# Machine Learning Approach for Rapid Estimation of Five-Day Biochemical Oxygen Demand in Wastewater

^{1}

^{2}

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## Abstract

**:**

_{4}-N), and Total Phosphorous (T-P) concentrations in wastewater. Twelve different transfer functions are investigated, including the common Hyperbolic Tangent Sigmoid (HTS), Log-sigmoid (LS), and Linear (Li) functions. This research evaluated 576,000 ANN models while considering the variable random number generator due to the ten alternative ANN configuration parameters. This study proposes a new approach to assessing water resources and wastewater facility performance. It also demonstrates ANN’s environmental and educational applications. Based on their RMSE index over the testing datasets and their configuration parameters, twenty ANN architectures are ranked. A BOD prediction equation written in Excel makes testing and applying in real-world applications easier. The developed and proposed ANN-LM 5-8-1 model depicting almost ideal performance metrics proved to be a reliable and helpful tool for scientists, researchers, engineers, and practitioners in water system monitoring and the design phase of wastewater treatment plants.

## 1. Introduction

_{5}) [1] (Table 1). It is a measurement of the organic contaminants in water that can be broken down by biological processes [1]. The main downside of this measurement is the time (5 days) required to complete it [2].

_{4}-N (Ammonium Nitrogen) and T-P (Total Phosphorous) makes it challenging to match all the detection methods to simultaneously measure BOD, COD, SS, T-N, NH

_{4}-N and T-P contents to evaluate the performance of wastewater treatment processes (Table 1). BOD, T-N and T-P, among others, are crucial parameters for estimating Water Quality Indices and assessing water bodies [4,5,6]. Moreover, the off-site detection and long detection times of the approaches mentioned above cannot meet the requirements of on-site, real-time monitoring of contaminants in automated water treatment operations [7]. According to Jouanneau et al. [1] the determination of BOD

_{5}is helpful in three ways: (a) it illustrates if the wastewater discharge and waste treatment technique comply with current objective values and legislation; (b) the COD/BOD

_{5}ratio demonstrates the biodegradable fraction of effluent; and (c) the ratio of BOD

_{5}to COD in wastewater treatment facilities represents the biodegradable portion of an effluent.

_{4}-N and T-P) included in the analysis of this study reveals that it is hard to use classical computing techniques such as regression analysis to delineate related issues and extract significant results. Concerning water and wastewater treatment and assessment of water quality, many research studies and scientific publications have been conducted out applying Artificial Intelligence Techniques [8,9,10]. In the last two decades, soft computing techniques such as Machine Learning (ML) proved reliable and robust methods to model such topics with a strongly non-linear nature [11,12,13,14,15].

**Table 1.**Groups of main methods for determining BOD, required time and measurement range for each method.

Method | Required Time (Median) | Measurement Range (mg L ^{−1}) | References |
---|---|---|---|

Chemical or Electrochemical measurement | |||

Standard reference method | 5 days | 0–6 | ISO 5815-1:2003 [18]; Jouanneau et al. [1] |

Modified reference method | 5 days | 0–6 | McDonagh et al. [19]; McEvoy et al. [20]; Xiong et al. [21]; Xu et al. [22] |

Photometric method | 5 days | 0–6 | Jouanneau et al. [1] |

Manometric method | 5 days | 0–700 | Jouanneau et al. [1] |

BOD prediction | |||

Biosensor based on bioluminescent bacteria | 72 min | 0–200 | Sakaguchi et al. [23,24] |

Microbial fuel cells | 315 min | 0–200 | Jouanneau et al. [1]; Kim et al. [25] |

Biosensor with entrapped bacteria | 10 min | 0–500 | Karube [26]; Liu et al. [27] |

**Table 2.**Approaches for estimating BOD, input, output variables and correlation coefficient (R

^{2}) for each approach.

Approach | Number of Input Variables | Input Variables | Output Variables | R^{2} | Type of Water | References |
---|---|---|---|---|---|---|

ANN | 4 | TSS, TS, pH, T | BOD, COD | 0.63–0.81 | wastewater | Zare Abyaneh [28] |

ANN | 11 | pH, TS, T-Alk, T-Hard, Cl, PO_{4}^{3−}, K, Na, NH_{4}-N, NO_{3}-N, COD | DO, BOD | 0.77–0.85 | river water | Singh et al. [29] |

ANFIS | 9 | pH, alkalinity, T-Hard, TS, TDS, K, PO_{4}^{3−}, NO_{3}^{−}, DO | BOD | 0.69–0.85 | river water | Ahmed and Ali Shah [30] |

