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The study assesses the optimal aeration efficiency of a stepwise cascade aeration system through experimental trials in a lab scale model setup, aimed at determining the geometric and flow characteristics of the cascade system. Subsequently, the collected datasets are employed to evaluate the efficacy of four advanced machine learning algorithms, namely K-nearest neighbour (KNN), gradient boosting regressor (GBR), decision tree regressor (DTR), and random forest regressor (RFR), in predicting the aeration efficiency at 20 °C (E20) of the cascade aeration system. The predictive machine learning tools are compared based on different performance indices and various graphical interpretations including comparative plot, heat plot, plot of relative error, violin diagram, and Taylor diagram. For assessing the accuracy of the best-fitted predictive model, i.e. GBR, a field-scale surface-water–based water treatment plant with a multi-stage filtration unit, which was set up in an arsenic-affected rural area of West Bengal, India, was used to validate the results, and findings were used to optimize the field-scale plant. It is observed that E20 is dependent on dimensionless discharge (dc/h), squares of the number of the steps (N2), and inclination (h/l) as per dimension analysis. The analysis reveals that with an increase in inclination, E20 for a specific number of cascade steps drops to a certain point and then increases. The highest aeration efficiency (E20) of 0.913 is observed at a hydraulic loading rate of 0.167 l/m2/s, N = 10 and h/l = 0.64. Furthermore, the results demonstrate that the GBR model (with R2 test value of 0.96 and MAE test value of 0.027) emerges as the most accurate regression tool, surpassing the other models in predicting E20 values. Additionally, the findings indicated that at the flow rates of 0.075, 0.1, 0.125, and 0.15 m3/m2/h with the inclination of 0.363 and N = 10, the dissolved oxygen in water increases by more than 5 mg/l, with corresponding aeration efficiencies (E20) of 0.757, 0.675, and 0.602, respectively. Machine learning models offer the potential to optimize the design of aeration structures for accurate prediction and facilitating cost efficiency. [ABSTRACT FROM AUTHOR]

This paper explores the ability of multivariate adaptive regression splines, decision trees, Gaussian processes, and multiple non-linear regression equation approaches to predict the aeration efficiency at various weirs and discusses their results. In total, 126 experimental observations were collected in the laboratory, of which 88 were arbitrarily selected for model training, and the rest were used for model validation. Various graphical presentations and goodness-of-fit parameters were used to assess the performance of the models. Performance evaluation results, Whisker plot, and Taylor's diagram indicated that the GP_rbf-based model was superior to other implemented models in predicting the aeration efficiency of weirs with CC (0.9961 and 0.9973), MAE (0.0079 and 0.0195), RMSE (0.0122 and 0.0251), scattering index (0.0594 and 0.1238), and Nash Sutcliffe model efficiency (0.9923 and 0.9564) values in the training and validating stages, respectively. The predicted values by GP_rbf lie within the ±30% error line in the training and validating stages, with most of it lying at/close to the line of agreement. The random forest model had better predictability than other decision tree models implied. The sensitivity analysis of parameters suggests shape factor and drop height as major influencing factors in predicting the aeration efficiency. HIGHLIGHTS Experimental study to evaluate aeration efficiency at various shapes of sharp-crested weir models.; Application of machine learning techniques to predict aeration efficiency of sharp-crested weirs.; Introduction of shape factor for different shapes of weirs as an input to ML models.; Use of graphs and goodness-of-fit parameters to assess the performance of applied ML models.; Sensitivity analysis.;

The biological treatment process (BTP) is responsible for removing chemical oxygen demand (COD) and ammonia using microorganisms present in wastewater. The BTP consumes large quantities of energy due to the transfer of oxygen using air pumps/blowers. Energy consumption in the BTP is due to low solubility of oxygen, which results in low aeration efficiency (AE). The aim of the study was to develop an AE model that can be used to monitor the performance of the BTP. Multilayer perceptron artificial neural network (MLP ANN) algorithm was used to model AE in the BTP. The performance of the AE model was evaluated using R2, mean square error (MSE), and root mean square error (RMSE). Sensitivity analysis was performed on the AE model to determine variables that drive AE. The results of the study showed that MLP ANN algorithm was able to model AE. R2, MSE, and RMSE results were 0.939, 0.0025, and 0.05, respectively, during testing phase. Sensitivity analysis results showed that temperature (34.6%), COD (21%), airflow rate (19.1%), and OTR/KLa (15.7%) drive AE. At high temperatures, the viscosity of wastewater is low which enables oxygen to penetrate the wastewater, resulting in high AE. The AE model can be used to predict the performance of the BTP, which will assist in minimizing energy consumption. HIGHLIGHTS Aeration efficiency increases with an increase in temperature.; Aeration efficiency decreases with an increase in airflow rate.; Temperature and airflow rate are the biggest driver of energy consumption.; Temperature, COD, and airflow rate control aeration efficiency in the biological treatment process.; High temperatures and airflow rates improve volumetric mass transfer coefficient.;

Aeration is the process of increasing the dissolved oxygen (DO) content of water, which is an important water quality parameter for the survival of aquatic life. In this process, large amounts of air bubbles develop; as a result, contact surface area increases, and hence the water-air-mass transfer accelerates. There are numerous methods for increasing DO concentration in water, including self-aeration, mechanical aeration, chemical aeration, and hydraulic structures. The hydraulic structures are an economical and efficient way of enhancing stream/river water aeration. Even though the water only comes into contact with the structure for a short while, it increases the amount of DO in a river system. In this study, an experimental investigation has been carried out to determine the aeration performance of different types of piano key weir (PKW). To this end, three different types (type-A, type-B, and type-C) of PKW laboratory-scaled models were tested. The results demonstrated that the type-A PKW created maximum oxygen transfer efficiency of the three PKW types. In addition, the results show that the aeration efficiency of all PKW models increases with drop height but decreases with increasing discharge over the weirs. HIGHLIGHTS This study is based on a comparative analysis of aeration performances of different types of piano key weir, which has not yet been published elsewhere.; Studying and comparing the aeration capacity of the different types of piano key weirs.; Studying the effects of drop height on aeration performance of piano key weirs.;

