Abstract - This study evaluated the effects of aeration (constant aeration, intermittent aeration and a lack of aeration) and hydraulic retention time (HRT) (2, 3 and 4 days) on a continuous process with cell recycling, using chitosan as a natural coagulant for the sedimentation of a C 1 mixed culture. This culture was used for the biodegradation of hydrocarbons present in the effluent contaminated with diesel oil and gasoline. The responses monitored included the turbidity removal (TR), total petroleum hydrocarbon (TPH) removal and volatile suspended solids (VSS). Constant aeration and an HRT of 4 days produced the best results for the continuous process, resulting in the highest TPH removals (94% and 75% reductions in the supernatant and reaction tank, respectively) and TR (95%). Keywords : Continuous process; Biodegradation; Chitosan; Mixed culture. INTRODUCTION The effluent generated in terrestrial fuel distribu-tion terminals usually has a high organic load that is the consequence of the presence of the hydrocarbon constituents of gasoline and diesel oil (complex mix-ture consisting basically of paraffinic, olefinic, ali-phatic hydrocarbons and aromatic compounds and, in smaller amounts, molecules containing sulfur, nitro-gen, metals, oxygen, etc). Therefore, biodegradation is impaired by recalcitrance of some of these com-pounds present in gasoline and diesel oil and the high organic load values occasioned by these hydro-carbons. The use of pure cultures (bacteria, yeasts or fila-mentous fungi) and mixed cultures for the decon-tamination of sites contaminated with petroleum and petroleum derivatives is often a promising techno-logical solution, which significantly reduces or elimi-nates the pollution load that may be present in the soil or in liquid media (Bielecka