# Experimental Evaluation of Tubular Flocculator Implemented in the Field for Drinking Water Supply: Application in the Developing World

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## Abstract

**:**

^{−1}. The results showed that HTF can be useful as a flocculation unit in a purification system.

## 1. Introduction

## 2. Materials and Methods

#### 2.1. The Description of the Location of the Study

#### 2.2. Design and Construction of the Pilot Treatment System

#### 2.2.1. Rapid Mixer

^{−1}, a retention time of 0.55 s, and a Froude number of 5.86, which allows it to maintain a hydraulic jump established for achieving adequate coagulation.

#### 2.2.2. Horizontal Flow Tubular Flocculator

#### 2.2.3. High-Rate Settler

^{3}/m

^{2}d, and (c) Reynolds Number of 71. Finally, a settler 0.6 m in width, 1.20 m in length, and 1.80 m in depth was obtained. Figure 1 shows the location of the high-rate settler, which was made of galvanized brass.

#### 2.2.4. Rapid Sand Filters

^{3}/m

^{2}/h was implemented to retain the particles that were not retained in the settler, and these filters were interconnected at the outlet with each other by means of valves located in the back. Individual valves located at the top of the filters were provided to evacuate the backwash water. For the design of the filters, the methodology used by Romero [23] and Arboleda [25] was used. A filter bed made up of gravel and sand was used. For the design, a filtration rate of 120 m

^{3}/m

^{2}/day and a sand depth of 0.6 m were used. The following characteristics were chosen for the sand: (a) Effective size TE = 0.55 mm, (b) a uniformity coefficient CU = 1.60, and (c) a porosity = 0.42. With the collaboration of the “Bayas” Water Board, the filters could be implemented using PVC pipes 300 mm in diameter. Each one of the four filters was built operating with a flow rate of 0.098 L/s and producing a flow of 0.39 L/s jointly. The other 0.61 L/s was sent to the DWTP filters. Figure 1 shows the location of the rapid sand filters after the settler.

#### 2.3. Hydraulic Evaluation of the Pilot Horizontal Tubular Flocculator

#### 2.3.1. Calculation of the Theoretical Retention Time

_{o}) in the HTF, in which V is the volume of the flocculator and Q is the flow rate of water entering the system. The volume of the HTF was determined from the length (L) and the radius (r) of the pipe (V = πr

^{2}L). The TRT was calculated for the five flows used (0.25, 0.5, 0.75, 1.0, and 2.0 L/s) and for the two lengths tested (L1 = 68.4 m and L2 = 97.6 m).

#### 2.3.2. Determination of Mean Retention Time

_{m}is the mean retention time, C

_{o}is the initial concentration of the tracer substance, and C

_{i}is the concentration in an instant t

_{i}.

#### 2.3.3. Hydraulic Characteristics of the HTF

#### 2.3.4. Calculation of the Velocity Gradient

^{−1}), h

_{f}is the head loss (m), ⍴ is the water density (kg/m

^{3}), g is the gravity (m/s

^{2}), µ is the dynamic viscosity of water (kg/m s), and t is the retention time (s).

^{−7}m PVC pipe was taken into account [34].

_{f}in Equation (16), taking into account the coefficient of kinetic load (K), which varies depending on the type of accessory.

_{a}is the load loss due to accessories (m) and K is the coefficient of kinetic load (dimensionless).

#### 2.4. Experimental Analysis for Evaluating the Horizontal Tubular Flocculator

#### 2.4.1. Pilot System Operation

#### 2.4.2. Determination of Optimal Dose of Coagulant

#### 2.4.3. Experimental Tests varying Lengths of the HTF, Flow Rates, and Turbidities of Raw Water

#### 2.4.4. Sampling and Parameter Analysis

#### 2.4.5. Removal Efficiency

#### 2.5. Statistical Analysis

#### 2.6. Construction Cost Comparison

_{M}is the maximum daily flow in mgd.

