A high concentration of dissolved oxygen is essential for the maintenance of healthy aquatic ecosystems. Aeration studies have been conducted in both closed systems and open channels utilizing conventional hydraulic structures. However, the feasibility of aeration through screens with square openings has not yet been explored. This study aimed to evaluate the aeration efficiency (E20) in an open channel system using screens with square jets. Five input parameters were analyzed: angle of inclination, number of square jets, discharge, cumulative hydraulic radius, and Froude number. The results showed that Nj, α, and Q significantly influence E20. The highest E20 recorded was 37% on level terrain with moderate discharge in the open channel. This method has the potential to enhance oxygen concentrations in rural regions where skilled labor and mechanised systems may be challenging. The study also focused on identifying suitable soft computing models for predicting E20. Five machine learning approaches were employed: artificial neural network, random forest with Bagging, Gaussian process utilizing the Pearson VII function kernel (GP_PUK), support vector machine with the PUK kernel function (SVM_PUK), and a radial basis function (SVM_RBF). The GP model employing the PUK kernel function demonstrated superior performance.

  • The relationship between the output variable (E20) and input variables (number of jets, discharge, angle of inclination, Froude number, and cumulative hydraulic radius) was analyzed.

  • Development and comparison of artificial neural network, support vector machine, Gaussian process, and Bagging random forest for the prediction of E20.

  • Sensitivity analysis is performed to determine the most important input parameters.

ANFIS

adaptive neuro-fuzzy inference system

ANN

artificial neural network

bdepth

bubble penetration depth

CaCl2

calcium chloride

CC

correlation coefficient

DO

dissolved oxygen

DOd

dissolved oxygen concentration of downstream

DOu

dissolved oxygen concentration of upstream

E20

aeration efficiency

GEP

genetic expression programming

GP

Gaussian process

HR

cumulative hydraulic radius

cumulative hydraulic radius of each jet

JL

jet length

Jpu/pr

jet pump pressure ratio

JT

jet thickness

JV

jet velocity

KLa20

volumetric oxygen transfer rate

LS-SVM

least square support vector machine

MAE

mean absolute error

ML

machine learning

MLR

multiple linear regression

Na2SO3

Sodium sulfite

Nj

number of plunging jets

O2

oxygen

OTC

oxygen transfer coefficient

OTE

oxygen transfer efficiency

P/V

jet power per unit volume

PUK

Pearson VII function kernel

Q

water discharge

RBF

radial basis kernel

RF

random forest

RMSE

root means square error

SRM

structural risk minimization

Std. dev.

standard deviation

SVM

support vector machine

SVR

support vector regression

T

water temperature

TNj

side length of the square

α

the angle of inclination of the open channel

θ

jet impact angle

Water resource concerns, such as reasoned usage pollution control, are acquiring the interest of scientists around the globe. Numerous sectors already require the use of biological methods to treat wastewater. Treating industrial effluents using aerobic biological methods results in quicker processes, eliminates unpleasant conditions, and yields clear effluents without odor and stability (Metcalf & Eddy 2003). There is much emphasis on water quality and maintaining water quality parameters in the earth's freshwater hydrosphere (rivers, lakes, and reservoirs). Dissolved oxygen (DO) concentration is among the most widely cited parameters. DO is often used as an indicator of the quality of the water used by humans or serving as a habitat for aquatic flora and fauna. Numerous organic, chemical, and biological processes that raise or lower local oxygen concentrations maintain it. Respiration by marine life, biodegradation of organic material, and other oxygen-consuming chemical reactions reduce DO concentration in the natural water. Photosynthesis by aquatic plant life can be a significant source of oxygen to a water body.

Similarly, aeration and other gas transfer activities are crucial in controlling untreated or wastewater pollution. In the aeration process through water jets, more extensive gas–liquid interfaces lead to air entrainment, which enhances the DO concentration in the water. This phenomenon proves effective in various industries, such as environmental sectors, where plunging liquid jets agitate the liquid pool's surface, enhancing the gas–liquid exchange. Two complementary processes commonly bring about air entrainment. The air boundary layer contracts due to contact strain at the intermittent point where air and water meet in the first mechanism.

On the other hand, the second phenomenon is the capture of air around a descending jet upon impact with a liquid pool (Qu et al. 2013; Hassan & Shabat 2023). The presence of air trapped on the water's surface leads to the formation of a sizable void resembling a cylinder at the lower part, which then gets compressed and gives rise to a bubbling column descending beneath the water's point of impact (Qu et al. 2011). The basis for aeration is the development of a sizable air–water interface in the liquid, which leads to the dissolution of O2 in water from the air being transported by a peculiar speed discharge jet with the free liquid surface. The interaction of an ‘impinging water jet's plume’ of air bubbles with water in a quiescent pool to transfer oxygen mass is called oxygenation by ‘plunging jets’ (Chipongo & Khiadani 2017). The mechanism of plunging overfall jets at hydraulic structures, i.e., weirs (Baylar 2000; Baylar et al. 2001), drop shafts, cascades (Baylar & Emiroglu 2005; Emiroglu & Baylar 2006) as well as floatation in water and wastewater treatment (Deswal 2008), biological aerated filters, bubble floatation of minerals, plunging breakers, chemical mixing, cooling systems in power plants that generate high turbulence activity at the free surface, enhances air–water transfer (Banks et al. 1984). It was observed by Baylar et al. (2009) that self-aeration in stepped cascades is a vital process in water treatment, while Wei et al. (2016) reported that flow turbulence is a critical factor for the self-aeration development process. In addition, the constraint of buoyancy on air bubble diffusion into the chute bottom decreased as the chute slope increased, making the development process for bottom self-aeration more pronounced. Toombes & Chanson (2005) mentioned the design of a stepped cascade specifically for water treatment through reoxygenation.

Similarly, studies of local surface aeration in open channels in association with hydraulic structures such as weirs, spillways, gates, and hydraulic jumps indicate significant water quality improvement due to oxygen transfer (Avery 1976; Avery & Novak 1978; Gulliver & Rindels 1993; Kobus & Koschitzky 2018). Conventional hydraulic structures, including weirs, can be utilized to increase aeration. Still, flumes may enhance the aeration process in a mild or insignificant slope canal where the drop is impossible (Dursun 2016).