The dissolved oxygen (DO) level in water is vital for water quality and supporting aquatic life. Hydraulic jumps involve rapid flow changes from super-critical to sub-critical, visible at abrupt bed slope shifts, like at spillway bases in rivers or canals. The hydraulic jump efficiently mixes oxygen from air into water and offers a cost-effective method of aeration by entraining air bubbles in the stream to improve oxygen transfer compared to traditional systems. The objective of this experimental research is to investigate the aeration performance with hydraulic jump parameters and establish correlations crucial to measuring aeration (or transfer) efficiency. Relationships between transfer efficiency, jump height, jump length, sequent depth ratio, discharge, inlet Froude number, and channel bed slope were determined. To investigate the nature of such relationships, a series of experiments were conducted in a rectangular tilt flume to test the aeration performance of forced submerged hydraulic jumps with five different discharges and five different smooth bed slopes. The inlet Froude number before the jump varied from 2.18 to 8.23. Experimental observation confirms a positive relationship between transfer efficiency and jump control parameters. During experimentation, transfer efficiency was found to vary between 9.4 % and 34 %. This research includes estimating the optimal transfer efficiency due to hydraulic jumps, which can help hydraulic engineers in building structures that can revitalize any degraded stream. • Analyze aeration efficiency (E) in hydraulic jump (HJ) with smooth bed slope and discharge. • Identify governing parameters using dimensional analysis to correlate E and HJ. • Achieved maximum of 89% velocity drop and 90.23% energy dissipation at 35 lps and 6° slope for optimal E improvement. • E increased from 9.4 to 34 % with increasing discharge (15–35 lps) and bed slope (0–6°). • Results can help to build structures to maintain healthy oxygen levels in water. [ABSTRACT FROM AUTHOR]

The scope of the paper is to analyse the different similarities of air entrainment among the hydraulic jumps, plunging jets, and plunging breaking waves and to discuss current practices. The measured data are reexamined and scrutinised to investigate the gas exchange phenomena through an air-water interface. In particular, oxygen transfer efficiency and penetration depth by air bubbles are discussed. The calculated results highlight that the oxygen transfer efficiency is decreased with the increase of energy dissipation rate both in plunging jets and breaking waves. In contrast, it is shifted almost parallel in the case of hydraulic jumps. In addition, the aeration lengths in the hydraulic jumps and penetration depths both in plunging jets and plunging breaking waves were dependent on the jet impact velocity. HIGHLIGHTS Air bubble entrainments through hydraulic jumps, plunging jets, and plunging breaking waves are studied.; Aeration lengths in the hydraulic jump and penetration depths in the plunging jets and plunging breaking waves were determined.; Dissolved oxygen, as well as oxygen transfer efficiency, were measured and compared among the phenomena.; Scale effects were observed among the phenomena in terms of the oxygenation.;

The improvement of wastewater treatment plants is an environmental and economic priority. The highest energy consumption in wastewater treatment plants relates to aeration units with the current technologies. Microorganisms can use air micro-nanobubbles (AMNBs) for biological activity due to AMNB’s high oxygen transfer rate, high stability in the aeration reactor, and increased contact surface. This study investigated the effect of aeration with AMNB on hydraulic retention time (HRT), energy consumption, chemical oxygen demand (COD), and nitrogen removal efficiency in the biological treatment of raw municipal wastewater without pretreatment for an extended time during cold and hot seasons. Suspended growth treatment and attached growth mode were studied by installing an active bio-curtain (ABC) as an improvement solution. In the presence of AMNB and ABC, effective micro-organisms significantly increased ten times as conventional activated sludges (CAS). Micro-nanobubble aeration helped the oxygen transfer and accelerated the aerobic layer formation, which took advantage of partial nitrification and denitrification for total nitrogen removal and resulted in total nitrogen removal by 99%. In comparison, 78% and 97% of COD removal in suspended and attached growth modes were achieved in the warm seasons at the optimum HRT of 9 h. In the cold seasons, with a decrease of about 5%, the COD removal yields 73% and 90% in the identical HRT (9 h), respectively. The aeration energy consumption in this study to eliminate the definite ratio of organic loads shows a reduction of about 40% compared to CAS. Excess sludge reduction has also been achieved by up to 70%. In conclusion, this research shows the potential and possibility of practical exploitation of the AMNB aeration and ABC to treat municipal wastewater. [ABSTRACT FROM AUTHOR]

The spray of water over a basin using a perforated disk accelerates oxygen transfer. The laboratory model, employed in the current work, consists of a vertical riser that discharges water by free fall into a basin. Four fall heights of water of 2.4, 1.8, 1.2, and 0.6 m were investigated to evaluate the performance of this system. This system was also tested at flow rates of 46.8, 93.7, 140.6, and 187.5 mL/s. This study showed that the oxygen mass transfer coefficient was directly proportional to both the fall height and flow rate of water. The maximum standard aeration efficiency (SAE) value was recorded at the maximum fall height of 2.4 m and flow rate of 187.5 mL/s, at which a maximum KLa20 = 1.82 h–1 was recorded. The multilinear regression-based model developed in this study successfully predicted mass transfer coefficient (KLa20) and standard aeration efficiency (SAE values that agree well with actual measurements under given conditions, with a scattering within ±5%. The optimum flow rate and fall height that achieve the minimum operating cost were obtained at certain KLa20 values. The cost of aeration of 1 m3 of water was calculated, ranging from 0.0076 to 0.008 USD/m3. [ABSTRACT FROM AUTHOR]

