Standard Aeration Efficiency Research Articles

Performance Assessment of Confined Tube Aerators in Parallel Configuration

Aeration plays a major role in the activated-sludge wastewater treatment process. Microbes require an oxygen-enriched environment to digest organic materials and remove nutrients from the wastewater stream. For providing this oxygen, artificial aeration is required, which is responsible for the majority of energy use in treatment plants. Typically, this is accomplished with diffused aerators, where pressurized air is forced through a porous medium at the bottom of deep basins, and bubbles float up through the water column transferring oxygen in the process. This is a relatively energy-intensive process, which is prone to fouling at the porous media. In this study, a Confined Tube Aeration (CTA) system is proposed, where a pump forces water through a Venturi injector, where air is naturally drawn in. At the Venturi discharge, the flow is diverted to a coiled tube in which oxygen transfer occurs. This study analyzes the effect of parallelizing the CTA system with multiple injectors and at varying pump speeds (flow rates). Using experimental and analytical means, the maximum standard aeration efficiency was found to be with three injectors in parallel, at maximum pump speed, and utilizing a CTA with diameter 31.75 mm and length 3.048 m. This value was found to be 0.542 kg O2/kWh, and represents a 25% increase over the single-injector case. Although the analyses herein utilize a relatively small (0.746 kW) pump, these results indicate that CTA systems may scale well to larger pump sizes necessary for full-scale municipal wastewater treatment.

Investigation on aeration efficiency and energy efficiency optimization in recirculating aquaculture coupling CFD with Euler-Euler and species transport model

Aeration plays a crucial role in maintaining the overall health and sustainability of the recirculating aquaculture system. Conventional aeration operates continuous and consumes 35.06 % of equipment energy consumption. How to optimize aeration while ensuring normal fish growth remains a great challenge. To address these challenges, this research paper established a coupled model of computational fluid dynamics and species transport model (CFD-STM). Aeration tests were carried out in a 33.3 m3 culture tank using a 0.31 m diameter aerator to find out the impacts of operating variables (aeration flow rate, bubble diameter, inlet velocity, and aerator position) on oxygen transfer using a microporous aeration system. A CFD-STM model was coupled to obtain the optimum values of aeration parameters. Results revealed that the Standard Aeration Efficiency (SAE) reductions by 32.1 % for 50 % larger aeration flow rate and 86.4 % for 50 % larger bubble diameter, as well as SAE achieved 5.67 kg/kWh with an aerator position scale factor equal to 0.48. In addition, the energy consumption of the Roots blower was compared for a single aeration and dissolved oxygen saturation. Results indicated that smaller bubbles microbubbles can effectively improve oxygen transfer coefficient. The energy consumption was reduced by 15.7 % for 50 % larger aeration flow rate and 38.6 % for 50 % lower bubble diameter. Based on the results, this study demonstrated that CFD is a useful tool to optimize the aeration system design and operation in order to enhance aeration efficiency. It provides a theoretical foundation the future optimization of energy conservation through intermittent aeration practices.

Improving the transfer of dissolved oxygen in a biological Fe2+ oxidation process using a venturi jet as an intensive aeration system

The low bio-production of Fe3+ as a leaching agent is one of the main limitations to implementing industrial bio-processes at feasibility conditions. The main limitation of the bio-oxidation process of Fe2+ is the low oxygen transfer to the aqueous phase because of the low oxygen solubility. This study assesses the effectiveness of the venturi jet as an innovative and intensive aeration device for overcoming the oxygen limitation in a continuous ferrous oxidation process in a fixed-bed reactor with immobilized acidithiobacillus ferrooxidans, in contrast to the conventional diffuser aeration device. Firstly, the influence of the airflow and the influence of the medium concentration were determined for the following parameters for both aeration devices; Volumetric mass transfer coefficient (kLa), Standard Oxygen Transfer Rate (SOTR), Standard Aeration Efficiency (SAE), and Standard Oxygen Transfer Efficiency (SOTE). Then, both aeration devices were compared in a continuous bio-oxidation process in an up-flow packed bio-reactor (UFPB). The system performance was assessed by monitoring temperature, pH, oxidation-reduction potential, and dissolved oxygen concentration for 69 days. Findings displayed that when aerating with the diffuser, the ferrous oxidation rate was restricted by the low dissolved oxygen availability, being about 1 ppm (1 mg L−1). Under these oxygen-limiting conditions, the maximum ferrous (Fe2+) oxidation rate was 9.09 g L−1 h−1. However, when aerating with the venturi jet, the dissolved oxygen concentration increased up to 2.70 mg L−1, achieving a maximum of 29.11 g L−1 h−1. So, this study has demonstrated that the change in the aeration device has resulted in an improvement in the process, achieving a 3.5-fold increase in the oxidation rate. Furthermore, the venturi jet offered additional advantages over the diffuser, such as requiring less power to deliver the same amount of air, being unaffected by jarosite precipitates, and not requiring a supply of compressed air.

