Continuous biodegradation of poisonous volatile organic compounds (VOC) which are released to the atmosphere during many industrial operations is one of the fastest-growing areas of bio-processes. Biological degradation of VOC’s provides a cost-effective and highly-efficient alternative to most of popular air-purification technologies such as absorption or high temperature catalytic oxidation. Considering that growth of bacteria colonies and sustaining microbiological activity are essential for proper operation of any bio-process it is clear that metallic materials (carbon or stainless steels) used for construction of bio-reactors piping/tubing pumps etc. will operate under a high threat of microbiologically influenced corrosion (MIC).Bio-processes are characterized by process dynamics that include substantive bacterial growth immobilization and reaction accompanied by typical operating fluctuations of process parameters like pH oxygen concentration or fluid composition (chlorides). These parameters can significantly alter the general corrosion rate as well as potential for localized corrosion. Additionally bio-degradation of sulphur-containing VOC’s usually involves formation of additional corrosive by-products including H2SO4 or H2S which may significantly accelerate corrosion processes. Online real-time corrosion monitoring in biological reactors and processes has become an important need for integrity management.Results from on-line corrosion measurements performed utilizing multiple electrochemical techniques in a large-scale continuous bio-degradation of VOC mixture are presented in this paper. The VOC mixture contains styrene alcohols and sulphur compounds (dimethylsulphide - DMS) involving mixture of Pseudomonas and Thiobacillus bacteria immobilized on fixed-bed of polypropylene rings. Corrosion measurements were obtained by using industrial-type electrochemical probes with three identical finger-type carbon steel electrodes (UNS G1018 AISI 1018) as well as stainless steels UNS S31603 (AISI 316L) and UNS S30400 (AISI 304) electrodes. Four corrosion variables – general corrosion rate localized corrosion potential (Pitting Factor) Stern-Geary parameter “B” and double-layer capacitance (CMI) were continuously recorded concomitant with other process parameters such as solution pH oxygen concentration flow rate temperature etc.Observed fluctuations of CMI values which reflect changes of interfacial capacitance were in line with bacteria growth showing the build-up of the bio-film. Critical influence of process parameters including VOC concentration or pH which favour rapid growth of bacteria were also observed. At low reactor load the measured corrosion rate of carbon steel was below 1mpy with several “peaks” up to 3mpy coinciding with upsets in bio-process conditions. Increase of the reactor load (VOC’s concentration on the inlet) resulted in a sharp increase of corrosion rate above 5-6mpy. Significant potential for localized corrosion (Pitting Factor) was always accompanied by distortions in bio-process parameters.Keywords: biodegradation MIC on-line corrosion monitoring VOC Pseudomonas Thiobacillus localized corrosion