Light stimulated H2O2 inhibition on methanogenesis during anaerobic digestion towards enhanced VFAs production
Jiasi Sun, Zhen He
Abstract
Producing volatile fatty acids (VFAs) from anaerobic digestion (AD) of sewage sludge is of strong interest and can be realized via arresting methanogens. Herein, in situ hydrogen peroxide (H 2 O 2 ) dosage has been demonstrated to be an effective approach to suppress methanogenesis and promote VFAs accumulation in the presence of illumination. Two AD reactors operating under different conditions produced average VFAs concentrations of 11,456.5 mg COD L −1 (R Light , 80 mg L −1 H 2 O 2 ) and 11,896.5 mg COD L −1 (R Dark , 380 mg L −1 H 2 O 2 ). The comparable VFAs concentrations indicated that methanogenic activity was effectively inhibited under both conditions, thereby preventing further conversion of VFAs to methane. However, visible light significantly reduced the H 2 O 2 dosage level from 380 to 80 mg L −1 to achieve complete methane inhibition, likely due to light-activated H 2 O 2 producing · OH. The light-exposed H 2 O 2 elevated intracellular reactive oxygen species (ROS) levels, leading to a sharp decline in methanogen abundance (only 5.02% remained compared to the inoculum). Firmicutes became dominant, increasing from 14.03 % (inoculum) to 52.35 % under high oxidative stress. Metagenomic functional predictions inferred microbial communities that tended to mitigate oxidative stress by reducing ROS generation, as shown by the relative gene abundance reduced from 0.0577 to 0.0487 %. A side-effect of H 2 O 2 inhibition was the enrichment of NH 4 + and PO 4 3− , increased by 1.44 and 5.26 times, respectively; those nutrient compounds could be potentially recovered.