Abstract Penetration experiments were carried out for a period of over two years at an experimental field located in Kusatsu City. The field was divided into two tanks and each tank filled with different types of soil. Polluted water discharged from the road surface was supplied to the field during storm events. The effluent from the field was composed of Surface and Infiltrated flow. The flow was gauged at three points and water sampled for quality analysis. In order to analyze measures against clogging, soil in one tank was replaced to investigate the recovery of soil contents, penetration efficiency, and purification efficiency. The other tank was researched continuously for 26 months to analyze the change of purification efficiency with precipitation characteristics and the continuous use the facility. Sustainability was analyzed by modeling long-term mass balance in the facilities using water quality data (COD, N, P and SS) and comparing the results with actual measured data of the change of pollutants in the soil. The facility achieved high pollutant removal efficiencies of between 50% - 90% during the survey. Simulation results using water quality data compared well with actual measured data of change of pollutants in soil
Trang 1EMPIRICAL STUDY ON EFFICIENCY AND SUSTAINABILITY OF SOIL PURIFICATION FACILITY FOR DISCHARGED POLLUTANTS FROM ROAD SURFACE
K Yamada1, T Shiota1, Y Nagaoka1, M Shiono2 and K Nishikawa3
1 Department of Environmental Systems Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga, 525-8577, Japan (E-mail: yamada-k@se.ritsumei.ac.jp)
2 Agrex Co Ltd., STS Bldg., 5-12-8, Nishinakajima, Yodogawa-ku, Osaka-shi, Osaka 532-0011, Japan (E-mail: masayuki_shiono@agrex.co.jp)
3 NJS Consultants Co Ltd., 9 -15 Kaigan 1 –Chome, Minato-ku, Tokyo 105-0022, Japan (E-mail: kouichi_nishikawa@njs.co.jp)
Abstract
Penetration experiments were carried out for a period of over two years at an experimental field located in Kusatsu City The field was divided into two tanks and each tank filled with different types of soil Polluted water discharged from the road surface was supplied to the field during storm events The effluent from the field was composed of Surface and Infiltrated flow The flow was gauged at three points and water sampled for quality analysis In order to analyze measures against clogging, soil
in one tank was replaced to investigate the recovery of soil contents, penetration efficiency, and purification efficiency The other tank was researched continuously for 26 months to analyze the change of purification efficiency with precipitation characteristics and the continuous use the facility Sustainability was analyzed by modeling long-term mass balance in the facilities using water quality data (COD, N, P and SS) and comparing the results with actual measured data of the change of pollutants in the soil The facility achieved high pollutant removal efficiencies of between 50% - 90% during the survey Simulation results using water quality data compared well with actual measured data of change of pollutants in soil.
Keywords
Road surface runoff, soil purification facility, model
INTRODUCTION
Lake Biwa is the largest lake in Japan, and it covers 1/6 of land area of Shiga Prefecture The water quality of the lake has been leveling off since 1980, and does not meet environmental standards (Figure 1) Thus, despite various measures undertaken to control pollution such as setting of environmental and effluent standards and construction of wastewater treatment plants, the water quality has not improved This is attributed to diffuse sources of pollution which are a significant source of pollution to the lake (Figure 2) Among diffuse sources of pollution, those from urban areas have increased due to increase in number of impermeable residential areas and surfaces Road surface runoff contributes a high proportion
of this pollutant load and therefore requires appropriate measures Soil penetration is considered as one of the measures
Figure 1 Trend of water quality of Lake Biwa, Shiga Prefectural Government (2004)
0 0.01 0.02 0.03
Environmental Standard
T-P
0
1
2
3
4
5
Environmental Standard
COD
0 0.1 0.2 0.3 0.4 0.5
Environmental Standard
T-N
00 0 1
1 9 9 5
T-South Lake North Lake
Trang 2Figure 3 Experimental facilities
