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Most frequently used biofuel is bioethanol. It can be formed from three types of feed stocks, namely sugar‐based (most common), starchy and lignocellulosic (require pre‐treatment). Production of bioethanol from sugar‐based crops was the most common method till 2003 and contributed nearly 60% in the worldwide production (Gupta et al. 2014, pp. 1–17). After sugar‐based crops (sugarcane, sorghum etc.), starch feedstock (corn, wheat, barley etc.) is used for bioethanol production followed by lignocellulosic feedstock (wood, straw, corncob etc.). Chemically lignocelluloses are mainly composed of carbohydrates (cellulose and hemi‐cellulose) and lignin along with some other quantities of biomass. Owing to the varying composition of lignocelluloses, several pre‐treatment processes were explored to obtain fermentable sugars. Advance researches are conducted for the various pre‐treatment processes because usage of lignocellulosic feedstock can lead to cost‐effective biofuel (Lund et al. 2016, pp. 36–38). Pre‐treatment process can be biological, physical and chemical depending upon the source and means of conversion procedure. Among the different methods for pre‐treatment, biological method which is a microbial process consumes less energy compared with the other two processes and moreover, a safe and environment‐friendly process (Potumarthi et al. 2013). Physical pre‐treatment can be done via mechanical comminution, steam explosion, ultrasonic radiation and extrusion process (Gupta et al. 2014, pp. 1–17). Under the chemical pre‐treatment methods, acid hydrolysis, alkaline hydrolysis, ammonia hydrolysis and ozonolysis are different available methods. Use of bioethanol‐blended gasoline in automobiles offers a viable option to cut down the use of petrol. This will also reduce the GHG emission along with contribution in achieving goals of Paris agreement.

Biodiesel is another biofuel that can be produced from oil‐based feedstock, animal fat wastes and waste cooking oils. Animal fat wastes are commonly obtained from chicken, cow, pork lard, fish and other animals. Oil‐based feedstock can be edible (soybean, corn etc.) or non‐edible. But, according to food first principle, use of edible feedstock is not promoted worldwide. However, continuous evolving technologies for converting biomass to fuels have enabled the bioenergy industry to utilize more of lignocellulosic biomass. Technological developments open doors for new types of feedstock for bioenergy production e.g. forest biomass, agricultural residue, perennial grasses and trees and even municipal waste (Lund et al. 2016, pp. 36–38).