irene seco manuel gómez alma schellart simon tait
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7th International Conference on Sewer Processes & Networks Wednesday 28 - Friday 30 August 2013 The Edge Conference Centre, Sheffield. Erosion resistance and behaviour of highly organic in-sewer sediment. Irene Seco Manuel Gómez Alma Schellart Simon Tait. - PowerPoint PPT PresentationTRANSCRIPT
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Irene SecoManuel GómezAlma SchellartSimon Tait
Erosion resistance and behaviour of highly organic in-sewer sediment
7th International Conference on Sewer Processes & NetworksWednesday 28 - Friday 30 August 2013The Edge Conference Centre, Sheffield
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Wet weather pollution from combined sewer systems
Release of in-sewer sediment deposits accumulated during dry-
weather constitute a major source of pollutants that affect the water
quality of receiving natural water bodies
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Long dry-weather periodsIntense precipitation events
Wet weather pollution from combined sewer systems
Rain regime
Particularities in the Mediterranean region in Spain:
cumulative precipitation = 600 mm/year(concentrater 50 days/year)
average dry-period between rain: 11 days
≈ 40% rainfall registered P(mm)>10mm
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Long dry-weather periodsIntense precipitation events
Wet weather pollution from combined sewer systems
Rain regime
In-sewer sediment accummulation and consolidation
Particularities in the Mediterranean region in Spain:
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Wet weather pollution from combined sewer systems
Low circulating flow(0.56 m3/s average Congost River. Vallès Oriental. Catalonia. Spain)
Low dilution capacity
Particularities in the Mediterranean region in Spain:
Flow regime in riversLong dry-weather periods
Intense precipitation events
Rain regime
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Wet weather pollution from combined sewer systems
Particularities in the Mediterranean region in Spain:
Low circulating flowLow dilution capacity
Flow regime in riversLong dry-weather periods
Intense precipitation events
Rain regime
High percentage of impervious surface in
Urban areas
Urban pattern
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Wet weather pollution from combined sewer systems
Particularities in the Mediterranean region in Spain:
Low circulating flowLow dilution capacity
Flow regime in riversLong dry-weather periods
Intense precipitation events
Rain regime
High percentage of impervious surface in
Urban areas
Urban pattern
Sewer solids mainly from wastewatersRelevant Organic
composition
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Wet weather pollution from combined sewer systems
Particularities in the Mediterranean region in Spain:
Significant volumes discharged in a shorttime from sewer network (CSO)Significant organic Pollution in natural streams and sea
Overflows during wet-weather
Low circulating flowLow dilution capacity
Flow regime in riversLong dry-weather periods
Intense precipitation events
Rain regime
High percentage of impervious surface in
Urban areas
Urban pattern
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Objectives of this study
Particular conditions of Build-up/Wash-off affects the initiation of sediment motion
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Objectives of this study
Consider potential incidence of the environmental conditions in-sewer on the transport loads and initiation of motion
Analyse changes in transport potential for different lengths of antecedent dry-weather periodsInvestigate erosion
behaviour of real in-sewer organic-rich
sediment collected in Spain
Particular conditions of Build-up/Wash-off affects the initiation of sediment motion
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• Long dry-weather period/Build-up
• Intense rainfall/Wash-off
Suitable to be applied to the particular Mediterranean climate and urban pattern
conditions
Objectives of this study
Improve prediction of in-sewer sediment transport loads
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Real in sewer sediment characteristics
Sediment collected from a sewer system (residential and commercial area in
Catalonia, Spain)
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Real in sewer sediment characteristics
relevant Organic content
(O.M. around 80%) organic nature of solid particles from domestic wastewaters, and the presence of
greasesCohesive properties
Sediment collected from a sewer system (residential and commercial area in
Catalonia, Spain)
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Real in sewer sediment characteristics
relevant Organic content
(O.M. around 80%) Related with the organic nature of solid particles from domestic wastewaters, and
the presence of greasesCohesive properties
d50 = 0.31 mm (310 µm)
Density = 1310 kg/m3
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.50
20406080
100 Sieving analysis of sewer sediment in natural state
mesh width (mm) % a
ccum
ulat
ed
on th
e sie
ve
Sediment collected from a sewer system (residential and commercial area in
Catalonia, Spain)
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Consolidation, microbiological degradation, chemical-biological interactions (bonding forces between particles )
Real in sewer sediment characteristics
Effects on the transport of solidssignificant influence on the incipient motion
Sediment with high organic content and cohesive properties
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Laboratory erosion measurement
Liem et al. (1997) investigation on erosional proecess of cohesive sediment using an in-situ measuring device. International Journal of Sediment Research, 12 (3), 139-147
Evaluation Erosion Rate
Assessment critical threshold of motion at solid-
fluid interface
Erosion meter devised (based on a design by Liem et al. 1997).
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Laboratory erosion measurement
A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event.