ANN | 11 | pH, T-Alk, T-Hard, TS, COD, NH_{4}-N, NO_{3}-N, Cl, PO_{4}^{3−}, K, Na | DO, BOD | 0.74–0.90 | river water | Basant et al. [31] |

ANN | 8 | T, turbidity, pH, CND, TDS, TSS, DO, COD | BOD | 0.69 | wastewater | Asami et al. [32] |

_{4}

^{3−}: phosphate, K: potassium, Na: sodium, NH

_{4}-N: ammonia nitrogen, NO

_{3}-N: nitrate nitrogen, NO

_{3}

^{−}: nitrate, DO: dissolved oxygen, COD: chemical oxygen demand, CND: electrical conductivity, TDS: total dissolved solids.

_{5}. Section 4 provides the presented results on the development of a closed-form equation for the estimation of BOD

_{5}in wastewater and the mapping of BOD

_{5,}revealing its strongly nonlinear nature. In Section 5 the limitations of the proposed model are presented, followed by concluding remarks in Section 6.

## 2. Research Significance

_{4}-N and T-P concentrations in wastewater. This study may provide a new idea for monitoring water resources and the performance of the wastewater treatment plant.

## 3. Materials and Methods

#### 3.1. Artificial Neural Networks

_{5}). Specifically, for the estimation of BOD

_{5}in wastewater concerning COD, SS, TN, NH

_{4}-N and TP, a plethora of different ANN architectures will be trained and developed. To this end, a detailed and in-depth investigation of the crucial parameters affecting the performance of ANN models, such as the number of neurons per hidden layers, activation functions, data normalization techniques and cost functions, has been conducted, and it is presented in the following sections.

#### 3.2. Experimental Database

_{5}in wastewater, an experimental database was created, comprised of 387 datasets that correspond to 387 laboratory measurements that were conducted at the entrance of the sewage treatment plant located at Komotini region, Northern Greece. The samples were collected on a monthly basis from 2014–2021. Standard analytical methods were used to determine all parameters. All analytical methods were described in detail for water and wastewater experiments [41]. For each wastewater sample six water quality variables were laboratory measured. Precisely, for each sample were estimated the COD, SS, TN, NH

_{4}-N, TP and BOD

_{5}concentrations. The measured values of the first five variables were used as input parameters, while the value of the sixth variable (BOD

_{5}) as the output parameter during the training and development process of ANN models. The database is presented in Table S1 of Supplementary Materials.

_{5}in relation with each one of the five input parameters using the Cosine Amplitude Method (CAM) [42] and the experimental database. Researchers have widely adopted CAM method to determine the effect of each input on the output [43,44,45,46].

_{5}.

#### 3.3. Sensitivity Analysis of the BOD_{5} on the Input Parameters Based on the Experimental Database

_{5}(Figure 4). This finding fully agrees with Pearson correlation factors presented in the preview’s subsection. Furthermore, it is worth noting that all the input parameters can be characterized as crucial since they have also strongly related to BOD

_{5}, achieving values greater than 0.98.

#### 3.4. Performance Indexes

^{2}) [49,51,52,53,54,55].

^{2}) to assess the predictive accuracy of models [30,53]. The comparison of the performance of mathematical using the Pearson correlation factor is considered precarious given that except the comparison of the values of R or R

^{2}it is also required the comparison of the inclination angle of the line. Such a case is when a mathematical simulant always predicts a constant value regardless of the input parameters values. In this case, the value of R = 1.00 while the inclination angle is equal to zero.

## 4. Results and Discussion

#### 4.1. Development of ANN Models

_{5}), achieves the best overall performance metrics, both in terms of RMSE (16.8563) and R (0.9443). The best ANN LM 5-8-1 model utilizes the MinMax function for data normalization, which converts input and output values between [−1.00, 1.00]. It also applies as activation functions the Log-Sigmoid function (LS) for the input layer and the Symmetric saturating linear function (SSL) for the output layer, with the MSE function as its cost function. Figure 5 exhibits the neuron layout and overall architecture of the best ANN LM 5-8-1 model. Table 7 displays detailed and in-depth achieved performance indices for both training and testing datasets of the best ANN LM 5-8-1 model. Its performance on training datasets is expected to improve, particularly in the a20-index, where it matches over 98% of the samples within a 20 percent margin. The same index is 100.00% when compared to the testing datasets, which is an excellent value. At this point should be noted that the better achieved indices for testing datasets compared to training datasets clearly depict that not overfitting problems is taken place. To the authors best knowledge, the achieved performance is the better than any other performance reported in the related topic.

