# Quantitative Detection of Clogging in Horizontal Subsurface Flow Constructed Wetland Using the Resistivity Method

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Measurement of Apparent Resistivity

^{2}); L is the distance of stainless steel bars in the Miller Soil Box (0.2 m); U is the voltage between two potential electrodes (V); I is the current of the closed circuit (A).

_{x}are empirical coefficients.

#### 2.2. Experimental Setup

_{Sed.}is the volume of added sediment, (L); V

_{Spa.}is the void space of clean gravel substrate (L).

#### 2.3. Measurement of Void Space, Water Content, and Hydraulic Conductivity

^{3}/s); A is the cross-sectional area of the cylinder (m

^{2}); L is the height of the substrate (m); ∆h is the hydraulic gradient (m).

#### 2.4. Statistical Analysis

## 3. Results and Discussion

#### 3.1. Apparent Resistivity of Wetland Mediums

#### 3.2. Effect of the Degree of Clogging on Apparent Resistivity

#### 3.3. Mathematical Model

#### 3.4. In Situ Detection of Clogging in a Lab-Scale HSSF CW

## 4. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Schematic diagram of the Miller Soil Box. A represents the ammeter; V represents the voltmeter; ~ represents the power; the red bars represent the electrodes; the grey shapes inside the box represent the substrate.

**Figure 2.**Schematic diagram of lab scale horizontal subsurface flow constructed wetland (HSSF CW) (plan view; different colors represent various sediment fractions (v/v); the crosses represent the positions of stainless-steel bar electrodes; the arrows represent the flow direction).

**Figure 3.**Change of apparent resistivity with sediment fraction (v/v) (from 0% to 60%) and draining time (from 0 min to 550 min).

**Figure 4.**Relationship between the electrical conductivity and water content of wetland substrates with different sediment fractions (v/v) (from 0% to 60%).

**Figure 5.**Linear regression of (

**a**) simulated sediment fraction (v/v) against actual sediment fraction (v/v) and (

**b**) hydraulic conductivity against actual sediment fraction (v/v).

**Figure 6.**Clogging contours in the HSSF CW based on (

**a**) the two-probe method and (

**b**) the four-probe method (plan view; different colors represent various sediment fractions (v/v); the crosses represent the positions of stainless steel bar electrodes; the arrows represent the flow direction).ϕ

Index | COD ^{1} (mg/L) | BOD_{5} ^{2} (mg/L) | TSS ^{3} (mg/L) | Temperature (°C) | pH | Conductivity (μS/cm) |
---|---|---|---|---|---|---|

Values | 253.8 ± 16.5 | 198.3 ± 13.0 | 69.0 ± 6.2 | 24.0 ± 2.7 | 7.5 ± 0.2 | 1752 ± 26.1 |

^{1}COD is chemical oxygen demand;

^{2}BOD is biochemical oxygen demand;

^{3}TSS is total suspended solids.

Index | Gravel | Sediment | Mixture ^{1} |
---|---|---|---|

Filling phase (Ω·m) | 29.8 ± 5.0 | 66.6 ± 5.2 | 34.4 ± 2.1 |

Draining phase (Ω·m) | 3174.8 ± 73.4 | 87.4 ± 7.6 | 132.1 ± 10.6 |

^{1}Mixture of gravel and sediment with a sediment fraction (v/v) of 40%.

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**MDPI and ACS Style**

Liu, H.; Hu, Z.; Song, S.; Zhang, J.; Nie, L.; Hu, H.; Li, F.; Liu, Z.
Quantitative Detection of Clogging in Horizontal Subsurface Flow Constructed Wetland Using the Resistivity Method. *Water* **2018**, *10*, 1334.
https://doi.org/10.3390/w10101334

**AMA Style**

Liu H, Hu Z, Song S, Zhang J, Nie L, Hu H, Li F, Liu Z.
Quantitative Detection of Clogging in Horizontal Subsurface Flow Constructed Wetland Using the Resistivity Method. *Water*. 2018; 10(10):1334.
https://doi.org/10.3390/w10101334

**Chicago/Turabian Style**

Liu, Huaqing, Zhen Hu, Shiying Song, Jian Zhang, Lichao Nie, Hongying Hu, Fengmin Li, and Zhengyu Liu.
2018. "Quantitative Detection of Clogging in Horizontal Subsurface Flow Constructed Wetland Using the Resistivity Method" *Water* 10, no. 10: 1334.
https://doi.org/10.3390/w10101334