Study on the Clogging and Regulation Measures of Bioretention

Facilities in Sponge City

Yuan Zhou

1,2 a

, Long Yang

1,† b

, Siyu Wang

, Yangyang Chu

, Min Zhang

and Xiangchun Wang

China Urban Construction Design & Research Institute Co. Ltd, 100120, Beijing, China

State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua

University, 100120, Beijing, China

Keywords: Bioretention Facility, Green Stormwater Infrastructure, Sponge City, Clogging, Regulation Measures.

Abstract: Bioretention facilities play an important role in regulating runoff, purifying water quality and preventing

urban waterlogging. However, clogging is the common and restrict problem after long-term operation of

these facilities, which affects the effective operation and ecological benefits. Clogging causes and influence

factors of bioretention facilities were summarized in this work. And corresponding regulation measures of

bioretention facilities in sponge city were studied systematically from five aspects: source control, operation

design, media optimization, vegetation selection, and management. A series of optimization measures were

recommended, such as apply novel snowmelt agents, add pre-treatment process, improve filter materials,

optimize plant species, update damaged cover and vegetation, and build a dynamic monitoring system. This

work could provide alternative strategies for the long-term operation of bioretention facilities, which play a

vital role in regulating runoff, purifying water quality and improving the construction of sponge city.

1 INTRODUCTION

Bioretention facility is one of the representative

measures of low-impact development and sponge

city construction, which can alleviate runoff

pollution, purify water quality, reduce the amount of

surface runoff and peak flow (Skorobogatov 2020).

Bioretention facilities mainly include bioretention

zone, rain garden, flower bed, biofilter trench and

ecological tree pond. Rainwater runoff contains a

variety of pollutants such as suspended solids (SS),

nitrogen and phosphorus, pathogenic bacteria, heavy

metals, snowmelt agents, pesticides and herbicides

(Zhang 2019). During the long-term operation,

bioretention facilities face some problems such as

excessive erosion, pollutants accumulation, media

clogging and plant death. And clogging has become

one of the most common and vital problems in the

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operation process of bioretention facilities (Tang

2017, Costello 2020, William 2019).

At present, many researches have focused on the

percolation performance, filler composition, plant

selection, model simulation and so on (Jiang 2019,

Andrew 2021). Li put forward improvement and

management suggestions for the construction

problems of bioretention facilities, such as

inconsistent construction with drawings and poor

drainage (Li 2020). However, researches on the

causing and influence factors of clogging and their

regulation methods of bioretention facilities are still

scattered. In this paper, the reasons and factors of

clogging that affected the operation of bioretention

facilities were systematically summarized, and the

regulation measures to optimize were

comprehensively proposed, which could provide a

reference for the actual operation of green

stormwater infrastructure in sponge city.

2 CLOGGING CAUSES

After long-time operation of bioretention facilities,

media clogging is one of the common problems and

1302

Zhou, Y., Yang, L., Wang, S., Chu, Y., Zhang, M. and Wang, X.

Study on the Clogging and Regulation Measures of Bioretention Facilities in Sponge City.

DOI: 10.5220/0011508900003443

In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 1302-1307

ISBN: 978-989-758-595-1

the water quality can’t meet the design requirements.

Permeability is used to characterize the clogging

degree of bioretention facilities (Ding 2019). In the

field investigation of bioretention facilities after

operation for 4 years, it was found that clogging

problem existed in 40% of the time during the

operation of the facilities (Coustumer 2012). The

causes and processes of clogging are complex and

simultaneous, which can be mainly divided into

physical clogging, chemical clogging and biological

clogging.

Physical clogging SS is the representative reason

of physical clogging, causing inorganic and organic

clogging (Conley 2020). Researches showed that the

main reason for inorganic clogging was suspended

particles with a particle size above 5 μm, and most

of them were inorganic minerals (e.g. quartz,

feldspar and other non-expansive minerals), which

could permeate with rainwater runoff and easily be

trapped on the surface of medium due to filtration

(Kandra 2017). SS with particle size during 0.22 μm

-5 μm could lead to organic clogging (Kandra 2017).