In this study, the potential of soft computing techniques, namely Random Forest (RF), M5P, Multivariate Adaptive Regression Splines (MARS), and Group Method of Data Handling (GMDH), was evaluated to predict the aeration efficiency (AE20) of Parshall and Modified Venturi flumes. Experiments were conducted for 26 various Modified Venturi flumes and one Parshall flume. A total of 99 observations were obtained from experiments. The results of soft computing models were compared with regression-based models i.e., with multiple linear regression (MLR) and multiple nonlinear regression (MNLR). Results of the analysis revealed that the MARS model outperformed other soft computing and regression-based models for predicting AE20 of Parshall and Modified Venturi flumes with Pearson's correlation coefficient (CC) = 0.9997, and 0.9992, and root mean square error (RMSE) = 0.0015, and 0.0045 during calibration and validation periods, respectively. Sensitivity analysis was also carried out by using the best executing MARS model to assess the effect of individual input variables on AE20 of both flumes. Obtained results on sensitivity examination indicate that the oxygen deficit ratio (r) was the most effective input variable in predicting the AE20 of Parshall and Modified Venturi flumes. HIGHLIGHTS Aeration efficiency of Parshall and Modified Venturi flumes was predicted by using soft computing techniques.; M5P, RF, MARS, and GMDH models were first employed to predict the aeration efficiency.; Outcomes of soft computing models were first compared against regression-based models.; Effectiveness of applied models was evaluated using performance evaluation indicators.; The MARS-based model outperformed other models.;

This work presents an experimental evaluation of a Venturi and Venturi-Vortex microbubble aeration system, taking as input variables the water-air flow ratio, water renewal time and area-volume ratio of the water tank. The aeration process response variables are defined in terms of oxygen transfer and aeration efficiency through the standard volumetric mass transfer coefficient (KLa20), standard oxygen transfer rate (SOTR), and standard aeration efficiency (SAE). Two methods of air injection were analyzed: 1. Air injection in the throat chamber of the Venturi generator; 2. air supplying in the suction side of the hydraulic pump of the aeration system. Experimental results indicate that the water renewal time variable (RT) is a statistically significant factor with respect to the KLa20, which can be maximized by decreasing RT. The effects of the variable flow ratio (FR) are greater than the effects of renewal time and area-volume ratio (AVR) concerning SOTR and SAE, indicating a maximum response with a minimum flow ratio, using the Venturi-Vortex microbubble generator. When the flow ratio decreases, the air flow increases, generating and transferring a greater amount of microbubbles (MB) into the water. It was found that increasing the air flow produced an increase in the standard oxygen transfer rate SOTR and standard aeration efficiency SAE. Results allow concluding that the injection of the air flow from the suction side of the pump promotes the generation of microbubbles (MB) for a maximum air flow allowed by the system. SOTR and SAE could be maximized whit the flow ratio factor and the Venturi-Vortex generator, supplying air flow from the suction side of the hydraulic pump.

For maintaining healthy streams and rivers, a high concentration of oxygen is desired and hydraulic structures act as natural aerators where oxygen transfer occurs by creating turbulence in the water. Aeration studies of conventional weirs are carried out widely in the past but at the same time, labyrinth weirs, where the weir crest is cranked thereby enhancing their crest length, have got a little notice. The test records were obtained through 180 laboratory observations on nine physical models to estimate aeration efficiency (E20) at labyrinth weirs (LWs). The E20 increases with the number of key as well as drop height and it is found to be highest for rectangular shape in comparison of the triangular and trapezoidal LWs, however, E20 decreases with the increase of discharge. Further, this work unravels the novel idea and potential of the M5P model tree (M5P), support vector regression machine (SVM), and Random Forest (RF) methods for estimation of aeration efficiency (E20) at LWs. The results depicted that the RF model performs best in determining the E20 at LWs. The results of sensitivity analysis further illustrated that drop height is the parameter that affects the prediction of E20 at the LWs most.

This study compares several advanced machine learning models to obtain the most accurate method for predicting the aeration efficiency (E20) through the Parshall flume. The required dataset is obtained from the laboratory tests using different flumes fabricated in National Institute Technology Kurukshetra, India. Besides, the potential of K Nearest Neighbor (KNN), Random Forest Regression (RFR), and Decision Tree Regression (DTR) models are evaluated to predict the aeration efficiency. In this way, several input combinations (e.g. M1-M15) are provided using the laboratory parameters (e.g. W/L, S/L, Fr, and Re). Different predictive models are obtained based on those input combinations and machine learning models proposed in the present study. The predictive models are assessed based on several performance metrics and visual indicators. Results show that the KNN-M11 model ( $ RMS{E_{testing}} = 0.002, R_{testing}^2 = 0.929 $ ), which includes W/L, S/L, and Fr as predictive variables outperforms the other predictive models. Furthermore, an enhancement is observed in KNN model estimation accuracy compared to the previously developed empirical models. In general, the predictive model dominated in the present study provides adequate performance in predicting the aeration efficiency in the Parshall flume.