Improving the performance of microbubble through the modification and optimization of venturi-type generator

Venturi-type generators are recognized as one of the most promising microbubble generators with potential in various fields. However, there is still room for further optimization of their performance to meet the requirements of real applications, such as aeration systems or water treatment applications. This research modified the geometry of a venturi-type generator with specific dimensions: a length of 80 mm, an inside diameter of 26 mm, a throat diameter of 7.2 mm, a convergent nozzle angle of 30°, a divergent diffuser angle of 30°, and an airflow inlet diameter of 6 mm. By varying the water flow rates (i.e., 22 L/min, 26 L/min, and 30 L/min) and air flow rates (i.e., 0.1 L/min, 0.2 L/min, and 0.3 L/min), the study observed the average diameter, size distribution, Standard Oxygen Transfer Rate (SOTR), and Standard Aeration Efficiency (SAE) of the generated microbubbles. This study aims to improve the performance of a microbubble generator, particularly by optimizing the relative size, distribution, and main parameters for real applications. The proposed modification and optimization successfully produced microbubbles with an average diameter of 180-450 μm. Furthermore, the optimal combinations of water and air flow rates (i.e., 30 L/min of water and 0.1 L/min of air) produced approximately 60% of microbubbles with a diameter of no more than 200 μm. These combinations also enable the delivery of a SOTR and SAE values of 0.94 kgO2/h and 1.73 kgO2/kWh, respectively.

Performance Assessment of Venturi-Assisted Confined Tube Aerators with Varying Diameter

A significant amount of energy in wastewater treatment plants is spent on aeration to treat the organic matter with microorganisms in an oxygen-enriched environment. In this study, a novel and simplistic aeration concept known as Confined Tube Aeration (CTA) is proposed, in which the main elements are a Venturi injector and a coiled tube at its outlet. Two Venturi injector diameters were chosen for evaluation in this study, measuring 1 inch (25.4 mm) and 4 inch (101.6 mm). In this study, a relationship was developed between air suction rate and pressure differential across the injector. Then, a numerical model was developed to analyze hydrodynamic conditions and evaluate system performance. The main findings are that the larger diameter aerator performs 20% better than the smaller injector in terms of standard aeration efficiency (SAE), with a maximal value of 0.74 kgO2/kWh found for the larger diameter system. These results suggest that future SAE improvements may be made for larger diameter systems in full-scale wastewater treatment applications with suitably designed injectors.

Investigating the performance of a perforated pooled circular stepped cascade aeration system for intensive aquaculture

Aeration plays a crucial role in aquaculture to maintain adequate dissolved oxygen (DO) levels in water, which is essential for supporting aquatic life. However, traditional aeration systems such as paddlewheel aerators or diffused air aerators often come with high energy consumption, frequent maintenance, and greater operational costs. To address these challenges, this research paper presents the development and evaluation of a more sustainable and cost-effective aerator, named the perforated pooled circular stepped cascade aerator (PPCSC), for intensive aquaculture. Laboratory experiments were conducted in a masonry tank to assess the performance of the PPCSC aerator with different bottom radii (Rb) and discharges (Q). The results showed that the highest standard aeration efficiency (SAE) of 4.564 ± 0.6662 kg O2/kWh was achieved with a bottom radii (Rb) of 0.75 m and a discharge (Q) of 0.016 m3/s. A developed regression model was found to effectively evaluate the standard oxygen transfer rate (SOTR) and SAE for different Rb and Q values used in the PPCSC system. Both Rb and Q were found to significantly impact the SOTR and SAE of the PPCSC aerator. Overall, the PPCSC aerator is a promising option for small-scale tank-based intensive aquaculture due to its high performance and lower operational costs.