In this study, purification of storm water runoff from road surface using a soil penetration demonstration experiment facility was investigated The decrease of penetration capacity and purification efficiency during continuous use of the facility was investigated The facility consisted of two tanks In one of the tanks, continuous use of the facility and change in purification efficiency depending on precipitation characteristics were analyzed with the results of experiments carried out over a period of 26 months starting in 2001 The soil in the other tank was replaced to consider measures against clogging by analyzing the recovery of soil contents, penetration efficiency and purification efficiency Sustainability was analyzed by modeling long-term mass balance in the facilities using water quality data (COD, N, P and SS) The calculated results were then compared with actual
measured data of the change of pollutants in the soil This study
was a continuation of earlier studies whose results are reported
elsewhere (Sugihara et al., 2000; Nishikawa et al., 2001;
Nishikawa et al., 2002)
Figure 2 Pollutant load going into Lake Biwa (Shiga Prefectural Government, 2004)
OUTLINE OF SURVEY
Experimental field and soil penetration facility
The outline of the soil penetration facility is shown
in Figure 3 and Table 1 The facility consisted of two
parallel soil tanks; Tank A and Tank B (Figure 3)
each with soil of 45 cm depth Tank A consisted of
two types of soil, 5 cm deep Akadama soil in the top
layer and 40 cm deep pit sand in the bottom layer
Tank B consisted of only pit sand Soil replacement
was carried out in Tank B in 2003 Runoff water
from 750 m2 of road surface area flows into the soil
penetration facility Inflow water leaves the facility
as Overflow or Infiltrated water The bottom of the
facility is covered with a water proof sheet to
comprehend the water balance Water that penetrates
through the soil is gathered at the bottom of the
facility and drained by a drainage pipe provided at
the bottom This water is referred to here as
Infiltrated water As Inflow water increases,
surface flow goes over the weir and is drained
This is called Overflow
Outline of measurement
The amount of Inflow water, Infiltrated
Industrial Agricultual
Land
Total amount
of Loads (t/day)
Water flow
Akadama soil
Pit sand
Points of Soil sampling
Points of Flow measurement and Water sampling
Soil
Inflow water
Infiltrated water
Overflow water
Weir
Weir
Overflow water
Infiltrated water
7m Inflow
Tank A
Tank B
Soil penetration facility 24.5m 2 ×2
Road Surface 750m 2
T-P T-N
13%
10%
28%
20%
29%
56.1
(t/day)
'95
15%
21%
34%
14%
16%
44.7 (t/day)
'05(Forecast)
16%
6%
26%
16%
36% 21.6 (t/day)
'95
27%
11%
8%
39%
15%
20.1 (t/day)
'05(Forecast)
16%
5%
39%
27%
13%
1.35 (t/day)
'95
36%
8%
19%
22% 15%
1.08 (t/day)
'05(Forecast) COD
Table 1 Outline of experimental facility
Lower layer Soil type
Pit sand (45)
Surface area Depth
Height
of weir Upper layer
Trang 3water and Overflow water were measured by a flow meter In addition, water quality analysis, soil content measurement and water permeability tests were carried out There were 219 rainfall events over the duration of the experiment Flow measurements for Inflow water, Infiltrated water and Overflow water were undertaken for all the rainfall events using an automatic flow meter installed on site Sampling for water quality analysis was done for 14 of the rainfall events (Table 2) SS, T-COD, T-N, T-P, D-COD, D-N and D-P were targeted in water quality analysis Soil was sampled from both the surface and at a depth of 5cm for soil content analysis In Tank A, which consisted of two types of soil, only Akadama soil was sampled Sampling was done at three sites at the upstream, mid-stream and downstream as shown in Figure 3 Soil sampling was done 22 times Carbon, nitrogen, phosphorus and particle size were targeted
in soil content measurement Sediments were collected from the road surface and analyzed for nitrogen, phosphorus and carbon content Permeability tests were done at three locations near the points used for soil sampling To measure permeability, the amount of water that flowed through a pipe installed in the soil over a fixed period of time was determined Permeability tests were undertaken 25 times (Table 2)
Table 2 Characteristics of selected storm events
-Water quality survey ID
Ave
rainfall intensity (mm/hr)
Antecedent days (day) Date
Precipi tation (mm)
Duration (hr)
Soil content survey ID
Water permeability survey ID
Max
rainfall intensity for 10 min (mm/hr）
Antecedent days (day) Date
Water
quality
survey
ID
Soil
