difficult to accurately simulate local variations in turbulence induced by air bubbles due to limitations of Reynolds averaging Navier Stokes (RANS) models. Simulation results revealed that MBR's fitted with hollow fibres in a vertical orientation in the filtration zone experienced 25% more membrane surface shear than horizontally oriented fibres at the same aeration intensity. The inclusion of baffles around the membrane modules promoted turbulence and increased shear in the upper section of the membrane module by approximately 30%. This is important for control of fouling along sections of the hollow fibre membrane that experience the highest transmembrane pressure and are more susceptible to fouling. Rotating the nozzle aperture to face the bottom of the tank increased the homogeneity of shear stress on the lower half of the module and increased shear on the upper half of the membrane surface. This effect was amplified by locating the air diffusers 100mm below the bottom of the module and aligning the aeration pipe in parallel with the direction of the fibre bundle. This research demonstrates the capability of using Computational Fluid Dynamics to optimise the design of the filtration zone comprising the membrane module, aeration system and MBR tank dimensions.