Hydrodynamics and mass transfer performance of microbubble flow in the bubble column with a contraction section

Bubble columns have many applications in the biochemical, petrochemical, and metallurgical industries. The gas-liquid system composed of microbubbles is characterized by significant phase interfacial area, high mass transfer efficiency, fast dissolution rate, strong adsorption capacity, and long self-sustaining time. This paper investigated the performance of pressurized dissolved gas microbubble generation (PDG) using a Venturi tube as the releaser using a plug-in online imaging instrument. The hydrodynamic and mass transfer characteristics of the microbubble flow generated by PDG in a bubbling column with a contraction section (BCS) were then investigated. One of the primary studies was the effect of the contraction section on the flow performance of the bubbles, the mass transfer performance, and the aeration efficiency of the PDG versus the throat inlet Venturi bubble generator (VBG). The results show that the initial bubble Sauter mean diameter is essentially constant with dissolved gas pressure, and the bubble size distribution(BSD) is similar. The bubble stream passing through the contraction section exhibits two different BSD at the center and side walls of the BCS outlet section. Microbubbles in the inlet section in the absence of external forces almost do not occur in bubble coalescence. The flow of bubbles in the contraction section is subject to a slight coalescence effect. The diameter of bubbles in the contraction section is mainly larger than 20 μm. In the contraction section, coalescence occurs mainly at the side wall. The way of occurrence is adsorption coalescence and collision coalescence. The bubbles move in a gradually confined space with a high degree of interference with each other's bubbles, and the liquid linear velocity acts as an ‘external force’ that benefits the flow of the bubbles out of the confined space. The standard aeration efficiency of PDG is 3–11 times higher than that of the VBG. At 0.3 MPa, the highest standard aeration efficiency for the PDG method was between 0.18 and 0.64 kgO2/kW∙h.

An artificial neural network-particle swarm optimization (ANN-PSO) approach to predict the aeration efficiency of venturi aeration system

In the present study, the artificial neural network-particle swarm optimization (ANN-PSO) approach was adopted for optimizing the standard aeration efficiency (SAE) of the venturi aeration system. Standard aeration efficiency (SAE) is the main parameter which is used to evaluate the effectiveness of an aerator. Aeration test were carried out in a 220 litre capacity tank to find out the impacts of operating variables on SAE using venturi aeration system. The operating variable includes throat length (L), hole diameter (d), and flow rate (Q), however, the output variable was selected as SAE to determine the model response. A 3-6-1 ANN model was developed for predicting the SAE of venturi aeration system, and the PSO algorithm was applied to obtain the optimum values of the operating variables of venturi aeration system. The effectiveness of the ANN modelling was evaluated using the coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) from the test data and forecasted data. The most appropriate optimal values of the operating variables i.e., L, d, and Q were found to be 1.82 mm, 2.00 mm, and 0.31 l/s, respectively. The optimal SAE under ideal working conditions was optimized to be 0.8333 kg O2/kWh. The applied ANN-PSO approaches can predict the optimal values satisfactorily with a maximum of 7.73% difference with the experimental values. Therefore, the suitability of the ANN-PSO approach can be useful to predict the aeration efficiency of venturi aeration system.

Design and experimental evaluation of a Venturi and Venturi-Vortex microbubble aeration system

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.

An experimental study of venturi aeration system

Aeration with a venturi aerator is efficient method to increase the dissolved oxygen (DO) concentration in water sources like rivers, waterways, ponds and water treatment plants. It is employed in aquatic animals' respiration and other biological processes as well as the removal of dissolved gases, dissolved metals, and volatile organic chemicals (VOC) in water. Aeration system efficiency is a crucial design factor, as aeration systems often account for the most energy draw and consumption. The study aims to evaluate the standard oxygen transfer rate (SOTR), standard aeration efficiency (SAE), volumetric oxygen transfer coefficient (KLa20) of venturi aeration system, air velocity and airflow rates at different water levels of the tank. Venturi aerator designed by Green Pumps and Equipments was used for experimentation. Air entrainment hole was fixed to 25 mm and 66 mm water inlet diameter. It was discovered that the rate of air flow rises as the tank's water level falls. The KLa20 was achieved at a rate of 2.58 h−1, SOTR at a rate of 0.323191 kgO2/hr, and SAE at a rate of 0.293594 kgO2/KWh, respectively. The findings suggest that venturi aeration may have a considerable impact on air entrainment and aeration efficiency. As a result, the venturi aeration system can be employed as an efficient aerator in aeration procedures.