content
survey
ID
Water permeability survey ID
Precipi tation (mm)
Duration (hr)
Ave
rainfall intensity (mm/hr)
Max
rainfall intensity for 10 min (mm/hr)
RESULTS AND DISCUSSION
Survey results
T-N content ratio Figure 4 shows the results of nitrogen content in the soil For Tank A the data
correspond to the content in the top layer Akadama soil only while for Tank B the data correspond to content in pit sand The initial nitrogen content of Akadama sand in Tank A was higher than that of pit sand of Tank B The nitrogen content in both Tanks increased with time In both Tank A and B, the content of nitrogen in the surface soil leveled off to a value comparable to that of sediment collected from the road surface (3.4 mg/g) The nitrogen content of soil at 5 cm depth remained constant from the start of the survey but begun to rise at a relatively slow rate at about the same time that the nitrogen content in the top soil begun level off In Tank B, after the soil was replaced (at 645 days) the nitrogen content recovered to almost the same level as that at the initial state The results of the subsequent measurements
showed an increasing tendency in nitrogen content similar to the situation before soil replacement
Trang 4The above results show that the nitrogen content in the soil at 5 cm did not rise significantly above the initial content at the start of the survey In other words, the results of the soil content survey showed that most of the nitrogen was stored in the upper 5 cm depth of the soil during 26 months (804 days)
Figure 4 T-N content in soil
Removal efficiency For the purpose of evaluating pollutant removal efficiency, Gross Removal Efficiency
(GRE) and Net Removal Efficiency (NRE) were defined as follows:
GRE = (Pollutant load held in soil)/( Pollutant load of Inflow) (1) NRE = (Pollutant load held in soil)/( Pollutant load of Inflow – Pollutant load of Overflow) (2) GRE and NRE are shown in Figure 6 GRE ranged between 60 – 95% and 20 – 95% for Tank A and Tank
B, respectively Except for the first three initial surveys, the average GRE in Tank A were about 75% for T-COD and T-P, 65% for T-N and 90% for SS In tank B, though the Overflow ratio (surface Overflow water / Inflow water) was comparatively high, the corresponding GRE values were about 60% for T-COD, 60% for T-P, 50% for T-N and 85% for SS before soil replacement The GRE values after soil replacement showed almost similar values as those before soil replacement, contrary to the expectation that the removal efficiency would improve with soil replacement In particular, for SS the average removal efficiency after soil replacement decreased to nearly 60%
On the other hand, NRE was higher than GRE by about 10% in Tank A, 20% in tank B before soil replacement and 5-20% in Tank B after soil replacement The relatively higher NRE for Tank B compared
to Tank A is due to the fact that the Overflow ratio was relatively higher in Tank B As with GRE, the NRE in Tank B after soil replacement was lower than that before soil replacement This could be attributed to the fact that the soil was unstable after replacement and therefore some of the soil may have flowed out together with infiltrated water However, the removal efficiencies after soil replacement show
an increasing tendency with time In particular, the removal efficiencies for the last two surveys after soil replacement (survey No wps13 and wps14) show a relatively high increase, indicating that the soil may have stabilized There is need to further study the recovery of purification capacity
0
1
2
3
4
5
Days
Days
0 1 2 3 4 5
Days
Surface Surface (after soil replacement) 5cm Depth 5cm Depth (after soil replacement)
Trang 5Figure 6 Pollutant removal efficiency in Tank A (upper graphs) and Tank B (lower graphs)
Simulation of long-term mass balance
Flow A conceptual diagram of mass balance in the soil treatment facility is shown in Figure 7
Simulation of long-term mass balance is considered for Tank A only where continuous survey was undertaken The effect of rainfall characteristics on the mass balance was investigated by classifying the rainfall events into 7 types according to the average rainfall intensity and the precipitation (Table 3)
Figure 7 Conceptual diagram of mass balance
Road surface runoff (Ro) was calculated as follows:
Ro = rr×(R - Iw) (3)
Table 3 Classification of rainfall
Net removal efficiency in soil Gross removal efficiency
0 20 40 60 80 100
Analysis No.
