Pierangela Cristiani*, Andrea Franzetti **, Giuseppina Bestetti ** Rivista: Electrochimical ACTA, Issue 1, Volume 54, Dicembre 2008 * CESI RICERCA ** UNIVERSITA’ DEGLI STUDI MILANO BICOCCA The present paper describes a new tool for on-line monitoring of biofilm growth in the soil. The work deals with the application in soil of the same electrochemical techniques already successfully used in water systems to monitor biofilm growth and mainly based on the cathodic polarisation of stainless steel electrodes. Experiments at laboratory level with sterilised and unsterilised soils, different soil humidities, different levels of nutrients have been performed by using a set of soil microcosms containing electrochemical probes. Weekly humidity tests and adjustments, chemical and microbiological analyses of the soils have been regularly carried out. Microbiological analyses and microscopy observation performed on the surface of the stainless steel electrochemical probes at the end of the tests confirmed a direct correlation between the increase of cathodic characteristic and the biofilm development on the working electrodes. The results suggest that simple electrochemical techniques are applicable in soil to monitor the early stage of biofilm growth on stainless steel. It was confirmed, in particular, a key role of soil humidity in the development of a stable and easily detectable biofilm. Soil humidity level resulted as the most critical and limiting factor for biofilm growth, more than the environment temperature, nutrient and carbon content. The best conditions to achieve a quick and full electro-active biofilm on electrodes in a soil microcosms suitable for experiments and studies at laboratory level have been detailed. © 2008 Elsevier Ltd. All rights reserved. Keywords: Biofilm; Soil; Biofuel cells; Stainless steels; Cathodic polarisation