Chemical clogging When rainwater runoff with

complex composition entered bioretention facilities,

it would cause changes in pH value, the contents of

carbonate and other chemical components of water,

resulting in precipitation of salt, iron and calcium

ions, and then forming chemical clogging (Wang

2012, Raham 2020). Studies found that TDS of

runoff in grassland and congested road surface was

pretty high, including bicarbonate and calcium ions,

leading to the risk of chemical clogging (Raham

2020). Kakuturu also found that NaCl could affect

permeability of facility and plant health, resulting in

clogging of bioretention system (Kakuturu 2015).

Biological clogging Under suitable conditions,

microorganisms in the facility could multiply rapidly

and form biofilms, which blocked the pores of filler

and reduced the water conductivity of aquifers (Liu

2017). Organic matters such as humus and fulvic

acid-like terrestrial organic matters, as well as

proteins were their original sources. Besides

microorganisms themselves, extracellular polymers

(EPS) secreted by microorganisms could also lead to

biological clogging. When the content of TOC in

runoff was higher than 25 mg/L, it was beneficial to

the large-scale reproduction of microorganisms and

secretion of EPS, resulting in a high risk of

biological clogging (Chris 2013).

3 INFLUENCE FACTORS OF

CLOGGING

3.1 Structure and Operation Mode

The structural characteristics of bioretention

facilities (e.g. submerged area, layered packing) and

the operation mode (e.g. wet-dry alternation, up-

flow mode) have vital influence on the clogging of

the facilities. Studies showed that high initial

permeability of facility, small thickness of media

layer, setting of submerged area and large particle

matters could aggravate the clogging of bioretention

facilities (Chen 2013, Read 2008). Many studies

demonstrated that dry-wet alternation can

significantly improve the oxygen supply conditions,

improve the removal of pollutants, enhance

permeability of the system, and thus effectively

control the clogging of facility (Jiang 2017, Pan

2020). In addition, it was found that the structure of

layered media effectively prolonged the time of

clogging, forming the aerobic-anaerobic conditions

and promoting denitrification to increase nitrogen

removal (Chen 2013, Li 2014). However, some

studies showed that the mixed packing may enhance

the connectivity of pore space and improve

hydraulic conductivity of the facility compared with

the layered media (Lefevre 2015). Zhang et al

(Zhang 2019) indicated that up-flow and mixed-flow

bioretention facility could delay the clogging time

by extending the path of runoff and hydraulic

retention time.

3.2 Media and Filler

Media is one of the important factors that affect the

pollution control and clogging problem in the

bioretention facilities. The characteristics of the

media, such as the degree of compaction, the

thickness of the filter layer and whether to add

carbon source, could all influence the permeability

of the bioretention system (Tian 2018, Qiu 2017).

Media compaction could increase the bulk density,

limit the penetration of plant roots, and lead to a

significant decrease in media permeability (Tian

2018). Study founded that sandy soil could bear

compaction while its infiltration rate decreased

significantly after compaction. As for clay soil, its

compaction and water saturation had both low

permeability (Qiu 2017). In addition, many studies

indicated that adding organic matters into filler

composition not only provided carbon source for

denitrification, but also provided carriers for

Study on the Clogging and Regulation Measures of Bioretention Facilities in Sponge City

1303

microorganisms, promoting the proliferation of

microorganisms, thus significantly reducing the bulk

density of media (Li 2019, Mu 2020). Additives

such as organic compost, biochar, sawdust, straw,

agricultural wastes could improve the penetration

rate and water holding capacity of media. For

example, adding biochar into media had a good

performance in hydrological effect and nitrogen

removal in the bioretention system (Mu 2020).

3.3 Vegetation

Vegetation played an irreplaceable role in

bioretention facilities, but the influence of vegetation

on clogging of bioretention system was complex and

controversial (Yu 2019, Knowles 2011, Hua 2014).

Some researchers pointed out that vegetation could

delay the clogging of the facility, on one hand,

vegetation could slow down the flow velocity of

runoff and reduce SS. On the other hand, the growth

of plant roots could promote the reproduction of

microbial communities and affected the activity of

rhizosphere microorganism, which were beneficial

to the degradation of pollutants, maintenance of

infiltration rate and prevention of clogging. Results

showed that plants in bioretention facilities,

especially those with thick and deep taproot, played

an important role in maintaining the permeability of

facilities (Yu 2019).