Experimental characterization of an oxygen transfer model of a fine pore diffuser aerator

Dissolved oxygen (DO) is an important aspect of water quality in aquaculture. To prevent oxygen deficiency, aeration is used to improve DO and increase yields in aquaculture farms. However, the experimental quantification of standard oxygen transfer rate (SOTR) of aerators is highly case dependent and varies under different aerator operational conditions. Hence, using SOTR for modeling, simulation, and aerator design purposes tends to be unreliable. This work validates an existing theoretical oxygen transfer model of an economical fine-pore diffuser using a bench-scale aeration system. Modifications were made to the model to account for physical conditions and to relate the model to SOTR. Aeration tests were conducted using various airflow rates and diffuser depths for three water volumes (137 L, 160 L, 192 L). As a parameter to the model, bubble diameters were determined for each experiment using an automated image processing tool developed for this study. The percentage error between the theoretical and experimental oxygen transfer coefficients range from 12.87% to 19.99% and are well within the 95% confidence interval of both respective results. The oxygen transfer coefficient and rate increased with diffuser submergence and airflow rate. However, standard aeration efficiency decreased exponentially with increasing airflow rates. The use of this model provides an approximate estimate of oxygen transfer rates in different conditions, which can be used to optimally design aerators and strategically create cost-saving practices for both intensive and extensive aquaculture applications.

Experimental study on design and operational performance of solar-powered venturi aeration system developed for aquaculture – A semi-floating prototype

Venturi-type injectors have been used usually due to the practical use and modular design that allows for quick configuration, ready-to-use, and low-cost solutions in the last years. This study aims to design a solar-powered venturi aeration system (SVAS) and determine its flow characteristics, standard, and real-time operational performance parameters. SVAS has a design providing the maximum vacuum and air velocity at air inlets and allowing for all technical measurements. Moreover, a solar-powered experimental apparatus having a weather station, a pool station, and a data logger station was constructed. Experiments were carried out using a plastic pool with a capacity of 4000 L, a diameter of 3 m and a depth of 0.75 m, four venturi injectors, and a submersible pump of 0.3 kW operated at the constant water flow regime of 4.1 m3 h-1. According to flow tests, the oxygen mass flow rates ranged from 2.77 to 2.84 kg h−1. The specific energy consumption values are 263.2 kJ per cubic meter for water flow and 380 kJ per kg for oxygen transfer.Standard performance experiments were repeated four times. The maximum overall oxygen mass transfer coefficient obtained during the experiments was 5.58 h−1. The maximum values of standard oxygen transfer rate (SOTR), standard aeration efficiency (SAE), and standard oxygen transfer efficiency (SOTE) were 0.206 kgO2 h−1, 0.681 kgO2 kWh−1, and 7.32%, respectively. The pool conditions were simulated using de-oxygenation and mixing systems to determine the operational performance. For simulation experiments, six procedures and two processes were applied. Throughout operational experiments of four days, real-time dissolved oxygen levels fluctuated between 1.05 mg L−1 and 6.65 mg L−1. The maximum performance values were 0.143 kgO2 h−1 for the actual oxygen-transfer rate, 0.474 kgO2 kWh−1 for aeration efficiency, and 5.1% for oxygen transfer efficiency.

Effect of Varying Discharge Rate on the Performance of Venturi Aeration System

Venturi aeration is an economical method to increase dissolved oxygen (DO) in aquatic water bodies. For this paper, aeration experiments were conducted with 200 litres volume of the water tank, having dimensions of 90 cm length, 55 cm breadth, and 45 cm depth. The venturi was fabricated keeping the dimension of converging and diverging length same, i.e., 76 mm and throat length of 100 mm. The venturi aeration system was operated with six different discharge rates (0.00025, 0.00033, 0.00042, 0.00050, 0.00058 and 0.00067 m3/s). This work is intended to estimate the effect of varying discharges on the efficiency of venturi aerator in terms of standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE). The experiment shows promising results in terms of SOTR and SAE at moderate to high discharge rates, on the other hand a declining trend is seen when the liquid discharge rate is too high. The oxygen transfer rate was found to have a good relationship with the discharge rate.

