3. Introduction
• Silage: compressed and
fermented grass or green
fodder, stored
anaerobically, as in a silo.
• Preserves food for cattle
through winter as
pasturing availability
decreases
• Retains nutritional value
better than regular hay
5. Objective
● Determine how much acid was produced by the bacteria in the silage
reactors along with how much hemicellulose (substrate) was consumed by
the bacteria under anaerobic conditions
○ How much of the grass would become fermented?
● One reactor had a sucrose solution and the other did not
○ Determine which reactor had the most acid production
7. Proposed Testing Techniques
● Technique used to measure carbon source/e- donor: COD
● Technique used to measure cell mass: Yield from measuring product form over time
● Technique used to measure products: Acidity (Acid titration)
8. Considerations
● How could the reactor
environment stay truly
anaerobic?
● Inoculation with bacteria
or use microbes already
on the grass?
● Use sucrose in one of the
reactors or an enzyme?
11. Methods
• Started with finding the dry weight and
bulk density of the grass in the can
• Took measurements from Can 1 (no
sucrose added) and Can 2 (sucrose
added) every other day
• Total of 5 measurements
• COD and acidity titrations.
14. pH and Acidity Titration Results
Table 1. Initial pH measurements of silos Table 2. Volume of 0.02 N NaOH added
in acid titration
Day Can 1 Can 2
0 7.67 7.47
1 7.60 7.97
2 8.30 8.44
3 8.01 8.77
4 8.74 8.79
5 8.89 8.93
Day Can 1, mL Can 2, mL
0 2.85 2.80
1 1.52 1.90
2 - -
3 0.39 -
4 - -
5 - -
15. COD Results
COD results from reactor 1
(no added sucrose)
COD results from reactor 2
(added sucrose)
COD Absorbance Values
Day Can 1 Can 2
0 0.422 0.478
1 0.548 0.470
2 0.330 0.284
3 0.466 0.400
4 0.396 0.500
5 0.288 0.458
Table 3: Absorbance values from COD tests in lab
Oxidation of organic compounds:
Colorimetric reaction (Reduction of Chromate):
16. COD Results
Figure 1. Standard Curve of COD versus Absorbance at 600 nm
Can 1 Can 2
Day Abs @
600nm
COD
conc.
Day Abs @
600nm
COD
conc.
0 0.422 7.604 0 0.478 8.613
1 0.548 9.874 1 0.47 8.468
2 0.33 5.946 2 0.284 5.117
3 0.466 8.396 3 0.4 7.207
4 0.396 7.135 4 0.5 9.009
5 0.288 5.189 5 0.458 8.252
Table 4. COD concentration of silos over time
17. No Added Sugar- Biomass formation
Figure 2: Stella model of substrate and
biomass concentration with time in reactor 1
(initial conditions shown far right)
Figure 3: Theoretical graph of
substrate and biomass formation in
reactor 1 based on Stella Model
Oxidation of glucose by heterotrophic bacteria under aerobic conditions:
18. Added Sugar- Biomass Formation
Figure 5: Theoretical Graph of substrate use and
biomass formation based on the Stella model
for reactor 2.
Figure 4: Stella model of substrate and
biomass concentration with time in reactor
2 (initial conditions shown far right).
19. No Added Sugar- Acid Production
Figure 6: Stella model showing
product formation and substrate
utilization with time in reactor 1
(initial conditions specified on
slide 18)
Figure 7: Graph of product formation and
substrate utilization based on the Stella model
for reactor 1
20. Added Sugar- Acid Production
Figure 8: Stella model showing
product formation and substrate
utilization with time in reactor 2
(initial conditions specified on
slide 19)
Figure 9: Graph of product formation and substrate
utilization based on the Stella model for reactor 2
21. Data Analysis
• pH increased with time
• Titrations showed organic acid in reactors for days 0-1, while increased pH
on days 2-5 indicated no acid production
• COD results showed organic compounds were oxidized, however, COD
concentrations differed day-to-day
• Assumptions were made to model the biomass formation of heterotrophic
bacteria and acetic acid product formation under the conditions of the
reactors
• 1000 C6H12O6+ 1740 O2 + 852 NH3 = 852 C5H7O2N + 1740 CO2 + 4296 H2O
• Used this formula to represent cell mass formed in order to get Yb, which would
be used in the Monod Model
• Adding sugar resulted in higher acid production and product formation
23. Conclusion
● Fermentation did not go as planned
○ pH increased with time and COD absorbance readings did not follow a trend
● Data used to model assumed aerobic growth of bacteria and anaerobic
production of acids
24. Conclusion
Max Biomass Yield-
No added sugar
Max Biomass Yield-
Added sugar
Max Product Yield-
No added sugar
Max Product Yield-
Added sugar
4500 mg/L 5000 mg/L 10,525 mg/L 11040 mg/L
Table 5: Approximate maximum biomass and product yields for theoretical simulations of
both silos
