Study on the Reduction Effect of Bioretention Facility on Typical

Heavy Metal Pollutants in Rainfall Runoff

Rubin Jia*, Jian Li, Yong Wang, and Di Tang

China Ji Kan Research Institute of Engineering Investigation and Design, Co., Ltd, Xi’an, 710043, China

Keywords: Bioretention facility, Urban runoff, Heavy metals, Reduction effect

Abstract: This paper studied the effect of different inflow water, heavy metal (Cu, Zn, Cd) concentration and rainfall

interval on heavy metal reduction in bioretention facility. The results showed that the removal ability of

heavy metals was different among the three bioretention facilities, and the removal effect of Cu was the best,

while the removal effect of Cd was not stable. High inflows reduce the reducton efficiency of heavy metals

in bioretention facilities. The concentration changes of heavy metals in influent did not significantly change

the reduction efficiency. After comprehensive comparison, it was found that the bioretention facility with

(sand + fly ash) as filler had the best reduction effect on heavy metals, and the removal rate reached 88%.

The research results can provide basic data support for the design and application of bioretention facility.

1 INTRODUCTION

Bioretention facility is an efficient and low-impact

development technology (LID) (Wu, 2006) that

integrates landscape, water quality purification and

rainfall runoff control. Some researchers have

carried out relevant research on the reduction effect

of bioretention facility (Zhang et al., 2021; Zhou,

2021), structural improvement (Pan et al., 2020),

matrix combination (Chen, 2020), filler type (Zhang

et al., 2020; Ellis et al., 1987) and some research

results have been achieved on the reduction effect of

nitrogen and phosphorus pollutants. However, there

are still problems about the stability and efficiency

of the technology, resulting in the reduction effect of

the technology in the application is often not high.

Especially, there are few studies on the mechanism

of heavy metal reduction. In the actual rainfall runoff

process, rainfall intensity, influent heavy metal

concentration and rainfall interval are also the key

factors determining the bioretention facility, which

directly affect the reduction effect of heavy metal

ions by bioretention facility. Based on the above

background, this paper uses simulated rainwater

pollution to study the removal effect of different

bioretention facility fillers on heavy metals in runoff

and its influencing factors, in order to provide

reference for the design and optimization of

bioretention facility.

2 RESEARCH METHOD

2.1 Bioretention Facility System

The biological retention facility is shown in Figure 1,

the size of the bioretention facility in this experiment

was 2.0m in length × 0.5m in width × 1.0m in depth,

and poplar and ryegrass were planted in the facility.

Each device from top to bottom are water storage

layer (10cm), planting soil layer (30cm), artificial

filler layer (60cm). Permeable geotextile is laid

between each filler medium. Perforated drainage

pipe is located at the bottom of the filler layer, and

the drainage pipe is wrapped by geotextile. Three

bioretention facilities (1#, 2# and 3#) were set up in

the experiment. There were only differences in the

artificial filler layer. The artificial filler layer was

sand + fly ash (volume ratio of 1:1), sand + green

zeolite (volume ratio of 1:1) and planting soil (Lin &

He, 2019).

2.2 Condition Setting of Test

Parameters

The effects of inflow rate, heavy metal (Cu, Zn, Cd)

concentration and rainfall interval on the reduction

of heavy metals in the system were investigated. The

inflow flow is reflected by the difference of rainfall

intensity, and other parameters (pollution

Jia, R., Li, J., Wang, Y. and Tang, D.

Study on the Reduction Effect of Bioretention Facility on Typical Heavy Metal Pollutants in Rainfall Runoff.

In Proceedings of the 7th International Conference on Water Resource and Environment (WRE 2021), pages 37-42

ISBN: 978-989-758-560-9; ISSN: 1755-1315

concentration is low, rainfall interval is 7days) are

consistent. The rainfall intensity is determined by the

rainstorm intensity formula (1) and the catchment

area of bioretention facilities in Xi’an. The designed

bioretention facility consumes 3 times of its own

surface area. The water calculation results are shown

in Table 1, and the rainfall intensity is determined

according to the road runoff monitoring results and

existing research (Chen et al., 2012; Dong, 2013).