0 20 40 60 80 100
Analysis No.
0 20 40 60 80 100
0 20 40 60 80 100
0
20
40
60
80
100
0
20
40
60
80
100
Analysis No.
R
O LO
Ro
LRo
I
LI
(Rainfall)
(Road surface runoff)
(Pollutant load of road surface runoff)
(Inflow water)
(Pollutant load of inflow)
(Overflow water) (Pollutant load of Overflow)
D LD
S
LS
F
LF
(Infiltrated flow)
(Pollutant load of infiltrated flow)
(Water held in soil)
(Pollutant load of water held in soil)
Infiltrated water Pollutant load of infiltrated water
Road Surface
Soil Field
F=I-O LF=LI-LO S=F-D LS=LF-LD
Rainfall type
Precipitation
R (mm)
Ave rainfall intensity
I (mm/hr）
B C D
3.0≦R ＜20.0
I ＜1.0
1.0≦I ＜4.0 4.0≦I
E F G
20.0≦R
I ＜1.0
1.0≦I ＜4.0 4.0≦I
Trang 6In Equation (3) rr is Road surface runoff ratio, R is precipitation (L) and Iw is Initial lost water (L) Initial
lost water was calculated by the amount of initial rainfall and the measured value of Road surface runoff According to Equation (1), rr was calculated as the slope of the regression equation of measured Road surface runoff and the difference between precipitation and Initial lost water Typical calculation results for rr for rainfall of type A are shown in Figure 8 The calculated values of runoff ratios are given in Table
4 The relationship between values of Ro estimated by Equation (3) and measured values is shown in
Figure 9
The gross quantity of Flow into soil (F) and Water held in soil (S) for one rainfall event were calculated from measured values of gross Inflow water (I), Overflow water (O) and Infiltrated water (D), as follows
(all units in liters):
F = I – O = I×(1 – ro) (4)
S = F – D (5)
In Equation (5), ro is Overflow runoff ratio of flow The Overflow runoff ration of flow is related to
Inflow water, cumulative rainfall, antecedent days of no rain and average of rainfall intensity Multiple
linear regression analysis with these four factors set as explanatory variables was used to calculate ro as
follows (Figures 10 and 11):
4
3 3
2 2
5 1
10
2
1 × − x + × − x + × − x + − × − x + − × − (6)
In Equation (6), x1 is Inflow water (L), x2 is cumulative rainfall (mm), x3 is the number of antecedent days
of no rain (days), and x4 is average of rainfall intensity (mm/hr)
R2 = 0.16
R2 = 0.42
R2 = 0.32
0.0 0.2 0.4 0.6 0.8 1.0
Ave rainfall intensity(mm/hr）
0 5000 10000 15000
Actual measurement（L）
Figure 9 Estimated and measured Road surface runoff
Figure 8 Road surface runoff and
precipitation (rainfall type A)
Table 4 Road surface
R2 = 0.8183
0 500 1000 1500
Precipitation reduced initial lost（L）
Precipitation reduced by initial lost water (L)
R2 = 0.04
R2 = 0.05
R2 = 0.06
0.0
0.2
0.4
0.6
0.8
1.0
Antecedent days (day)
2000mm～
△ 1000mm～2000mm
Figure 10 Overflow runoff ratio
and antecedent days of no rain
Figure 11 Overflow runoff ratio and rainfall intensity
Rainfall
type
Runoff ratio,
rr
Trang 7Figure 15 Overflow runoff ratio of load and flow
Figure 16 Estimated and measured values of pollution load (T-N)
The relationship between gross Flow into Soil (F) and gross Infiltrated water (D) is shown in Figure 12,
and the regression equation is given in below:
The relationship between values estimated by the model and values measured by water quality survey and flow rate survey is shown in Figure 13
Figure 12 Infiltrated water and Flow into soil
Mass balance of pollution load Pollution load was calculated by the relationship between Road surface
runoff (Ro) and Pollutant load from road surface runoff (LRo) As an example, the following relationship
was established for T-N (Figure 14):
LRo=0.5833×Ro0 3785 (8)
The amount of pollutant load in overflow was calculated by the regression analysis of Overflow runoff
ratio of flow (ro) and Overflow runoff ratio of load (Lro) The following relationship was established for
T-N (Figure 15):
Lro=0.6059×ro (9)
T-N
R2 = 0.5291 0
10
20
30
40
50
