In fact, algae represent an interesting alternative to the production of first or second generation biofuels, thanks to an high photosynthetic yield and hence, a lower land competition with food production and a better control of ground emissions. In addition, the ability to use CO2 directly from industrial emissions as a resource of carbon for the growth of microalgae is a promising feature for fluegas mitigation. Hence if used as an interface between biowaste and energy production, macroalgae allows direct utilization of biowaste and, at the same time transforms negative environmental externalities into positive ones. A Life cycle assessment (LCA) is fundamental in order to optimize the overall process from the environmental point of view, addressing the attention on the environmental “hot spots” of the process. The LCA methodology is one of the best suitable instruments for understanding the environmental benefits and the share of non-renewable sources still needed for the process. It is an interest to investigate a transformation system coupling the anaerobic digestion of raw algae (for production of biogas and after upgrading methane as biofuel) and the algal production itself. The benefits can be focused also on the recirculation of the liquid fraction of the digestates toward the algal ponds and a significant fertilizers recycling. The purpose of this paper is to carried out an environmental assessment of the use of biogas from algae as a biofuel for the heat and electricity production on a cogeneration (CHP) unit (40kW) and compares it in case of natural gas supplies.