_{5}in wastewater both for training and testing datasets.

#### 4.2. Closed-Form Equation for the Estimation of BOD_{5} in Wastewater

_{5}, using COD, SS, TN, NH

_{4}-N and TP are expressed by the following equation for the optimum developed ANN LM 5-8-1 model:

_{5}present in the database used for training and developing ANN models. The satlins and logsig are the symmetric saturating linear transfer function (SSL) and the Log-sigmoid transfer function (LS), respectively, as discussed. Their details (equations and graphs) are presented in detail in Table A1 of the Appendix A.

_{4}-N and TP). It is expressed as:

#### 4.3. Mapping of BOD_{5}

_{5}. Based on the results of this analytical investigation they were derived a set of contour maps of the BOD

_{5}in relation of the input parameters (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12). Based on these figures, it is shown in a robust manner that the proposed ANN-LM 5-8-1 model ensures that the known and widely encountered phenomenon of overfitting is not taking place. This is implied by the fact that all the derived charts and the derived curves are exceptionally smooth and do not display sudden variations having as a result to exhibit the laws that govern the variation of BOD

_{5}concerning COD, SS, TN, NH

_{4}-N and TP.

^{−1}, respectively, and SS varies between 200 and 300 mg L

^{−1}. Figure 8 and Figure 9, the variations of COD and TN present smooth curvature, searching all over the map area. A more detailed look at Figure 8 (left corner) shows that the lowest contents of COD and TN, the BOD presents the highest value only in one part of the map. It is found that the COD and TN are sensitive to BOD parameter. Figure 10, Figure 11 and Figure 12 presents that for lowest contents of TP and TN, the BOD has moderate value when SS ranges from 250 and 300 mg L

^{−1}, and NH

_{4}-N and COD is 60 and 400 mg L

^{−1}, respectively. A more detailed look at Figure 12, presents that the lowest concentrations of TP and TN, the BOD shows the highest value in the significant part of the map.

## 5. Limitations and Future Works

_{5}in wastewater.

## 6. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Notation

ANN(s) | Artificial Neural Network(s) |

BOD | Biochemical Oxygen Demand |

BPNN | Back Propagation Neural Network |

COD | Chemical Oxygen Demand |

CS | Compressive Strength |

HL | Hard-limit transfer function |

HTS | Hyperbolic Tangent Sigmoid transfer function |

Li | Linear transfer function |

LS | Log-Sigmoid transfer function |

MAPE | Mean Absolute Percentage Error |

MSE | Mean Square Error |

${\mathrm{n}}_{e}$ | Effective Porosity |

${N}_{ip}$ | Number of input parameters |

${N}_{n}$ | Number of hidden layers |

${N}_{op}$ | Number of output parameters |

${N}_{td}$ | Number of datasets |

NRB | Normalized Radial Basis transfer function |

NH_{4}-N | Ammonia Nitrogen |

PLi | Positive Linear transfer function |

R | Pearson correlation coefficient |

RB | Radial Basis transfer function |

${\mathrm{R}}_{\mathrm{n}}$ | Schmidt hammer rebound number |

SHL | Symmetric hard-limit transfer function |

SM | Soft Max transfer function |

SS | Suspended Solids |

SSE | Sum Square Error |

SSL | Symmetric Saturating Linear transfer function |

TB | Triangular Basis transfer function |

TN | Total Nitrogen |

TP | Total Phosphorous |

UCS | Unconfined Compressive Strength |

${\mathrm{V}}_{\mathrm{p}}$ | Ultrasonic Pulse Velocity |

WWTP(s) | Wastewater Treatment Plant(s) |

## Appendix A

SN | Transfer Function/Equation/Matlab Function | Graph |
---|---|---|

1 | The symmetric saturating linear transfer function (SSL) | |

$a=f\left(n\right)=\{\begin{array}{c}-1,\\ \begin{array}{c}n,\\ -1,\end{array}\end{array}\begin{array}{c}n\le -1\\ \begin{array}{c}-1n1\\ n\ge 1\end{array}\end{array}$ | ||

$a=f\left(n\right)=\mathrm{satlins}\left(n\right)$ | ||

2 | The log-sigmoid transfer function (LS) | |

$a=\frac{1}{1+\mathrm{exp}\left(-n\right)}$ | ||

$\mathrm{a}=f\left(n\right)=\mathrm{logsig}\text{}\left(\mathrm{n}\right)$ |

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**Figure 3.**Scatter plots and histograms of the studied input and output parameters: (

**a**,

**b**) COD; (

**c**,

**d**) SS; (

**e**,

**f**) TN; (

**g**,

**h**) NH

_{4}-N; (

**i**,

**j**) TP; and (

**k**,

**l**) BOD

_{5}.