Surface runoff, Ro （L)
0 5000 10000 15000 20000
measured value（L）
R2 = 0.9451
0
5000
10000
15000
volume of Flow into soil：F（Ｌ）
Figure 14 Pollutant load
and Road surface runoff
Figure 13 Estimated and measured values of flow
Overflow runoff ratio (flow), ro (%)
R2 = 0.966
R2 = 0.939
R2 = 0.8874
R2 = 0.9284
0 10 20 30 40 50
0 5 10 15 20
measured load(g)
Measured load (g)
Measured value (L)
Flow into soil, F (L)
△ Pollutant load held in soil Pollutant load in overflow Pollutant load into soil
Trang 8Measured values of Pollutant load into soil (LS) and Pollutant load infiltrated (LD) were calculated from
water quality analysis data The relationship between the measured values and values estimated by the
model equations above is shown in Figure 16
Comparison between simulation results based on water quality data and actual measurement data of
pollutant load in soil Gross water flow and gross pollutant load of road surface runoff, overflow water,
flow into soil, infiltrated water and water held in soil were calculated for all the precipitation data (total
precipitation 3,300 mm) from September 2001 to November 2003 The simulation results of gross water
balance and gross pollutant load balance are shown in Tables 5 and 6, respectively From the results of
soil content survey before and after the simulation term, the contents of pollutants at 5 cm-depth and
surface soil were calculated, assuming the following values: specific gravity as 2.65, void ratio as 50%
and proportion of particles under 75 µm as about 35% Comparisons of increase in soil pollutant content
amounts are shown in Table 6 Simulation results of (LS) compared well with measured data
Table 5 Simulation results of gross water balance (mm)
I O F D S
Table 6 Simulation results of gross pollutant load balance and increased soil contents (g)
Pollutant load of inflow water (LI) 1699.5 511.9 179.8 123.1
Pollutant load of overflow water (LO) 228.4 69.1 21.4 11.8 Model simulation Pollutant load of flow into soil (LF) 1471.1 442.8 158.3 111.3
Pollutant load of infiltrated water (LD) 423.6 57.0 20.6 9.2
Pollutant load of water held in soil (LS) 1047.9 385.8 137.8 102.2 Actual measurement Increase in pollutant amount in soil 1006.4 145.8
CONCLUSIONS
Sustainability of a soil penetration facility for storm water runoff was analyzed by carrying out a mass
balance analysis using data measured from surveys of permeability, flow rate and water quality The
simulation results were compared with actual measured data of pollutant content in soil The following
results were obtained:
1 Nitrogen accumulated in the upper 5 cm layer of soil in of the soil purification facility
2 Average pollutant removal efficiencies of 50% - 90% were obtained for COD, N, P and SS An
obvious decline in pollutant removal efficiency was not seen in the facility over the two years the
survey was carried out However, further studies are needed to investigate recovery of the pollutant
removal efficiency after soil replacement
3 Mass balances of flow and pollutant load in the penetration facility were carried out Regression
equations relating flow and pollutant load to rainfall characteristics were established
REFERENCES
Sugihara, M., Yamada, K., and Terada, A (2000) Study on soil filtration treatment for pollutants from
road surface during storm events Proceedings, 3rd Annual Symposium, JSWE, 95-96
Nishikawa, K., Sugihara, M and Yamada, K (2001) Study on soil penetration facility for pollutants
discharged from road surface Proceedings, 56th Annual Meeting, JSCE, 488-489
Nishikawa, K., Sugihara, M., and Yamada, K (2002) Study on removal by soil of pollutants discharged
from road surface during storm events Proceedings, 6th International Conference on Diffuse Pollution,
IWA, 616-621
Shiga Prefectural Government (2004) http://www.pref.shiga.jp/index.html