WATER I NNOVATE Pascal Harper Product Manager. 2 Application Areas for Greenfield Sites...
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Transcript of WATER I NNOVATE Pascal Harper Product Manager. 2 Application Areas for Greenfield Sites...
WATERWATER IINNOVATENNOVATE
Pascal HarperProduct Manager
2
Application Areas for
• Greenfield Sites– Incorporate odour emissions into process selection.
• Process Upgrades– Model comparisons between current and upgrade scenarios.– Provide variable emission rate data for OCU design (peak to
mean ratios).
• Odour Management Planning– Diurnal profiling of odour emissions.– Changes to process operation influencing odours (liquor return
rates/timings).
3
4
Odour modelling currently:
• Neglects formation and emission
• Doesn’t consider perception
• Focuses on dispersion using:
– emission rate estimation• simple measurements, lit. data, educated guesses
– steady state values• ER almost always treated as a constant in modelling
Background
5
• Emission rates are driven by:
– High mass transfer coefficient KL (wind/flow turbulence)
– High surface area A
– High odorant concentration in liquid phase CL (quality)
• Emission rate variations can be significant
H
CCAKER GLL
Importance of Emission Rates
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• Analytical metric required for:– Modelling formation / transformation in the liquid phase– Modelling mass transfer from liquid to atmosphere– Modelling dispersion in the atmosphere
• Sensory metric required for:– Modelling human perception & likeliness of complaint
• ODOURsim® uses H2S as proxy for odour– Often the dominant odorant in wastewater– Easy to measure– Formation / transformation / mass transfers models available– Correlates with sensory measurements
Choice of Metric
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ODOUR Correlation - Primary Treatment Processes
C(ou) = 10759C(H2S)0.9078
R2 = 0.978
1
10
100
1000
10000
100000
1000000
0.01 0.1 1 10 100
H2S (ppm)
Od
ou
r (o
u m
-3)
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• Describes H2S behaviour in liquid phase
• Based on Hvitved-Jacobsen sewer model– Biofilms and suspended biomass– Considers anaerobic - aerobic
conditions– Useful for H2S formation
• Modified by:– Adding mechanism for H2S to
SO42- oxidation
• Describes movement of H2S & O2 into and out of liquid phase
• Based on mass transfer models for VOCs & O2 in the literature– quiescent surfaces, weirs/drop
structures, channels, dissolved air aeration, surface aeration, trickling filters
Liquid Phase Formation Model
Mass Transfer Emission Model
Model Basics
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- Model Application
• Applied to hypothetical situation:– 10 km sewer
• Flows part-full at flows < daily average (Aerobic)• Flows full at flows > daily average (Anaerobic)
– Feeds simple primary treatment only STW
• Studies:– Effects of wind-driven PST emissions– Effects of flow & quality driven emissions
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• Wind blowing over liquid surface drives emissions– Induces turbulence (and increases surface area) through formation of
waves
• Model simulation:– Used constant sulphide concentration in PST– Calculate emission rate vs. wind speed for 1 years Met. Data
– Apply results to dispersion model:• Using constant emission rate (the average for year)• Using variable emission rate linked to wind speed
0
5
10
15
20
25
30
35
40
Emission rate (g s-1 m-2)
% o
f hou
rs
avg
- Wind-Driven PST Emissions
11
Demonstrates importance of linking emission rate to wind speed for liquid surface emissions.
The constant (average) ER over-predicts odour footprint:• ER value too high at low wind speeds when dispersal poor• ER value too low at high wind speeds when dispersal good
- Wind-Driven PST Emissions
12
• Diurnal variations in influent wastewater drives emissions
– High flows induce turbulence over weirs – High sulphide concentrations in liquid phase
due to anaerobic conditions in the sewer
• Model simulation:
– Use constant wind speed over PSTs– Calculate emission rate vs diurnal flow and
load over 24 hrs– Observe:
• peaks in surface emissions due to elevated sulphide levels
• peaks in weir section emissions due to high flows
– Apply results to dispersion model using range emission rates calculated
0.00
0.05
0.10
0.15
0.20
0.25
0 4 8 12 16 20 24
Time (hour)
Co
ncen
trati
on
(g
m-3
)
0
0.2
0.4
0.6
0.8
1
1.2
Flo
w (
m3 s
-1)
SO
SH2S
Flow
0.0E+00
5.0E-05
1.0E-04
1.5E-04
2.0E-04
2.5E-04
0 4 8 12 16 20 24
Time
Em
issio
n R
ate
(g
s-1)
0
0.05
0.1
0.15
0.2
0.25
0.3
Flo
w (
m3 s
-1)
Surface ER
Weir ER
Total ER
Flow
- Flow and Quality Driven Emissions
13
Demonstrates the importance of linking emission rate to flow and quality parameters for weir and surface emissions.
There is a potential for large error in dispersion model predictions if single spot ER measurements used
- Flow & Quality Driven Emissions
14
Outcomes
• Emission rate variability is real
• Emission rate variability is driven by flow, quality, wind speed and temperature effects
• Emission rate variations have a significant impact on dispersion model predictions
• Emission rate variations should be included in dispersion model predictions– Percentile predictions have limited meaning if significant source of
variability is ignored
15
ODOURsim®
- Data Requirements
16
Case study
• Sampled Wastewater characteristics
– TCOD, SCOD, SH2S, pH, Temperature
• Micrometeorological Study carried out
– Measured H2S concentrations on site
– Measured wind velocity and direction– AERMOD model used to fit emissions
• Emission rates calculated by ODOURsim® used as hourly emission file in AERMOD
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- Emission variation over 48 hrs
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ODOURsim
UKWIR
Micromet
- Calibration Comparison
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ODOURsim
UKWIR
Micromet
- Validation Comparison
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Static emission ratesODOURsim® variable
emission rates
98 percentile contour plots