Hema Rughoonundun
Research Week
2008
Outline of Presentation
Introduction
• The MixAlco Process
Fermentation of sludge
• Sludge
• Materials and Methods
• Results
Conclusion
• Energy Potential of sludge
Common Energy Routes
Thermochemical
Common Energy Routes
Sugar
Less Common Energy Routes
Carboxylate
The MixAlco Process
 The MixAlco process has been developed by Dr M
Holtzapple and his team from the Department of
Chemical Engineering, Texas A&M University.
 The process is a patented technology that converts any
biodegradable material (e.g, sorted municipal solid waste,
sewage sludge, industrial biosludge, manure, agricultural
residues, energy crops
into a mixed alcohol fuels containing predominantly 2propanol, but also higher alcohols up to 7-tridecanol
(Holtzapple et al., 1999).
Stages of Development
1998
Pilot Scale
(200lb/day)
1991
Laboratory
Investigation
2007
Demonstra
tion Plant
(5 ton/day)
2009
Demonstration
Plant
(100 ton/day)
MixAlco
…
the
Process
Process
Mixed
Alcohol
Fuels
Carboxylate
Salts
Biomass
Pretreat
Ferment
Dewater
Mixed
Ketones
Thermal
Conversion
Hydrogenate
Lime
Lime Kiln
Calcium Carbonate
Hydrogen
Complex organic matter
Carbohydrates, proteins, fats
Fermentation
Hydrolysis
1
Soluble organic molecules
Sugars, amino acids, fatty acids
2
Acidogenesis
Volatile fatty acids
Acetic acid
3
Hydrogen, H2
Carbon dioxide, CO2
Acetogenesis
4
Methanogenesis
Methane, CH4
Carbon dioxide, CO2
4
Methanogenesis
Composition
of
the
Mixed
alcohols
What is Mixed Alcohols
Advantages of the MixAlco Process
1.
Acetic acid, unlike ethanol, is biologically produced
from simple sugars without the production of carbon
dioxide:
C6H12O6 → 2 CH3CH2OH + 2 CO2
(Biological production of ethanol)
C6H12O6 → 3 CH3COOH
(Biological production of acetic acid)
Hence, on a Mass basis, the yield is higher for acetic acid compared to
ethanol fermentation.
Advantages of the MixAlco Process
2. C6H12O6
G = -48.56 kcal/mol
glucose
2C2H5OH + CO2
ethanol
C6H12O6
glucose
3 C2H3OOH
acetic acid
G = -61.8 kcal/mol
The actual stoichiometry is more complex
C6H12O6
6 acetate + 2 propionate + butyrate + 5CO2 +
(67 mol%) (22 mol%)
(11mol%) 3 CH4 +
6H2O
Advantages of the MixAlco Process
 Substrates
Lignocellulosic
Municipal solid waste
Any biodegradable material!!
Advantages of the MixAlco Process
 Does not require sterile condition
 Does not require expensive enzymes
 Good Energy Yield
Energy (MJ/L)
Gasoline
Mixed Alcohols
Ethanol
34.9
29
23.4
Fermentation of Sludge using MixAlco Process
 Methodology
I. Substrates
 Mixed Sludge
Physical Properties
Moisture
%
97.92 ± 0.02
Volatile Solids
64.62 ± 0.068
Ash
35.38 ± 0.068
Fermentation of Sludge using MixAlco Process
 Mixed Sludge
Elements
%
Glucose
5.267
Xylose
4.180
Mannose
4.214
Total Nitrogen
4.405
Total Phosphorous
1.298
Total Potassium
0.221
Fermentation of Sludge using MixAlco Process
II. Apparatus
Centrifuge bottle bioreactor (Ross, 1998)
Fermentors in Roller Apparatus
Fermentation of Sludge using MixAlco Process
 III. Conditions of Experiments
 Solids concentration of 50 g/L
 Marine Innoculum (12.5%)
 Temperature 550C
 Gas vented and sample of liquid taken every 2 days
 pH adjusted using ammonium bicarbonate
 Iodoform used as inhibitor used (0.8µL every 2 days)
Fermentation of Sludge using MixAlco Process
 Parameters analysed
 pH
 Volume of gas
 Gas Composition
Nitrogen, Methane and Carbon dioxide
Apparatus: Gas Chromatograph
(Agilent 6890 series, Agilent Technologies, Palo Alto, California) equipped
with a thermal conductivity detector (TCD)
Fermentation of Sludge using MixAlco Process
 Parameters analysed
 Total Carboxylic Acids
Apparatus:
Agilent
6890
gas
chromatograph
(Agilent Technologies, Palo Alto,
California) equipped with a flame
ionization detector (FID) and a 7683
series injector.
Results
Graph of Total Carboxylic acids v/s Time
Total Carboxylic Acids (g/L)
12
10
8
6
4
2
0
0
2
4
6
8
10
12
14
16
18
Time (days)
20
22
24
26
28
30
Results
 Yield Parameters
Parameter
Value
Average Acid Concentration (g/L)
10.72
Yield
(g total acids produced/g VS fed)
0.34
Conversion
(g VS digested/ g VS fed)
0.43
Total Acids Selectivity
(g total acids produced/g VS digested)
0.79
Total Acid Productivity
(total acids produced/ total liquid volume . Time)
0.34
Results
Composition of mixed acids
12%
13%
Ethanoic acid
Propanoic acid
9%
66%
Butanoic acid
Valeric acid
Conclusion
Significance of results for Mauritius
 Sludge production by 2015
= 122,260 tonnes/ year
 Dry sludge (25 % solids)
= 30,565 tonnes/year
 Assuming Volatile solids %
= 65%
 Expected yield of Acids
= 0.34 g Acids/g VS fed
 Energy Value of Mixed Acids = 29MJ/L
Conclusion
 Total carboxylic acids production = 6755 tonnes/year
 Potential in terms of
Energy
= 192, 424 GJ
2. Tonne of Oil equivalent
= 4596 toe
3. Money (at 82 USD per barrel) = Rs 80.4 million
4. Gasoline (60% Efficiency)
= 4053 tonnes
1.
Thank you