A viable solution for residual biomass exploitation to reduce the cost related to biomass disposal and simultaneously create profit by electrical and thermal energy use is combined heat and power generation over the micro-scale of power (m-CHP) based on biomass gasification. The exploitation and improvement of these systems were the main objectives of the Italian project “PROMETEO – Production of electrical, thermal and cooling energy with m-CHP fueled by residual biomass”, funded by the local Ministry of Economic Development (MISE). The present work shows an extended experimental activity based on a 20kW micro-cogeneration system as powered by two types of residual lignocellulosic biomasses briquettes in a demonstrative environment site identified in a waste management and storage plant in the Municipality of Mugnano, Naples, in the south of Italy. The m-CHP plant is made of a gasifier, a syngas cleaning circuit and a spark ignition (SI) internal combustion engine (ICE) connected to an electric-generator. The electrical output was meant to power the plant machines for the operations of waste storage. For both biomasses, tests were conducted for the complete characterization of the system in low and medium load and in different spark ignition timing to assess the system sensitivity. The m-CHP performance was investigated with a complete characterization of the syngas and tar compositions, main pollutant emissions and internal combustion engine analyses, aimed at the evaluation of the energetic and environmental efficiencies. An analysis of the air quality near the site by evaluating CO, O3, NO2, C6H6 and PM10 concentration was also carried out. The ultimate purpose of the present work is the demonstration of the advantages of the employment of biomass-powered cogeneration systems in the Mediterranean regions.