Sometimes, a natural gas exchange at the free surface is insufficient to offset the oxygen consumption caused by pollutants in water pollution abatement. Increasing the amount of oxygen transferred into the body of water requires local aeration. Local surface aeration processes in open channel flows mainly occur at hydraulic jumps, drop structures, and weirs, increasing the oxygen transfer by entrained air bubbles. As a result, the air entrainment and oxygen transfer properties are now crucial design parameters for many hydraulic structures. Furthermore, effective water resource management and wastewater treatment system design depend on the aeration process performed by water jets under the static head, which eliminates the cost of electrical energy and enhances the treatment efficiency capability of an open channel flow system.

One of the ways of wastewater treatment is screening, which removes large suspended contaminants from the waste stream to prevent scouring and damage to downstream structures. This procedure removes the larger suspended and floating objects, such as fibers, paper, rags, string, and other materials. The geometry of the holes in a screen can be different; however, they are often rectangular or round. At the entrance of the hydraulic section, e.g., trenches, barrages, water intakes, and pumping stations, trash screens are commonly employed to capture flowing waste that could cause issues downstream. Screens are used in open channels to ensure the removal of coarse pollutants. Screens were first introduced as energy dissipators in the research conducted by Rajaratnam & Hurtig (2000). Their research shows that screens help stabilize the location of hydraulic jumps and dissipate more energy than free hydraulic jumps. Numerous other studies that followed examined the impact of various factors, including porosity and screen location (Rajaratnam & Hurtig 2000), screen location and thickness (Çakır 2003), the effects of sloping screens (Bozkus et al. 2007), different types of hydraulic jumps (Sadeghfam et al. 2015), and the combination of screens with baffle-like structures (Daneshfaraz et al. 2017). Despite all these applications, the utility of screens and their geometry with input parameters such as tilt angle, discharge, number of jets, cumulative hydraulic radius, and Froude number to increase DO concentration in an open channel has created a considerable gap in measuring the aeration efficiency (E20), and the impact of such input parameters on E20 requires detailed investigations.

During the literature review, it was found that the experimental work takes a lot of time, cost, and energy to assess E20 with various input parameters. Therefore, a review of the predictive models was utilized to reduce the experimental work for estimating the E20. Predictive models for E20 are critical for reducing energy costs, optimizing biological processes, maintaining regulatory compliance, and ensuring the long-term sustainability of operations in water treatment, aquaculture, and other aeration-dependent industries. Soft computing has attracted much attention in the engineering field (Govindaraju 2000; Azamathulla 2012; Sihag et al. 2018; Sihag et al. 2019a, 2019b, 2020, 2022; Bhoria et al. 2021; Sepahvand et al. 2021; Singh et al. 2021, 2022, 2023; Nivesh et al. 2022; Sharma et al. 2022, 2023; Upadhya et al. 2022a, 2022b; Yamini et al. 2022; Sazonov et al. 2023; Arora et al. 2024; Singh & Minocha 2024a, 2024b) and hydrological studies (Danboos et al. 2023; Dullah et al. 2023; Latif & Ahmed 2023; Singh & Minocha 2024b, 2024c). Soft computing methods have proved their efficacy in the realm of aeration. In their study, Baylar et al. (2008) effectively utilized adaptive neuro-fuzzy inference system and least square support vector machine to analyze datasets containing the rate of air entrapment and E20 measurements acquired through descending jets emanating through weirs having triangular geometry. Predictive formulas using multiple linear and multiple nonlinear regressions were employed to assess the effectiveness of different modeling techniques. Bagatur & Onen (2014) examined the efficacy of genetic expression programming (GEP) to establish a connection between the variables of a triangle weir and the air entrainment rate and E20. In the studies (Deswal 2011; Bagatur & Onen 2014; Deswal & Pal 2015), support vector machine (SVM) and Gaussian process (GP) regression techniques achieved good predictive performance of the O2 mass transportation coefficient of Nj plunging into a still water pool. GEP and artificial neural network (ANN) modeling were used to compare the kernel functions based on multiple linear regression and support vector regression (SVR) to model mass transfer by vertical and inclined Nj. Using nonlinear regression and ANN approaches, Kramer et al. (2016) efficaciously assessed the depth of plunging water jets with extended discharge. Kumar et al. (2021) studied plunging jets' O2 mass transfer characteristics.

The literature review established that investigating the effect of screens on E20 has a broad scope of exploration in open channel flow by plunging water through jets of different shapes. In this study, a square-shaped plane was considered to keep its higher HR than a circle. Also, the predictive models were utilized to reduce the experimental work for estimating the E20. Predictive models for E20 are critical for reducing energy costs, optimizing biological processes, maintaining regulatory compliance, and ensuring the long-term sustainability of operations in water treatment, aquaculture, and other aeration-dependent industries.

The objectives of the study were as follows:

  • 1. To determine the relationship between the output variable (E20) and input variables (number of jets, discharge, angle of inclination, Froude number, and cumulative hydraulic radius) provided by screens with square jets.

  • 2. To calculate the E20 experimentally and predict using an ANN, support vector machine, Gaussian process, and Bagging random forest (RF).

  • 3. To compare the results of the optimized models on the basis of correlation coefficient (CC), root means square error (RMSE), and mean square error (MSE).

  • 4. A sensitivity analysis for each input parameter is done to find the most influential parameter.

The current investigation was carried out in a tilting flume with dimensions of 45 cm × 25 cm × 500 cm (Figure 1). A water depth gauge was attached to the channel to measure the water level during the experiment run (shown as ‘1’ in Figure 1). ‘2’ in Figure 1 shows the place where a set of seven acrylic screens with square-shaped holes varied in number: 1, 2, 4, 8, 16, 32, and 64, responsible for generating square jets, were placed in the channel, meanwhile ‘3’ is the position where actual aeration was taking place. Each screen was evaluated for α values of 0°, 1.5°, and 3° and Q-values of 3.41, 3.84, 4.75 L/s. These values were maintained in the channel using a tilt angle arrangement and pressure gauges attached in the channel, shown as ‘4’ and ‘5’ in Figure 1. A sluice valve attached to the setup was used to maintain the discharge of water in the channel (‘6’ in Figure 1). The discharge was measured using the rectangular weir attached at the end of the flume. A 2HP electric motor was attached, which helped circulate water during experimentation. The flow area in the tilting flume was kept constant, corresponding to which square jets were perforated on acrylic screens. The study deals with single and multiple plunging jets (1–64). Table 1 shows the description based on which the square jets were made on the screen, as shown in Figure 2.
Table 1

Description of square plunging jets

Number of jets (Nj)Side (cm)Perimeter (cm)Area of each jet (cm2)Total area (cm2)
5.54 22.18 30.75 30.75 
3.92 15.68 15.37 
2.77 11.09 7.68 
1.96 7.82 3.84 
16 1.38 5.54 1.92 
32 0.98 3.92 0.96 
64 0.69 2.77 0.48 
Number of jets (Nj)Side (cm)Perimeter (cm)Area of each jet (cm2)Total area (cm2)
5.54 22.18 30.75 30.75 
3.92 15.68 15.37 
2.77 11.09 7.68 
1.96 7.82 3.84 
16 1.38 5.54 1.92 
32 0.98 3.92 0.96 
64 0.69 2.77 0.48 
Figure 1

Experimental setup. (a) Deoxygenated water sample; (b) oxygenated water sample; (1) water depth gauge; (2) jet device secured in channel; (3) plunging jet (formed) impinging into water pool; (4) tilt angle arrangement; (5) pressure gauges; (6) sluice valve; (7) 2HP motor; (8) water tank.

