Franz Kevin F.Geronimo
(Franz Kevin F. Geronimo)
MarlaC. Maniquiz-Redillas
(Marla C. Maniquiz-Redillas)
홍정선
(Jungsun Hong)
김이형
(Lee-Hyung Kim)
†
-
공주대학교 건설환경공학과
(Department of Civil and Environmental Engineering, Kongju National University)
© Korean Society on Water Environment. All rights reserved.
Key words(Korean)
Bioretention, Event mean concentration, Flow attenuation, Green infrastructures, Low Impact Development
1. Introduction
Bioretention systems, also known as rain gardens, biofilters or bioswales are considered
as the most widely implemented stormwater management practice which began in the late
1980’s (Cho et al., 2013; Kim, Sung et al., 2011; Kluge et al., 2016; Trowsdale and Simcock, 2011). Commonly, bioretention systems were employed to highly urbanized land uses to obtain
different stormwater management objectives including flood and peak flow mitigation,
stormwater runoff quality improvement and groundwater recharge. Bioretention systems
are generally small, and aesthetically pleasing which acts as urban green spaces especially
in urban areas (Geronimo et al., 2014). Mechanisms including sedimentation, filtration, infiltration, sorption, biological
uptake, evapotranspiration, bioremediation and phytoremediation were incorporated
in the system making it an advance stormwater management technology (Endreny and Collins, 2009; Kazemi et al., 2011; Maniquiz-Redillas and Kim, 2016). In addition to its treatment functions, bioretention systems promotes biodiversity
thereby mimicking and preserving the pre-developed state of an area which is the primary
goal of low impact development (LID) and green infrastructures (GI) (Kim, Kim et al., 2011; Flores et al., 2015).
In USA and Australia, bioretention systems exhibited up to 100% TSS removal efficiencies
and - 49% to 90% TP removal efficiencies (Li et al., 2014; Mangangka et al., 2015). In addition, the bioretention system studied by Khan et al. (2012) in Canada exhibited almost 92% and greater than 95% runoff volume and peak flow reduction,
respectively. Although bioretention systems were widely utilized in different countries,
its application in South Korea still required further evaluation. In this research,
two laboratory scale system was developed for Type A and Type B bioretention systems.
Specifically, this study identified design factors affecting the performance of four
bioretention systems in reducing stormwater peak flow, runoff volume and pollutants.
2. Materials and Methods
2.1. Bioretention Filter Media and Physical Design
Four bioretention systems were developed and investigated in this study. Type A and
Type B bioretention systems were identical in media configuration but has different
dimensions as demonstrated in Fig. 1. Type A-C and Type A-FC were planted with perennials such as Chrysanthemum zawadskii var. latilobum (Chrysanthemum) and Aquilegia flabellata var. pumila (Fan columbine), respectively. On the other hand, shrub species such as Rhododendron indicum Linnaeus (Azalea) and Spiraea japonica (Japanese meadowsweet) were planted in Type B-A and Type B-JM, respectively. The total facility volume
of Type A bioretention systems were 47% less than Type B. In addition, Type B bioretention
systems incorporated infiltration mechanism to evaluate its contribution to the overall
performance of bioretention systems and groundwater recharge. Table 1 exhibited other physical characteristics of each bioretention system. The woodchip
mulching occupied 5% of the bioretention total facility volume for each bioretention
types serving as the top-most filter media. Main filter media used to primarily treat
particulates for both bioretention types were soil, sand and gravel. Lastly, geotextile
filter fabric was installed as the base filter material of each bioretention types.
Typical engineered filter media of bioretention systems were composed of surface hardwood
mulch layer, middle sand, soil and silt mixture layer and bottom sand or gravel layer
(Kluge et al., 2016; Thompson et al., 2008).
Fig. 1. Schematic of each lab-scale bioretention type.
