The diagram illustrates the cyclical process by which ethanol – a biofuel – is produced from plant biomass, showing each stage from growth and harvest through chemical and biological conversion to end-use as a transport fuel, and the subsequent return of carbon dioxide to the environment.
Overall, the production of ethanol can be summarised in three principal phases: biomass growth and harvest, mechanical and biochemical processing that converts cellulose into fermentable sugars and then into ethanol, and combustion of ethanol in vehicles, which emits carbon dioxide that is reabsorbed by plants, thus completing the cycle.
Initially, sunlight and atmospheric carbon dioxide drive photosynthesis, enabling trees and crops to accumulate cellulose-rich biomass. Once mature, this biomass is mechanically harvested and subjected to pre-processing, which breaks down large plant material into smaller fragments and isolates cellulose for subsequent treatment.
The extracted cellulose is then conveyed to processing facilities where it is chemically or enzymatically hydrolysed into simple sugars. Microbial agents are introduced to these sugars to ferment them, producing ethanol as a metabolic by-product.
Finally, the produced ethanol is distributed and combusted in cars, trucks and aircraft, releasing carbon dioxide. Crucially, the diagram emphasises the regenerative aspect of the system: the CO₂ emitted during fuel use is recycled into the atmosphere and subsequently absorbed by growing plants, making the process effectively part of a closed carbon loop when managed sustainably.