9302.0

)813.16(

)lg1658.11(833.2785







FqQ





Formula:

q is the design rainstorm intensity [ L / (sꞏhm

) ].

P is the design recurrence period. T is rainfall

duration.

Qs is designed for rainwater flow (L/s).

ø is the runoff coefficient.

F is catchment area (hm

Figure 1: Schematic diagram of bioretention facilities.

Table 1: Water Quantity Calculation Table.

return

period

P/a

duration of

rainfall

t/min

rainfall intensity

q/(L/s.ha)

runoff

coefficientφ

catchment area

F/ha

designed

discharge

Qs/

(

L/s

)

design flow

V/L

Rainfall

5 120 52.0922 0.9 0.0017 0.0798 573.7561 33.67

2 120 38.7762 0.9 0.0017 0.0594 427.2015 25.08

0.5 120 18.6300 0.9 0.0017 0.0287 205.3210 12.11

The concentration of heavy metals remained

constant during simulated rainfall. Cu, Zn and Cb

were selected as typical heavy metals with the

highest detection frequency and concentration in

Xi’an rainfall runoff process. The concentration of

heavy metals was set according to the monitoring of

pollutants in Xi’an rainfall (Guo, 2015; Davis et al.,

2009

)

. The concentration of heavy metals included

high and low concentrations. When the rainfall

interval is 7 days and the monitoring period is 5

years, the concentrations of three heavy metals were

Cu (CuCl

ꞏ2H

O), 0.1mg/L and 0.05mg/L. Zn

(ZnSO

ꞏ7H

O), 1.5mg/L and 0.8mg/L. Cd

(CdCl

ꞏ2.5H

O), respectively.0.05 mg/L and 0.03

mg/L. The rainfall interval was set to 3d, 5d and 7d,

the concentration of heavy metals was set at low

concentration, and the rainfall intensity was 2a.

2.3 Analysis Methods and Evaluation

Criteria of Heavy Metals

The concentration of heavy metal ions was

determined by flame atomic absorption spectrometry

(AAS), and the instrument was AAS Zeenit 700

atomic absorption spectrometer. The purification

effect of bioretention facilities is quantitatively

analyzed, and Ri represents the removal rate. The

calculation formula is as follows:

100





Formula:

is influent pollutant concentration, mg/L.

C is effluent pollutant concentration, mg/L.

3 RESULTS AND ANALYSIS

3.1 Influence of Inflow Water on Heavy

Metal Reduction Rate of Biological

Retention Facilities

The influence of biological retention facilities on

heavy metal reduction under different influent

WRE 2021 - The International Conference on Water Resource and Environment

conditions is shown in Figure 2, under the rainfall

conditions corresponding to the 2a and 5a return

periods, the increase of inflow flow reduced the

reduction efficiency of heavy metals in the three

types of bioretention facilities, and the reduction

efficiency of the three heavy metals under different

inflow flow conditions showed Cu>Zn>Cd. Under

the two inflow conditions, the reduction efficiency of

Zn changed little, while the reduction efficiency of

Cu and Cd changed significantly, and the reduction

efficiency of the system decreased under large flow

conditions. This may be due to the increase of inflow

water, the hydraulic retention time in the

bioretention facilities, becomes shorter, and large

water will wash out the heavy metals adsorbed by

the biological retention matrix filler, resulting in the

increase of the concentration of heavy metal

pollutants measured in the effluent.

In the two-year return period, the removal rates

of Cu (>80%) in the three bioretention facilities were

higher than those in the other two heavy metals. The

Cu and Zn reduction efficiency of 1 # bioretention

device is higher. The removal rate of Cd was

obviously low. Davis proved through a series of

experimental studies that the type of matrix filler in

bioretention facilities had a great impact on the

removal effect of heavy metals, mainly because the

physical and chemical properties of matrix fillers

were different, and the removal effect and

mechanism of heavy metals were also different.