Figure 1

Experimental setup. (a) Deoxygenated water sample; (b) oxygenated water sample; (1) water depth gauge; (2) jet device secured in channel; (3) plunging jet (formed) impinging into water pool; (4) tilt angle arrangement; (5) pressure gauges; (6) sluice valve; (7) 2HP motor; (8) water tank.

Close modal
Figure 2

Model of square jets used in the study.

Figure 2

Model of square jets used in the study.

Close modal

Methodology

Seven interchangeable acrylic screens with 1, 2, 4, 8, 16, 32, and 64 jets were included in the aeration apparatus (Figure 2). Three values of Q (3.41, 3.84, and 4.75 L/s) and angle of inclination of the open channel (0°, 1.5°, and 3°) were examined for each screen. Every screen was positioned within the tilting flume and adjusted so water could only enter the downstream pool through one or more jet holes. The Wrinkler method was used to determine the DO of the water sample. So, sodium sulfite (Na2SO3) and a cobalt chloride (CoCl2) catalyst were added to the water tank to deoxygenate the water before the testing started. A sample of oxygen-depleted water taken upstream of the screen was used to determine the initial concentration of dissolved oxygen (DOu) using the azide modification method (APHA 2005). Aeration was carried out for a predefined duration (t = 2 min). Subsequently, a sample of oxygenated water was obtained in order to calculate the DOd (dissolved oxygen content in the water downstream of the screen) following time ‘t.’ The water temperature was recorded adequately throughout the studies using a laboratory thermometer. Special care was taken to address uncertainty during the experimentations. To avoid error and uncertainty in the DO measurement, the results of the Wrinkler method were compared with the results obtained from the Multimeter (HACH) with the IntelliCAL LDO101 prob. The comparison suggested that there was an uncertainty band of + 0.01 mg/L, which was acceptable. Similarly, for the identification of uncertainty in the measurement of the discharge, the discharge measured from the rectangular weir was calibrated against the results of pitot tubes, and it was found that the error band was ± 0.03 L/s, which was also acceptable.

The following equations (Equations (1)–(3)) were applied to determine the E20 value (Gulliver et al. 1998).
(1)
where r represents the oxygen aeration deficient ratio and represents the saturated concentration of DO.
The E20 signifies complete oxygen transfer to water, with a value of unity, whereas DOd and DOu indicate nil oxygen transfer downstream and upstream, respectively. To maintain consistency in the experimental procedure, the outcomes acquired at various T are standardized to 20° by utilizing the subsequent equation, ensuring homogeneity. Gulliver et al. (1998) and Novak et al. (1999) formulated the following time-independent formula to determine the oxygen aeration efficiency, E:
(2)
where is the oxygen transfer efficiency (OTE) at 20 °C and f is the aeration exponent, was obtained as follows:
(3)
In addition, ANN, RF_Bagging, GP, and SVM soft computing approaches were used to create models that predicted E20. The size of the dataset was 63 observations, which were split up in the ratio of 2:1 in training and testing datasets, respectively. The traits of both datasets show (Table 2) the data characteristics such as mean, median, standard deviation. A representation of the procedure is shown in Figure 3.
Table 2

Dataset characteristics for training and testing

αQNjHRFroude numberE20
Training dataset 
Mean 1.50 3.95 18.90 0.61 3.13 0.26 
Median 1.50 3.84 8.00 0.49 2.90 0.27 
Standard deviation 1.24 0.55 22.54 0.41 1.17 0.06 
Kurtosis −1.54 −1.25 0.11 −0.68 −0.79 −0.60 
Skewness 0.00 0.61 1.26 0.75 0.43 −0.33 
Minimum 0.00 3.41 1.00 0.17 1.50 0.13 
Maximum 3.00 4.75 64.00 1.39 5.92 0.37 
Testing dataset 
Mean 1.50 4.11 16.62 0.62 3.19 0.26 
Median 1.50 3.84 8.00 0.49 3.39 0.26 
Standard deviation 1.25 0.59 19.38 0.41 1.23 0.05 
Kurtosis −1.58 −1.89 1.62 −0.56 0.52 −0.98 
Skewness 0.00 0.06 1.51 0.82 1.03 0.40 
Minimum 0.00 3.41 1.00 0.17 2.01 0.19 
Maximum 3.00 4.75 64.00 1.39 5.92 0.36 
αQNjHRFroude numberE20
Training dataset 
Mean 1.50 3.95 18.90 0.61 3.13 0.26 
Median 1.50 3.84 8.00 0.49 2.90 0.27 
Standard deviation 1.24 0.55 22.54 0.41 1.17 0.06 
Kurtosis −1.54 −1.25 0.11 −0.68 −0.79 −0.60 
Skewness 0.00 0.61 1.26 0.75 0.43 −0.33 
Minimum 0.00 3.41 1.00 0.17 1.50 0.13 
Maximum 3.00 4.75 64.00 1.39 5.92 0.37 
Testing dataset 
Mean 1.50 4.11 16.62 0.62 3.19 0.26 
Median 1.50 3.84 8.00 0.49 3.39 0.26 
Standard deviation 1.25 0.59 19.38 0.41 1.23 0.05 
Kurtosis −1.58 −1.89 1.62 −0.56 0.52 −0.98 
Skewness 0.00 0.06 1.51 0.82 1.03 0.40 
Minimum 0.00 3.41 1.00 0.17 2.01 0.19 
Maximum 3.00 4.75 64.00 1.39 5.92 0.36 
Figure 3

Flow chart of methodology.

Figure 3

Flow chart of methodology.

Close modal

The present section represents the experimental findings of the tilting flume equipment of the hydraulics lab. The input parameters, such as α, varied from 0° to 3°, Q from 3.41 to 4.75 L/s, Nj from 1 to 64, and HR from 0.0375 to 1.56 cm. The experimental results showed that the parameters studied significantly impact E20.

