Mass transfer and bioremediation of naphthalene, 2-methylnaphthalene and 1,5-dimethylnaphthalene have been studied in a rotating bioreactor modified with the addition of baffles and beads. Mass transfer rates of these low solubility organic particles dissolving in water (based on the working volume of the bioreactor) were highest in the bioreactor that combined beads and baffles, with the overall mass transfer coefficient (K(L)a) reaching up to 25 h(-1). Based on its capacity to hold the largest volume of polluted media, the simple baffled bioreactor was considered to be the optimum roller bioreactor design. Using Pseudomonas putido, the bioremediation rate of naphthalene reached 61 mg/l-h in this vessel and using mixed substrates, the bioremediation rate of 2-methylnaphthalene reached 30 mg/l-h. The dissolution rates for hydrophobic particles into the culture media during the bioremediation process were up to four times higher compared to mass transfer rates into abiotic controls, which was likely due to the production of biosurfactants by P. putida.