3.2 Effect of Influent Heavy Metal

Concentration on Heavy Metal

Reduction in Three Bioretention

Facilities

Under different concentrations of heavy metals, the

removal efficiency of heavy metals by bioretention

facilities with three kinds of fillers is shown in figure

3. In the 1 # bioretention facility, the reduction

efficiency of Cu and Zn was more than 70%, while

the reduction efficiency of Cd was significantly

lower (about 15%). The reduction efficiencies of Cu,

Zn and Cd in device 2# were significantly different

from those in device 1#, and the reduction rates from

high to low were Cu> Zn>Cd. The distribution of

heavy metal reduction efficiency in 3# plant is

similar to that in 1# plant. The reduction efficiency

of Cu and Zn is significantly higher, while the

reduction efficiency of Cd is 17-25%. Under the

condition of high concentration influent, the

reduction efficiency of heavy metals by bioretention

facilities was slightly lower than that under low

concentration influent, which may be mainly related

to the adsorption rate of fillers. When the

concentration of heavy metal ions in the influent is

high, the filler cannot adsorb all metal ions, so there

will be a large number of unabsorbed metal ions

discharged from the detention facilities with the

effluent. Comprehensive three types of bioretention

facilities can be concluded that the reduction

efficiency of 1# and 3# devices is higher, and the

reduction effect of 3# on Cd is obvious.

(a) 1#

(b) 2#

Figure 2: Effects of three bioretention facilities on heavy

metal reduction under different inflow conditions.

Study on the Reduction Effect of Bioretention Facility on Typical Heavy Metal Pollutants in Rainfall Runoff

3.3 Effect of Rainfall Interval on Heavy

Metal

Reduction by Three

Bioretention Facilities

The reduction efficiency of heavy metals in

bioretention facilities with three fillers is

significantly different under different rainfall

intervals, as shown in Figure 4. The removal rate of

Cd in the three bioretention facilities had no

significant change with the increase of rainfall

interval time, and the reduction effect was

maintained at 15-25%, indicating that the length of

rainfall interval had little effect on the purification

effect of heavy metal Cd. The difference is that the

removal rates of Cu and Zn in the three bioretention

facilities have a relatively obvious change trend with

the rainfall interval. The reduction efficiency of Cu

in 1# device increases with the increase of the

interval, and the reduction efficiency can reach 88%

at the interval of 15 days, while the reduction

efficiency of Zn in different rainfall intervals is not

obvious, reaching the highest at 7 days. Cu and Zn

reduction efficiency of 2# device increased with the

increase of rainfall interval, and reached the

maximum reduction efficiency at 15d. The reduction

efficiencies of Cu and Zn in device 3# were like

those in device 1#, and the maximum reduction rate

of Zn (about 90%) appeared in the rainfall interval of

7d, while the reduction rate of Cu did not change

basically in the rainfall interval > 7d, and the optimal

reduction rate could reach 80%. Based on the results

of three types of bioretention facilities in different

inflow rates, influent concentrations, and rainfall

intervals, it can be concluded that the bioretention

facilities of 1# (sand + fly ash) artificial substrate

have better reduction efficiency and stability for

heavy metals.

(a) 1#

(b) 2#

Figure 3: Effects of three bioretention facilities on heavy

metal reduction under different heavy metal

concentrations.

4 CONCLUSIONS AND

SUGGESTIONS

(1) Bioretention facilities with different fillers have

different reduction effects on three typical heavy

metals. In the three types of systems, the reduction

effect of heavy metals from high to low is

Cu>Zn>Cd, and the reduction efficiency of Cu and

Zn is more than 70%, while the reduction efficiency

of Cd is significantly lower, and the efficiency is less

than 30%.

