With the inevitable depletion of the petroleum supply and increasing energy
demands in the world, interest has been growing in bioconversion of lignocellulosic
biomass (e.g., sugarcane bagasse). Lignocellulosic biomass is an abundant, inexpensive,
and renewable resource. Most of current conversion technologies require expensive
enzymes and sterility. In contrast, the patented MixAlco process requires no enzymes or
sterility, making it attractive to convert lignocellulosic biomass to transportation fuels
and valuable chemicals. This study focuses on pretreatment and thermophilic
fermentation in the MixAlco process.
Ammonium bicarbonate (NH4HCO3) was discovered to be a better pH buffer than
previously widely used calcium carbonate (CaCO3) in anaerobic fermentations under
thermophilic conditions (55°C). The desired pH should be controlled within 6.5 to 7.5.
Over 85% acetate content in the product was found in paper fermentations and bagasse
fermentations. Hot-lime-water-treated bagasse countercurrent fermentations buffered by
ammonium bicarbonate achieved 50–60% higher total product concentrations than those
using calcium carbonate. It was nearly double in paper batch fermentations if the pH
was controlled around 7.0.
Ammonium bicarbonate is a “weak” methane inhibitor, so a strong methane
inhibitor (e.g., iodoform) is still required in ammonium bicarbonate buffered
fermentations. Residual calcium salts did not show significant effects on ammonium
bicarbonate buffered fermentations. Lake inocula from the Great Salt Lake, Utah, proved to be feasible in ammonium
bicarbonate buffered fermentations. Under mesophilic conditions (40°C), the inoculum
from the Great Salt Lake increased the total product concentration about 30%, compared
to the marine inoculum. No significant fermentation performance difference, however,
was found under thermophilic conditions.
The Continuum Particle Distribution Model (CPDM) is a powerful tool to predict
product concentrations and conversions for long-term countercurrent fermentations,
based on batch fermentation data. The experimental acid concentrations and
conversions agree well with the CPDM predictions (average absolute error < 15%).
Aqueous ammonia treatment proved feasible for bagasse. Air-lime-treated bagasse
had the highest acid concentration among the three treated bagasse. Air-lime treatment
coupled with ammonium bicarbonate buffered fermentations is preferred for a “crop-tofuel”
process. Aqueous ammonia treatment combined with ammonium bicarbonate
buffered fermentations is a viable modification of the MixAlco process, if “ammonia
recycle” is deployed.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1655 |
| Date | 2007 May 1900 |
| Creators | Fu, Zhihong |
| Contributors | Holtzapple, Mark T. |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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