BIOFUEL FERMENTATION

The last few years have seen dramatic increases in the price of fuel leading to various nations trying to find the alternatives to the fuel addiction. Biofuel in the form of ethanol have been seen as one of the most attractive source of biofuel to replace or supplement existing fuel demands.

Using alcohol as “gasohol” for automobiles is not really a new idea as Brazil has always been exploiting this technology for decades. This is not surprising as Brazil have enormous tracts of lands that can be used to grow sugar canes from where the sugar for the fermentation of alcohol is derived.

The technology to produce alcohol from sugars is through the process of fermentation, whereby microorganisms such as yeasts and certain species of bacteria have the ability to convert sugar through their metabolism to form alcohol as their main fermentation products.

In the fermentation of sugar to alcohol, economic factors play the most crucial roles. No industry will survive if it cannot make profits.

Analyzing the fermentation of alcohol from sugar raw materials, the two main constraints are:

1 High cost of substrates or raw materials for fermentation

2 High costs of product recovery

Now let us look closely at these two factors.

RAW MATERIALS

The main source of alcohol fermentation is sugar. There are many plants that can be the source of sugars such as sugar canes, sugar beets and others. However, the supply of these sugars is also required for human consumption. It is not wise to use substrates used by human for foods to be used as raw materials for fermentation as the increase in demand for the substrates will affect the prices of sugar in the market or would make the fermentation process costly.

It is the usual practice in industrial fermentation to choose a source of carbohydrates which are cheap to make the process economically viable. This is the reason why in most industrial fermentations the industries either opt for agricultural waste residues such as pineapple skins or they go for substrates which are not in high demand as food for the population such as starch from sago or tapioca.

PRODUCT RECOVERY

Alcohol is a short chain fermentation product produced by microbial metabolism. It is only produced at very low concentrations and dissolved in the fermentation broth. Recovery of the alcohol is energy intensive and expensive and requires complex distillation.

MAKING THE FERMENTATION PROCESS VIABLE

There are many attempts to improve the alcohol fermentation process ranging from:

1 Improving the fermentation environment through optimal

temperature and ph range

2 Improving the nutrients required for the growth of microorganisms

3 Using the proper microorganisms

4 Improving fermentation operation parameters such as mixings,loading rate

MAXIMIZING FERMENTATION THROUGH THE MICROBES

In this blog we will be looking into improving the fermentation through microbial component.

Let us look at the simple equation of producing alcohol by microorganisms using sugars:

SUBSTRATE-------->MICROORGANISMS -------> ALCOHOL

From the above simple model we see that the sugar substrate is being utilized by the microorganisms to form alcohol by fermentation

The microorganism that produce the alcohol from sugar are usually yeasts such as the common Saccharomyces cerevisiae which are normally used in the fermentation of alcoholic beverages. There are other bacteria such as Zymomonas mobilis which could offer better fermentation yield.

If we want to improve the alcohol fermentation process we do have a choice of other yeasts and bacteria. The choice of the microorganism to run the fermentation must fulfil certain criteria:

1 Are we producing alcohol for industrial purposes and not for beverages?

2 Are the microorganism chosen show high alcohol productivity?

3 Are the microorganisms pathogenic or non pathogenic?

4 Are the microorganisms chosen capable of using cheaper source of substrates?

5 What are their optimal range of temperature and ph?

6 Are the microorganism chosen capable of tolerating high alcohol concentration?

7 If we use certain microorganisms such as yeasts will we be facing strains of 'killer yeasts' that can kill normal yeasts?

That is why feasibility studies need to be done initially in choosing the right strain or microorganism before we decide to go ahead with any fermentation process. If the project fails on paper or in the preliminary studies it is wiser to abandon the project and not to incur financial loses at the end of the day after large amount of capital has been pumped