Table 1. Physical design characteristics of bioretention types
|
Parameter
|
Unit
|
Type A
(A-C: Chrysanthemum and A-FC: Fan columbine)
|
Type B
(B-A: Azalea and B-JM: Japanese meadowsweet)
|
|
Number of plants
|
-
|
28
|
14
|
|
Infiltration capability
|
-
|
No
|
Yes
|
|
Dimension (l × w × h)
|
m
|
0.95 × 0.5 × 0.45
|
1.5 × 0.4 × 0.6
|
|
Storage volumea |
m3 |
0.03 (16%)
|
0.06 (16%)
|
|
Woodchip volumea |
m3 |
0.01(5%)
|
0.02 (5%)
|
|
Soil volumea |
m3 |
0.07 (39%)
|
0.14 (39%)
|
|
Sand volumea |
m3 |
0.04 (20%)
|
0.07 (20%)
|
|
Gravel volumea |
m3 |
0.04 (20%)
|
0.07 (20%)
|
2.2. Experimental Conditions, Data Collection and Analyses
Synthetic stormwater runoff was prepared by diluting one to two kg of sediments, collected
from a 100% impervious road, into 2 m3 of tap water. Each experimental run was conducted during 120 min. The four bioretention
systems were subjected to five inflow rates of 2, 3, 4, 5 and 6 L/min representing
55%, 60%, 65%, 70% and 75%, respectively of rainfall depth occurring in Cheonan city,
South Korea. Experimental scenarios were demonstrated in Fig. 2 wherein chemical properties of water and plants were tested in accordance with the
standard methods for examination of water and waste water and handbook of reference
methods for plant analysis, respectively (APHA, AWWA, and WEF, 1992; Kalra, 1998).
Fig. 2. Experimental scenarios, monitoring and analyses conducted in each bioretention system.
The pollutant removal efficiency of the four bioretention systems developed was evaluated
using EMC and pollutant loads. EMC represents a flow-weighted average concentration,
computed by dividing the total pollutant mass by the total runoff volume for event
duration. In addition, the summations of the inflow, infiltrated and discharged volume
were calculated for each storm event to determine the volume retention capacity of
each bioretention system. Lastly, pollutant mass reduction of the system was calculated
by dividing the difference of the summation of influent and summation of effluent
loading with the summation of influent loading, also known as summation of loads method.
Results were statistically analyzed using SYSTAT 12 and Origin Pro 8 package software
including analysis of variance (one-way ANOVA). Significant differences between parameters
were accepted at 95% confidence level, signifying that probability (p) value was less
than 0.05.
3. Results and Discussion
3.1. Hydraulic Conditions and Flow Attenuation
The hydraulic conditions of each bioretention system were summarized in Table 2. Based on the results, the difference in volume retention between each bioretention
types was associated with the difference in facility total volume between Type A and
Type B bioretention systems. Type B bioretention systems were 0.17 m3 greater than Type A bioretention systems. In addition, 8% of the inflow volume was
reduced through infiltration mechanism employed in bioretention Type B-A and Type
B-JM. Apparently, the hydraulic retention time (HRT) observed in Type A-C was 0.36
and 0.44 hours less than Type B-A and Type B-JM, respectively. Similar HRT was observed
in Type A-FC wherein Type B-A and Type B-JM were greater by 0.35 and 0.43 hours. These
findings suggested that by increasing the facility total volume by 53% and incorporating
infiltration mechanism to similar bioretention design, volume retention capacity may
be increased to more than twice. Likewise, an increase of more than five times the
original HRT may also be expected. In a real scale bioretention system, HRT was determined
to be a critical factor influencing the treatment performance by biological processes
(Liu et al., 2014).