## 3. Results

#### 3.1. This Evaluation of the Theoretical Retention Time in the Tubular Flocculator

#### 3.2. Evaluation of Mean Retention Time

#### 3.3. Evaluation of the Hydraulic Behavior of the HTF by Means of the Wolf Resnick Simplified Method

#### 3.4. Velocity Gradient Evaluation

^{−1}, which is the maximum value recommended for conventional flocculators [23]. However, if the range suggested by Mohammed and Shakir [46] for G is taken into account, which is 10 and 75 s

^{−1}, only flows of 0.5, 0.75, and 1 L/s meet the range established by these authors. After the analysis of the values of the theoretical gradients with respect to the real gradients, it can be seen that the theoretical gradients are slightly less than the real gradients at each flow rate. This situation occurs because the mathematical models indicate ideal values due to the fact that these models do not take into account the real physical and geometric conditions of a certain unit.

#### 3.5. Evaluation of the Dose of Coagulant

#### 3.5.1. Dosage Curve Obtained by Jar Test

^{−1}, obtained by applying Equation (12) for the aforementioned retention time.

#### 3.5.2. Applied Doses in Field Trials

#### 3.6. Turbidity and Color Removal Efficiency

#### 3.6.1. Impact of HTF on Turbidity and Color Removal Efficiency after Settler

#### 3.6.2. Impact of HTF on Turbidity and Color Removal Efficiency after the Filter

#### 3.7. Comparison of Turbidity and Color Removal between the Pilot System and the Conventional Plant

#### 3.7.1. Statistical Summary of the Efficiency of the HTF + Settler System

#### 3.7.2. Statistical Summary of the Efficiency of the HTF + Settler + Filter System

#### 3.8. Comparison of Means with Wilcoxon Test

#### 3.9. Turbidity Removal Estimation Model

^{−1}. For a given gradient, the efficiency increases with the turbidity of the raw water used in this study from 10 to 246 NTU. The velocity gradient associated with raw water turbidity constitutes an optimum value for a given efficiency.

^{2}is the square of the correlation coefficient or determination coefficient (R

^{2}∈ [0, 1]), Adjusted R

^{2}is the R

^{2}adjusted by the number of variables of the model (Adjusted R

^{2}∈ [0, 1]), and Se is the standard error of the estimation. Durbin–Watson values should be greater than 1.5 and less than 2.5 to indicate that the multiple linear regression data are free of first-order linear autocorrelation. For efficiency, the Durbin–Watson values were 1.618 and 1.711 in the linear model and in the model applying logarithms, respectively. In both models, the Durbin–Watson values are within the accepted range.

^{2}of 0.47. The second model was a closer representation due to the fact that it had an adjusted R

^{2}of 0.65, as a result of the application of logarithms in the model according to Al-Zubaidi et al. [48]. Vaneli and Teixeira [49] found turbidity removal estimation models for helical flocculators whose R

^{2}was 0.5.

#### 3.10. Control Test

#### 3.11. Comparison of Costs

^{3}/m

^{2}d, while it was 120 m

^{3}/m

^{2}d in the pilot settler. Considering that the efficiency decreases as the sedimentation load increases, the aforementioned could have influenced the existence of a lower turbidity and color removal efficiency in the pilot settler. The filtration rate was the same in both the DWTP Bayas filters and the pilot filters.

^{−1}for the design flow rate, allowing the union of these in larger aggregates or flocs, with sufficient cohesion and density to submit them to the next stage of sedimentation. The aforementioned gradients prevented the breakage and disintegration of the already-formed flocs. For a flow rate of 2 L/s, the gradient was 123 s

^{−1}; however, the efficiency was acceptable, with the only limitation being that the filtration run decreased to 8 h.

^{−1}, which is somewhat higher than the maximum (100 s

^{−1}) recommended by the literature.

^{3}/h) than those used in the aforementioned studies. In the studies by Kurbiel et al. [17], two diameters of 71.4 and 86.4 mm were used, which are slightly smaller than the one used in the present study, and for this reason, Kurbiel et al. [17] used flow rates of 3.5 and 4 m

^{3}/h. The gradients in the studies in Table 17 were between 10 and 100 s

^{−1}, which is recommended for tubular flocculators, with the exception of the study carried out by Oliveira and Teixeira (2018). The retention times used in the studies realized by Kurbiel et al. [17] and Oliveira and Teixeira (2018) were relatively low compared to the time used in the present study.

#### 3.12. Pilot Treatment System

## 4. Conclusions

^{−1}. A specific methodology for the design of tubular hydraulic flocculators has to be investigated, considering that the present study used the design methodology of hydraulic screen flocculators to establish the size of the pilot HTF.

