Integration of in-situ and ex-situ power-to-gas (PtG) strategy for simultaneous bio-natural gas production and CO emission reduction.

A novel system integrating an in-situ and ex-situ power-to-gas (PtG) system was developed in the current study. A continuous stirred-tank reactor (CSTR) was operated using cattle manure as substrate at mesophilic temperature (37 °C ± 2 °C). The CH content in the biogas was upgraded to above 95% by H injection, which meets the highest criteria for grid injection without requiring CO removal. Furthermore, the bio-nature gas production was promoted by external CO and H injection. The volumetric methane production rate (VMPR) was significantly increased by 739% from 117.4 mL L·d to 985 mL⋅L⋅d, which is higher than in other studies. Meanwhile, the volumetric biogas production rate (VBPR) was increased by 36.9% by H injection, increasing the conversion efficiency (82.56%) of the chemical oxygen demand (COD) to CH. A significant increase in the specific methanogenic activity of dissolved hydrogen (SMA(H)) and the enrichment in hydrogenotrophic methanogens (Methanobacterium) demonstrate that the CH production pathway was converted from acetoclastic methanogenesis (AM) pathway to hydrogenotrophic methanogenesis (HM) pathway. It is postulated that the change in proportion of different pathways of the CH production was caused by the strengthening of key enzymes (coenzyme F hydrogenase and coenzyme-B sulfoethylthiotransferase) by H injection. The integrated system represents a promising approach to achieve simultaneous CO emission reduction and bio-natural gas production.