Wastewater treatment plants (WWTPs) are no longer considered pollution removal systems but rather resources (nutrients and energy) recovery plants. Legislation imposing more stringent effluent requirements and the need energy self-sufficient or even energy-positive plants are the main drivers for the research and development of new WWTP configurations. While a lot of effort has been focused on developing new processes for nutrient recovery, limited efforts have been allocated to maximizing energy recovery from the organic load. Within this context, high-rate activated sludge (HRAS) is the most promising alternative technology to redirect carbon (organic compounds) towards energy as biogas. This is a critical review of the last decade's development of new alternatives for carbon redirection to improve the energy balance of WWTPs on both the laboratory and the industrial scale. Display omitted •C redirection technologies challenges are reviewed.•Bio-sorption/HRAS processes demonstrated high organic matter removal efficiencies.•Bio-sorption/HRAS systems are beneficial in terms of a global energy balance.•60% of C is expected to be redirected to the sludge during the bio-sorption step.•The main challenge of Bio-sorption/HRAS is focused on sludge settling properties.