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 3.**Location of sampling points: (a) S1 Raw water, (b) S2 settled water, and (c) S3 filtered water.

**Figure 7.**Efficiency of turbidity removal in the settler: (

**a**) With HTF of 68.4 m; (

**b**) with HTF of 97.6 m, and (

**c**) in the filter of the DWTP “Bayas”. The bluish-green boxes correspond to a flow of 0.25 L/s, the brown boxes correspond to a flow of 0.5 L/s, the turquoise boxes correspond to a flow of 0.75 L/s, the beige boxes correspond to a flow rate of 1.0 L/s, purple boxes correspond to a flow rate of 2.0 L/s.

**Figure 8.**Color removal efficiency in the settler: (

**a**) With HTF of 68.4 m, (

**b**) with HTF of 97.6 m, and (

**c**) in the filter of the DWTP “Bayas”. The bluish-green boxes correspond to a flow of 0.25 L/s, the brown boxes correspond to a flow of 0.5 L/s, the turquoise boxes correspond to a flow of 0.75 L/s, the beige boxes correspond to a flow rate of 1.0 L/s, purple boxes correspond to a flow rate of 2.0 L/s.

**Figure 9.**Turbidity removal efficiency in the filter: (

**a**) With HTF of 68.4 m, (

**b**) with HTF of 97.6 m, and (

**c**) in the filter of the DWTP “Bayas”. The bluish-green boxes correspond to a flow of 0.25 L/s, the brown boxes correspond to a flow of 0.5 L/s, the turquoise boxes correspond to a flow of 0.75 L/s, the beige boxes correspond to a flow rate of 1.0 L/s, purple boxes correspond to a flow rate of 2.0 L/s.

**Figure 10.**Color removal efficiency in the filter: (

**a**) With HTF of 68.4 m, (

**b**) with HTF of 97.6 m, and (

**c**) in the filter of the DWTP “Bayas”.

**Figure 11.**Average, maximum, and minimum values of RE in the pilot settler with HTF of 68.4 m, with HTF of 97.6 m, and in the settler of the DWTP Bayas: (

**a**) Turbidity and (

**b**) color. The pink boxes correspond to the PTS with a 68.4m long tubular flocculator, the turquoise boxes correspond to the PTS with a 97.6m long tubular flocculator and the Light Steel Blue boxes correspond to the “Bayas” DWTP.

**Figure 12.**Average, maximum, and minimum values of the RE in the pilot filter with HTF of 68.4 m, with HTF of 97.6 m, and in the DWTP Bayas filter: (

**a**) Turbidity and (

**b**) color. The pink boxes correspond to the PTS with a 68.4m long tubular flocculator, the turquoise boxes correspond to the PTS with a 97.6m long tubular flocculator and the Light Steel Blue boxes correspond to the “Bayas” DWTP.

**Figure 13.**Implementation of the Pilot Treatment System. The upper left figure shows the HTF implementation; in the upper right, the implementation of the settler is presented. The complete experimental system is presented in the lower left and right figures, as follows: (a) HTF, (b) high-rate settler, and (c) rapid sand filters.

HTF Length (m) | Flow Rate (L/s) | Theoretical Retention Time (min) | Mean Retention Time (min) |
---|---|---|---|

68.4 | 0.25 | 36.97 | 32.20 |

0.50 | 18.48 | 19.10 | |

0.75 | 12.32 | 14.33 | |

1.0 | 9.24 | 7.25 | |

2.0 | 4.62 | 4.42 | |

97.6 | 0.25 | 52.67 | 52.05 |

0.50 | 26.33 | 22.43 | |

0.75 | 17.56 | 16.11 | |

1.0 | 13.17 | 12.30 | |

2.0 | 6.58 | 5.22 |

Length (m) | Flow Rate (L/s) | Equation | R^{2} | %p | %M | m |
---|---|---|---|---|---|---|

HTF 68.4 | 0.25 | log [1 − F(t)] = 8.75064 − 8.42073 (t/to) | 98.33 | 89.74 | 10.26 | −0.15 |

0.5 | log [1 − F(t)] = 10.1537 − 6.50166 (t/to) | 99.00 | 91.03 | 8.97 | −0.71 | |

