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. RESULTS: A continuous-upflow packed bed bioreactor (CPR) was built using an inexpensive support made of volcanic and alluvial stones. The biodegradation experiments conducted with a 12-month-old biofilm at a fixed HRT of 0.5 h, recorded removal of up to 97.9% at a diesel concentration of 1120 mg L-1 with GAELE. A first-order rate constant of 0.10 h-1 was calculated. Kinetic analysis using Arvin's model, which introduces mass transfer to the biofilm, showed statistical differences in the kinetic rate parameters (P < 0.001). Moreover, GAELE significantly increased biodegradability at high concentrations, with BOD5 and COD removals up to 90.8 and 80.7%, respectively. Putative hydrocarbon degrading bacteria responsible for the degradation under nitrate-reducing conditions were positively identified. CONCLUSIONS: The continuous-upflow packed bed reactor was capable of high percentage diesel biodegradation at short HRTs. The use of GAELE increased diesel availability and thus enhanced hydrocarbon removal. Therefore, CPR packed with volcanic and alluvial stones combined with GAELE showed potential for the remediation of diesel-impacted sites. Copyright (C) 2012 Society of Chemical Industry