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Dark fermentative bioethanol production process yields carbon dioxide (CO 2 ) and organic acids as by-products. The so-yielded CO 2 is a nearly saturated gas of high CO 2 purity, which is commonly utilized in food industries as supplements. The potential utilization pathways for the CO 2 generated and released from the ethanol fermentation process (denoted as “fermentation CO 2 ”) include production of biofuels by CO 2 fixation of microalgae and succinic acid fermentation by non-photosynthetic microorganisms. This study compared the performances of these two CO 2 fixing pathways using Chlorella vulgaris or Actinobacillus succinogenes cultures. The highest carbon fixation rate achieved by Actinobacillus succinogenes was 388.8 g/L-d in 2-L reactor, which is about 188 times to that by Chlorella vulgaris (2.06 g/L-d) in the reactor at the same volume. This study ultimately demonstrated the advantages of adopting succinic acid production process compared to those frequently addressed in literature using microalgae-based biofuels. [ABSTRACT FROM AUTHOR]

Zymomonas mobilis cells were immobilized with a novel Fe 2 O 3 -modified polyvinyl alcohol (PVA) matrix to perform continuous ethanol fermentation with very high efficiency. The key operating parameters, such as glucose feeding concentration, dilution rate, and cells loading were optimized to achieve high bioethanol production performance at a high dilution rate and high glucose utilization efficiency. The optimal conditions for ethanol fermentation with the modified PVA immobilized cells were determined as: cell loading, 40% ( w/v ); glucose feeding concentration, 125 g/L; hydraulic retention time (HRT), 2 h (or 0.5 h −1 dilution rate). The bioethanol productivity was nearly doubled (31.09 g/L/h) when the PVA-immobilized cells were modified with 1% ( w/v ) Fe 2 O 3 . The modified PVA-immobilized cells could be utilized for more than 20 days without losing their activity. [ABSTRACT FROM AUTHOR]

Efforts to optimize bioethanol production were made by modifying culture condition of the yeasts used. Two commercial yeast (New Aule alcohol yeast and New Aule baker's instant dry yeast) were grown in sugarcane molasses under different condition with and without aeration in order to compare the productivity of both yeast. The fermentation processes were carried out in batch condition for 72 hours incubation time. Aeration rate of 0.3 vvm were provided for four hours at the early stage of the aerated cultures. The level of ethanol produced by New Aule Alcohol Yeast was 74.8 g/L with ethanol productivity of 2.078 g/L/h and yield (Yp/s) was at 0.378 g/g. Aeration of 0.3 vvm did not affect the level of ethanol produced, yielded 0.338 gram of ethanol per gram of substrate used. Interestingly, the result showed that the New Aule baker's instant dry yeast produced higher ethanol compare to that of its alcohol yeast. Without aeration, New Aule baker's instant dry yeast produced 102.854 g/L. Meanwhile, the aerated culture of this yeast increase the ethanol production to the level of 120.917 g/L with productivity 3.359 g/L/h and ethanol yield 0.669 g/g, indicating the differences in oxygen sensitivity of both commercial yeast. [ABSTRACT FROM AUTHOR]

Concentration of ethanol from the fermentation broth is an energy-intensive process. Very high gravity (VHG) process with modified polyvinyl alcohol-immobilized Zymomonas mobilis cells integrated with in situ bioethanol removal via vacuum membrane distillation (VMD) was proposed to mitigate product inhibition effects in VHG fermentation. The proposed VHG + VMD system, at 300 g/L glucose loading, produced 127.4 g/L (16.1% v/v) ethanol, at 63.7 g/L−h productivity and 84.9% glucose conversion rate, which is the highest in reported literature. [ABSTRACT FROM AUTHOR]