0.75 | log [1 − F(t)] = 11.7424 − 7.43647 (t/to) | 96.08 | 92.15 | 7.85 | −0.71 | |

1.0 | log [1 − F(t)] = 12.9807 − 12.9278 (t/to) | 97.45 | 92.85 | 7.15 | −0.08 | |

2.0 | log [1 − F(t)] = 7.7437 − 4.73155 (t/to) | 98.86 | 88.56 | 11.44 | −0.84 | |

HTF 97.6 | 0.25 | log [1 − F(t)] = 9.54051 − 6.08172 (t/to) | 97.59 | 90.51 | 9.49 | −0.73 |

0.5 | log [1 − F(t)] = 10.366 − 8.02142 (t/to) | 98.52 | 91.20 | 8.80 | −0.41 | |

0.75 | log [1 − F(t)] = 10.8456 − 8.32531 (t/to) | 95.66 | 91.56 | 8.44 | −0.42 | |

1.0 | log [1 − F(t)] = 9.05445 − 6.2873 (t/to) | 92.85 | 90.05 | 9.95 | −0.59 | |

2.0 | log [1 − F(t)] = 16.1483 − 13.0555 (t/to) | 92.77 | 94.11 | 5.89 | −0.03 |

Length (m) | Flow Rate (l/s) | Theoretical Hydraulic Gradient (s^{−1}) | Real Hydraulic Gradient (s^{−1}) |
---|---|---|---|

HTF 68.4 | 0.25 | 6.15 | 6.59 |

0.5 | 16.22 | 16.54 | |

0.75 | 29.27 | 27.14 | |

1 | 41.13 | 46.44 | |

2 | 109.62 | 112.09 | |

HTF 97.6 | 0.25 | 6.21 | 6.24 |

0.5 | 16.97 | 18.39 | |

0.75 | 29.50 | 30.80 | |

1 | 41.35 | 42.78 | |

2 | 110.13 | 123.67 |

Author | Velocity Gradient (s^{−1}) | Retention Time (min) |
---|---|---|

Smethurst | 20–100 | 10–60 |

Arboleda | 10–100 | 15–20 |

Insfopal (horizontal flow) | - | 15–60 |

Hardenbergh and Rodie | - | 20–50 |

Fair and Geyer | - | 10–90 |

AWWA | 5–100 | 10–60 |

**Table 5.**Statistical Parameters of the Turbidity and Color Removal Efficiency after HTF + Settler in the Studied Systems.

System | Turbidity (%) | Color (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|

Mean | Me | SD | Min | Max | Mean | Me | SD | Min | Max | |

HTF 68.4 m | 75.45 | 80.73 | 20.89 | 22.79 | 95.00 | 71.53 | 77.62 | 20.45 | 17.42 | 90.77 |

HTF 97.6 m | 77.41 | 85.42 | 19.37 | 38.68 | 95.73 | 73.39 | 80.11 | 18.06 | 38.46 | 91.35 |

DWTP Bayas | 91.80 | 96.19 | 7.56 | 72.53 | 98.33 | 90.14 | 96.19 | 7.67 | 71.72 | 98.78 |

**Table 6.**Turbidity values in NTU and color in UC Pt-Co obtained at the outlet of the settler and the filter.

Flow (L/s) | Settler Outlet | Filter Outlet | ||||||
---|---|---|---|---|---|---|---|---|

HTF 68.4 m | HTF 97.6 m | HTF 68.4 m | HTF 97.6 m | |||||

Turbidity | Color | Turbidity | Color | Turbidity | Color | Turbidity | Color | |

0.25 | 7.78 | 73.40 | 5.87 | 60.00 | 0.21 | 0 | 0.24 | 0 |

0.50 | 7.11 | 67.00 | 6.99 | 65.00 | 0.32 | 0 | 0.29 | 0 |

0.75 | 7.88 | 72.90 | 7.39 | 70.40 | 0.41 | 0 | 0.35 | 0 |

1.0 | 7.08 | 68.00 | 11.00 | 91.00 | 0.34 | 0 | 0.39 | 0 |

2.0 | 23.05 | 148.35 | 15.39 | 119.6 | 0.56 | 1 | 0.63 | 1 |

**Table 7.**Statistical Parameters of the Turbidity and Color Removal Efficiency after HTF + Settler + Filter in the Studied Systems.