This work is an experimental study on the oxygen transfer capability and efficiency in a pilot‐scale decelerated oxidation ditch equipped with fine bubble diffusers and impellers (inducing horizontal liquid flows). Aqueous solutions of carboxymethyl cellulose (CMC) exhibiting shear‐thinning rheological properties are selected to simulate activated sludge in the oxidation ditch process. The effect of air flow rate and horizontal liquid velocity along the loop channel on oxygen transfer capability and aeration efficiency is examined in tap water and CMC aqueous solutions. The standard volumetric mass transfer coefficient KLa20, standard oxygen transfer efficiency (SOTE), and standard aeration efficiency (SAE) are introduced to study the oxygen mass transfer performance and energy consumption efficiency in the oxidation ditch. The results show that KLa20, SOTE, and SAE in CMC aqueous solutions follow similar trends observed in tap water. Due to the effect of shear‐thinning rheological properties, KLa20, SOTE, and SAE in CMC aqueous solutions are smaller than those in tap water. Two dimensionless numbers, Froude number and Ohnesorge number are introduced to study the oxygen transfer efficiency through the consideration of the combined influence of aeration, crossflow, gas bubble size, and physical properties of the liquid phase. [ABSTRACT FROM AUTHOR]

A newly developed bio‐reactor design for municipal sewage treatment was evaluated on a pilot scale (150 m3/d). The reactor system included both anaerobic/anoxic and aerobic treatment stages with external/internal airlift circulation loops integrated with a central sedimentation chamber. The design was conceived to enhance the removal of organic compounds and nutrients (phosphorus and nitrogen) within a smaller footprint than existing treatment processes. The downcomer of the internal circulation loop is integrated with the sedimentation tank facilitating high efficiency solid‐liquid separation in a compact configuration. The external/internal airlift circulation stages increase the potential for bio‐reactivity, while reducing energy consumption for process flows. Overall, the integrated configuration reduces the footprint required compared to conventional systems with equivalent hydraulic loads, ie, hydraulic retention time of ~12.8 hours with a hydraulic loading area of 10.3 m3/d/m2. The trial run data indicated removal efficiencies for COD, phosphorous, ammonia, and total nitrogen of 94.5%, 94.5%, 96.8%, and 78.6% respectively. Moreover, the treatment system also demonstrated a robust capacity to handle a wide range of COD influent concentrations (ie, ~ 120‐860 mg/L). [ABSTRACT FROM AUTHOR]

We studied new micro-perforated diffuser concepts for the aeration process in wastewater treatment plants and evaluated their aeration efficiency. These are micro-perforated plate diffusers with orifice diameters of 30 µm, 50 µm and 70 µm and a micro-perforated tube diffuser with an orifice diameter of 50 µm. The oxygen transfer of the diffuser concepts is tested in clean water, and it is compared with commercial aerators from the literature. The micro-perforated tube diffuser and micro-perforated plate diffusers outperform the commercial membrane diffusers by up to 44% and 20%, respectively, with regard to the oxygen transfer efficiency. The most relevant reason for the improved oxygen transfer is the fine bubble aeration with bubble sizes as small as 1.8 mm. Furthermore, the more homogenous cross-sectional bubble distribution of the micro-perforated tube diffuser has a beneficial effect on the gas mass transfer due to less bubble coalescence. However, the pressure drop of micro-perforated diffusers seems to be the limiting factor for their standard aeration efficiencies due to the size and the number of orifices. Nevertheless, this study shows the potential for better aeration efficiency through the studied conceptual micro-perforated diffusers.

This paper presents a comparative experimental study of different configurations of mechanical surface aerators used in wastewater treatment plants. A laboratory scale tank equipped with different configurations for aeration process was installed to compare the standard aeration efficiency and power consumption of curved blade impellers with 3, 6, 9, and 12 blades. Different parameters thought to have significant effects on standard aeration efficiency (SAE) and power consumption, such as submergence depth and rotating speed were studied. Results show that an optimum configuration (9 blades) has the highest aeration efficiency (2.60 Kg. O 2 /KW.hr) at 500 rpm. Also, a submersion depth ratio of 0.35 was optimum, giving the highest standard aeration efficiency, as increasing submergence depth ratio above this value causes drop in standard aeration efficiency as a result of inevitable increase in input power consumption in this case. [ABSTRACT FROM AUTHOR]

The efficiency of active aeration (AE) of constructed wetlands expressed as the ratio between implied oxygen consumption and oxygen delivered to the system is comprehensively reviewed in this paper. The aeration efficiency appears to be rather low with a mean value of 1.73% and median value of 0.48% of oxygen used in the systems for situations with only partial aerobic degradation of the pollutants. For full aerobic degradation, the mean value of AE is 3.74% but median value is much lower 1.08%. For both cases, the standard deviation is higher than the mean value (4.95% and 10.87% respectively), so there is a lot of variability in the data. For systems with the Forced Bed Aeration the results are more uniform and are close to the literature values given for this system, which is an implication that the proposed methodology might be potentially used for rough estimate of the aeration efficiency. [ABSTRACT FROM AUTHOR]

