Effect of Bioretention on Pollutant Reduction in Urban Road 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, Urban road runoff, Pollutant, Reduction

Abstract: Bioretention is an efficient low impact development to reducing urban non-point source pollution. This paper

studies a bioretention which was settled on one sides of urban roads. In three rainfall events, the content of

TSS (Total Suspended Solids), TN (Total Nitrogen), TP (Total Phosphorus) NH

-N, NO

3—

N, Cu and Zn in

inflow and outflow of the bioretention were analysed, and the bioretention's ability to reduce pollutants was

evaluated. This work provides a reference for the design and construction of bioretention.

1 INTRODUCTION

In recent years, urban non-point source pollution,

especially road runoff pollution under rainfall

conditions, has attracted more and more attention

(Abi Aad et al., 2014). How to effectively control road

rainwater runoff pollution and improve rainwater

utilization rate in the process of rapid urbanization is

a new challenge for urban environment and municipal

management departments (U. S. EPA, 2000). Low

impact development (LID) is an effective measure to

manage rainwater and pollutants in situ through

source and decentralized measures (Ahiablame et al.,

2012). Ecological detention basin, as a typical LID

measure, has strong applicability with design and

construction, and is applied in many cities in China.

Hao (2020) studied the "ecological" and "functional"

aspects of the evaluation and analysis of runoff on the

operation effect of biological retention facilities.

Bioretention can collect road rainwater runoff,

adsorb pollutants in runoff through fillers, and then

supplement groundwater. Many researchers have

systematically studied the effect of Bioretention on

runoff branch reduction, the adsorption capacity of

filler types on pollutants, and the relationship between

layout and runoff reduction. Lu et al. (2021) used LID

facilities to control urban road rain water

significantly, which can effectively reduce runoff,

reduce peak flow and delay peak rain time. But for

different rainfall intensity conditions, bioretention on

road runoff pollutant reduction effect is rarely

reported.

In this study, through the establishment of

bioretention facilities on both sides of urban roads, the

water quality of inflow and outflow of bioretention

facilities under rainfall conditions was monitored, and

the reduction effects of bioretention facilities on

COD, SS, TN and TP in urban road runoff pollutants

were studied, so as to provide reference for exploring

and optimizing the effect of bioretention facilities in

practical application.

Figure 1: Schematic diagram of bioretention (Unit: m).

2 MATERIAL AND METHODS

2.1 Experimental Installation

As shown in Figure 1, the design size of bioretention

is 10 m × 1 m × 1 m, and the inlet is close to the road

edge. At the bottom of the bioretention, 5cm thick

gravel layer is easy to disperse water. The substrate of

bioretention is sand and fly ash, and the bottom layer

is fly ash (30 cm). The last time is coarse sand (30

cm). The substrate covered the planting soil layer

(30cm). The bioretention has a concave depth of 5 cm,

which is convenient for water collection and

infiltration. A perforated pipe with a diameter of 1 cm

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

Effect of Bioretention on Pollutant Reduction in Urban Road Runoff.

In Proceedings of the 7th International Conference on Water Resource and Environment (WRE 2021), pages 449-452

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

449

is installed at the bottom of the bioretention to collect

rainwater from infiltration into the sampling pit.

The plants planted in the bioretention were

boxtree and ryegrass (1: 1). Boxwood (Buxus sinica

(Rehd. et Wils.) Cheng) which is shade-tolerant and

light-happy can maintain good growth in general

indoor and outdoor conditions. And soil requirements

are not strict while it is better to use loose and fertile

sandy loam. Ryegrass (Lolium perenne L.) is a

perennial plant with a stalk height of 30 – 90 cm.

Excellent forages are widely introduced and

cultivated in various regions. Ryegrass likes a cool

and moist climate. Better moisture resistance, but

poor drainage or high groundwater level is also

adverse to ryegrass growth. Intolerance to drought,

especially high heat and drought in summer, is more

unfavorable.

2.2 Experimental Method

In this experiment, two typical rainfall events were

monitored, and rainfall intensity, rainfall and rainfall

duration were recorded respectively. Rainfall

characteristics are shown in table 1. The analysis and

determination of water quality indexes of influent and

effluent of Bioretention mainly refer to the national

standard determination method.

Table 1: Rainfall characteristics.

Rainfall events rainfall duration /h rainfall /m

rainfall intensit

/mmꞏh clea

-da

efore Rain/da

Events 1 3.5 12 3.12 20

Events 2 2.5 9.2 3.5 10

Events 2 4 30 8.3 6

3 RESULTS AND ANALYSIS

3.1 Removal Effect of Bioretention on

TSS In Urban Road Runoff

Figure 2: Removal effect of bioretention on TSS.

