Concept:
Green fuel, also known as biofuel, refers to energy sources derived from renewable biological materials. Unlike fossil fuels, these are considered carbon-neutral because the carbon released during combustion was recently absorbed by the organic matter during growth.
Step 1: Define the source.
Green fuels are produced from "bio-waste" or biomass, which includes agricultural residues, animal waste, wood, and specific energy crops.
Step 2: Exclude non-biological wastes.
• Metal, plastic, and electronic wastes are non-biodegradable and are recycled or managed as hazardous waste; they are not primary sources of "green" energy.
• Chemical waste is industrial byproduct and generally toxic.