Using the MixAlco process, biomass can be converted into carboxylic acids, which can be chemically converted into mixed alcohol
fuels. This study focused on the use of countercurrent fermentation to anaerobically convert sugarcane bagasse and chicken
manure to mixed carboxylic acids using a mixed culture of mesophilic microorganisms from terrestrial and marine sources. Bagasse
was pretreated with lime to increase digestibility. The continuum particle distribution model (CPDM) simulated continuous
fermentors based on data collected from batch experiments. This model saves considerable time in determining optimum operating
conditions. For an 80% bagasse/20% chicken manure fermentation with terrestrial inoculum at a volatile solids loading rate
(VSLR) of 7.36 g/(L of liquid·d) and a liquid residence time (LRT) of 8.88 d, total carboxylic acid productivity, total acid
selectivity, and yield were 2.49 g/(L of liquid·d), 0.581 g of total acid/g of VS digested, and 0.338 g of total acid/g of
VS fed, respectively, at a concentration of 18.7 g of total acid/L. At the same VSLR and LRT, fermentation with marine inoculum
gave higher total acid productivity, total acid selectivity, and yield than fermentation with terrestrial inoculum. For an
80% bagasse/20% chicken manure fermentation with marine inoculum at a VSLR of 3.83 g/(L of liquid·d) and an LRT of 12.1 d,
total carboxylic acid productivity, total acid selectivity, and yield were 1.38 g/(L of liquid·d), 0.667 g of total acid/g
of VS digested, and 0.359 g of total acid/g of VS fed, respectively, at a concentration of 16.2 g of total acid/L. 相似文献
Bacillus anthracis is an endospore-forming bacterium that causes inhalational anthrax. Key virulence genes are found on plasmids (extra-chromosomal, circular, double-stranded DNA molecules) pXO1 (ref. 2) and pXO2 (ref. 3). To identify additional genes that might contribute to virulence, we analysed the complete sequence of the chromosome of B. anthracis Ames (about 5.23 megabases). We found several chromosomally encoded proteins that may contribute to pathogenicity--including haemolysins, phospholipases and iron acquisition functions--and identified numerous surface proteins that might be important targets for vaccines and drugs. Almost all these putative chromosomal virulence and surface proteins have homologues in Bacillus cereus, highlighting the similarity of B. anthracis to near-neighbours that are not associated with anthrax. By performing a comparative genome hybridization of 19 B. cereus and Bacillus thuringiensis strains against a B. anthracis DNA microarray, we confirmed the general similarity of chromosomal genes among this group of close relatives. However, we found that the gene sequences of pXO1 and pXO2 were more variable between strains, suggesting plasmid mobility in the group. The complete sequence of B. anthracis is a step towards a better understanding of anthrax pathogenesis. 相似文献
Nutrients are essential for microbial growth and metabolism in mixed-culture acid fermentations. Understanding the influence
of nutrient feeding strategies on fermentation performance is necessary for optimization. For a four-bottle fermentation train,
five nutrient contacting patterns (single-point nutrient addition to fermentors F1, F2, F3, and F4 and multi-point parallel
addition) were investigated. Compared to the traditional nutrient contacting method (all nutrients fed to F1), the near-optimal
feeding strategies improved exit yield, culture yield, process yield, exit acetate-equivalent yield, conversion, and total
acid productivity by approximately 31%, 39%, 46%, 31%, 100%, and 19%, respectively. There was no statistical improvement in
total acid concentration. The traditional nutrient feeding strategy had the highest selectivity and acetate-equivalent selectivity.