**Figure 4.**Sensitivity analysis of the Biochemical Oxygen Demand (BOD

_{5}) on input parameters based on the experimental database.

**Figure 6.**Experimental vs. predicted values of the five-day biochemical oxygen demand (BOD

_{5}) in wastewater for training and testing datasets, using the developed ANN LM 5-8-1 model.

**Figure 7.**BOD

_{5}contour maps for three different values of SS (in mg L

^{−1}) while NH

_{4}-N = 60 mg L

^{−1}and TP = 8 mg L

^{−1}are constant: (

**a**) SS = 200; (

**b**) SS = 250; and (

**c**) SS = 300.

**Figure 8.**BOD

_{5}contour maps for three different values of NH

_{4}-N (in mg L

^{−1}) while SS = 250 mg L

^{−1}and TP = 8 mg L

^{−1}are constant: (

**a**) NH

_{4}-N = 50; (

**b**) NH

_{4}-N = 60; and (

**c**) NH

_{4}-N = 70.

**Figure 9.**BOD

_{5}contour maps for three different values of TP (in mg L

^{−1}) while SS = 250 mg L

^{−1}and NH

_{4}-N = 60 mg L

^{−1}are constant: (

**a**) TP = 6; (

**b**) TP = 8; and (

**c**) TP = 10.

**Figure 10.**BOD

_{5}contour maps for three different values of SS (in mg L

^{−1}) while NH

_{4}N = 60 mg L

^{−1}and COD = 400 mg L

^{−1}are constant: (

**a**) SS = 200; (

**b**) SS = 250; and (

**c**) SS = 300.

**Figure 11.**BOD

_{5}contour maps for three different values of NH

_{4}-N (in mg L

^{−1}) while SS = 250 mg L

^{−1}and COD = 400 mg L

^{−1}are constant: (

**a**) NH

_{4}-N = 50; (

**b**) NH

_{4}-N = 60; and (

**c**) NH

_{4}-N = 70.

**Figure 12.**BOD

_{5}contour maps for three different values of COD (in mg L

^{−1}) while SS = 250 mg L

^{−1}and NH

_{4}-N = 60 mg L

^{−1}are constant: (

**a**) COD = 300; (

**b**) COD = 400; and (

**c**) COD = 500.

**Table 3.**Statistical analysis of the input and output parameters used in this research for the training and development of artificial neural networks.

Variable | Symbol | Units | Category | Data Used in NN Models | ||||
---|---|---|---|---|---|---|---|---|

Min | Average | Max | STD | CV | ||||

Chemical Oxygen Demand | COD | mg L^{−1} | Input | 211.00 | 410.73 | 551.00 | 71.37 | 0.17 |

Suspended Solids | SS | mg L^{−1} | Input | 142.00 | 228.34 | 302.00 | 27.64 | 0.12 |

Total Nitrogen | TN | mg L^{−1} | Input | 44.20 | 66.44 | 84.25 | 9.17 | 0.14 |

Ammonia Nitrogen | NH_{4}-N | mg L^{−1} | Input | 39.30 | 52.52 | 70.10 | 7.67 | 0.15 |

Total Phosphorous | TP | mg L^{−1} | Input | 2.96 | 5.86 | 8.65 | 1.17 | 0.20 |

Biochemical Oxygen Demand | BOD_{5} | mg L^{−1} | Output | 128.00 | 238.27 | 348.00 | 45.35 | 0.19 |

Variable | Symbol | COD | SS | TN | NH_{4}-N | TP | BOD_{5} |
---|---|---|---|---|---|---|---|