Abstract Stepped weir is a commonly used hydraulic structure in water treatment plants to enhance the air-water transfer of oxygen or nitrogen and volatile organic components. The flow regimes on stepped weir are classified into nappe, transition and skimming flow. This study presents the novel application of artificial intelligence methods to evaluate the aeration efficiency over stepped weir for the three flow regimes. Two methods were adopted in this study, namely, the evolutionary polynomial regression (EPR) and the M5 model tree (M5 MT). A total of 151 laboratory experimental data sets were collected from the literature to train and test the artificial intelligence models. The Mallow's coefficient C P was used to determine the effective variables affecting aeration efficiency. It was found that weir steps number, slope, the flow Reynolds number, and the ratio of the critical flow depth to the step height are the most important variables providing the lowest C p. Both the EPR and M5 MT methods provided satisfactory predictions for the aeration efficiency. The two methods have high values of correlation coefficient R > 0.93 and low values for the root mean square error RMSE< 0.052 and relative mean absolute error RMAE< 0.065. However, the EPR method has an advantage over the M5 MT method that it provides one equation for each regime, while the M5 MT method provides a number of equations for each regime. This will make the equations of the EPR method more attractive to the practitioners compared to the equations of the M5 MT method. It was found that the equations obtained from artificial intelligence methods in this study perform better than the currently existing equations in the litrature obtained from regressive methods. Highlights • A new empirical equation for the prediction of the aeration efficiency of stepped weir is developed. • Experimental data covering a broad range of hydraulic conditions are collected. • Sensitivity of the developed models for various predictors is quantified. [ABSTRACT FROM AUTHOR]

This study investigated the impact of five different carrier media on oxygen transfer efficiency and flow mixing in a 2 m 3 moving attached growth system pilot-plant. The five media studied varied in shape (cylindrical and spherical), size, voidage and protected surface area (112–610 m 2 /m 3 ). In clean water tests, the media enhanced the overall oxygen transfer efficiency by 23–45% and hydraulic efficiency (HE) by 41–53%, compared with operation with no media. When using spherical media (Media 1, 2 and 3), the presence of biofilm increased the HE to 89, 93 and 100%, respectively. Conversely, Media 4 and 5 with biofilm contributed to a reduction in HE to 74 and 63%, respectively. The media protected surface area, the parameter traditionally selected to design biofilm processes, did not correlate with HE or with oxygen transfer efficiency in clean water tests. This study provides clear evidence that other media physical properties play a role in the mixing and oxygen transfer in moving attached growth systems. A correlation (R 2 ) of 0.89 and 0.90 was obtained between the media dimensionality times voidage (Di × Voi) and HE, with and without biofilm development, respectively. The combination of parameters (Di × Voi/HE) also correlated well with oxygen transfer efficiency in clean water (R 2 of 0.92 without biofilm and R 2 of 0.88 with biofilm). Dimensionality and voidage should be utilised to design and optimise media size and shape, to enhance mixing and oxygen transfer, ultimately contributing to energy savings and higher removal efficiencies. [ABSTRACT FROM AUTHOR]

The performance of a pilot-scale superoxygenation system was evaluated in clean water and mixed liquor. A mass balance was applied over the pilot-scale system to determine the overall oxygen mass transfer rate coefficient (K L a, h −1 ), the standard oxygen transfer rate (SOTR, kg O 2 d −1 ), and the standard oxygen transfer efficiency (SOTE, %). Additionally, the alpha factor (α) was determined at a mixed liquor suspend solids (MLSS) concentration of approximately 5 g L −1 . SOTEs of nearly 100% were obtained in clean water and mixed liquor. The results showed that at higher oxygen flowrates, higher transfer rates could be achieved; this however, at expenses of the transfer efficiency. As expected, lower transfer efficiencies were observed in mixed liquor compared to clean water. Alpha factors varied between 0.6 and 1.0. However, values of approximately 1.0 can be obtained in all cases by fine tuning the oxygen flowrate delivered to the system. [ABSTRACT FROM AUTHOR]

The present study investigates the accuracy of five different data-driven techniques in estimating oxygen transfer efficiency in baffled chutes: feedforward neural network (FFNN), radial basis neural network (RBNN), generalized regression neural network (GRNN), adaptive neuro fuzzy inference system with subtractive clustering (ANFIS-SC), and adaptive neuro fuzzy inference system with fuzzy c-means clustering (ANFIS-FCM). Baffled apron chutes or drops are used on channel structures to dissipate the energy in the flow. A baffled chute design is effective both in energy dissipation and in aerating the flow and reducing nitrogen supersaturation. There is a close relationship between energy dissipation and oxygen transfer efficiency. This study aims to determine the aeration efficiency of baffled chutes with stepped (S), wedge (W), trapezoidal (T), and T-shaped (T-S) baffle blocks. The performances of the FFNN, RBNN, GRNN, ANFIS-SC, and ANFISFCM models are compared with those of multilinear and nonlinear regression models. Based on the comparisons, it was observed that all data-driven models could be successfully employed in modeling the aeration efficiency of S, W, and T-S baffle blocks from the available experimental data. Among data-driven models, the FFNN model was found to be the best. [ABSTRACT FROM AUTHOR]

