GENERATIONS OF BIOFUELS
1⃣ First Generation (1G) Biofuel - derived from edible crops grown on arable land. For e.g. sugarbeet, sugarcane, wheat, corn.
It has high carbon content.
2⃣ Second Generation (2G) Biofuel - produced from non-edible crops / leftover non-edible parts of food crops having high ligno-cellulosic content, mostly grown on non-arable land. For e.g. woodchip, straw, rice husk
Carbon emissions < 1st Generation biofuels.
3⃣ Third Generation (3G) Biofuel - produced from microalgae (cynanobacteria) and macroalgae (seaweeds)
It is carbon-neutral (CO2 emitted = CO2 sequestered)
4⃣ Fourth Generation (4G) Biofuel - produced from genetically engineered plant biomass or genetically-modified crops and microbes.
It is carbon-negative.
Genetically-engineered crops can produce ultra clean "carbon-negative" fourth-generation biofuels.
Biofuels that are carbon negative are fuels that remove more carbon from the atmosphere than they put back in through burning.