Gasification of sewage sludge allows the recovery of energy, and produces a mix of CO, CO₂ and H₂ called synthesis gas (or syngas), which can be fermented by acetogenic bacteria to added-value products. This work presents the conversion of syngas to organic acids and alcohols using both pure and mixed cultures. Pure culture kinetic experiments with Clostridium carboxidivorans P7 resulted in the production of high concentrations of acetate (454 mgC/L), and also ethanol (167 mgC/L). The pH was the main factor driving solventogenesis, with about 50% of the products in the form of alcohols at pH 5. On the other hand, lab-scale experiments using a carboxydotrophic mixed culture from the genus Clostridium enriched from anaerobic digester sludge of a municipal wastewater treatment plant was capable of producing mainly butyrate and butanol, with maximum concentrations of 1,184 mgC/L and 277 mgC/L, respectively.