Relationship between number of jets (Nj) and E20

Figure 4 demonstrates the impact of the number of jets (Nj) on E20 at angles of inclination (θ) 0° (Figure 4(a)), 1.5° (Figure 4(b)), and 3° (Figure 4(c)). The relationship between the number of square jets and E20 is trending upwards, suggesting that as jet count increases, so does E20. When the discharge and angle of inclination remain constant, Nj =1 provides less aeration (about 0.1322–0.187) than multiple jets. As shown in Figure 4(a), a screen with Nj = 64 operates under similar conditions but produces aeration up to 0.2878. Figure 4(a) also displays the impact of jets on E20 at a constant angle of inclination and a 3.84 L/s discharge rate. It is significant to note that the number of jets affected the rate of change of E20 at this discharge rate since the rate of change of E20 increases at Nj = 4. The highest aeration gained in the experiment with Nj = 64 is 0.3129. This finding is consistent with the discharge rate of 4.75 L/s, which suggests that a single jet can achieve an aeration range of 0.13223–0.1874. In contrast, the E20 of multiple jets (Nj = 2 to Nj = 64) working at the same parameters increases, with efficiency values ranging from 0.161 to 0.3472. Similarly, as observed in Figure 4(b), Nj = 1 provides less aeration than multiple jets when the discharge and angle of inclination are constant. When utilized in similar circumstances, Nj = 64, for example, increases aeration, particularly 0.2890. When the discharge is changed to 3.84 L/s, the number of jets impacts this discharge rate, as it is crucial to remember that the rate of change of E20 increases until Nj = 4. The test with Nj = 64 reports a maximum aeration of 0.323. This result is consistent with a 4.75 L/s discharge rate. Figure 4(b) study concludes that the range of aeration attained by a single jet is 0.1543–0.1985. With efficiency values ranging from 0.1731 to 0.3586, multiple jets exhibit superior E20 when employed in similar settings (from Nj =2 to Nj =64). Graphical representations of the effects of Nj on E20 for discharge rates of 3.41, 3.84, and 4.75 L/s at α = 3o are shown in Figure 4(c). Additionally, it is observed that the aeration rate is highest at Nj = 16 and then becomes constant. The same result is exhibited when discharge is changed to 3.84 L/s and constant angle. It is observed that Nj =1 attains aeration between 0.1989 and 0.2322, as opposed to Nj = 64, which attains aeration between 0.31171 and 0.3913. The system's aeration ranges from 0.1323 to 0.2322 when a single jet is used, indicating that a single jet provides less air entrainment. However, the number of jets in the screen increases aeration over time, and the screen with the most jets, i.e., Nj = 64, gives an E20 range of 0.2878 to 0.3695 from 0° to 3° of the angle of inclination. Nj values range from 1 to 16, and a substantial increase in E20 is observed for all tested tilt degrees. E20 is gradually increasing for Nj greater than 16. This increase in E20 for numerous plunging jets with an increase in the Nj may be attributed to more air or oxygen due to the increased surface area of numerous jets in contact with the atmosphere due to entrained jets.
Figure 4

Effect of the number of jets on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Figure 4

Effect of the number of jets on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Close modal

Relationship between discharge (Q) and E20

Figure 5 depicts the effect of Q on E20 for various jet numbers and α. The pattern of increasing E20 concerning increasing Q is observed in all cases of Nj ranging from 1 to 64. It is also observed that as Q increases from 0 to 39%, the increase in E20 varies between 0.44 and 50.43% for Nj ranging from 1 to 64. E20 is found to be more with multiple jets than with single jets for a given Q. Figures 5(a) and 6(b) show that the E20 achieved is in the range of 0.1–0.35, whereas Figure 5(c) shows that the maximum E20 is obtained at 64 jets and 4.75 L/s.
Figure 5

Effect of Q on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Figure 5

Effect of Q on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Close modal
Figure 6

Effect of α on E20 at Q (a) 3.41, (b) 3.84, and (c) 4.75 L/s.

Figure 6

Effect of α on E20 at Q (a) 3.41, (b) 3.84, and (c) 4.75 L/s.

Close modal

The increase in E20 is due to higher Q, which enhances the momentum of the flow in jet(s) at elevated velocities, with the amplified surface region of air–water interaction resulting from the increased count of jet orifices and the generation of heightened turbulence at more significant outflows. Conversely, the jets acquire the essential kinetic energy to permeate more profoundly into the reservoir when the outflow surpasses 3.41 L/s, and a larger contact area between air and water forces more oxygen into the pool. It was observed that the higher the Q, the higher the E20.

Relationship between the angle of inclination (α) and E20

α affects E20, as shown in Figure 6. The trend is similar and consistent with all α, i.e., 0°, 1.5°, and 3°. The smallest angle, 0°, has the most minor effect on E20 compared to the α at 1.5° and 3°. The increase in E20 in 3° is up to 37%. This study's most efficient screen model uses Nj 1–64 jets at maximum Q and α = 3°. It can be deduced from Figure 6 that E20 increases as the α increases. The reason for this is due to the high velocity at higher angles. The increase in E20 with α is due to the jet's more incredible momentum at greater speeds, as well as an increase in air–water contact area due to the increased Nj and the creation of more turbulence at higher Q. The jets, on the other hand, acquire the essential kinetic power to delve further into the tank as the discharge exceeds 3.41 L/s. More oxygen is compelled into the pool due to a larger air–water contact area.

Effect of the Froude number on aeration efficiency of square geometry

The Froude number is calculated using the following equation:
(4)

The various parameters used in calculating the Froude number are listed in Table 3. The total flow area is 30.75 cm2, so the square () side length reduces with increased Nj values. The Froude number values increase with the increase in Q and a decrease in .