Household food waste (FW) management has become an emerging environmental issue affecting sustainable urban development. The application of in-sink domestic food waste disposers (FWDs) have brought significant public attentions due to its simplified waste handling process and reduced household expenses. However, the potentail negative impacts of mixing FW in the sewer system, i.e., the reduction of aeration efficiency in wastewater treatment processes (WWTPs) and corresponding increase of greenhouse gas (GHG) emission, has not been quantified. In this study, real-time oxygen transfer efficiency in processing water was measured in WWTPs receiving negligible amount of FW and compared with those receiving sewage combined with FWD effluent. WWTP receiving sewage with FW had 6–10% lower oxygen transfer rate than those without FW, resulting in extra energy consumptions of 0.25–0.30 kWh/m3 and GHG emissions of 0.35–0.41 kg CO 2 /m3. For estimating the substantial impacts of FWD to the carbon cycle, sludge treatment scenarios were designed among anaerobic digestion (AD), incineration, and direct landfill disposal. Compared with AD (−0.07 kWh/kg) and incineration (0.112 kWh/kg), FWD/WWTP consumed more energy (0.69–0.9 kWh/kg) and most of which (∼64%) was required by aeration. The operating costs of WWTPs also increased by 1.6–2.1 times in comparison with those did not receive FW. The application of FWD, however, could reduce the overall GHG emissions by 35.2% in comparison with direct landfilling. Decision-makers should guide householders and waste management practitioners through new policies such as carbon credits and/or waste charging scheme to support more environmental-friendly disposal methods of FW, especally when the maturity of socio-economic conditions are of concerns. Compared with AD and incineration, FWD may be a compromising alternative to control GHG emissions with existing wastewater treatment facilities especially to those regions where complete FW classification and treatment are not well-established. [Display omitted] • Carbon emission in wastewater treatment plants with food waste disposer was studied. • Dynamic changes of oxygen transfer efficiency were monitored. • Additional energy consumption from aeration was quantified by off-gas tests. • Diffusor fouling cost in non-food sewage was calculated for the first-time. • Energy/carbon balance for region-based food waste diversions was reported. [ABSTRACT FROM AUTHOR]

This paper contemplates the review of aeration efficiency with commonly used different aeration systems such as Venturi flumes, Weirs, Conduits, Stepped channels, In Venturi Aeration, the SAE value grows fast with the number of air holes. In Weir Aeration, it was found that among all the different labyrinth weir structure, triangular notch weirs are known for the optimum results for air entrainment. The ANN model was developed with parameters discharge (Q) and tail water depth (T w ) which showed that Q is more influential parameter than T w . In conduits structure, it was found that circular high head gated conduits have better aeration performance than other conduits. Aeration efficiency in Stepped channels cascades may range from 30% to 70%. The sensitivity analysis with ANN model showed that discharge (Q) followed by number of steps (N) was the most influential parameter in E 20 . Bubble size was the important parameter to undertake when using bubble diffuser. The oxygen transfer efficiency (OTE) in jet diffusers was predicted developing an ANN model. It was found in sensitivity analysis that the input of 'velocity' is highly sensitive to OTE. According to literature, jets can provide OTE in the range of 1.91- 21.53kgO 2 /kW-hr., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 Published by Elsevier B.V.)

The primary purpose of a weir is to measure discharge. Moreover, it can be used as a tool to increase aeration efficiency in rivers, fish hatcheries, and water treatment plants. A free overfall jet from a weir plunging into downstream water causes entrainment of the air bubbles if the free overfall jet velocity exceeds a certain critical value and hence aeration occurs. In recent years, different soft computing systems have been successfully employed for the solution of complex problems. The aim of this study is to develop models to estimate air entrainment and aeration efficiencies of weirs using soft computing systems. For this aim, genetic expression programming, a recently developed artificial intelligence technique, is used. Genetic Expression Programming (GEP) is a genetic algorithm as it uses populations of individuals, selects them according to fitness, and introduces genetic variation using one or more genetic operators. GEP is preferred since it generates a mathematical function which fits to given experimental data. The results indicate that there are good agreements between the measured values and the values obtained by the genetic expression programming models. These good agreements confirm the validity of the developed genetic expression programming models. [ABSTRACT FROM AUTHOR]

Stepped chutes that are commonly used for gabion weirs, river training, irrigation channels, and storm waterways have become popular in recent years mainly due to the intrinsic low-cost and the speed of construction. Stepped chutes are used also for in-stream re-aeration and in water treatment plants to enhance the air-water transfer of atmospheric gases and of volatile organic components. In a stepped chute, the provision of steps can produce significant energy dissipation. This paper seeks the effect of energy dissipation over stepped chutes on aeration efficiency. It is observed from the results that aeration efficiency increases with increasing energyloss ratio. There is higher energy dissipation in nappe flows than skimming flow situations and nappe flow regime lead to greater aeration efficiency than skimming flow regime. Moreover, regression equations are obtained relating aeration efficiency to stepped chute slope and energy-loss ratio. For this aim, genetic expression programming, a recently developed artificial intelligence technique, is used. The model equations obtained have high correlation coefficients and low minimum square error values. [ABSTRACT FROM AUTHOR]

The oxygen transfer at a hydraulic structure happens by self-aeration through the spillway and by flow aeration in the hydraulic jump downstream of the hydraulic structure. Spillways with their water-air controlling mechanisms are important not only for their structural properties but also for their effects on stream ecology. Spillway types also affect the efficiency of aeration. Decisions on the types of spillway should be made by taking the environmental conditions and flow rates into consideration. This paper compares the aeration efficiency of stepped and smooth spillways. Empirical correlations predicting length of the non-aerated flow region and aeration efficiency are developed. Smooth and stepped spillways cause increased dissolved oxygen (DO) concentrations at the downstream part of the channel. DO concentration changes are shown to depend on the flow types, discharge rates, tailwater depth and travelling times. [ABSTRACT FROM AUTHOR]

Aeration is a mass transfer process between the atmosphere and water. Aeration is used for water quality enhancement in sewage treatment plants and in polluted rivers and lakes. This can be enhanced by creating turbulence in the water. Plunging overfall jets from weirs are a particular instance of producing such turbulence. In this paper, two intelligent models are realized to predict the air entrainment rate and aeration efficiency of weirs. Least square support vector machine (LS-SVM) is used as intelligent tool. Threefold cross validation test method is used to evaluate the performance of LS-SVM models. The correlation between predicted and measured values is found 0.99 for air entrainment rate and 0.98 for aeration efficiency. The test results indicate that the LS-SVM can be used successfully in predicting the air entrainment rate and aeration efficiency of weirs. Moreover, the performances of the LS-SVM models are compared with multi nonlinear and linear regression models. [Copyright &y& Elsevier]

