Four different physicochemical pretreatments on an anaerobic inoculum used for alcohol production from acetate and butyrate are evaluated. Experiments were conducted in single batches using acetate and butyrate as substrates at 30°C and with a pressurized headspace of pure H2 at 2.15 atm (218.2 MPa). Thermal and acidic-thermal pretreatments lead to higher production of both ethanol and butanol. Modelling shows that the highest attainable concentrations of ethanol and butanol produced were 122

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... L−1 and 97 mg L−1 for the thermal pretreatment (after 17.5 days) and 87 mg L−1 and 143 mg L−1 for the acidic-thermal pretreatment (after 18.9 days). Thermodynamic data indicated that a high H2 partial pressure favoured solventogenic metabolic pathways. Acidic-thermal pretreatment selected a bacterial community more adapted to the conversion of acetate and butyrate into ethanol and butanol, respectively. Thermal-acidic pretreatment was unstable, showing significant variability between replicates. Acidic pretreatment showed the lowest alcohol production.