Biofuel production by co-pyrolysis of sewage sludge and other materials: a review

The unsustainable management of sewage sludge induces environmental and economic issues, yet sewage sludge is a promising feedstock for the production of biofuels by pyrolysis. Actual challenges include poor chemical stability, high water content, high viscosity, high concentrations of nitrogen, and the presence of oxygen in the produced biofuels. Moreover the produced biochars contain elevated amounts of toxic metals and, as a consequence, may not be used in agricultural soils. Here we review the co-pyrolysis of sewage sludge with other materials to enhance bio-oil quality. Several studies show that co-pyrolysis of sewage sludge with non-biomass materials reduces water, oxygen and nitrogen contents, activation energy, and enthalpy; and increases the calorific value.