Total acid productivity depends on carbon–nitrogen ratio. 相似文献
Applied Biochemistry and Biotechnology - Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of switchgrass. After studying many conditions, the... 相似文献
Municipal solid waste (MSW) and sewage sludge (SS) were combined and anaerobically converted into carboxylate salts by using
a mixed culture of acid-forming microorganisms. MSW is an energy source and SS is a source of nutrients. In this study, MSW
and SS were combined, so they complemented each other. Four fermentors were arranged in series for a countercurrent fermentation
process. In this process, the solids and liquid were transferred in opposite directions, with the addition of fresh biomass
to fermentor 1 and fresh liquid media to fermentor 4. An intermediate lime treatment of solids exiting fermentor 3 before
entering fermentor 4 was applied to improve the product acid concentration from the untreated MSW/SS fermentations. All fermentations
were performed under anaerobic conditions at 40°C. Calcium carbonate was added to neutralize the carboxylic acids and to control
the pH. Iodoform was used as a methanogen inhibitor. Carboxylic acid concentration and gas composition were determined by
gas chromatography. Substrate conversion was measured by volatile solids loss, and carboxylic acid productivity was calculated
as the function of the total carboxylic acids produced, the amount of liquid in all fermentors, and time. The addition of
intermediate lime treatment increased product concentration and conversion by approx 30 and 15%, respectively. The highest
carboxylic acid concentrations for untreated MSW/SS fermentations with and without intermediate lime treatment were 22.2 and
17.7 g of carboxylic acid/L of liquid, respectively. These results confirm that adding a treatment step between fermentor
3 and fermentor 4 will increase the digestibility and acid productivity of the fermentation. 相似文献
The MixAlco 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 mixed alcohol fuels containing predominantly
2-propanol, but also higher alcohols up to 7-tridecanol. The feed stock is treated with lime to increase its digestibility.
then, it is fed to a fermentor in which a mixed culture of acid-forming microorganisms produces carboxylic acids. Calcium
carbonate is added to the fermentor to neutralize the acids to their corresponding carboxylate salt. The dilute (−3%) carboxylate
salts are concentrated to 19% using an amine solvent that selectively extracts water. Drying is completed using multi-effect
evaporators. Finally, the dry salts are thermally converted to ketones which subsequently are hydrogenated to alcohols. All
the steps in the MixAlco process have been proven at the laboratory scale. A techno-economic model of the process indicates
that with the tipping fees available in New York ($126/dry tonne), mixed alcohol fuels may be sold for $0.04/L ($0.16/gal)
with a 60% return on investment (ROI). With the average tipping fee in the United States rates ($63/dry tonne), mixed alcohol
fuels may be sold for $0.18/L ($0.69/gal) with a 15% ROI. In the case of sugarcane bagasse, which may be obtained for about
$26/dry ton, mixed alcohol fuels may be sold for $0.29/L ($1.09/gal) with a 15% ROI. 相似文献
The Ammonia Fiber Explosion (AFEX) process treats lignocellulose with high-pressure liquid ammonia and then explosively releases the pressure. The combined chemical effect (cellulose decrystallization) and physical effect (increased accessible surface area) dramatically increase lignocellulose susceptibility to enzymatic attack. For example, bagasse digestibility is increased 5.5 times and that of kenaf core is increased 11 times using extracellular cellulases fromTrichoderma reesei. In this study, we applied the AFEX process to mixed municipal solid waste (MSW) and individual components (e.g., softwood newspaper, kenaf newspaper, copy paper, paper towels, cereal boxes, paper bags, corrugated boxes, magazines, and waxed paper). Softwood newspaper proved to be the most difficult component to digest because of its high lignin content. A combination of oxidative lignin cleavage and AFEX was required to increase softwood newspaper digestibility substantially, whereas AFEX alone was able to make kenaf newspaper digestible. Because most MSW components have been substantially delignified in the paper-making process, AFEX only marginally increased their digestibility.
Previous studies have shown that oxidative lime pretreatment is an effective delignification method that improves the enzymatic
digestibility of many biomass feedstocks. The purpose of this work is to determine the recommended oxidative lime pretreatment
conditions (reaction temperature, time, pressure, and lime loading) for Alamo switchgrass (Panicum virgatum). Enzymatic hydrolysis of glucan and xylan was used to determine the performance of the 52 studied pretreatment conditions.
The recommended condition (110°C, 6.89 bar O2, 240 min, 0.248 g Ca(OH)2/g biomass) achieved glucan and xylan overall yields (grams of sugar hydrolyzed/100 g sugar in raw biomass, 15 filter paper
units (FPU)/g raw glucan) of 85.9 and 52.2, respectively. In addition, some glucan oligomers (2.6 g glucan recovered/100 g
glucan in raw biomass) and significant levels of xylan oligomers (26.0 g xylan recovered/100 g xylan in raw biomass) were
recovered from the pretreatment liquor. Combining a decrystallization technique (ball milling) with oxidative lime pretreatment
further improved the overall glucan yield to 90.0 (7 FPU/g raw glucan). 相似文献