Ethanol, also called alcohol or ethyl alcohol, is a clear, colourless liquid and the main ingredient in alcoholic beverages like beer, wine or brandy. Because of its physical and chemical properties, it is also used as an ingredient in a range of products, like paints, coatings, lacquer thinners, cleaning detergents, printing inks and fuel.
So, is there a difference between ethanol and bioethanol? And what is the fuss about bioethanol? Chemically, ethanol and bioethanol are the same. The only difference is the way in which they are manufactured. Bioethanol is considered to be made through an eco-friendlier process using the fermentation of agricultural feedstocks such as sugar beets, corn, straw, and wood. Ethanol, or Synthetic Ethanol, is made from petrochemical feed stocks or fossil fuels, primarily by the acid-catalysed hydration of ethylene.
A common question is whether bioethanol is more environmentally friendly than synthetic ethanol, and, truthfully, the jury is still out on that matter. The decision between the two lies solely upon the source of the ethanol and whether or not that source is sustainable. Synthetic production which relies on fossil fuels is obviously a less clean and sustainable production method. On the other hand, Bioethanol is made from organic and food sources, most commonly corn and sugarcane. However, this may not be sustainable either as valuable crops, cropland and water that could be used for food to consume are instead being burned as fuel.
A WORD ON FOOD WASTE
According to the WWF about one third (1/3rd) of food produced in South Africa is lost through waste and ends up in landfills. This leads to environmental problems such as land pollution and global warming due to production of green-house gases such as methane and carbon dioxide. Of the total food production of about 31.1 million tonnes per year, a portion of 10.2 million tonnes is wasted. The Council for Scientific and Industrial Research (CSIR) has valued this loss at R61.5 billion. The energy consumption used to produce this food loss is equivalent to 12.85 million MJ, an amount that can provide the entire City of Johannesburg power requirements of 11 600 GWh for about 4 months. The water consumption used to produce this food loss is about 1,5 billion m3 which is approximately 15% of the total national annual rainfall of 10.24 billion m3, a massive amount to waste especially for South Africa as it’s the 30th driest country on the planet.
BIOETHANOL FROM FOOD WASTE
The manufacturing process for bioethanol typically consists of pre-treatment, hydrolysis, fermentation, and distillation.
Biomass feedstocks generally have a rigid, or hard structure that cannot be broken down by micro-organisms. Pre-treatment breaks down this structure and makes this available for breakdown by enzymes and micro-organisms. This can be achieved by various methods such as physical crushing, milling, steam explosion etc.
In this step, the pre-treated biomass is broken down into simple sugars by a chemical reaction called hydrolysis. In this hydrolysis reaction, the complex chains of sugars are broken, releasing simple sugars which fermentation micro-organisms can use for food and produce ethanol as a by-product.
The glucose is converted to ethanol, through a process called fermentation. Fermentation is a series of chemical reactions that convert sugars to ethanol. The fermentation reaction is caused by yeast or bacteria, which feed on the sugars. As the sugars are consumed, ethanol and carbon dioxide are produced.
Once sugars have been completely converted to alcohol, distillation is used to separate the ethanol from other components in the fermentation mixture.
With current feedstocks such as sugarcane, maize and sugar beet, the microorganisms and enzymes required for hydrolysis and fermentation are known and their performance is predictable. With food waste, which can be variable, work still needs to be done to optimise the processes.
This is where we come in. Our research focuses on innovative cultivation and extraction of specialised bioactive compounds for various applications. This includes enzymes and micro-organisms that are suitable for production of ethanol from food waste in all its varying compositions.