Table 2. Hydraulic condition of the bioretention systems
|
Parameter
|
Unit
|
Type A
|
Type B
|
A-C
(Chrysanthemum)
|
A-FC
(Fan columbine)
|
B-A
(Azalea)
|
B-JM
(Japanese meadowsweet)
|
|
No. of test run
|
-
|
12
|
12
|
13
|
14
|
|
ADDa |
day
|
3.1 ± 1.7
|
3.1 ± 1.5
|
3.4 ± 5.2
|
3.3 ± 5
|
|
Inflow volumea |
m3 |
0.46 ± 0.21
|
0.47 ± 0.21
|
0.49 ± 0.2
|
0.49 ± 0.18
|
|
Retainedb |
%
|
12 ± 7
|
14 ± 6
|
30 ± 13
|
28 ± 11
|
|
Infiltratedb |
%
|
-
|
-
|
8 ± 8
|
8 ± 5
|
|
HRTa |
min
|
4.2 ± 2.6
|
4.6 ± 2.1
|
25.8 ± 16.3
|
23.4 ± 14
|
The average changes in inflow and outflow rates per experimental run time were exhibited
in Fig. 3. Apparently, the flow attenuation time of Type B bioretention systems were 10 to
60 minutes longer than Type A. Flow attenuation was observed only during the first
20 minutes of discharge in each bioretention Type A wherein beyond this time, the
difference between inflow and outflow rates decreased and stabilized (Type A-C: CV
= 0.02 to 0.06; Type A-FC: 0.02 to 0.07). On the other hand, the difference between
inflow and outflow rate in Type B-A declined and stabilized after 80, 60, 60, 30,
30 minutes of discharge considering 2, 3, 4, 5 and 6 L/min inflow rates, respectively
(CV = 0.02 to 0.1). Lastly, Type B-JM achieved reduction and stabilization of the
difference in inflow and outflow rates after 60, 50, 40, 30, 30 minutes of discharge
considering 2, 3, 4, 5 and 6 L/min inflow rates, respectively (CV = 0.02 to 0.08).
These findings were mainly associated with the difference in total facility volume
between Type A and Type B bioretention systems. In addition, the mean infiltration
rate (0.04 ± 0.04 L/min) employed in Type B bioretention systems also contributed
to its flow attenuation capability.
Fig. 3. Changes in the mean flow rates (inflow and outflow) of the bioretention systems with respect to experimental run time.
3.2. Characterization of Event Mean Concentrations
Fig. 4 shows the ranges of inflow and outflow EMC in each bioretention system. TSS, TN and
TP inflow EMC (EMCin) were significantly reduced to outflow EMC (EMCout) by both bioretention types compared with p<0.05. No significant difference was observed between the soluble heavy metals EMCin and EMCout in each bioretention system developed. Except for Cd in Type B-A, the mean EMCin of soluble metals such as Cu and Pb were reduced by 4% to 26% and 4% to 32%, respectively
compared to mean EMCout. The minimum and maximum values of EMCout of all the constituents in each bioretention
types were less than the minimum and maximum values of EMCin except for Cd in B-RL.
These findings implied that the systems developed showed efficiency in reducing pollutant
EMC. Apart from the difference in facility total volume between the two bioretention
types, and infiltration mechanism employed in the bioretention Type B-A and Type B-JM,
the difference in pollutant removal efficiency of each bioretention systems was also
found to be associated with the difference in the filter media depth. Filter media
depth of bioretention Type A-C and Type A-FC were only 66% of the filter media depth
of Type B-A and Type B-JM. Davis et al. (2003) identified that facility depth was an affecting factor to allow effective pollutant
removal in the bioretention systems.
Fig. 4. Boxplots of inflow and outflow pollutant event mean concentration in the bioretention systems.
