Propagated fixed-bed mixed-acid fermentation: Part I: Effect of volatile solid loading rate and agitation at high pH

► Propagated fixed-bed four-stage fermentations at high pH. ► Effect of continuous or periodic mixing and volatile solid loading rate (VSLR). ► Increased VSLR did not affect yield. Continuous mixing gave high conversion and yield. ► Increased VSLR and liquid retention time gave higher conversion and lower selectivity. ► Operating at high pH (∼9) gave high selectivity to acetic acid but lower yield.