It is important to predict aeration efficiency in stepped cascades because they are used in most water treatment applications for re-oxygenation. The flow conditions on stepped cascades have been classified into nappe, transition and skimming flows. Due to the different mechanisms of air entrainment in the nappe, transition and skimming flow conditions, the aeration efficiencies of the three flow conditions differ significantly from each other. In this paper, two intelligent models were created to predict flow condition and aeration efficiency in stepped cascades using critical flow depth, step height and channel slope information. Least square support vector machine (LS-SVM) was used as intelligent tool. The performances of LS-SVM models were evaluated by 3-fold cross validation test method. The correlation between observed and predicted flow condition is 0.99 and the correlation between measured and predicted aeration efficiency is 0.89. The test results indicated that the LS-SVM can be used successfully in predicting flow condition and aeration efficiency in stepped cascades. [Copyright &y& Elsevier]

Abstract: A free overfall jet from a weir plunging into downstream water causes entrainment of the air bubbles if the free overfall jet velocity exceeds a certain critical value and hence aeration occurs. This study investigates the free overfall jets from triangular sharp-crested weirs and effect on their air entrainment rate and the aeration efficiency. An expert system based on adaptive network based fuzzy inference system (ANFIS) was obtained for predicting air entrainment rate and aeration efficiency of weirs. The performance of ANFIS model was compared with multi nonlinear and linear regression models. There were good agreements between the measured values and the values obtained using the ANFIS model. [Copyright &y& Elsevier]

In a stepped-channel chute, the chute face is provided with a series of steps, from near the crest to the toe. Like many other high-speed flow configurations in hydraulic engineering, stepped-channel chute flows are characterized by the large amount of self-entrained air. Air entrainment on stepped-channel chutes is also recognized for its contribution to the oxygen transfer. The flow conditions in stepped-channel chutes have been classified into nappe flows, transition flows, and skimming flows. In this study, the aeration efficiency of stepped-channel chutes was investigated, and in particular, the effect of varying flow regimes. The results indicated that the nappe flow regime led to the larger aeration efficiency than the other flow regimes. Moreover, the mass transfer equations were developed to predict the aeration efficiency of the stepped-channel chutes in terms of dissolved oxygen. There is good agreement between the measured aeration efficiency values and the values computed from the predictive equations. [ABSTRACT FROM AUTHOR]

Abstract: Hydrodynamics and gas–liquid mass transfer in a rectangular airlift loop reactor with an internal baffle has been studied in this work. Measurements were carried out for two- and three-phase systems using air–water and air–water–polystyrene particles. The effects of the superficial gas velocity and solid loading up to 15% (v/v) were examined and correlations describing the hydrodynamics and gas–liquid mass transfer behaviours were proposed. The experimental results of mass transfer were compared with those of the literature. It was found in all cases that the gas hold-up in the riser and downcomer and volumetric mass transfer coefficient increased with increasing the superficial gas velocity, while the liquid velocity in the downcomer increased with U gr until 0.033ms−1 and then decreased to reach a plateau value for U gr >0.04ms−1. It was also found that the liquid velocity and the volumetric mass transfer coefficient decreased only with the initial addition of solid for U gr higher than 0.02ms−1 and that the gas hold-up in the downcomer was significantly influenced by the presence of solid for a concentration above 10% (v/v), while the gas hold-up was almost not affected in the riser. The aeration efficiency was also calculated and was found to be in the range 2.54–4.41kg O2/kWh. [Copyright &y& Elsevier]

The aeration systems of two full-scale, activated-sludge basins were compared during a period of three years, under the same operating conditions, using dynamic offgas testing. Only the material of the diffuser was different (membrane versus ceramic-tube diffusers). The investigation has shown that, although the membrane diffusers have higher initial standard-oxygen-transfer efficiency (αSOTE) and standard-aeration efficiency (αSAE), these decreased over time, while the αSAE of the ceramic diffusers started lower, but increased slightly over the whole period. A cost comparison makes clear how important it is to evaluate the aeration system under process conditions. The operating costs were the dominant factor (∼10x higher than capital costs), and operating costs were approximately 20% higher for membrane versus ceramic diffusers. The poor performance of the membrane-tube diffusers under process conditions could be explained on the basis of the actual αAE values in the basin, not the standardized values. [ABSTRACT FROM AUTHOR]

We studied new micro-perforated diffuser concepts for the aeration process in wastewater treatment plants and evaluated their aeration efficiency. These are micro-perforated plate diffusers with orifice diameters of 30 µm, 50 µm and 70 µm and a micro-perforated tube diffuser with an orifice diameter of 50 µm. The oxygen transfer of the diffuser concepts is tested in clean water, and it is compared with commercial aerators from the literature. The micro-perforated tube diffuser and micro-perforated plate diffusers outperform the commercial membrane diffusers by up to 44% and 20%, respectively, with regard to the oxygen transfer efficiency. The most relevant reason for the improved oxygen transfer is the fine bubble aeration with bubble sizes as small as 1.8 mm. Furthermore, the more homogenous cross-sectional bubble distribution of the micro-perforated tube diffuser has a beneficial effect on the gas mass transfer due to less bubble coalescence. However, the pressure drop of micro-perforated diffusers seems to be the limiting factor for their standard aeration efficiencies due to the size and the number of orifices. Nevertheless, this study shows the potential for better aeration efficiency through the studied conceptual micro-perforated diffusers. [ABSTRACT FROM AUTHOR]

