Ethanol microbial production

Owing to diminishing fossil fuel reserves, alternative energy sources need to be renewable, sustainable, efficient, cost-effective, convenient and safe.1 In recent decades, microbial production of ethanol has been considered as an alternative fuel for the future because fossil fuels are depleting. Several microorganisms, including Clostridium sp. and yeast, the well-known ethanol producers Saccharomyces cerevisiae and Zymomonas mobilis, are suitable candidates to produce ethanol.2,3... 

Some yeasts and bacteria are able to produce different alcohols like ethanol and butanol as well as polyols like glycerin and 2,3-butandiol. These compounds- are used in drinks such as beer and wines, and also may be used in or as solvents, drugs, chemicals, oils, waxes, lacquers, antifreezing and antifoaming agents, precipitants, dyestuff, pomades, raw materials for chemical syntheses, motor fuels, and carbon sources for SCP production. These products are mainly synthesized from petroleum — derived materials like ethylene and acetaldehyde. However, because of the insufficient availability and high prices of the raw materials, the microbial production of alcohols has become an interesting area for many researchers. 

A total of almost 250 ISPR projects in microbial whole cell biotechnology are listed in Table 2. Over one third of these projects have dealt with the production of organic solvents such as ethanol, butanol, acetone or propanol (90 projects). Ethanol (70% of all the solvents) has been by far the most important microbial product for which different ISPR techniques have been applied. The second most important class of products involved in ISPR projects have been organic acids such as lactic, acetic, butyric, or propionic acid (54 projects). Most of effort in this product class has focused on lactic acid (55% of all organic acids). Important ISPR activities have also been reported for the microbial production of various aromas and fine chemicals (30 projects in each product category). A considerable amount of ISPR approaches have been shown in steroid conversions (17 projects) and the production of secondary metaboHtes and various enzymes (13 projects in each product category). 

One major product of this application of industrial fermentation is baker s yeast biomass. Baker s yeast is required for making bread, bakery products, beer, wine, ethanol, microbial media, vitamins, animal feed, and biochemicals for research. 5feast is produced in lai e aerated fermenters of up to 200,000 liters. Molasses is used as a nutrient source for the... 

Occasionally the synthesis of a microbial product, for example that of ethanol from glucose, is catalysed by non-viable cells (section 6.2.1.1). Then the process is properly catalytic because the Saccharomyces cerevisiae cells do not change, for a time at least. However there are some industrially important reactions in which micro-organisms are first grown to a high biomass and are then added to a substrate which is almost quantitatively converted to a product. These are effectively catalytic processes in which one or a few enzymes in the organism transform an added substrate into a useful product. These transformations are divorced from cell growth, in contrast to syntheses such as those in which carbohydrates are converted into citric acid or complex feedstocks into secondary metabolites. 

The study of microbial production of 1,3-propanediol has an interesting history (reviewed by Biebl et al. 1999). It is one of the oldest fermentation products known and has been studied for over 100 years. For a number of years, interest in the fermentation was due to its potential as an outlet for surplus glycerol. Glycerol can be made via a chemical process, or it can be derived from various agricultural fats during the production of fatty acids and soaps. Increased availability of low-cost glycerol might be expected in the future, as it is a by-product of such processes as transesterification of fats for biodiesel production as well as the process for ethanol production by yeast. 

The industrial focus on 1,3-propanediol has sparked interest in the microbial production of 1,2-propanediol. Some work has focused on the fermentation process of 1,2-propanediol as well as the metabolic engineering of pathways for its production. In early work with C. thermosaccharolyticum, various process conditions were examined such as temperature, pH, gas phase composition, and substrate concentration. This work was conducted in a volume of 2 1. The maximum cell concentration achieved was in the range of 1.0-1.3 g/1. The temperature range examined was 50-65 °C, and the optimal temperature for production was 60 °C. At higher temperatures, lactate decreased and ethanol increased. The pH range studied was from 6.0 to 7.2. At the optimal pH of 6.0, a concentration of 5.6 g/1 of 1,2-PD was obtained. Other fermentation conditions were examined such as... 

Taherzadeh MJ, Karimi K (2008) Pretreatment of lignocellulosic wastes to improve ethanol and biogas production a review. Int J Mol Sci 9 1621—1651. doi 10.3390/ijms9091621 Tsuge T (2002) Metabolic improvements and use of inexpensive carbrni sources in microbial production of polyhydroxyalkanoates. J Biosci Bioeng 94(6) 579-584. doi 10.1016/S1389-1723(02)80198-0... 

The separation of 1,3-PD from the fermentation broth accoxmts for around 50% of the microbial production cost (Zeng and Sabra, 2011). The recovery of 1,3-PD is carried out using evaporation, distillation, pervaporation, liquid-liquid extraction, and ion-exchange chromatography (Xiu and Zeng, 2008). Using an aqueous two-phase extraction in the presence of ethanol and ammonium sulfate results in a maximum partition coefficient with a 94% recovery (Li et al., 2009). 

Ethanol fermentation is a particularly good example of product accumulation inhibiting the microbial culture. Most strains of yeast have a much slower alcohol production rate when ethanol reaches about ten percent, and the wine or said strains that achieve over 20 percent by volume of ethanol are very, very slow. A system known as the Vacuferm for removal of alcohol by distillation as it is formed is... 

Immobilisation of Microbial Cells for the Production of Organic Acid and Ethanol... 

Use of biofilm reactors for ethanol production has been investigated to improve the economics and performance of fermentation processes.8 Immobilisation of microbial cells for fermentation has been developed to eliminate inhibition caused by high concentrations of substrate and product, also to enhance productivity and yield of ethanol. Recent work on ethanol production in an immobilised cell reactor (ICR) showed that production of ethanol using Zymomonas mobilis was doubled.9 The immobilised recombinant Z. mobilis was also successfully used with high concentrations of sugar (12%-15%).10... 

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