BACKGROUND: Biodegradation of diesel hydrocarbons using bioreactors has been proposed as an alternative for diesel contaminated sites remediation. To make this alternative feasible, several factors must be optimized or improved: reducing hydraulic retention times (HRT) and applying design methods to enhance the access of the microorganisms to low soluble and recalcitrant compounds like hydrocarbon fuels. In the present work a time and cost efficient continuous-flow packed bed bioreactor at low HRT was designed and evaluated. The effect of non-previously studied anionic surfactant GAELE (glycolic acid ethoxylate lauryl ether) was also investigated.

BACKGROUND Two 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. RESULTS The Monod model revealed that both μmax,h and italicKShfor the C10–C18 chains were 2.5‐fold and 11‐fold, respectively, lower than those of chains C20–C22. 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 C10–C22 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. CONCLUSION The influent diesel concentration interval of 1008–1344 mg L−1 was the range over which the maximum utilization rates of chains C10–C22 decreased from 1.12 to 0.57 vss−1 due to the inhibitory action of chains C10–C18 (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. © 2014 Society of Chemical Industry