Feasibility of anaerobic digestion from bioethanol fermentation residue

•Maximum CH4 conversion rate of fermentation residue is 84.8% at 5 g COD/L of residue.•Appropriate F/M ratio was significant on anaerobic digestion of fermentation residue.•Inhibitory effects on anaerobic digestion can be overcome by increasing cell.•Formic acid is strong inhibitor than levulinic acid on anaerobic digestion.

The focus of this study was the reuse of red algal ethanol fermentation residue as feedstock for anaerobic digestion. Levulinic acid and formic acid, the dilute-acid hydrolysis byproducts, inhibited methanogenesis at concentrations over 3.0 and 0.5 g/L, respectively. However, the inhibition was overcome by increasing inoculum concentration. A series of batch experiments with the fermentation residue showed increased methane yield and productivity at higher inoculum concentration. The maximum methane conversion rate of 84.8% was found at 5 g COD/L of fermentation residue at 0.25 g COD/g VSS of food-to-microorganism (F/M) ratio. The red algal ethanol fermentation residue can possibly be used as a feedstock in anaerobic digestion at appropriate concentration and F/M ratio.