Fig. 1From: Resource recovery and waste-to-energy from wastewater sludge via thermochemical conversion technologies in support of circular economy: a comprehensive reviewConventional and alternative thermochemical conversion methods for wastewater sludge along with their extent of energy and nutrient recovery. The intermediate steps such as drying and downstream processing steps for the products are not shown in this representative figure. The dotted lines in gray represent the residual biosolids produced from the AD which can then proceed to any of the other methods. Symbols: seedling, nutrient recycling; flame, energy (heat); lightning, electricity; droplet, bio-oilBack to article page