Table 3

Results of parameters used in Fr. no calculation for square jets

NjThe cross-sectional area of each jet (cm2)Side length (cm)Froude number
Q = 3.41 L/s
= 110.89 cm/s
Q = 3.84 L/s
= 124.87 cm/s
Q = 4.75 L/s
= 154.47 cm/s
30.75 5.545268 1.503535 1.69313 2.094367 
15.375 3.921097 1.788014 2.013482 2.490636 
7.687 2.772634 2.126319 2.394447 2.961882 
3.843 1.960548 2.528634 2.847494 3.522291 
16 1.921 1.386317 3.00707 3.38626 4.188733 
32 0.960 0.980274 3.576028 4.026965 4.981271 
64 0.480 0.693159 4.252639 4.788895 5.923763 
NjThe cross-sectional area of each jet (cm2)Side length (cm)Froude number
Q = 3.41 L/s
= 110.89 cm/s
Q = 3.84 L/s
= 124.87 cm/s
Q = 4.75 L/s
= 154.47 cm/s
30.75 5.545268 1.503535 1.69313 2.094367 
15.375 3.921097 1.788014 2.013482 2.490636 
7.687 2.772634 2.126319 2.394447 2.961882 
3.843 1.960548 2.528634 2.847494 3.522291 
16 1.921 1.386317 3.00707 3.38626 4.188733 
32 0.960 0.980274 3.576028 4.026965 4.981271 
64 0.480 0.693159 4.252639 4.788895 5.923763 

Figure 7(a)–7(c) shows how the Froude number affects the E20 of screens with square jets at α = 0°, 1.5°, and 3°, respectively. It has been demonstrated that E20 increased along with the Froude number values. As shown in Figure 7(a), the aeration rate rises when the angle of inclination and discharge are both constant. It also shows the impact of the Froude number on E20 at a constant angle of inclination and a 3.84 L/s discharge rate. At this discharge rate, the Froude number starts to show its effects as the rate of change of E20 rises from the Froude number of less than 2. This finding is consistent with the results corresponding to a discharge rate of 4.75 L/s. The impact of the Froude number on E20 provided by screens with square jets at α = 1.5° is displayed in Figure 7(b). It has been shown that when the Froude number values rise, so does E20. Figure 7(b) shows that the rate of aeration increases when both the discharge and angle of inclination are constant. The effect of the Froude number on E20 at a constant angle of inclination and a 3.84 L/s discharge rate is also shown in Figure 7(b). It is important to note that at this discharge rate, the Froude number's effect is noticeable because the rate at which E20 changes rises from a Froude number value of less than 2. Figure 7(c) shows the effect of the Froude number on E20 at α = 3° for Q-values of 3.41, 3.84, and 4.75 L/s. The relation between the Froude number and E20 is increasing. As observed, the E20 is highest at a higher Froude number value. In conclusion, in Figure 7(a)–7(c), it is noted that E20 rises with a rise in the Froude number. The E20 also noted an increase in Q-value from 3.41 to 4.75 L/s and α from 0° to 3° due to higher fluid velocity and increased inclination angle of the slope that affect the Froude number of the fluid. As the fluid velocity increases, the Froude number increases, indicating that the effects of inertia become more dominant. Similarly, increasing the inclination angle of the slope also leads to an increase in the Froude number. Furthermore, the E20 of a system is affected by the Froude number, as it influences the air entrainment rate. When the Froude number is low (Froude number <1), the flow is considered subcritical, and air bubbles tend to rise slowly and follow the flow, resulting in less air entrainment in the fluid. Conversely, with high Froude numbers (Froude number >1), the flow is considered supercritical, which causes air bubbles to break up into smaller ones due to high turbulence in a water pool, leading to increased air–water interfacial area and thus enhanced air entrainment rate. Therefore, to attain maximum E20, an optimal Froude number must be achieved.
Figure 7

Effect of the Froude number on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Figure 7

Effect of the Froude number on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Close modal

Relationship between cumulative hydraulic radius (HR) and E20

The cumulative cumulative hydraulic radius (HR) is extremely important for fluid mechanics in an open channel. It is determined using the following equation.
(5)
(6)
where TNj is the side length of the square.
Figure 8(a)–8(c) shows the impact of HR on the E20 at different discharge rates and angles of inclination, and it shows that there is an increasing trend between HR and the E20. The E20 also increases with an increase in α from 0° to 3° and the Q-value from 3.41 to 4.75 L/s. The wetted perimeter decreases with increasing HR, indicating that a smaller amount of water is near the channel portion, which lowers the resistance to flow and enables more discharge to pass through it, resulting in increased E20.
Figure 8

Effect of HR on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Figure 8

Effect of HR on E20 at α (a) 0°, (b) 1.5°, and (c) 3°.

Close modal

Artificial neural network

Neural networks play a significant role in human structure. The phrase ‘artificial neural network’ describes computer systems whose core idea is derived from biological brain networks. The quantity of momentum, learning rate, iterations, and hidden nodes are only a few of the parameters set by the user to get the optimum model. In Figure 9, the input variables are X1Xn, while the weight is represented by W0Wn. Each input variable has a weight attached to it that controls the neuron's output. The neural network (NN) outputs may be changed by modifying the values of these synaptic weights. Adjusting the synaptic weights inside the network until the mean absolute error (MAE) between the anticipated and observed output values is reduced is called training.

Support vector machine

The primary computational task of SVM involves solving a convex quadratic optimization problem to ensure optimal results (Cortes 1995). The results of SVM are better than other machine learning (ML) techniques that depend on minimizing empirical risks (Thissen et al. 2003). When applying SVM to solve regression problems, three critical factors come into play (Samui 2008). At first, SVM performs regression by employing a collection of linear methods specified within a space of increased dimensions. Additionally, SVM employs Vapnik's ε-regression coefficients calculated using an insensitive loss function. Furthermore, assess the associated risk. Finally, structural risk minimization is a concept that SVM integrates. The goal of SVR is to diagnose an f(t) function for data from the training stage (D) with the most significant margin from the training goal values (N).

The correct choice of kernel determines how well SVM algorithms work. The Pearson VII function kernel (PUK) and radial basis kernel (RBF) were finalized, and their expressions are given in the following equations, respectively (Sihag et al. 2019a, 2019b).

RBF:
(7)
PUK:
(8)

Gaussian process

The GP regression model relies on the idea that neighboring observations can convey information about one another, as Rasmussen & Williams (2006) expressed. This approach involves explicitly describing a prior probability throughout the function space. The advantage of GP is that it can swiftly calculate a latent function's previous certainty. A GP is characterized by the average value m(x) and the kernel variable (or covariance variable) k(x, x′). The subsequent equations define these functions.
(9)
The mean vector indicates the function's central tendency, which is generally believed to be zero (Rasmussen 2003). The covariance matrix defines the structure and shape of the function. The relation between the input and output variables is shown as follows:
(10)
where ε represents the uncorrelated noise, characterized by a probability distribution with a zero mean.

Bagging random forest

Numerous ensemble methods, including boosting, Bagging, and, more recently, RF, have gained wide popularity (Breiman 1996, 2001; Freund & Schapire 1996; Liaw & Wiener 2002). RF is a structured collection of tree predictors created by sampling random vectors from input vectors. Breiman (2001) developed the RF algorithm, an exceptionally effective tool for classification and regression tasks (Scornet et al. 2015). This approach combines a mixture of successful and unsuccessful attempts by utilizing variables based on optimal divisions. By assembling a cluster of arbitrary trees, the RF technique produces forests driven by chance (Mohanty et al. 2019). In RF, Bagging and random subspace methods are combined, and a majority vote determines the outcome.

