While source separation of waste packaging materials for recycling is well established in several metropolitan areas, the collection of food waste from the households is less widespread because of its more difficult implementation. Source segregation of food waste in densely populated areas is raising new interest, as the availability of biogas following its anaerobic digestion (AD) paves the road to a number of possibilities, from electric energy production to its upgrading to biomethane and subsequent feeding in to the natural gas network or in vehicles as a fuel. The study addresses this waste management option by analysing a real metropolitan situation where food waste currently ends up mixed with the residual waste in a waste-to-energy plant (WTE). We assume to establish a new collection scheme for household food waste, followed by its treatment in a new AD and post-composting facility. A comparative life cycle assessment was carried out, where possible synergies between the existing WTE plant and the new one were evaluated. All new scenarios based on AD attained similar or better results compared with the reference scenario for almost all of the impact indicators. The most robust indication is related to global warming potential, with a potential improvement of up to 37%. Finally, a sensitivity analysis was carried out to assess the effect of the variation of the most relevant parameters. Results have proven to be very sensible to the hypothesis on the type of substituted electric energy. All the other examined sensitivities resulted in variations well below 10%.