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Importance of Anaerobic Respirometer For Model Calibration and Process Monitoring Fasil Haile Co-authors: David Ikumi, Tanush Wadhawan, Ryu Suzuki, Chris deBarbadillo, Mattew Higgins, Sudhir Murthy, Haydee De Clippeleir, Ahmed Al-Omari, and George Ekama
Overview of presentation
• Background to the Anaerobic Digestion (AD) process • AD model structure of the study • Hypothesis of the study • Model calibration and model based control progress
AD
Advantages: • Reduces sludge hauling cost
– Low volume of sludge – Lower cost of sludge stabilizations – Class A Biosolids
• Potential to digest high organic waste. • Assist in creating green infrastructure
– Energy self-efficient WWTPs
(for electricity, heating, vehicles, pipelines)
AD
Co-products (e.g. solid fertilizers, liquid fertilizers, compost, livestock bedding)
Biogas
AD
Disadvantages: • Instability and susceptible to failure
– Costly to restart the process – Absence of robust control mechanism – Operate below optimal capacity
Organic waste
AD Biogas
Thermal energy
Electrical energy
Fuel
Engine Generator
AD model
ENERGY NEUTRALITY for
WWTPs WITHOUT
COMPROMISING EFFLUENT WATER
QUALITY!
Need for AD process Intensification Process instability to changes in operating conditions
Operators are required
to understand
the mechanism
of failure
Use of AD Mathematical models Introduced an improved approach
Comparison of PWM_SA_ADM
Model Consideration IWA/ADM1 ASDM/BioWin PWM_SA_ADM
Material Physical states
Two phase (Liquid-Gas) Three phase (Solid-Liquid-Gas)
Three phase (Solid-Liquid-Gas)
Substrate Characterization
Carbohydrates, lipids and proteins.
Carbohydrates, lipids and proteins.
Characterized in the generic form CxHyOzNaPbSc
Mass balance base
Charge Balance COD balance Elemental (C, H, O, N, P, and S), COD and charge mass balance based
pH Prediction Do NOT include precipitation
Include Weak Acid/Base Aqueous Chemistry and precipitation
Include Weak Acid/Base Aqueous Chemistry, pK value correction and ion pairing and precipitation
Effect of high Hydrogen Partial pressure on Acidogens
NOT included NOT included Included
PWM_SA_ADM Biological reactions schematics
Biodegradable Particulate organics (BPO) of Primary Sewage Sludge (PS) and WAS
Glucose
Propionate
Hydrogen Acetate
Carbon Dioxide
Methane
Hydrolysis of PS BPO
Acidogenesis High pH2 Acidogenesis Low and High pH2
Acetogenesis
Acetoclastic Methanogenesis under low ammonia conc.
Hydrogenotrophic Methanogenesis
Hydrolysis of WAS BPO
Acetate Oxidizing Bacteria under high ammonia conc.
Model Calibration Ikumi et al (2011)
0
20
40
60
80
100
0 20 40 60 80
COD
Rem
oval
(%)
AD Sludge age (days)
COD Removal Rates
Simulated
Measured
0
10
20
30
40
50
60
70
0 20 40 60 80
TKN
Rel
ease
d as
FSA
(%)
AD Sludge Age (days)
FSA Released
Measured
Simulated
0
500
1000
1500
2000
2500
0 20 40 60 80
Alka
linity
(mg/
l as C
aCo 3
)
AD Sludge Age (days)
H2CO3 Alkalinity
Measured
Simulated
012345678
0 20 40 60 80
pH
AD Sludge Age (days)
Digester pH
Measured
Simulated
Respirometer generated gas profiles
0
500
1000
1500
2000
2500
3000
3500
-5 5 15 25
Gas
Pro
duct
ion
Rat
e (m
l/hr)
Time After Feed (hours)
10 days15 days18 days
Source: Suzuki et al. (2014)
Respirometer generated gas profiles
Comparison of OUR and respirometer profiles. The OUR profile shows Monod kinetic relationships and are used to estimate the maximum specific growth rate (µmax) and infinity constants (Ks) of the mixed liquor. Similar to the OUR the area under the peak of the respirometer profile represents the rbCOD fraction and the area below represents the sbCOD concentrations. The slope change between the peak and the plateau represents the hydrolysis kineties of the particulate COD of the organics. The plateau represents the endogenous decoy.
OU
R
Gas
pro
duct
ion
Time Time
rbCOD
sbCOD
rbCOD
sbCOD
Endogenous oxygen uptake Very slowly biodegradable
Model Calibration
Units Feed Concentrations
Measured Reactor Concentrations
Simulated Reactor Concentrations
SRT Days 10 10
tCOD Mg/LCOD 103,000 52,000 53,950
sCOD Mg/LCOD 19,000 9,400 8,150
VFA Mg/L 2,000 155 120
TKN Mg/LTKN-N 5,200 4,500 4,757
Ammonia-FSA Mg NH3-N/L 300 1,600 1,520
TSS Mg/LTSS 56,000 45,000 50,500
VSS Mg/LVSS 42,000 22,000 23,700
Unbiodegradable particulate organics
Mg/L 30,000 31,000 30,285
Biodegradable particulate organics
Mg/L 54,000 11,400 10,050
Calculated Elemental Composition
C1H1.8852O0.51/37N0.1016 C1H1.42172O0.38285N0.108184
Measured feed and reactor concentrations compared to simulated reactor concentrations. A good VSS and COD match was achieved which defined the choice of the model kinetics calibration.
Model Calibration
Conclusion
Using real time dynamic model simulation data • Characterize the feed sludge and operating
conditions in model platform. ‒ COD, TKN, TP, TSS, VSS, pH, Alkalinity, SRT, Temp.,
Flow, Load,..etc.
• Using simulation results to predict the performance of the AD for the given influent sludge characterization.
References
• Brouckaert C.J., Ikumi D.S. and Ekama G.A. (2010). A 3-phase anaerobic digestion model. In proceedings. 12th IWA Anaerobic Digestion Conference (AD12), Guadalajara, Mexico, 1-4 Nov, 2010.
• Ikumi D.S, Harding T.H., Brouckaert C.J. and Ekama G.A. (2013). Plant-wide integrated biological, chemical and physical bioprocesses modelling of wastewater treatment plants in 3 phases (aqueous-gas-solid). Research Report W136, Dept. of Civil Eng., University of Cape Town, Rondebosch, 7701, Cape, South Africa.
• Suzuki Ryu, Tanush Wadhawan, Sudhir Murthy, Bernhard Wett, Imre Takács and Matthew Higgins. 2014. Modelling Thermally Pretreated Mesophilic Anaerobic Digestion. 4th IWA/WEF Wastewater Treatment Modelling Conference, Spa, Belgium, March 30th – April 2nd
• Wett, B; Takács, I.; Batstone, D.; Wilson, C.; Murthy, S. (2012). Anaerobic model for high-loaded or high-temperature digestion – additional pathway of acetate oxidation. Proc. WEFTEC, New Orleans.
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