Chemical Oxygen Demand | COD | 1.00 | 0.29 | 0.78 | 0.72 | 0.54 | 0.78 |

Suspended Solids | SS | 0.29 | 1.00 | 0.35 | 0.30 | 0.18 | 0.43 |

Total Nitrogen | TN | 0.78 | 0.35 | 1.00 | 0.72 | 0.64 | 0.74 |

Ammonia Nitrogen | NH_{4}-N | 0.72 | 0.30 | 0.72 | 1.00 | 0.27 | 0.58 |

Total Phosphorous | TP | 0.54 | 0.18 | 0.64 | 0.27 | 1.00 | 0.60 |

Biochemical Oxygen Demand | BOD_{5} | 0.78 | 0.43 | 0.74 | 0.58 | 0.60 | 1.00 |

Parameter | Value | Matlab Function(s) |
---|---|---|

Training Algorithm | Levenberg-Marquardt Algorithm | trainlm |

Normalization | Without any normalization Minmax in the range [0.10–0.90], [0.00–1.00] and [−1.00–1.00] Zscore | Mapminmax zscore |

Number of Hidden Layers | 1 | |

Number of Neurons per Hidden Layer | 1 to 50 by step 1 | |

Control random number generation | 10 different random generation | rand(seed, generator), where the generator range from 1 to 10 by step 1 |

Training Goal | 0 | |

Epochs | 200 | |

Cost Function | Mean Square Error (MSE) Sum Square Error (SSE) | mse sse |

Transfer Functions | Hyperbolic Tangent Sigmoid transfer function (HTS) Log-sigmoid transfer function (LS) Linear transfer function (Li) Positive linear transfer function (PLi) Symmetric saturating linear transfer function (SSL) Soft max transfer function (SM) Competitive transfer function (Co) Triangular basis transfer function (TB) Radial basis transfer function (RB) Normalized radial basis transfer function (NRB) Hard-limit transfer function (HL) Symmetric hard-limit transfer function (SHL) | tansig logsig purelin poslin satlins softmax compet tribas radbas radbasn hardlim hardlims |

**Table 6.**Architectures and hyperparameters of the top twenty developed ANN LM models based RMSE index and testing phase.

Ranking | Normalization Technique | Cost Function | Transfer Function | Architecture | Datasets Performance Indices | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|

Input Layer | Output Layer | Testing | Training | All | |||||||

R | RMSE | R | RMSE | R | RMSE | ||||||

1 | Minmax [−1.00, 1.00] | MSE | logsig | satlins | 5-8-1 | 0.9443 | 16.8563 | 0.9208 | 17.6044 | 0.9217 | 17.6065 |

2 | Minmax [0.10, 0.90] | MSE | poslin | satlins | 5-29-1 | 0.9421 | 17.8418 | 0.9057 | 19.1355 | 0.9110 | 18.7234 |

3 | Minmax [−1.00, 1.00] | SSE | tribas | tansig | 5-14-1 | 0.9407 | 17.7982 | 0.9319 | 16.3818 | 0.9287 | 16.8636 |

4 | Minmax [0.10, 0.90] | MSE | tansig | purelin | 5-13-1 | 0.9406 | 17.5336 | 0.9238 | 17.2764 | 0.9214 | 17.6425 |

5 | Minmax [0.10, 0.90] | MSE | softmax | radbas | 5-17-1 | 0.9400 | 17.7336 | 0.9156 | 18.1454 | 0.9164 | 18.2035 |

6 | Minmax [−1.00, 1.00] | MSE | tansig | purelin | 5-11-1 | 0.9400 | 17.5935 | 0.9298 | 16.6148 | 0.9224 | 17.5536 |

7 | Minmax [0.10, 0.90] | MSE | logsig | satlins | 5-8-1 | 0.9399 | 17.5855 | 0.9161 | 18.1001 | 0.9179 | 18.0053 |

8 | Minmax [0.10, 0.90] | SSE | softmax | logsig | 5-29-1 | 0.9396 | 17.7540 | 0.9311 | 16.4914 | 0.9275 | 17.0689 |

9 | Minmax [0.10, 0.90] | SSE | satlins | purelin | 5-15-1 | 0.9394 | 18.6357 | 0.9012 | 19.6172 | 0.9066 | 19.3523 |

10 | Minmax [0.00, 1.00] | MSE | logsig | satlins | 5-5-1 | 0.9393 | 18.7060 | 0.9136 | 18.4874 | 0.9150 | 18.5984 |

11 | Minmax [0.10, 0.90] | SSE | softmax | satlins | 5-26-1 | 0.9393 | 18.1376 | 0.9077 | 18.9646 | 0.9116 | 18.7815 |

12 | Minmax [0.00, 1.00] | MSE | softmax | purelin | 5-41-1 | 0.9388 | 17.8211 | 0.9217 | 17.5291 | 0.9215 | 17.7143 |