Design characteristics of showering aeration system

AbstractThe showering aeration system (SAS) was designed and its performance was evaluated by conducting the aeration experiments in a tank of dimension 2 × 4 × 1.5 m. Initially, the aeration experiments were conducted to optimize the radius of curvature of the SAS with different values, such as = 0, 5, 10, 15, and 20 mm, and maintain other geometric parameters, i.e. number of holes in the shower (); height of water fall (H); diameter of the shower hole (d); volume of water under aeration (V) and water flow rate (Q) as constants. The optimum radius of curvature () was found to be 10 mm. The aeration experiments were further conducted with four different non-dimensional geometric parameters such as the number of holes , the ratio of the height of water fall to the length of shower arm the ratio of the diameter of the hole to the length of shower arm and the ratio of the volume of water to the cube of the length of shower arm The Response Surface Methodology and Box–Behnken Design were used to optimize the non-dimensional geometric parameters of the SAS to maximize the Non-Dimensional Standard Aeration Efficiency. The result indicates that the maximum NDSAE of 16.98 × 106 was obtained from the SAS performance at = 80; = 2; = 4 and = 48.

Optimizing the aeration performance of a perforated pooled circular stepped cascade aerator using hybrid ANN-PSO technique

Artificial aeration system for aquaculture ponds becomes essential to meet the oxygen requirement posed by the aquatic species. The performance of an aerator is generally measured in terms of standard aeration efficiency (SAE), which is significantly affected by the different geometric and dynamic parameters of the aerator. Therefore, to enhance the aeration performance of an aerator, these parameters need to be optimized. In the present study, a perforated pooled circular stepped cascade (PPCSC) aerator was developed, and the geometric and dynamic parameters of the developed aerator were optimized using the hybrid ANN-PSO technique for maximizing its aeration efficiency. The geometric parameters include consecutive step width ratio (Wi-1/Wi) and the perforation diameter to the bottom-most radius ratio (d/Rb), whereas the dynamic parameter includes the water flow rate (Q). A 3–6-1 ANN model coupled with particle swarm optimization (PSO) approach was used to obtain the optimum values of geometric and dynamic parameters corresponding to the maximum SAE. The optimal values of the consecutive step width ratio (Wi-1/Wi), the perforation diameter to the bottom-most radius ratio (d/Rb), and the water flow rate (Q) for maximizing the SAE were found to be 1.15, 0.002 7 and 0.016 7 m3/s, respectively. The cross-validation results showed a deviation of 3.07 % between the predicted and experimental SAE values, thus confirming the adequacy of the proposed hybrid ANN-PSO technique.

PERFORMANCE EVALUATION OF LOCALLY FABRICATED MECHANICAL SURFACE AERATOR

Experimental analysis for a fabricated Low-Speed surface aerator that can be used in wastewater and water treatment is presented in this research. The designed impeller configuration was tested to determine its power consumption, standard oxygen transfer rate (SOTR), and standard aeration efficiency (SAE). Impeller oxygen transfer and power consumption in a scaled laboratory tank were measured during aeration phase. The impeller was consisting of 8 inclines flat blades with an angle of 45° from center of the disc, was operated at 3 different immersion depths and 5 different rotational speeds for examining the impact of such factors on impeller efficiency. The results recorded that the best standard aeration efficiency for this configuration is (0.206 Kg. O2/KW.hr) at 120rpm and 7cm depth of the submersion, i.e. submersion depth to impeller diameter (h/D) ratio equals 0.175. Submergence depth increase beyond this limit would result in SAE decrease and definitely result into more power consumption.

Influence of the angle and perimeter of contact of the blades in a horizontal axis aerator on the transfer of dissolved oxygen

Dissolved oxygen (DO) is a fundamental parameter in water bodies that can be supplied using horizontal axis mechanical agitators. However, blade geometry and operating conditions can influence the process cost. In this work, it is studied the effect of the perimeter and angle of impact of the blades on the water in a prototype of horizontal axis mechanical aeration, starting from the DO transfer analysis. Measurements were made on anoxic water samples using two types of blades with the same area, varying their perimeter and angle of impact. Other parameters that influence the DO transfer process were controlled in this work. The results show the increase in the perimeter, and blade impact angle with the water body, which generates a reduction in the standard aeration efficiency (SAE) up to 30 % in the process. In that way, it is obtained the best results for the prototype Type II blades with a KLa value of 3.69 h-1, and a SAE of 0.47 kgO2∙kW-1h-1 when using an impact angle of 13.5 °. In general, the geometry of the blades is a fundamental design parameter, which influences the transfer of dissolved oxygen in the water. The results of this study can contribute to improving the efficiency of these mechanical systems, reducing the energy consumption associated with oxygenation processes.

