The degradation of benzene in groundwater at concentrations as high as 2,000 mg L −1 was studied using a four-column trickling-flow fixed-film biological reactor with recirculation. A decrease in the content of benzene was achieved, its concentration falling to 0.55 µg L −1 . On the contrary, high levels of diesel fuel were not diminished sufficiently with this mode of operation of the reactor. Thus, a submerged reactor was tested as a modification to the conventional trickling-flow configuration. This modified fixed-film reactor was effective when high loadings of diesel were present as an emulsion. The concentration of diesel was reduced from 2,000 to 0.12 mg L −1 after 8 days of treatment. In both cases, the reactors were packed with a carbonaceous material and were operated in semibatch mode with recirculation. The final concentration of benzene fell below the permissible limit established by Mexican law, and the results for both pollutants also met the concentration limits required by the German law for drinking water, 0.001 mg L −1 for benzene and 0.1 mg L −1 for total hydrocarbons.

The degradation of diesel and phenanthrene in waste water was studied in a column combining a submerged trickling-flow with a fixedfilm at a determined biofilm thickness with recirculation. Degradation efficiencies were found to be high with the production of a biofilm thickness of 789 μm structured in a package material with proper adsorption and physicochemical properties necessary to reach a stable state condition for the degradation of recalcitrant components in 78% at a retention time of 3 h. Improved degradation rates were reached with a biofilm built from an adapted inoculum that showed the presence of Pseudomonas sp., Klebsiella sp. Enterobacter in a concentration of 6.45×10 9 CFU mL −1 . Moreover, the biodegradation rate of the inoculumn was quantified. The diesel kinetic experimental data were well described by Gompertz model which provides a specific grow rate (Kb) of 0.76±0.36 h −1 and a correlation of R 2 =0.93. The integral approach study of the variables of a complex degradation process lead to improve the complete operation of the reactor in comparison with other more specific component-based approaches.