BACKGROUNDTwo kinetic models for diesel degradation in a continuous-flow reactor at a retention time of 1.5 h were compared. One model included the Monod equation and the other, a biphasic model, did not involve Monod parameters. The experiment included two Pseudomonas species. A thermodynamic study on the nitrate-reducing degradation of diesel was performed in addition to a BOD5 /COD ratio to evaluate the biodegradability of both the diesel components and their residual concentrations. RESULTSThe Monod model revealed that both (max,h) and KShfor the C-10-C-18 chains were 2.5-fold and 11-fold, respectively, lower than those of chains C-20-C-22. The biphasic model failed to detect the influent concentration range at which the biofilm slowed down processing the substrates. The shifts of the influent-to-effluent BOD5/COD ratios from 0.67 to 0.80 and from 0.80 to 0.95, for the lowest and highest substrate concentrations, respectively, confirmed that residuals in the effluent can be degraded. Stoichiometric calculations for C-10-C-22 revealed theoretical spontaneous release of Gibbs free energies from -6.89 to -70.27 kJ, and electromotive forces from 4.4 to 45.51 mV for both the lowest and highest diesel concentrations, respectively. CONCLUSIONThe influent diesel concentration interval of 1008-1344 mg L-1 was the range over which the maximum utilization rates of chains C-10-C-22 decreased from 1.12 to 0.57 vss(-1) due to the inhibitory action of chains C-10-C-18 (P<0.05). Following the degradation of diesel, the organic residuals left in the effluent can be easily assimilated. The nitrate-reducing degradation was able to produce an electromotive force spontaneously. (c) 2014 Society of Chemical Industry