Chain elongation of acetate and ethanol in an upflow anaerobic filter for high rate MCFA production

► A new reactor system for chain elongation in non-sterile conditions was investigated. ► The volumetric MCFA production rate is in the range of other fermentation processes. ► The volumetric caprylate production rate was improved more than 16 times. ► Highest reported caprylate concentration by chain elongation was achieved. ► By increasing the ethanol load, the selectivity of MCFA production improved.