However, some researchers believed that plants

contributed to more organic matters, thus

accelerating the clogging of the system. Kadlec

(Knowles 2011) found that 5%-15% of plant

residues was difficult to degrade, which was easy to

cause clogging. Hua (Hua 2014) indicated that

plants played different roles in the whole clogging

process of bioretention facility. In the early stage,

plant roots restricted water flow, while in the later

stage, growing roots opened new pore spaces to

improve permeability. Therefore, it is necessary to

consider the combination of vegetation in order to

improve the efficiency of pollutant removal and

alleviate the clogging of bioretention system.

3.4 Microorganism

The pores in the bioretention system could easily be

blocked by the propagation of microorganisms in

bioretention facilities. Studies pointed out that

microorganisms such as algae and bacteria would

accumulate on the surface of the bioretention media,

and the reproduction of microorganisms greatly

reduced the permeability coefficient of the system

(Hua 2014). With the proliferation of

microorganisms, the pore volume in the media

gradually decreased. Microorganisms and their

metabolites could block the gaps in the bioretention

facility and reduce the permeability coefficient of

system. The specific growth rate of microorganisms,

substrate concentration and initial concentration of

soil microorganisms all could limit permeability

reduction. Robert confirmed that the development of

clogging was highly related to the total biological

oxygen demand and the cumulative mass density

load of SS.

4 REGULATION MEASURES

4.1 Source Control

As a result of steel and chemical production

activities, atmospheric deposition, tire wear, exhaust

emissions and the use of pesticides, herbicides,

deicing agents, etc. A large number of pollutants

would enter the bioretention facilities with rainwater

runoff, including SS, TN, TP, metal ions, and

organic pollutants, etc. Many researchers indicated

that the spatial and temporal distribution of rainfall

runoff, pollutant concentration, underlying surface

types and rainfall characteristics including intensity,

duration and frequency, had great influence on

clogging of bioretention facilities (Jiang 2017, Read

2008). For example, higher concentration of influent

and higher rainfall intensity could more easily lead

to clogging of bioretention facility (Jiang 2017). For

reducing the influence of 54rainwater runoff on

clogging, environmentally friendly chemicals such

as biological pesticides, biological attractants, and

snowmelt agents should be used to reduce the

accumulation and improve their own degradation.

Different clean deicers should be rationally selected

according to road conditions, temperature, design of

pretreatment diversion should be carried out.

4.2 Operation Design

In order to prevent the clogging and accumulation of

pollutants in the bioretention facilities, it is

necessary to take into account their structural

characteristics and functions. Factors such as rainfall

recurrence period, pretreatment process, operation

mode, pollutant load, hydraulic retention time, and

design of submergence zone were suggested

(Coustumer 2012, Li 2019). For example,

appropriate dry period was conducive to the

ventilation of substrate and rapid degradation of

organic matter. It was found that the permeability

ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics

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and hydraulic conductivity of the facility could be

improved and the clogging problem could be

alleviated by setting the submergence zone (Tian

2018). The addition of pretreatment facilities such as

pre-ponds and vortex ponds would remove large

particles in runoff ahead of time, slowed down the

flow rate and prevented the snowmelt from entering

directly into the infiltration area in winter (Chris

2013). For serious pollution and salinization of soil

caused by rainwater runoff areas, measures should

be taken to discard the flow and salt drainage.

4.3 Media Optimization

In order to alleviate clogging, measures of media

optimization mainly include three aspects:

combination and proportion of fillers, organic

carbon source addition, and filling mode (Tian 2018,

Qiu 2017, Li 2019), shown as Table 1. It is often

necessary to improve the ratio of fillers or to add

additives. The selection of the fillers should follow

the principles of easy to obtain, moderate cost, local

applicability, and have good permeability, large

specific surface area and good decontamination

ability, such as zeolites, vermiculites, fly ash, perlite,

aluminum sludge and river sediments. New

functional fillers like reed, biochar and recycled

aggregates were also recommended to improve the

permeability of facilities (Tian 2018, Qiu 2017).

