Towards sewage sludge based biofuels via thermochemical conversion – A review

Wastewater treatment leads to an increase in sewage sludge production. Sewage sludge consists, in general, of non-toxic organic matter and therefore can be utilized as a biomass resource for energy production. Energy recovery from sewage sludge via thermochemical valorization processes seems of great potential. Processes’ products can be used as bio-fuels, while minimization of the environmental impacts can be also achieved. In particular, wet sewage sludge pyrolysis-partial gasification at high temperatures and especially gasification give a new perspective for hydrogen-rich fuel gas production. Co-processing of sewage sludge with biomass improves the fuel's characteristics and enhances the processes efficiency. In addition, blends of sewage sludge with biomass contribute in diluting the inorganic and toxic compounds. Towards that direction, algae production using wastewater resources and then to be used for biofuels production seems a sustainable solution that is the reason why exploitation of such a material through thermochemical processes is under intensive discussion.