The document discusses how wastewater treatment plant (WWTP) sludge is being transformed from a waste to a resource through innovative technologies and business models. It provides five examples of WWTPs that have adopted these new paradigms: 1) Using technologies like thermal hydrolysis in France to reduce sludge volumes and recover energy. 2) Combining WWTP sludge and organic waste in Denmark to produce biogas and fertilizer. 3) Optimizing biogas production in France for grid injection. 4) A new business model in France where sludge and other waste are treated for double recovery. 5) An incineration plant in Hong Kong that ensures energy recovery from sludge while integrating with the local community.