Intermittent energization improves anaerobic digestion of microbial electrolysis cell-assisted nitrogen-rich sludge under mesophilic and thermophilic conditions

Anaerobic digestion of nitrogen-rich sludge is limited by hydrolysis and threatened by high ammonia nitrogen. Anaerobic digestion of microbial electrolysis cell-assisted (AD-MEC) can effectively improve hydrolysis and system stability. However, prolonged energisation can exacerbate energy consumption and lead to a reduction in economic benefits. The effects of AD-MEC on the anaerobic digestion performance of nitrogen-rich sludge under mesophilic and thermophilic conditions with different energization times (0 h, 3 h, 6 h, 12 h and 24 h per day) were investigated. AD-MEC enhances the concentration of anaerobically digested soluble chemical oxygen demand and volatile fatty acids. The AD-MEC digester in 12 h-ON/12 h-OFF energization mode under mesophilic conditions had a methane yield of 133.3 +/- 6.1 mL g  1-VSadded, which was enhanced by 23.7% compared with the control. The AD-MEC digester in 12 h-ON/12 h-OFF energized mode under thermophilic conditions promoted the recovery of the destabilized digester with a methane yield of 43.9 +/- 2.1 mL g  1-VSadded, which was 14.5% higher compared with the control. Microbial communities showed that mesophilic AD-MEC enriched hydrogenotrophic methanogens dominated by Methanosarcina, and thermophilic AD-MEC enriched Coprothermobacterota phylum bacteria and hydrogenotrophic methanogens promoted recovery of the destabilized digester. Therefore intermittent energization of the AD-MEC using the 12 h-ON/12 h-OFF mode can enhance methane yield and save energy.