Proper addition of carbon sources can increase the

permeability of bioretention facilities and effectively

alleviate their clogging. However, it was also

pointed out that excessive addition of carbon source

could increase the background value of phosphorus,

leading to release of phosphate and worsening water

quality (Li 2019). Therefore, the dosage of organic

matter should be strictly controlled, and the US

design manual recommended that the content of

organic matter in the packing should not exceed 5%.

Table 1: Media optimization for bioretention facilities.

Measures Composition

combination and proportion of

filler

sand and fly ash

aluminum sludge and zeolite

sand, perlite, vermiculite

volcanic rock, spongy iron

vermiculite, zeolite, sand

organic carbon source addition

biochar, activated carbon

recycled building aggregates

compost, newspaper, sawdust,

straw

filling mode

layered packing

mixed packing

4.4 Vegetation Selection

In general, vegetation in bioretention facilities

should be reasonably allocated according to their

cold and drought tolerance, soil permeability and

type, facility scale and structure, and runoff water

quality (Mu 2020, Yu 2019). The following aspects

should be paid attention to when selecting vegetation

in different bioretention facilities: (i) local species

should be the main species, the remaining species

could be matched reasonably, and the plants with

strong adaptability should be selected preferably; (ii)

plants with well-developed roots, large stems and

leaves that can penetrate through soil layer, strong

cold-resistance and drought-resistance, strong

purification ability are preferred; (iii) plants that can

accumulate pollutants such as heavy metals are

preferred; (iv) plants with large biomass and short

growth cycle are selected; (v) low maintenance cost,

certain economic value and landscape effect, and the

diversity of plant landscape in different seasons

should be considered.

Study on the Clogging and Regulation Measures of Bioretention Facilities in Sponge City

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5 MAINTENANCE AND

MONITORING

At present, the design and construction standards of

sponge city construction in China are established,

but the operation and maintenance of bioretention

facilities still lack (Yin 2021, Yang 2020, Mu 2020).

In order to ensure the treatment effect of

bioretention facilities, prevent clogging and achieve

long-term stability of facilities, the following

measures are recommended: (i) regular inspection

and dredge of garbage and sediment in the spillway,

and regular cleaning of the sand deposit; (ii) regular

vegetation maintenance according to the condition

of plants growth and soil humidity; (iii) to clean or

replace the surface fillers regularly and slow down

the growth of microorganisms; (iv) to take plant

anti-freezing measures and appropriate cover in the

packed bed to slow down the freezing rate in winter.

In addition, it should be monitored throughout the

whole process according to the runoff process,

realizing dynamic monitoring and intelligent

management through the on-line monitoring, digital

information platform and wireless network (Yang

2020).

6 CONCLUSION

As a representative measure in construction of

sponge city, bioretention facilities faced clogging

after long-term operation and maintenance,

therefore, it was of guiding significance to analyse

the reasons and influence factors of clogging in

facilities and put forward corresponding solutions.

This paper sorted out the control measures and

suggestions from combination of source reduction,

process optimization and operation management,

providing reference for long-term stability and

operation for green storm water infrastructure in

sponge city:

(i) The causes and processes of clogging were

complex and simultaneous, including physical

clogging, chemical clogging and biological

clogging, which mainly caused by SS, inorganic

ions, TOC, microorganisms and their EPS.

(ii) Utilization of environment-friendly

chemicals, optimization of structure by pretreatment

process, modified fillers, reasonable planting of

vegetation, maintenance and monitoring system

were suggested to improve facility performance and

alleviate clogging.

(iii) Combination of plant, microorganism,

pollutant migration mechanism to solve the problem

of clogging; prediction and model simulation of

clogging time; as well as monitoring methods and

equipment of clogging need further development.

ACKNOWLEDGMENTS

This work was supported by the the Science

Foundation of China Urban Construction Design &

Research Institute Co., Ltd. (Y09S21009), and and

the Science and Technology Planning Project of

Ministry of Housing and Urban-Rural Development

of the People’s Republic of China (No. 2019-K-142)

for financial support.

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