System | Turbidity (%) | Colour (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|

Mean | Me | SD | Min | Max | Mean | Me | SD | Min | Max | |

HTF 68.4 m | 98.80 | 99.39 | 1.43 | 93.65 | 99.90 | 99.93 | 100 | 0.24 | 98.82 | 100 |

HTF 97.6 m | 98.74 | 99.33 | 1.52 | 93.40 | 99.86 | 99.91 | 100 | 0.35 | 98.23 | 100 |

DWTP | 98.78 | 99.51 | 1.41 | 94.87 | 99.85 | 100 | 100 | 0 | 100 | 100 |

Observation 1 | Observation 2 | p-Value | Interpretation |
---|---|---|---|

Turbidity RE in settler using 68.4 m HTF | Turbidity RE in settler using 97.6 m HTF | 0.55 | No Significant Difference |

Turbidity RE in filter using 68.4 m HTF | Turbidity RE in filter using 97.6 m HTF | 0.74 | No Significant Difference |

Turbidity RE in settler using 68.4 m HTF | Turbidity RE in the DWTP Bayas settler | <0.0001 | Significant Difference |

Turbidity RE in filter using 68.4 m HTF | Turbidity RE in the DWTP Bayas filter | 0.39 | No Significant Difference |

Turbidity RE in settler using 97.6 m HTF | Turbidity RE in the DWTP Bayas settler | 0.0002 | Significant Difference |

Turbidity RE in filter using 97.6 m HTF | Turbidity RE in the DWTP Bayas filter | 0.31 | No Significant Difference |

Variable | Efficiency | Reynolds | MRT | Gradient | Flow Rate | Turbidity | Length |
---|---|---|---|---|---|---|---|

Efficiency | 1 | ||||||

Reynolds | −0.39 | 1 | |||||

MRT | 0.24 | −0.76 | 1 | ||||

Gradient | −0.39 | 1 | −0.71 | 1 | |||

Flow Rate | −0.39 | 1 | −0.76 | 1 | 1 | ||

Turbidity | 0.62 | 0.04 | −0.03 | 0.04 | 0.04 | 1 | |

Length | 0.05 | 2.12 × 10^{−16} | 0.22 | 0.002 | −2.97 × 10^{−15} | 0.02 | 1 |

**Table 10.**Statistical values obtained from regression analysis for turbidity removal efficiency models.

Model | R | R^{2} | Adjusted R^{2} | Se | Durbin-Watson |
---|---|---|---|---|---|

1 | 0.701 | 0.491 | 0.47 | 12.62 | 1.618 |

2 | 0.815 | 0.664 | 0.65 | 0.067 | 1.711 |

Modelo | Non-Standardized Coefficients | Standardized Coefficients | t | Sig. | ||
---|---|---|---|---|---|---|

B | Dev. Error | Beta | ||||

1 | (Constant) | 72.077 | 3.234 | 22.284 | <0.001 | |

Turbidity | 0.146 | 0.024 | 0.664 | 6.196 | <0.001 | |

Gradient | −0.159 | 0.053 | −0.319 | −2.981 | 0.005 | |

2 | (Constant) | 1.670 | 0.048 | 35.061 | <0.001 | |

LogGradient | −0.079 | 0.024 | −0.283 | −3.258 | 0.002 | |

LogTurbidity | 0.190 | 0.021 | 0.794 | 9.136 | <0.001 |

Obtained Model | Adjusted R^{2} |
---|---|

$Efic=72.077-0.159\mathrm{G}+0.146\mathrm{T}$ | 0.47 |

$Efic={10}^{\left[1.67-0.079\mathrm{log}\left(\mathrm{G}\right)+0.19\mathrm{log}\left(\mathrm{T}\right)\right]}$ | 0.65 |