The precision of the models utilizing ANN, GP, and RF_Bagging for E20 at square jets in an open channel was assessed using three statistical measurements: CC, MAE, and RMSE. Additionally, a scatter plot was employed for visual examination. Table 4 presents the explanation of the above evaluation criteria. The calculations for CC, MAE, and RMSE are outlined in the following equations:
(11)
(12)
(13)
where () represents the observed value, () represents the predicted value, and (presents the mean of the predicted value.
Table 4

Indices interpretation

Evaluation indicesDescription
CC: correlation coefficient Range Correlation level 
0.80–1.00 Very extremely favorable 
0.60–0.79 Extremely favorable 
0.40–0.59 Moderately favorable 
0.20–0.39 Slightly favorable 
0.00–0.19 Very slightly favorable 
−1.00 to 0.80 Extreme negativity 
−0.79 to −0.60 Substantially negative 
−0.59 to −0.40 Medium negative 
−0.39 to −0.20 Weak negative 
−0.19 to −0.01 Very weak negative 
MAE: the term MAE refers to errors that are evenly distributed. 0 < MAE < ∞ 
RMSE: the RMSE is the sample std. dev. of the variances between estimated and the values observed. 0 < RMSE < ∞ 
Evaluation indicesDescription
CC: correlation coefficient Range Correlation level 
0.80–1.00 Very extremely favorable 
0.60–0.79 Extremely favorable 
0.40–0.59 Moderately favorable 
0.20–0.39 Slightly favorable 
0.00–0.19 Very slightly favorable 
−1.00 to 0.80 Extreme negativity 
−0.79 to −0.60 Substantially negative 
−0.59 to −0.40 Medium negative 
−0.39 to −0.20 Weak negative 
−0.19 to −0.01 Very weak negative 
MAE: the term MAE refers to errors that are evenly distributed. 0 < MAE < ∞ 
RMSE: the RMSE is the sample std. dev. of the variances between estimated and the values observed. 0 < RMSE < ∞ 
Table 5

User-defined parameters set for the current study

Applied soft computing modelParameter and value
ANN Hidden layer neurons: 15; Training time = 100 
RF_Bagging Seeds = 15 
GP_PUK Omega = 6; Sigma = 6 
SVM_RBF Gama = 0.01 
SVM_PUK Omega = 9; sigma = 13 
Applied soft computing modelParameter and value
ANN Hidden layer neurons: 15; Training time = 100 
RF_Bagging Seeds = 15 
GP_PUK Omega = 6; Sigma = 6 
SVM_RBF Gama = 0.01 
SVM_PUK Omega = 9; sigma = 13 

ANN model

WEKA software was employed to predict E20 with ANN. Diverse ANN structures underwent testing until the optimum outcomes were achieved. Selecting ANN parameters, such as hidden nodes, learning rate, and network geometry, can be challenging. ANN undergoes training with a solitary hidden layer, facilitating trial-and-error optimization of network geometry. In this study, the hidden layer neurons is 15, with a momentum of 0.1, a learning rate of 0.2, and a training time of 100 (see Table 5). Figure 10 illustrates the actual and projected values of E20 during both the training and testing stages, derived from the ANN technique. The findings demonstrate the accuracy of the prediction of results by the networks. The statistical error measures for the anticipated E20 from training and testing the ANN model are outlined in Table 6, encompassing the RMSE and MAE. Figure 10 displays that most data points in both the testing and training phases are within +15% of the agreement line and hence are near to it, indicating the suitability of the ANN-based model for E20 prediction. The results exhibit substantial consensus between actual and projected values. During the testing phase, ANN yields satisfactory outcomes with a CC value of 0.9595 and errors such as RMSE (0.0215) and MAE (0.018).
Table 6

Statistical indices of soft computing models

SCMCCRMSEMAE
Training dataset 
ANN 0.9843 0.0195 0.0166 
RF_Bagging 0.9848 0.0115 0.0092 
GP_PUK 0.9708 0.0267 0.0211 
SVM_RBF 0.9801 0.012 0.0093 
SVM_PUK 0.9856 0.01 0.0068 
Testing dataset 
ANN 0.9595 0.0215 0.018 
RF_Bagging 0.9295 0.0198 0.0175 
GP_PUK 0.9644 0.0239 0.0198 
SVM_RBF 0.9637 0.0144 0.0127 
SVM_PUK 0.9624 0.0144 0.0124 
SCMCCRMSEMAE
Training dataset 
ANN 0.9843 0.0195 0.0166 
RF_Bagging 0.9848 0.0115 0.0092 
GP_PUK 0.9708 0.0267 0.0211 
SVM_RBF 0.9801 0.012 0.0093 
SVM_PUK 0.9856 0.01 0.0068 
Testing dataset 
ANN 0.9595 0.0215 0.018 
RF_Bagging 0.9295 0.0198 0.0175 
GP_PUK 0.9644 0.0239 0.0198 
SVM_RBF 0.9637 0.0144 0.0127 
SVM_PUK 0.9624 0.0144 0.0124 
Figure 10

Scatter plot showing actual and predicted values of E20 using ANN for (a) training and (b) testing subsets.

Figure 10

Scatter plot showing actual and predicted values of E20 using ANN for (a) training and (b) testing subsets.

Close modal

RF–Bagging model

The RF-based model was also implemented using WEKA software. Developing the RF model is also an error method that requires setting some user-defined parameters. The scattering details of experimental and predicted values of E20 using the RF model with training and testing datasets are shown in Figure 11. It is observed that every scattering offers the most favorable agreement with the line of agreement.
Figure 11

Scatter plot showing actual and predicted values of E20 using RF_Bagging for (a) training and (b) testing subsets.

Figure 11

Scatter plot showing actual and predicted values of E20 using RF_Bagging for (a) training and (b) testing subsets.