13 | Minmax [0.10, 0.90] | MSE | tansig | purelin | 5-8-1 | 0.9388 | 17.6942 | 0.9160 | 18.1425 | 0.9179 | 17.9936 |

14 | Minmax [0.10, 0.90] | MSE | softmax | radbas | 5-23-1 | 0.9388 | 19.0606 | 0.9135 | 18.4091 | 0.9155 | 18.4651 |

15 | Minmax [0.10, 0.90] | MSE | logsig | logsig | 5-12-1 | 0.9387 | 16.7798 | 0.9320 | 16.3995 | 0.9282 | 16.8627 |

16 | Minmax [0.00, 1.00] | MSE | softmax | purelin | 5-22-1 | 0.9387 | 18.2816 | 0.9105 | 18.6790 | 0.9125 | 18.6410 |

17 | Minmax [0.00, 1.00] | MSE | softmax | poslin | 5-22-1 | 0.9387 | 18.2816 | 0.9105 | 18.6790 | 0.9125 | 18.6410 |

18 | Minmax [0.00, 1.00] | MSE | tansig | satlins | 5-6-1 | 0.9386 | 17.5546 | 0.9164 | 18.0637 | 0.9166 | 18.1632 |

19 | Zscore | MSE | poslin | purelin | 5-9-1 | 0.9385 | 18.1809 | 0.9076 | 18.9472 | 0.9105 | 18.7648 |

20 | Minmax [0.00, 1.00] | SSE | tansig | purelin | 5-7-1 | 0.9384 | 17.1610 | 0.9100 | 18.7052 | 0.9110 | 18.7294 |

Model | Datasets | Performance Indices | ||||
---|---|---|---|---|---|---|

a20-Index | R | RMSE | MAPE | VAF | ||

ANN LM 5-8-1 | Training | 0.9806 | 0.9208 | 17.6044 | 0.0582 | 84.7803 |

Test | 1 | 0.9443 | 16.8563 | 0.0571 | 89.1499 |

IW{1,1} | ${\left[\mathsf{L}\mathsf{W}\left\{2,1\right\}\right]}^{\mathit{T}}$ | $\left[\mathsf{B}\left\{1,1\right\}\right]$ | $\left[\mathsf{B}\left\{2,1\right\}\right]$ | ||||
---|---|---|---|---|---|---|---|

(8 × 3) | (1 × 8) | (8 × 1) | (1 × 1) | ||||

3.8747 | −3.3026 | 0.8841 | 9.8281 | −1.9581 | 2.9497 | 9.6809 | −0.4917 |

−3.8650 | 3.1701 | 0.9485 | −1.1494 | 1.9099 | −2.6746 | 2.1566 | |

1.2295 | −2.3973 | −1.2553 | 2.7258 | −2.3405 | −2.3231 | 1.0974 | |

−4.6036 | 3.7836 | 0.8690 | −4.0565 | 7.1579 | −1.1579 | −1.3150 | |

−3.0096 | 3.4372 | 0.3911 | −0.1472 | 2.3667 | 2.2639 | 2.2077 | |

−1.0593 | −4.5452 | 1.0995 | −4.5926 | −1.9055 | −0.6063 | 6.0657 | |

−4.7120 | 3.0951 | −2.9974 | −9.7771 | 2.9426 | 2.6242 | −10.6922 | |

1.6124 | −9.0346 | 0.1278 | 3.6006 | 8.0047 | 0.3364 | 7.7832 |

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## Share and Cite

**MDPI and ACS Style**

Asteris, P.G.; Alexakis, D.E.; Tsoukalas, M.Z.; Gamvroula, D.E.; Guney, D.
Machine Learning Approach for Rapid Estimation of Five-Day Biochemical Oxygen Demand in Wastewater. *Water* **2023**, *15*, 103.
https://doi.org/10.3390/w15010103

**AMA Style**

Asteris PG, Alexakis DE, Tsoukalas MZ, Gamvroula DE, Guney D.
Machine Learning Approach for Rapid Estimation of Five-Day Biochemical Oxygen Demand in Wastewater. *Water*. 2023; 15(1):103.
https://doi.org/10.3390/w15010103

**Chicago/Turabian Style**

Asteris, Panagiotis G., Dimitrios E. Alexakis, Markos Z. Tsoukalas, Dimitra E. Gamvroula, and Deniz Guney.
2023. "Machine Learning Approach for Rapid Estimation of Five-Day Biochemical Oxygen Demand in Wastewater" *Water* 15, no. 1: 103.
https://doi.org/10.3390/w15010103