BACKGROUND: Biodesulfurization (BDS) is a complementary technology to hydrodesulfurization since it allows the removal of recalcitrant sulfur compounds present in fossil fuels. The cost of culture medium to produce the biocatalysts is still one limitation for BDS application. Carob pulp, as an alternative carbon source, can reduce this cost. However, the presence of sulfates is critical, since BDS is inhibited at very low concentrations. Thus, the goal of this work was to optimize the process of sulfur precipitation on carob pulp liquor. RESULT: The effect of BaCl2 concentration (00.5%) and exposure time (636 h) on sulfate removal from carob pulp liquor was studied according to a statistical design following the Doehlert distribution for two factors. This experimental design determined that 0.5% BaCl2 concentration for 21 h were adequate conditions for sulfate removal from carob pulp liquor using BDS. CONCLUSION: These results demonstrate that it is possible to use alternative carbon sources derived from agro-industrial wastes for BDS, even those with high sulfur levels. For future industrial application, an inexpensive culture medium would have to be employed in a large-scale process and carob pulp liquor could be the carbon source. (c) 2012 Society of Chemical Industry