Normally, we cannot increase capacities of ethanol fermentation processes to 100% because they are biological ones originating in a yeast’s cell. Besides necessitating sugar for ethanol fermentation, some parts of yeast’s cells are used for self-growth and self-repair, and, in the outside environment, contaminating diseases exist to take sugar away for other activities. Typically, capacities of ethanol production at the factory level are between 85 and 90%, depending on different conditions during production. If raw materials commonly used in Thailand are calculated, namely molasses, around 260 liters of ethanol can be made per a ton of molasses; 156 liters of ethanol per a ton of fresh cassava and 400 liters per a ton of sliced cassava.
There are several ways to improve processes to empower capacities for ethanol production, but 3 of them will be discussed here: 1) Control of contamination, 2) Unfermentable sugar utilization and 3) Yeast activity.
1. Control of contamination
Contaminating diseases during production include yeast, bacteria and fungi, but bacteria usually causes damages to ethanol fermentation. It can be divided into 2 types: the positive and negative ones. The negative one causes initial contamination and, as time passes by, it will be weak or ridded of a fermenting barrel when ethanol is increasingly concentrated. The positive bacteria, especially Lactobicillus Bacillus Streptococcus and Leuconostoc, can cause more damages as it takes sugar away for other activities and creates toxic substances to weaken yeast. Finally, the amount of ethanol is less than expected or fermentation processes suffer failure.
This type of bacteria can be controlled or killed by effective biocides which can enhance fermentation capacities from 1-4% more. However, using biocides, which are mostly antibiotics and ionophores, has to be concerned with selection of effective, reliable and environmentally-friendly products which are not drug resistant.
Besides, using other types of chemical substances, such as chlorine dioxides, is considered effective in controlling and resisting contamination in fermentation processes. Limitation exists, however, from the substances in terms of resisting yeast’s growth and other activities, too. As a result, no more than 50 ppm concentration can be used as the substances will enhance capacities of fermentation from 1-2% which is a lot less than using biocides.
2. Unfermentable sugar utilization
Individual raw materials yield ethanol differently, depending on the amount of existing flour and sugar. Molasses, for instance, has fermentable sugar (The one from which yeast can use to produce ethanol, such as sucrose, glucose and fructose) of around 46%, depending on capacities of each sugar mill, quality of cane for extraction and how to keep molasses before using.
In addition, other kinds of sugar from which yeast typically cannot use to ferment ethanol, such as trisaccharide dextran short-chain oligosaccharides and medium-chain oligosaccharides, can be used to enhance ethanol production. These kinds of sugar are called unfermentable and there are around 0.5-2.0% of them.
In terms of using unfermentable sugar to enhance ethanol production, various enzymes are mostly used, such as dextranase and amylase, because they enable digestion of the said compound until it becomes smaller or altered in quality so that yeast can use it for ethanol fermentation. To design the product, many kinds of enzymes are typically used at the same time with specific proportion – enzyme cocktails – because there are different types of unfermentable sugar of which the amount is not much. Various enzymes have to be used to obtain as much ethanol as possible. In case enzyme cocktails are well designed according to the amount and types of unfermentable sugar, more 2-3% capacities of ethanol production will take place.
Nevertheless, difficulty and complexity of using unfermentable sugar relies mainly on types and quality of raw materials, which we cannot exactly control as they alter under environmental conditions, such as types of plants to be used, temperature and soil quality in each area. When raw materials change, the amount and types of unfermentable sugar also change, resulting in enzyme cocktails that were once effective become ineffective upon changes of raw material sources.
The management of the aforementioned requires rapid testing and monitoring systems. Once raw materials are changed, a test must confirm the function. If any functions do not work, raw materials must be stopped immediately to reduce damage and waste of budget. New development and testing systems of enzyme cocktails should be introduced to incoming raw materials. Consequently, ways of using unfermented sugar to increase ethanol production, despite various enzyme cocktails, are not much widely and continuously used at industrial levels.
3. Yeast activity
Fermentation of ethanol at industrial levels employs cheap agricultural products like fresh and sliced cassava as raw materials, or even any byproducts of low quality like molasses. Most of them are already contaminated throughout production processes. In industrial fermentation, barrels cannot be completely free from any diseases because capital costs for production need to be lowered as much as possible. The factors cause fermentation processes experience contamination as well as other things found with raw materials. Such is an environment that makes yeast stressful. If yeast is not sufficiently strong, capacities of ethanol production will be low.
Concerning ways to strengthen yeast during ethanol fermentation processes, different substances are usually added, such as free amino nitrogen (FAN) and minor nutrients. Appropriate number of additional substances will increase ethanol products effectively. From personal experiences, to obtain more FAN to yeast includes adding protein compounds like agricultural leftovers from paddy and corn which are partially decomposed until there is functional FAN. Otherwise, some products may be made by cocktails production composed by FAN from agricultural materials and protease enzymes so that an initial FAN exists and is ready for immediate use. The protease enzyme will decompose protein compounds and release more FAN. This process can enhance 1-3% of production capacities.
To make the picture clearer, enhancement of production from fermentation can be compared to the fact that the same number of raw materials can yield how many more liters of ethanol. For example, in case one uses molasses, fresh or sliced cassava as raw materials 260, 156 and 400 liters of ethanol can be produced respectively. If one enhances more 3% of production capacities, one can produce 268, 161 and 412 liters of ethanol per ton respectively. In comparison with an ethanol factory with 200,000 liters of production capacities per day, one can earn around 150,000 Thai Baht daily (In case ethanol costs 24 Thai Baht per liter.) or more than 48 million Thai Baht annually.
The above-mentioned 3 ways to improve production capacities for ethanol, nevertheless, are rather difficult and time-consuming for starting a test. Controlling factors of the test, assessment that requires precision and correctness as well as a design for practical use at industrial levels need tools and personnel with abilities, knowledge and experiences. Most important for success is policy and attitudes of executives who would seriously like to improve capacities of their own factories and business.