From sewage sludge to sustainable transportation fuels: Quo vadis?

The production of liquid biofuels has gained increased attention given many reasons, including the depletion of fossil fuels, the abilities of biofuels in reducing greenhouse gas emissions, and the large availability of biofeedstock. Among the outcomes from COP26, it is urged to accelerate efforts toward biofuels production, with a particular emphasis on wastes and residues as target feedstocks. Therefore, this chapter highlights the recent progress in liquid biofuels production from pyrolysis of sewage sludge (SS), a significant municipal solid waste that cannot be prevented. The various methods recently employed to improve the biocrude properties are thoroughly discussed, such as pretreatment of the SS, coprocessing of SS with other biowastes, the catalytic processing focusing on biomass-based biochar as an alternative catalyst, and the catalytic upgrading of the biocrude in a post-treatment stage. The possible reaction mechanisms behind each method are briefly presented.