Pilot System | Turbidity Removal (%) | Color Removal (%) |
---|---|---|

Settler + filter (Coagulated water without HTF) | 49.3 | 51.1 |

HTF_68.4m + Settler + filter (No coagulant) | 16.38 | 12.91 |

HTF_97.6m + Settler + filter (No coagulant) | 20.12 | 16.73 |

Flow Rate (L/s) | Flow Rate (mgd) | Construction Cost (USD) |
---|---|---|

0.25 | 0.0057 | 6187.96 |

0.5 | 0.0114 | 8453.00 |

0.75 | 0.0171 | 10,145.00 |

1.0 | 0.0228 | 11,547.14 |

2.0 | 0.0456 | 15,773.86 |

N° | Item | Unit Price | Quantity | Final Price |
---|---|---|---|---|

1 | PVC pipe 110 mm × 1.00 mpa × 6 m U/Z | 28.75 | 15 | 431.25 |

2 | PVC elbow 110 mm × 90 U/Z | 16 | 26 | 416.00 |

3 | Tee PVC 110 mm U/Z | 51 | 1 | 51.00 |

4 | PVC bell flange mm U/Z | 23 | 2 | 46.00 |

5 | Repair joint 110 mm U/Z | 11 | 4 | 44.00 |

6 | Elbow 110 mm E/C | 11 | 6 | 66.00 |

7 | Wafer valve of 110 mm (ductile iron) | 128.5 | 1 | 128.50 |

9 | PVC ball valve 110 mm | 52 | 1 | 52.00 |

10 | Pipe rack (iron) | 840 | 1 | 840.00 |

Total | 2074.75 |

Component | Retention Time (min) | Surface Load (m^{3}/m^{2}d) |
---|---|---|

Pilot Horizontal Tubular Flocculator (HTF) | 12.5 | |

Conventional horizontal screen flocculator | 21.0 | |

Conventional DWTP High Rate Settler Bayas | 25.0 | 94 |

High rate pilot settler | 12.0 | 120 |

Conventional DWTP Sand Filter Bayas | 120 | |

Pilot sand filter | 120 |

Author | Flocculator Length (m) | Pipe Diameter (mm) | Gradient G (s^{−1}) | Flow Rate (m^{3}/h) | Time (s) | Initial Turbidity (NTU) | Efficiency(%) |
---|---|---|---|---|---|---|---|

(Tse et al., 2011) [14] | 28 | 9.5 | 40 | 0.13 | 650 | 50 ± 5 | 94 |

(Kurbiel et al., 1989) [17] | 20 | 71.4 | 52.7 | 3.5 | 82.3 | 68.8 | |

(Kurbiel et al., 1989) [17] | 20 | 86.4 | 33.2 | 4 | 105 | 54.3 | |

(Oliveira and Teixeira, 2018) [51] | 11.37 | 1.58 | 160 | 0.12 | 56.2 | 50 | 82.3 |

This study | 68.4 | 110 | 46 | 3.6 | 435 | 206.1 | 91.37 |

This study | 97.6 | 110 | 42 | 3.6 | 738 | 249.6 | 85.32 |

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## Share and Cite

**MDPI and ACS Style**

García-Ávila, F.; Méndez-Heredia, A.; Trelles-Agurto, A.; Sánchez-Cordero, E.; Alfaro-Paredes, E.A.; Criollo-Illescas, F.; Tonon-Ordoñez, M.D.; Heredia-Cabrera, G.
Experimental Evaluation of Tubular Flocculator Implemented in the Field for Drinking Water Supply: Application in the Developing World. *Water* **2023**, *15*, 833.
https://doi.org/10.3390/w15050833

**AMA Style**

García-Ávila F, Méndez-Heredia A, Trelles-Agurto A, Sánchez-Cordero E, Alfaro-Paredes EA, Criollo-Illescas F, Tonon-Ordoñez MD, Heredia-Cabrera G.
Experimental Evaluation of Tubular Flocculator Implemented in the Field for Drinking Water Supply: Application in the Developing World. *Water*. 2023; 15(5):833.
https://doi.org/10.3390/w15050833

**Chicago/Turabian Style**

García-Ávila, Fernando, Angel Méndez-Heredia, Alex Trelles-Agurto, Esteban Sánchez-Cordero, Emigdio Antonio Alfaro-Paredes, Freddy Criollo-Illescas, María D. Tonon-Ordoñez, and Gina Heredia-Cabrera.
2023. "Experimental Evaluation of Tubular Flocculator Implemented in the Field for Drinking Water Supply: Application in the Developing World" *Water* 15, no. 5: 833.
https://doi.org/10.3390/w15050833