By analyzing the removal effect of bioretention on

TSS in road rainwater runoff, it can be seen from

Figure 2 that in the first rainfall, the influent TSS was

160 mg / L, and after the treatment of bioretention, the

effluent TSS was 53.4 mg / L, with a removal rate of

67%. In the second rainfall process, the TSS content

in the influent and effluent of the biological detention

facility was higher than that of the first rainfall period.

The TSS removal rate of the detention facility also

increased to 76%, which was the highest in the three

rainfall processes. During the third precipitation

period, the removal rate of TSS by bioretention was

the lowest, only 58 %. There are many factors

affecting the removal rate of TSS in bioretention, and

rainfall intensity is an important factor. When the

rainfall intensity is large, the hydraulic load is strong,

and the impact on the bioretention is enhanced, which

is easy to cause the increase of TSS content in the

effluent.

3.2 Removal Effect of Bioretention on

COD in Urban Road Runoff

Figure 3: Removal effect of bioretention on COD.

By analyzing the removal effect of bioretention on

COD in road rainwater runoff, it can be seen from

Figure 3 that in the three rainfall processes, the

removal rate of COD by bioretention was 68 % – 89

%, and the removal rate in the third rainfall process

was the highest. In addition to the removal of COD by

substrate adsorption in bioretention, the growth and

reproduction of a large number of microorganisms

living in fillers also play an important role in COD

degradation.

WRE 2021 - The International Conference on Water Resource and Environment

450

Figure 4: Removal effect of bioretention on Nitrogen.

3.3 Removal Effect of Bioretention on

Nitrogen in Urban Road Runoff

By analyzing the removal efficiency of various forms

of nitrogen (TN, NH

-N and NO

-N) by

bioretention, it was found from Figure 4 that the

removal rate of TN was 47 % -65 %, and the average

removal rate was 56 %. The removal rate of NH

-N

was 61% ~ 88%, and the average removal rate was

73%. The removal rate of NO

-N was 53 % ~ 66 %,

and the average removal rate was 60 %. It can be seen

that the bioretention has the best removal effect on

ammonia nitrogen, and the removal effect of the most

total nitrogen is relatively poor. In the later practical

application, if the TN content in the effluent needs to

be controlled, the substrate and filler need to be

adjusted and optimized to achieve better total nitrogen

removal.

3.4 Removal Effect of Bioretention on

TP In Urban Road Runoff

As shown in Figure 5, analysis of the removal effect

of total phosphorus by bioretention showed that the

removal rate was the highest in the first rainfall

process, reaching 66%. The removal rate of the

second rainfall was 52 %, and that of the third rainfall

was low, only 44 %. This may be related to the large

intensity of the third rainfall. Under the condition of

strong hydraulic load, the total phosphorus in the

rainwater runoff is less adsorbed by the filler of the

biological retention facility and is discharged with the

secondary effluent of the retention facility, resulting

in low yield efficiency.

Figure 5: Removal effect of bioretention on TP.

Figure 6: Removal effect of bioretention on heavy metals

(Cu, Zn).

3.5 Removal Effect of Bioretention on

Heavy Metals in Urban Road

Runoff

As shown in Figure 6, the removal rate of Cu by

bioretention was 57 % – 80 %, with an average of 70

%. The removal rate of Zn by bioretention was 69 %

– 83 %, and the average removal rate was 69 %. It can

be seen that the bioretention has a good removal rate

Effect of Bioretention on Pollutant Reduction in Urban Road Runoff

451

of two typical heavy metals in road rainwater runoff,

which may be due to the small particle size of fly ash

and strong adsorption capacity, which can quickly

combine with metal cations to remove heavy metal

pollutants in water

(Li et al., 2016).

4 CONCLUSIONS AND

SUGGESTIONS

Bioretention have certain purification capacity for

various pollutants in road rainwater runoff (Cheng et

al., 2009)

. By analyzing the concentrations of TSS,

TN, TP and heavy metal pollutants in the influent /

effluent of the bioretention, it was found that the

concentrations of various pollutants in the effluent

decreased, indicating that the bioretention facility is

an effective rainwater treatment facility for road

runoff.

Rainfall characteristics (rainfall, rainfall intensity,

rainfall duration, etc.) have a certain impact on the

treatment efficiency of bioretention, especially

rainfall intensity (

Wang et al., 2014). Under the

condition of high rainfall intensity, the inflow of

biological detention facilities is large, the turbulent

kinetic energy of water body is strong, and the

hydraulic load is large, which may reduce the

purification effect of bioretention (

Wang et al., 2015).

Therefore, in the design process of bioretention, the

local rainfall characteristics and the hydraulic

characteristics of road rainwater runoff should be

fully considered in order to design reasonable

bioretention.

ACKNOWLEDGMENTS

This research was supported by the Key Research and

Development Program of Shaanxi

Province(2017ZDXM-SF-081).

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