Biogas can be upgraded to methane biologically by adding H2 to biogas reactors. The process is called biological methanation (BM) and can be done in situ in a regular biogas reactor or the biogas can be transferred to a separate ex situ upgrading reactor. The hybrid BM concept, a combination of in situ and ex situ BM, has received little attention, and only a few studies have been reported. The hybrid BM has the advantage of resolving the issue of pH increment during in situ BM, while the size of the ex situ BM reactor could be reduced. In this study, the efficiency of in situ and hybrid biological methanation (BM) for upgrading raw biogas was investigated. The hybrid BM system achieved a CH4 yield of 257 mL gVS−1 when degrading a feedstock blend of manure and cheese waste. This represented an increase in methane yield of 76% when compared to the control reactor with no H2 addition. A 2:1 H2:CO2 ratio resulted in stable reactor performance, while a 4:1 ratio resulted in a high accumulation of volatile fatty acids. H2 consumption rate was improved when a low manure–cheese waste ratio (90%:10%) was applied. Furthermore, feeding less frequently (every 48 h) resulted in a higher CH4 production from CO2 and H2. Methanothermobacter was found to dominate the archaeal community in the in situ BM reactor, and its relative abundance increased over the experimental time. Methanosarcina abundance was negatively affected by H2 addition and was nearly non-existent at the end of the experiment. Our results show that hybrid BM outperforms in situ BM in terms of total CH4 production and content of CH4 in the biogas. In comparison to in situ BM, the use of hybrid BM increased CH4 yield by up to 42%. Furthermore, addition of H2 at 2:1 H2:CO2 ratio in in situ BM resulted in stable reactor operation.

中文翻译：

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原位和混合反应器系统生物甲烷化过程中操作条件对甲烷产量和微生物群落组成的影响


通过向沼气反应器添加氢气，沼气可以通过生物方式升级为甲烷。该过程称为生物甲烷化（BM），可以在常规沼气反应器中原位进行，也可以将沼气转移到单独的异位升级反应器中。混合BM概念，即原位BM和异位BM的结合，很少受到关注，并且只有少数研究被报道。混合BM的优点是解决了原位BM过程中pH值升高的问题，同时可以减小异位BM反应器的尺寸。在本研究中，研究了原位和混合生物甲烷化（BM）对原料沼气进行升级的效率。混合 BM 系统在降解粪便和奶酪废物的原料混合物时，CH4 产量达到 257 mL gVS−1。与未添加氢气的对照反应器相比，这表明甲烷产率增加了 76%。 2:1 H2:CO2 比例可实现稳定的反应器性能，而 4:1 比例则导致挥发性脂肪酸大量积累。当采用较低的粪便-奶酪废物比例（90%:10%）时，氢气消耗率得到提高。此外，饲喂频率较低（每 48 小时一次）会导致 CO2 和 H2 产生更高的 CH4 产量。研究发现，甲烷嗜热杆菌在原位 BM 反应器中的古菌群落中占主导地位，并且其相对丰度随着实验时间的推移而增加。甲烷八叠球菌丰度受到 H2 添加的负面影响，在实验结束时几乎不存在。我们的结果表明，混合沼气在甲烷总产量和沼气中甲烷含量方面优于原位沼气。与原位 BM 相比，混合 BM 的使用使 CH4 产量提高了 42%。 此外，在原位 BM 中以 2:1 H2:CO2 比例添加 H2 可使反应器稳定运行。