Enhancement of anaerobic acidogenesis by integrating an electrochemical system into an acidogenic reactor: Effect of hydraulic retention times (HRT) and role of bacteria and acidophilic methanogenic Archaea

• Adding Fe electrode into an acidogenic reactor (R1) improved acidogenesis efficiency.
• At short HRT, R1 still showed high COD removal and acidification efficiency.
• Coupling of Fe2+ and electric field accelerated the hydrolysis rate of polysaccharide.
• R1 is expected to replace traditional anaerobic digester for industrial wastewater treatment.

In this study, an acidogenic reactor packed with a pair of Fe–carbon electrodes (R1) was developed to enhance anaerobic acidogenesis of organic wastewater at short hydraulic retention times. The results indicated that the acidogenic efficiency was improved by settling a bio-electrochemical system. When hydraulic retention times decreased from 12 to 3 h, R1 showed 18.9% more chemical oxygen demand removal and 13.8% more acidification efficiency. After cutting off the voltage of R1, the COD removal decreased by about 5%. Coupling of Fe2+ leaching and electric field accelerated the hydrolysis of polysaccharide, relieving its accumulation in the sludge phase. Several acidophilic methanogenic Archaea such as Methanosarcina sp. were enriched in R1, which was favorable for consuming organic acids and preventing excessive pH decline. Thus, the developed acidogenic reactor with Fe–carbon electrodes is expected to be potentially effective and useful for wastewater treatment.