Review on Biofuel Production from Agricultural Waste in a Sustainable Way: Pathways, Processes and Technological Advances

Production of sustainable and renewable energy has become vital in today’s world owing to the increasing use of fossil fuels, which are anticipated to disappear in the near future. One of the ways of doing this is by generating energy from waste. Globally, around 140 million tons of biomass is generated which is equivalent to 50 million tons of oil. The review discusses various methods for generating energy from agricultural waste. Agricultural wastes like the lignocellulosic materials (for example straws), animal manure and food residues, have high potential to be used for biofuel production. Biomass feedstocks are rich in oxygen and carbon, and have low percentage of sulphur making them suitable for the conversion process. The review includes two major pathways for biofuel production; biological, chemical and thermochemical. The biological pathways include fermentation and anaerobic digestion, while chemical and thermochemical pathways include pyrolysis and gasification. Anaerobic digestion produces methane rich biogas through a series of bacterial processes. Pretreatment methods including physical, chemical and biological ways, are used to enhance sugar conversion. Further, pyrolysis converts the biomass into bio-oil, which is used as an alternative to traditional fuels (like petroleum, diesel etc) with certain limitations. On the other hand, gasification produces syngas by the burning of feedstock in controlled conditions. Syngas can be processed into liquid hydrocarbons using Fischer-Tropsch synthesis. Technologies like oxyfuel combustion reduce CO2 emission and improve process efficiency. Some challenges that may arise include the moisture content already present in agricultural waste and the processing costs influenced by the various unit operations involved. Overall the study discusses the potential of agricultural waste to be used for biofuel production, paving the way to sustainable and renewable energy systems.