(2) Inflow rate, influent heavy metal

concentration and rainfall interval affected the

reduction effect of bioretention facilities on heavy

metals. Compared with the case when the rainfall

return period was 5a, the bioretention facilities had

higher purification efficiency for heavy metals when

the rainfall return period was 2a. The increase in the

concentration of heavy metals entering the

WRE 2021 - The International Conference on Water Resource and Environment

bioretention facilities will increase the metal content

in the effluent of the system, but the overall

reduction efficiency of the system is not significantly

affected. Higher rainfall intervals contribute to more

Cu and Zn reductions, while the reduction efficiency

of Cd fluctuates less in different intervals.

(3) The reduction effect of three types of filler

bioretention facilities on heavy metals from high to

low was 1#>3#>2#, indicating that sand + fly ash as

artificial matrix has better stability for heavy metal

reduction in bioretention facilities.

(a) 1#

(b) 2#

Figure 4: Effects of three bioretention facilities on heavy metal reduction under different rainfall intervals.

ACKNOWLEDGMENTS

This research was supported by the Key Research

and Development Program of Shaanxi Province

(2017ZDXM-SF-081).

REFERENCES

Chahal, M. K., Shi, Z., & Flury, M. (2016). Nutrient

Leaching and Copper Speciation in Compost

-Amended Bioretention Systems. Science of the Total

Environment, 556, 302-309.

Chen, H. J. (2020). The effects of different fillers on the

effects of biological retention facilities are described.

Jiangxi Chemical Industry, 6, 6-8.

Chen, Y., Zhao, J. Q., Hu, B., Liu, J., & Mao, H. Q. (2012).

First flush effect of urban trunk road runoff in Xi’an.

Chinese Journal of Environmental Engineering, 6(3),

929-935.

Dong, W. (2013). Characteristics and control of non-point

source pollution in northwest China -- a case study of

Xi’an city. Xi 'an, Xi’an University of Technology.

Study on the Reduction Effect of Bioretention Facility on Typical Heavy Metal Pollutants in Rainfall Runoff

Davis, A. P., Hunt, W. F., & Traver, R. G. (2009).

Bioretention Technology, Overview of Current

Practice and Future Needs. Journal of Environmental

Engineering, 135(3),109-117.

Ellis, J. B., Revitt, D. M., Harrop, D. O. (1987). The

contribution of highway surfaces to urban stormwater

sediments and metal loadings. Science Total

Environment, 59, 339-349.

Guo, W. J. (2015). Research on Urban Rainfall-runoff

Pollution Characteristics and Load Estimation in Xi`an.

Xi 'an, Xi’an University of Technology.

Lin, Z. Z., & He, Q. M. (2019). Composition of

Bioretention System and Optimization of Engineering

Design Parameters. Water Purification Technology,

38(12), 116-121.

Pan, J. K., Liu, Y., Qu, Y., & Gao, J P. (2020). Removal

effect of compound packing biological retention

facility on runoff pollutants. The people of the Yellow

River, 42(08), 93-99.

Wu, R. F. (2006). Urban stormwater runoff pollution

control technology. Industrialsafety and environmental

protection, 32(02), 41-42．

Zhang, T., Feng, Y., He, M. Z., Gu, Z. G., & Bai, X.

(2020). Filling Layer’s Optimal Ratio of Bioretention

Facilities Based on Removal Effect of Nitrogen and

Phosphorus in Initial Rainwater Runoff. China Rural

Water and Hydropower, 6, 82-86.

Zhang, S., Li, J. Q., Li, X. J., & Sun, Y. (2021) Reduction

Effect of Bioretention on Urban Stormwater Runoff

Thermal Pollution. China Water & Wastewater,

37(03), 116-120.

Zhou, S. Y. (2021). Review on Rainwater Runoff Control

by Bioretention Facilities. Tianjin Construction

Science and Technology, 31(06), 7-11.

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