Fermentation biomass production

Fermentation biomass productivities usually range from 2 to 5 g/(l h). This represents an oxygen demand in the range of 1.5 to 4 g 0/(l h). In a 500-m fermenter, this means achievement of a volumetric oxygen transfer coefficient in the range of 250 to 400 h"f Such oxygen-transfer capabihties can be achieved with aeration rates of the order of 0.5 (volume of air at STPA ohime of broth) and... 

Fermentation biomass productivities usuafiy range from 2 to 5 g/liter/hr. This represents... 

When excess substrate interferes with growth and/or product formation. One example is the production of baker s yeast. It is known that relatively low concentrations of certain sugars repress respiration and this will make the yeast cells switch to fermentative metabolism, even under aerobic conditions. This, of course, has a negative effect on biomass yield. When maximum biomass production is aimed at, fed batch cultures are the best choice, since the concentration of limiting sugar remains low enough to avoid repression of respiration. 

Biofuel generation from sweet sorghum Fermentative hydrogen production and anaerobic digestion of the remaining biomass. Biores. Technol. 99 (1), 110-119. 

Fig. 1. General overview of a PHA production process. All PHA production processes consist of a fermentation and a recovery step, followed by polymer processing for specific applications. In many cases the fermentation is divided into two stages, a biomass production and a PHA accumulation stage (for further detail see text). Several methods for recovery of the material have been described, of which solvent-based and non-solvent-based recovery protocols are illustrated...

The medium composition used in the fed-batch process was optimized, resulting in cell densities near 100 g l-1. By using an exponential feed rate resulting in a growth rate of 0.05 h-1, a maximum biomass concentration of 112 g 1 1 was attained, with a biomass productivity of 1.8 g 1 1 h. The poly(3HAMCL) productivity however was low, 0.34 g 1 1 h, caused by a steady decrease of the poly(3HAMCL) content during the last part of the fermentation [51]. When this optimized medium composition was used in the continuous culture system described above, a maximum biomass concentration of 18 g 1 1 was reached. The PHA content however remained low at approximately 10% [51]. It is still unclear what causes these low PHA contents. 

C02 exists under anaerobic conditions in wastewater. They also found that typically 50% of the C02 was produced by the sulfate-reducing bacteria, the other half by the fermenting biomass. However, the net production rate of Ss was typically about 70% of the total produced Ss by anaerobic hydrolysis [Equation (7.10)]. Hence, this equation may, even in a reduced form, be valuable for the estimation of the production of readily biodegradable substrate under anaerobic conditions. 

The bacterial population faced with the "autumn-input" was derived from an anoxic population (fermentative bacteria, sulfate reducers) which prevailed during summer stagnation. Within this population the input of freshly produced organic material caused a drastic shift. Bacteria primarily reacted with a strong increase in cell volume (biomass production). Deviating from its "normal" distribution (cf. above), the size spectrum was dominated by medium and large-size cells. Following the final breakdown and sedimentation of the autumn phytoplankton bloom, the bacteria subsequently responded with cell division (increase in cell number). 

Earlier studies have been done by pure cultures of anaerobic bacteria to study the conversion of carbohydrates (such as glucose and starch) to hydrogen gas, e.g., Aspergillus terreus (Emtiazi et al., 2001) and Clostridium (Taguchi et al., 1994). Recently, the considerable attention of research activity on fermentative hydrogen-production has been focused on the conversion of biomass reproducible resources to hydrogen by mixed cultures... 

The growth of immobilized cells ceased once the nitrogen source was exhausted, as reported by Nava et al. (17) (Fig. 3). After that, immobilized cells were released from the immobilization support and became free cells. Gibberellic acid production (0.160 g/L) was effective once the ammonia was exhausted, and it continued until total glucose consumption. In the case of immobilized cells cultured in a stirred reactor, Fig. 4 shows the fermentation kinetics. One can observe some differences related to the immobilized biomass production, and the uptake in nitrogen and carbon sources. However,... 

Louis Pasteur found that aeration increases biomass production and decreases the kinetics of sugar consumption and ethanol production (Pasteur 1861). He, therefore, concluded that aeration inhibits alcoholic fermentation (Packer 1974). 

If organisms could be found or metabolically engineered that efficiently ferment both the pentoses and hexoses under practical conditions at high yields and short residence times, fermentation ethanol technology would then have reached another plateau with low-cost lignocellulosic feedstocks. Simultaneous saccharification and fermentation or separate saccharification and fermentation of essentially all the sugars that make up the polysaccharides would each be able to approach the theoretical limit of fermentation ethanol production from the polysaccharides in low-cost lignocellulosic biomass. 

Lactic acid is a major end product from fermentation of a carbohydrate by lactic acid bacteria (Tormo and Izco, 2004). However, lactic acid can be produced commercially by either chemical synthesis or fermentation. The chemical synthesis results in a racemic mixture of the two isomers whereas during fermentation an optically pure form of lactic acid is produced. However, this may depend on the microorganisms, fermentation substrates, and fermentation conditions. Lactic acid can be produced from renewable materials by various species of the fungus Rhizopus. This has many advantages as opposed to bacterial production because of amylolytic characteristics, low nutrient requirements, and the fungal biomass, which is a valuable fermentation by-product (Zhan, Jin, and Kelly, 2007). 

Continuous lactic acid production from whey permeate is carried out in a process that consists of three separate operations in (1) a bioreactor, (2) an ultrafiltered (UF) model, and (3) an ED cell. With the UF process, recycling of all or part of the biomass is achieved. It is also possible to separate low molecular weight metabolites, such as sodium lactate, resulting from lactose fermentation. This product can then be extracted and concentrated continuously by ED. A disadvantage of continuous lactic acid production is, however, that it tends to clog the ultrafiltration membranes, which restricts permeate flow (Bazinet, 2004). 

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