Simulation of dry-weather periods
• Different lengths: 16, 64, 140 hours• Environmental conditions:
Anaerobic and Aerobic• Constant low shear stress:
0.15 N/m2 (dry-weather flows inside conduits)
Consolidation period Erosion phase Sampling and Analysis
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Simulation of dry-weather periods
• Different lengths: 16, 64, 140 hours• Environmental conditions:
Anaerobic and Aerobic• Constant low shear stress:
0.15 N/m2 (dry-weather flows inside conduits)
Laboratory erosion measurement
A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event.
Consolidation period
Simulation flows at start of storm
event
Increasing shear stress is applied
in a stepwise way
Erosion phase Sampling and Analysis
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Simulation of dry-weather periods
• Different lengths: 16, 64, 140 hours• Environmental conditions:
Anaerobic and Aerobic• Constant low shear stress:
0.15 N/m2 (dry-weather flows inside conduits)
Laboratory erosion measurement
A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event.
Consolidation period
Simulation flows at start of storm
event
Increasing shear stress is applied
in a stepwise way
Erosion phaseSediment samples
collected during erosion tests at each shear stress
intervalRemaining
sediment after tests collected
Sampling and Analysis
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Main Results
Average erosion rate (q) linked to the applied shear stress (tb)
Aerobic
0 0.2 0.4 0.6 0.8 10.00
0.40
0.80
1.20
1.60
2.00
Applied shear stress (Tau_b) [N/m2]er
osio
n ra
te (E
) [g/
m2/
s]
0 0.2 0.4 0.6 0.8 10.00
0.40
0.80
1.20
1.60
2.00
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
0 0.2 0.4 0.6 0.8 10.00
0.40
0.80
1.20
1.60
2.00
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
0 0.2 0.4 0.6 0.8 10.00
0.40
0.80
1.20
1.60
2.00
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
0 0.2 0.4 0.6 0.8 10.00
0.40
0.80
1.20
1.60
2.00
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
Anaerobic
T116h
T3140h
T264h
T416h
T564h
Erosion rate of sediments monitored in terms of Suspended Sediment concentration
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Main ResultsErosion Rate valuesComparison between tests with increasing length of periods of consolidation.
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
[g/
m2/
s]
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
[g/m
2/s]
16h (T1)
64h (T2)140h (T3)
16h (T4)
64h (T5)
AerobicAnaerobic
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Main ResultsErosion Rate valuesComparison between tests with increasing length of periods of consolidation.
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
[g/
m2/
s]
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
[g/
m2/
s]
16h (T1)
64h (T2)140h (T3)
16h (T4)
64h (T5)
AerobicAnaerobic
drop in overall values of Erosion Rates as length dry-period increase
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Main Results
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
Tests with the same consolidation period and different environmental ambience.
(T1) Anaerobic
(T4) Aerobic
64h consolidation period
16h consolidation period
(T2) Anaerobic
(T5) Aerobic
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Main Results
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
0 0.2 0.4 0.6 0.80.0
0.4
0.8
1.2
1.6
2.0
Applied shear stress (Tau_b) [N/m2]
eros
ion
rate
(E) [
g/m
2/s]
Tests with the same consolidation period and different environmental ambience.
(T1) Anaerobic
(T2) Anaerobic(T4) Aerobic
(T5) Aerobic
64h consolidation period
16h consolidation period
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Conclusions
Laboratory tests to estimate erosional resistance from highly organic sediment beds under storm runoff conditions
Improvements in prediction of in-sewer sediment transport loads
(Mediterranean conditions)
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Conclusions
Environmental conditions influence over sediment-bed
nature and structure
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Conclusions
Increase of erosional strength with depth
Increment of resistance against erosion (as consolidation dry-period lengthen and oxygen is available)
Environmental conditions influence over sediment-bed
nature and structure
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Conclusions
comparing with results obtained with low-organic sediment and synthetic sediment (differences in sediment properties)
Lesser magnitudes of Critical Shear Stresses
Increase of erosional strength with depth
Increment of resistance against erosion (as consolidation dry-period lengthen and oxygen is available)
Environmental conditions influence over sediment-bed
nature and structure
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Conclusions
Future investigations aimed to:
- asses critical shear stress in highly organic sediment beds
- analyse influence of temperature in dry-period
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Concerned about pollution control
Thank you for your attention
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Long dry-weather periodsIntense precipitaction events
Wet weather pollution from combined sewer systems
Particularities in the Mediterranean region climate in Spain:
0102030405060708090
100
0510152025303540Pm (mm)
mean T (°C)
aver
age
cum
mul
ative
Pr
ecip
itatio
n (m
m)
mea
n Te
mpe
ratu
re (°
C)
day-precipitation = 4 day/monthcumulative precipitation = 600 mm/year
(concentrater in spring and fall)average dry-period between rain: 11
daysMax. dry-period: 70 days (2010-2012)
Intense precipitation events following long dry-periods
≈ 40% rainfall registered P(mm)>10mm
Rain regime
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Main results
Erosion of sediments from bed during tests were monitored in terms of Suspended Sediment concentration and related
with Erosion Rate
q : average Erosion Rate in a applied Shear Stress
step (tb) linked to Suspended Sediment Concentration (CSS)
V : water volume of the column over sediment sample
AS : surface area bed subjected to erosion