Wastewaters treatment with biological processes is widely applied as a reliable solution to water pollution in urban areas. This process produces sludges and process waters. Sludges can be furtherly threated in dedicated plants to produce biogas, that can then be used to produce heat in specific plants, but it is sometimes simply burned using flares. A possible alternative use of biogas is the coupling with a CHP generator which can be used to produce electrical energy and heat. In the present paper, it is investigated the possible exploitation of the sludges produced by a wastewater treatment plant for feeding a sludge treatment plant, both in Genoa (Italy), in order to produce biogas. This work is based on the analysis of available data (2009-2018) provided by the sludge treatment plant technical staff, which showed strong variations in sludge flow rates as a result of the variation of incoming wastewater load. Since the available data is not always correlated with wastewater incoming flows and biogas production, starting from data provided for similar plants operating in Italy, it was possible to estimate a theoretical biogas production which was considered as the reference trend.