This paper focuses on applications and electrical valorisation of microbial fuel cells (MFCs), a promising energy harvesting technique, suitable as clean power source to supply low power devices in wireless sensor networks (WSN) for environmental and agricultural monitoring. An MFC is a bioreactor that converts energy stored in chemical bonds of organic matter into electrical energy, through a series of reactions catalysed by microorganisms. An MFC can operate as bioreactor, as bioremediator and as biosensor. In the past decade, the evolution of low power electronics has made MFCs technology more attractive, because it has become suitable for low-power devices forming complete systems, such as the nodes of a WSN. Moreover, MFCs gained more interest because they can generate electric power while treating wastes. Unlike other fuel cells, MFCs can continuously generate clean energy at normal temperature and atmospheric pressure without any supplementary maintenance. Additionally, MFC may be used directly as a biosensor to analyse parameters like pH and temperature or arranged in the form of a cluster of devices to be use as a small power plant. A series of test was performed for the electrical valorisation of reactors as well as biosensor issues.