Close modal

GP-based E20 model

Developing GP models (‘Gaussian noise,’ μ, η, and φ) involves an iterative process. The model was constructed using a PUK kernel function. The ‘Gaussian noise’ (1) was constant for an accurate assessment. The ideal values for variables set by the user were μ = 6 and φ = 6 (see Table 5). Regarding the GP model development (Table 6), the PUK function exhibited favorable performance compared to alternative models. Figure 12(a) and 12(b) displays the GP_PUK model's results in the training and testing stages, respectively, indicating that all data points fell within a +25% range of dispersion in both stages. Figure 12 and Table 6 prove that the PUK kernel function-based GP model exhibited comparable outcomes, thereby establishing its suitability for predicting E20 by square jets in open channels. The following values were obtained by evaluating the PUK-based GP models throughout the evaluation phase: CC is 0.9644, RMSE is 0.0239, and MAE is 0.0198. Evaluation of assessment parameters revealed that the PUK-based GP model outperformed other models to a slight extent.
Figure 12

Scatter plot showing actual and predicted values of E20 using GP for (a) training and (b) testing subsets.

Figure 12

Scatter plot showing actual and predicted values of E20 using GP for (a) training and (b) testing subsets.

Close modal

SVM_RBF and SVM_PUK models

The WEKA 3.9 application was utilized to execute the SVM framework. The outcomes of the SVM models for the forecast of square jets E20 are featured in Table 6. When compared in testing, the SVM model utilizing the PUK kernel outperformed the RBF kernel (CC = 0.9624, 0.9637; RMSE = 0.0144, 0.0144; and MAE = 0.0124, 0.0124, respectively, for the RBF and PUK kernel). Figure 13 illustrates the execution of the most accurate SVM model for estimating E20. Generally, the SVM model is suitable for E20 calculations. Figure 13(a) and 13(b) depicts that throughout both the developmental and testing stages, the data points are closely aligned with the agreement line and fall within the +25% error range.
Figure 13

Scatter plot showing the actual and predicted values of E20 using SVM for (a) and (c) training and (b) and (d) testing subsets.

Figure 13

Scatter plot showing the actual and predicted values of E20 using SVM for (a) and (c) training and (b) and (d) testing subsets.

Close modal

Comparison of applied models

This section deals with the comparison of applied models in the current investigation. The models ANN, RF_Bagging, GP_PUK, and SVM (PUK and RBF) were used to anticipate E20. Five input parameters, α, Q, Nj, HR, and Froude number, were considered to evaluate these models. The outcomes of testing each created model against three statistical evaluation criteria are shown in Table 6. Figure 14 illustrates the consistency of every model used with experimental data, and it can be inferred from the graphical display that the models created for the study are effective at forecasting E20. To arrive at the ultimate results, it is also necessary to analyze the errors for each model, which are depicted in Figure 15. It demonstrates that ANN has more significant errors than other models in both the training and testing datasets. The errors of the RF technique were barely detectable during training but sharply increased during testing.
Figure 14

Comparison graph of applied soft computing models with experimental data.

Figure 14

Comparison graph of applied soft computing models with experimental data.

Close modal
Figure 15

Applied soft computing model errors during the training and testing stage.

Figure 15

Applied soft computing model errors during the training and testing stage.

Close modal

Sensitivity analysis

A sensitivity analysis was conducted to identify the primary input variable affecting the prediction of E20 in open channel flow for hollow square jets. The dataset that yielded the best performance, GP_PUK, was utilized. Each time, one input variable was removed to create a different training dataset, and the outcomes were measured using CC, MAE, and RMSE. The extent of change observed in these evaluation parameters indicates the variable's influence on E20. Findings from Table 7 indicate that HR depth is the most dominant variable, significantly impacting the prediction of E20 compared to other input variables. The HR is calculated as .

Table 7

Sensitivity analysis

A function containing input parameters resulting in E20Input parameter eliminatedStatistics metrics
CCMAERMSE
E20 = f (HR, α, Nj, Froude number, QNone 0.9644 0.0198 0.0239 
E20 = f (α, Nj, Froude number, QHR 0.8828 0.0254 0.0307 
E20 = f (HR, Nj, Froude number, Qα 0.9104 0.0226 0.0279 
E20 = f (HR, α, Nj, Froude number) 0.951 0.0215 0.0259 
E20 = f (HR, α, Froude number, QNj 0.9591 0.0227 0.0266 
E20 = f (HR, α, Nj, QFroude number 0.9624 0.0225 0.0271 
A function containing input parameters resulting in E20Input parameter eliminatedStatistics metrics
CCMAERMSE
E20 = f (HR, α, Nj, Froude number, QNone 0.9644 0.0198 0.0239 
E20 = f (α, Nj, Froude number, QHR 0.8828 0.0254 0.0307 
E20 = f (HR, Nj, Froude number, Qα 0.9104 0.0226 0.0279 
E20 = f (HR, α, Nj, Froude number) 0.951 0.0215 0.0259 
E20 = f (HR, α, Froude number, QNj 0.9591 0.0227 0.0266 
E20 = f (HR, α, Nj, QFroude number 0.9624 0.0225 0.0271 

Where ‘A’ is the cross-sectional area and ‘P’ is the wetted perimeter, P will be lower if R is greater. It means less water is in contact with the channel section, resulting in less resistance to the flow and allowing more discharge to pass through it. As a result, higher HR results in greater efficiency. The second influential parameter to affect E20 is α. It adds the horizontal component of water weight, which enhances water velocity. The higher velocity tends to increase E20. Apart from α, Nj significantly influences E20 to a greater extent.

Discussion

Screens have been used in open channels for a long time to ensure the removal of coarse pollutants. Screens were first introduced as energy dissipators in the research studies. Furthermore, water treatment facilities make extensive use of screens. As the incoming water is subjected to additional treatment procedures, screens are used in these facilities as a first treatment step to remove oversized particles and solids. Specific mesh sizes are integrated into the screens used in water treatment plants so that varied-sized particles can be successfully captured and retained. Screens lessen the strain on downstream structures and enhance the effectiveness of ensuing treatment operations by removing these bigger particles early on. However, their performance in providing aeration and increasing the DO concentration has recently been realized. In the current work, seven acrylic screens with Nj values of 1, 2, 4, 8, 16, 32, and 64 and a flow area of 30.75 cm2 were used to study aeration in open channel flow. In order to permit water to flow through the perforations in the screens, each screen was positioned and fastened to the three sides of the tilting flume cross section except the top width.

The input parameters, such as α, Nj, Q, HR, and Froude number, were considered for the study. Each parameter studied had a significant effect on E20. Single jets transmit oxygen at a rate that is much lower than that of multiple jets. The results of the current investigation also suggest that E20 increases along with discharge. A higher jet impact angle may boost oxygenation by causing more bubbles to interact with the water in the pool due to deeper jet penetration and a higher jet angle, which would increase oxygen transfer. According to the current study, aeration improves as the flume tilting angle rises, reaching a maximum of 0.37 (or 37%) at a 3° angle. Deswal & Verma (2007a, 2007b) found that the oxygen transferred by multiple jets is much higher than that of a single plunging jet. Shukla & Goel (2018) reported that a solid jet aerator's oxygenation performance is enhanced when it employs several jets instead of a single plunging jet. They also demonstrated how better oxygenation is brought about by higher discharge. When the Nj falls between 1 and 64 and the Q falls between 3.41 and 4.75 L/s, E20 performs best. The most efficient range is from Nj 1 to 16.