3.3. Pollutant Load Ratio
Based on Fig. 5, TSS attained the lowest load ratio (Loadout/Loadin) among the constituents analyzed in Type A and Type B bioretention systems (TSS load
ratio: Type A-C = 0.06; Type A-FC = 0.07; Type B-A = 0.06; Type B-JM = 0.08). These
results signified that 94%, 93%, 94% and 92% TSS load reduction were attained by Type
A-C, Type A-FC, Type B-A and Type B-JM, respectively. The results also showed that
Type A and Type B bioretention systems exhibited good nutrient reduction evident through
the load ratios of TN and TP. Type A bioretention systems exhibited almost 20% greater
TN load ratios compared to Type B bioretention systems. Likewise, the TP load ratios
of Type A bioretention systems were two folds greater than Type B. Greater nutrient
uptake by shrubs and infiltration mechanism employed in bioretention type B were the
factors affecting the difference between the nutrient reduction efficiencies of the
bioretention systems developed. 0.4% to 4% of TN and 10% to 21% of TP inflow load
were up taken by shrubs planted in Type B bioretention systems. On the other hand,
perennials planted in Type A bioretention systems up taken inflow TN and TP loads
ranged from 0.1% to 0.3% and 0.2% to 11%, respectively. In addition, the infiltration
mechanism employed in bioretention Type B accounted for 3% TN and 1% and TP removal
by the systems. Longer HRT observed in Type B compared to Type A bioretention systems
also contributed to improved nutrient removal similar to the study conducted by Liu et al. (2014). Lastly, the load ratios for soluble metals exhibited by Type A bioretention systems
were greater than the load ratios in Type B. These findings suggested that the systems
developed can satisfactorily remove nutrient constituents and high reduction with
respect to the TSS concentration can be expected from the system. On the other hand,
lower heavy metal removal efficiency was exhibited by the systems developed compared
to particulate and nutrient constituents.
Fig. 5. Relationship of inflow and discharged pollutant load in the bioretention systems.
4. Conclusion
Bioretention systems, an innovative example of green infrastructure were currently
utilized in different parts of the world due to its capability to promote biodiversity
thereby mimicking and preserving the pre-developed state of an area. Four laboratory
scale bioretention systems were investigated and compared to identify factors affecting
the hydraulic capabilities and pollutant removal efficiencies in each system and be
used to design similar bioretention system. Based on the results of this study, the
followings conclusions were summarized as follows:
-
Greater total facility volume of Type B bioretention systems and infiltration mechanism
employed in bioretention Type B yielded to increased volume retained, longer HRT and
longer peak flow attenuation compared to Type A.
-
The four bioretention systems significantly reduced TSS, TN and TP concentrations
(p<0.05) signifying that the bioretention systems developed were effective in particulate
and nutrient reduction.
-
Total facility volume, infiltration mechanism, filter media depth, longer HRT and
plant species were identified as the factors affecting the difference in pollutant
removal efficiency between Type A and Type B bioretention systems.
The design of bioretention Type B-A and Type B-JM were advantageous considering greater
volume retention, groundwater recharge, longer HRT and peak flow attenuation and greater
pollutant removal efficiency. On the other hand, the design of bioretention Type A-C
and Type A-FC was more appropriate for design considering reduced groundwater contamination.
The findings and design factors identified in this study may be significantly used
to design and improve the performance of similar bioretention system in the future.
5. 국문요약
식생체류지는 도시 강우유출수 관리를 위한 저영향개발 및 그린인프라 기술이며, 개발이전의 상태를 최대한 유지하는 강우유출수 관리기술로 자연을 모방하면서
생태계의 다양성 을 향상시키는 기술이다. 본 연구는 식생체류지의 물순환 능 력과 비점오염물질의 저감효율에 영향을 끼치는 인자를 도 출하기 위하여 4개의
식생체류지 시스템에 대하여 연구를 수행하였다. 2개의 식생체류지, 즉 Type A-C와 Type A-FC 에는 국화와 매발톱꽃이 식재되었으며, Type
B-A와 Type B-JM식생체류지에는 진달래 및 조팝나무와 같은 관목식물 이 식재되었다. 연구결과 식생체류지의 유출저감, 저류량 및 오염물질 저감에
영향을 끼치는 인자로는 TV, 침투기작, 여 과재의 두께와 식생 종류로 나타났다. Type B-A와 Type B-JM식생체류지 설계시에는 유출저감,
지하수 충진, 긴 체 류시간과 첨두유출량 저감과 비점오염물질 저감을 고려하여 설계가 필요한 것으로 나타났다. 반면에 Type A-C와 Type A-FC
식생체류지 설계시에는 지하수 오염 저감을 중요하게 고려하여야 하는 것으로 나타났다.
Acknowledgement
This research was supported by a grant (E416-00020-0602-0) from Public Welfare Technology
Development Program funded by Ministry of Environment of Korean government. The authors
are grateful for their support.
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