Microbubbles with slow rising speed, higher specific area and greater oxygen dissolution are desired to enhance gas/liquid mass transfer rate. Such attributes are very important to tackle challenges on the low efficiency of gas/liquid mass transfer that occurs in aerobic wastewater treatment systems or in the aquaculture industries. Many reports focus on the formation mechanisms of the microbubbles, but with less emphasis on the system optimization and assessment of the aeration efficiency. This work assesses the performance and evaluates the aeration efficiency of a porous venturi-orifice microbubble generator (MBG). The increment of stream velocity along the venturi pathway and orifice ring leads to a pressure drop (Patm > Pabs) and subsequently to increased cavitation. The experiments were run under three conditions: various liquid velocity (QL) of 2.35–2.60 m/s at fixed gas velocity (Qg) of 3 L/min; various Qg of 1–5 L/min at fixed QL of 2.46 m/s; and free flowing air at variable QLs. Results show that increasing liquid velocities from 2.35 to 2.60 m/s imposes higher vacuum pressure of 0.84 to 2.27 kPa. They correspond to free-flowing air at rates of 3.2–5.6 L/min. When the system was tested at constant air velocity of 3 L/min and under variable liquid velocities, the oxygen dissolution rate peaks at liquid velocity of 2.46 m/s, which also provides the highest volumetric mass transfer coefficient (KLa) of 0.041 min−1 and the highest aeration efficiency of 0.287 kgO2/kWh. Under free-flowing air, the impact of QL is significant at a range of 2.35 to 2.46 m/s until reaching a plateau KLa value of 0.0416 min−1. The pattern of the KLa trend is mirrored by the aeration efficiency that reached the maximum value of 0.424 kgO2/kWh. The findings on the aeration efficiency reveals that the venturi-orifice MBG can be further optimized by focusing on the trade-off between air bubble size and the air volumetric velocity to balance between the amount of available oxygen to be transferred and the rate of the oxygen transfer. [ABSTRACT FROM AUTHOR]

Barbotage reactors such as airlift reactors (ALR) and bubble column reactors (BCR), due to their two-phase flow systems, were investigated in many research papers. In their basic design variants, they are typically used to lift, mix, and aerate liquids, while, when equipped with additional elements in hybrid variants, their individual properties, i.e., lifting, mixing, and aeration of liquids, can significantly change with the same reactor geometry. The object of this study was to develop a hybrid barbotage reactor in various structural design variants. The structure consisted of a barbotage column of 50 mm in diameter, used to transport a water–air mixture outside the reactor (so-called external loop). The installation was additionally equipped with a nozzle in order to improve mixture aeration and circulation efficiency. The nozzle was mounted at various heights of the column pump segment. Additionally, the reactor was equipped with s moving bed in two variants (20% and 40% reactor capacity) in order to determine its effect on the mixture aeration and circulation conditions. Based on the measurement results, aeration curves were prepared for various structural design and column packing variants of the reactor. Properties of the two-phase mixture were determined for both parts—ALR and BCR. Technological and energy parameters of the aeration process were calculated, and the results obtained for the individual structural design variants were compared. It was found that, for the most advantageous design, in terms of aeration efficiency, the aeration nozzle should be placed in the mid-length of the pump segment of the barbotage column, irrespective of the hybrid reactor packing rate with the moving bed. The reactor packing with the moving bed resulted in a decreased mean water velocity in the reactor. For most analyzed structural design variants, the respective packing with the moving bed had no significant effect on aeration efficiency. Only for one structural design variant did the lack of packing significantly improve oxygen levels by as much as approximately 41%. [ABSTRACT FROM AUTHOR]

The aim of the present study was to compare the oxygen transfer efficiency in a conventional activated sludge and a membrane bioreactor system. The oxygen transfer was evaluated by means of the oxygen transfer coefficient and α-factor calculation, under different total suspended solids concentration, extracellular polymeric substances, sludge apparent viscosity and size of the flocs. The oxygen transfer coefficient and α-factor showed an exponential decreasing trend with total suspended solid, with a stronger oxygen transfer coefficient dependence in the conventional activated sludge compared to the membrane bioreactor. It was noted that the oxygen transfer coefficient in the conventional activated sludge become comparable to that in membrane bioreactor when the total suspended solid concentration in the conventional activated sludge was higher than 5 g L−1. Operating under high carbon to nitrogen ratio, the oxygen transfer coefficient increased in both conventional activated sludge and membrane bioreactor because of sludge deflocculation and it was noticed a weaker dependence of the oxygen transfer coefficient with total suspended solid. The results indicated that the most important parameters on the oxygen transfer efficiency were in order: the total suspended solid concentration, flocs size, sludge apparent viscosity and extracellular polymeric substances content. Based on the influence of the main biomass features affecting the oxygen transfer coefficient and considering the typical operating conditions in both systems, those of membrane bioreactor appeared to be more favorable to oxygen transfer efficiency. The paper provides a useful insight about some peculiarities of oxygen transfer in a conventional activated sludge and a membrane reactor system, highlighting new and useful information in the light of a more sustainable management of these systems. Image 1 • A comparison between the oxygen transfer in CAS and MBR bench plant was carried out. • (k L a) 20 and α-factor showed exponential trends with TSS for both CAS and MBR. • (k L a) 20 values higher in MBR within a TSS range between 4 gTSS L−1 and 6 gTSS L−1. • Under similar conditions features of sludge in MBR more favorable to oxygen transfer. • TSS, EPS and viscosity should be controlled to optimize aeration efficiency. [ABSTRACT FROM AUTHOR]