Furthermore, the current study's findings showed that a higher discharge tent amounts to higher E20 in the open channel flow system. It also indicated that higher α boosts oxygenation, presumably due to enhanced bubble contact with the water in the pool brought on by deeper jet entry and higher jet angle resulting in higher O2 transfer (Kumar et al. 2018a, 2018b). The current study found that as the α increases, the E20 also improves, reaching up to 0.37 (or 37%) at the highest angle of 3°. Cihat Tuna et al. (2014) showed that the Froude number and the relationship between the cross-sectional areas of the water flow and the conduit had a particularly substantial impact on E20. Another literature by Puri et al. (2023a, 2023b) suggested that there has been an increase in the Froude number with higher Q and O2 transfer. The present study's findings also confirm that E20 and the Froude number directly relate to each other. Soft computing techniques include fuzzy logic, genetic algorithms, ANN, ML, and expert systems. E20 prediction is a high-priority study for densely polluted water management resources. The prediction of E20 was the focus of the study; therefore, the efficacy of soft computing models of ANN, RF_Bagging, SVM (PUK and RBF kernels), and GP (PUK kernel) to estimate square jet aeration in an open channel flow was investigated in the current study. The selection was based on the type of classifiers of soft computing models, such as NN, decision trees, ML, such as support vector machines, and a Gaussian process. Accordingly, the aforementioned soft computing models were applied to assess the prediction capabilities of such classifiers. Five input parameters, α, Q, Nj, HR, and Froude number, were utilized to obtain the predicted values of E20. The effectiveness of models was compared using several statistical criteria such as CC, MAE, and RMSE. It has been observed that the CC value of RF_Bagging drops from 0.9848 to 0.9295 during the testing stage and hence declines its performance. The highest CC value exhibited by GP_PUK during the testing stage was 0.9644. The results showed that the GP_PUK model was found to be outperforming other models in prediction capability for E20 due to its CC value in the testing stage. In the testing stage, the CC values found in ANN, RF_Bagging, SVM_RBF, and SVM_PUK were 0.9595, 09295, 0.9637, and 0.9624. GP is an ML method frequently employed for quantitative issue forecasting (Sihag 2018; Puri et al. 2023a, 2023b). The performance of GP_PUK has been found to be the best in various studies, such as the prediction of river discharge (Nivesh et al. 2022) and the prediction of infiltration rates in permeable stormwater channels (Yaseen et al. 2021). The sensitivity analysis revealed that the input parameter HR is highly sensitive to E20 in aeration through square jets in an open channel flow system. Earlier, the prediction for E20 was devoid of input parameters such as tilt angle, discharge, number of jets, cumulative hydraulic radius, and Froude number in an open channel with square jets (Malik & Kumar 2015; Mahdiyar et al. 2019; Natarajan & Sudheer 2020; Sihag et al. 2020; Yaseen et al. 2021; Essam et al. 2022; Nivesh et al. 2022; Ehteram et al. 2023; Ibrahim et al. 2023) by developing GP_PUK, ANN, RF_Bagging, SVM_RBF, and SVM_PUK soft computing models.

The practical implication of the study is that the DO level in the water has been raised to the level at which the square geometry of plunging jets is quite helpful in achieving E20 to the extent of 37%. This increase can be useful for cultivating sericulture, which is helpful for progressive aquatic life sustainability. On the other hand, the stakeholders can cut the cost of treatment by using oxygenated water to supply water to civic bodies. The enriched, oxygenated water can also be congenial to the agricultural and horticultural produce. The oxygenated water is produced by utilizing the square geometrical plunging jets under gravity in open channel flow, for which no electrical power supply is required. Thus, no energy cost is involved.

In order to ascertain the effectiveness of aerating deoxygenated water with a square plunging jet made from acrylic screens, the current study investigates the effects of tilt angle, discharge, number of jets, cumulative hydraulic radius, and Froude number. The experimental results showed that increased tilt angle and discharge helped E20 positively. The increase of discharge from 3.41 to 4.75 L/s, tilt angle from 0° to 3°, and number of jets (Nj) from 1 to 64 increased E20 from 20 to 76%. In an open channel with a modest Q and a comparatively smooth surface, the most significant E20 reached was about 37%. The aeration with achieved efficiency is good enough for sustainable sericulture and water bodies requiring continuous aeration. The simplicity of an open channel system with simple acrylic screens does not require skilled artistry. It is easily manageable by the end users of the rural population, where sophisticated systems may not be feasible. If used, the cost of an automated system can be reduced to a greater extent due to the availability of already treated water with higher E20. Focusing on simple and easily manageable systems significantly contributes to sustainable water management practices.

  • The study was further expanded to predict the E20 obtained experimentally by developing suitable soft computing models. The following ML algorithms, ANN, RF_Bagging, GP_PUK, SVM_PUK, and SVM_RBF, were utilized to develop soft computing models. The GP model with the PUK kernel function outperformed all other models with statistical indices such as CC value of 0.964, MAE value of 0.0159, and RMSE value of 0.019 in the testing stage.

  • According to sensitivity analysis, the cumulative hydraulic radius was most sensitive to E20 out of five input parameters.

  • There is ample scope for conducting studies related to volumetric oxygen transfer (KLa20), OTE, and standard oxygen transfer efficiency for open channel water flow systems for studying oxygen transfer. In addition, the effect of hydraulic jump and Reynolds number can also be explored in such an open channel flow system. Head loss was not measured; future recommendations can be to study head loss. Multivariate polynomial regression can be done on the current data to study the effect of interactions among input variables.

The authors thank the deanship of scientific research at King Khalid University for funding this work through a large group project under grant number (RGP. 2/94/44). The authors duly acknowledge with thanks the contribution of the authors from the literature whose research articles have been cited in this study.

The data have been taken from the experimental work performed by authors in the Hydraulics Lab of Shoolini University, Solan, Himachal Pradesh, India, 173229.

No funding source is available for the current study.

D.P. collected the experimental data, wrote the draft preparation. P.S. reviewed and edited the article. M.S.T. supervised the article, B.S. proofread edited.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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