Propagated fixed-bed mixed-acid fermentation: Effect of volatile solid loading rate and agitation at near-neutral pH

► Propagated fixed-bed four-stage fermentations at near-neutral pH. ► Effect of continuous or periodic mixing and volatile solid loading rate (VSLR). ► Continuous mixing gave higher yields and selectivities. ► Increased VSLR and liquid retention time decreased yield, conversion, selectivity. ► Operating at near-neutral pH achieved better performance than high pH.