In-situ biological CO₂ methanation (BM) in a biogas reactor by the addition of H₂ is an attractive low-cost biogas upgrading process, as it does not require investment in a new reactor and can be incorporated into existing biogas plants. On the other hand, maintenance of stable reactor performance during in-situ BM is challenging due to factors such as high H₂ partial pressure and CO₂ depletion which may lead to an increase in pH. Thus, BM that uses two-serial connected continuous stirred tank reactors (CSTRs) could be an option. For such a process set-up, the second reactor acts as an upgrading reactor (UR) and a secondary CH₄ producer for slow-degrading substrates such as straw and manure. In this study, improvement of the BM process was attempted by varying the mixing speed and gas recirculation to enhance hydrogen transfer to the liquid phase of the UR. The experiments showed that the mixing speed and gas recirculation had a significant effect on BM in CSTRs. CH₄ production from BM was highest at 170 rpm, but the total CH₄ production fell above 140 rpm due to reduced production of CH₄ from the manure substrate. The CH₄ production rate from CO₂ and H₂ conversion was further enhanced as the output gas was recirculated at 12.20 mL min⁻¹. Further gas recirculation above 12.20 mL min⁻¹ did not improve BM.

通过添加H ₂在沼气反应器中进行原位生物CO ₂甲烷化（BM）是一种有吸引力的低成本沼气升级工艺，因为它不需要投资购买新的反应器，并且可以合并到现有的沼气厂中。另一方面，由于诸如H ₂分压高和CO ₂耗尽等因素可能导致pH升高，因此在原位BM期间维持稳定的反应器性能是有挑战性的。因此，使用双串联连续搅拌釜反应器（CSTR）的BM是一种选择。对于这样的过程设置，第二个反应器充当升级反应器（UR）和第二个CH ₄缓慢降解的基质（例如稻草和肥料）的生产商。在这项研究中，尝试通过改变混合速度和气体再循环以增强氢向UR液相的转移来改善BM工艺。实验表明，混合速度和气体再循环对CSTR中的BM具有显着影响。BM的CH ₄产量最高，为170 rpm，但总的CH ₄产量下降至140 rpm以上，这是由于粪便基质中CH _4的产量减少。随着输出气体以12.20 mL min ^-1再循环，来自CO ₂和H ₂转化的CH ₄生产率进一步提高。。高于12.20 mL min ^-1的进一步气体再循环并不能改善BM。