Prediction of standard aeration efficiency of a propeller diffused aeration system using response surface methodology and an artificial neural network

AbstractAeration experiments were conducted in a masonry tank to study the effects of operating parameters on the standard aeration efficiency (SAE) of a propeller diffused aeration (PDA) system. The operating parameters included the rotational speed of shaft (N), submergence depth (h), and propeller angle (α). The response surface methodology (RSM) and an artificial neural network (ANN) were used for modelling and optimizing the standard aeration efficiency (SAE) of a PDA system. The results of both approaches were compared for their modelling abilities in terms of coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE), computed from experimental and predicted data. ANN models were proved to be superior to RSM. The results indicate that for achieving the maximum standard aeration efficiency (SAE), N, h and α should be 1,000 rpm, 0.50 m, and 12°, respectively. The maximum SAE was found to be 1.711 kg O2/ kWh. Cross-validation results show that best approximation of the optimal values of input parameters for maximizing SAE is possible with a maximum deviation (absolute error) of ±15.2% between the model predicted and experimental values.

Two-Phase Flow Mass Transfer Analysis of Airlift Pump for Aquaculture Applications

Airlift pumps can be used in the aquaculture industry to provide aeration while concurrently moving water utilizing the dynamics of two-phase flow in the pump riser. The oxygen mass transfer that occurs from the injected compressed air to the water in the aquaculture systems can be experimentally investigated to determine the pump aeration capabilities. The objective of this study is to evaluate the effects of various airflow rates as well as the injection methods on the oxygen transfer rate within a dual injector airlift pump system. Experiments were conducted using an airlift pump connected to a vertical pump riser within a recirculating system. Both two-phase flow patterns and the void fraction measurements were used to evaluate the dissolved oxygen mass transfer mechanism through the airlift pump. A dissolved oxygen (DO) sensor was used to determine the DO levels within the airlift pumping system at different operating conditions required by the pump. Flow visualization imaging and particle image velocimetry (PIV) measurements were performed in order to better understand the effects of the two-phase flow patterns on the aeration performance. It was found that the radial injection method reached the saturation point faster at lower airflow rates, whereas the axial method performed better as the airflow rates were increased. The standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) were calculated and were found to strongly depend on the injection method as well as the two-phase flow patterns in the pump riser.

Performance evaluation of venturi aeration system

The venturi aeration is an effective practice to increase the dissolved oxygen accessibility in the water bodies. This study aims to optimize the various geometrical parameters of the venturi aeration system. A non-dimensional technique was applied to find the optimum performance of various geometric parameters i.e. throat lengths (tl), number of air holes (N), and converging and diverging angles (α and β). These experiments have been carried out using 1124 L capacity of tank having dimensions of 105 cm long, 105 cm wide and 102 cm deep. The experiments were conducted at a constant flow velocity of water (1.096 m/s) with varying throat length (tl = 20–100 mm keeping 20 mm as interval between two consecutive length), number of air holes (N = 1–17 at an equal hole to hole distance of 5 mm between them), and converging and diverging angles (α and β = 10°, 15°, 20° and 25°). Multiple non-linear regression equations were also developed from the linear relation with the dependent variable (Non-dimensional form of standard aeration efficiency, NDSAE) and independent variables (tl and N). With the geometrically optimized venturi aerator the optimum performance was found for tl =100 mm, N = 17, and α and β = 15°. The maximum value of standard oxygen transfer rate (SOTR) and standard aeration efficiency (SAE) obtained was 0.0216 kgO2/h and 0.611 kgO2/kWh respectively. From the non-dimensional study, it was found that the NDSAE is the function Reynolds number (Re) and Froude number (Fr). The simulation equations were developed on the basis of Re and Fr for NDSAE, and subjected to 7.378 × 10−6 <Re < 3.689 × 10-5 and 0.163 <Fr < 0.817, respectively.