The inoculum to substrate (I:S) ratio is a crucial operating parameter during the start-up period of anaerobic digestion (AD) processes and this ratio shows high differentiation with respect to substrate composition. While spent coffee grounds (SCG) have started to gain attraction in AD as a co-substrate due to their vast production and promising methane potential, there is still not enough information on the operative environment of SCG-based biogas reactors. This study investigated the optimal I:S ratio during anaerobic co-digestion of SCG and cow manure. Biochemical methane potential tests were conducted at mesophilic conditions and the influence of I:S ratio on methane production and digestion stability was evaluated at a wide range of I:S ratios from 0.5:1 to 4:1 (volatile solids (VS) basis). Methane yields increased gradually starting from the I:S ratio of 0.5:1 up to 3:1 and the highest methane yield (225 mlCH4 gVS-1) was achieved at the I:S ratio of 3:1. Comparatively lower methane yields were obtained at the ratios of 3.5:1 and 4:1. Instable AD conditions were established at the lowest I:S ratio examined (0.5:1), which caused volatile fatty acid (VFA) accumulation. The results highlighted that anaerobic co-digestion of SCG and cow manure is a promising approach, while the I:S ratio should be well-maintained due to the high potential risk of rapid and/or excess VFA production of these feedstocks.

中文翻译：

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在对废咖啡渣和牛粪进行厌氧共消化期间，寻找最佳接种物与底物的比例。

接种物与底物（I：S）的比例是厌氧消化（AD）过程启动期间的关键操作参数，相对于底物组成，该比例显示出很高的差异性。尽管废咖啡渣（SCG）由于其大量生产和有希望的甲烷潜力而开始在AD中作为共同的底物获得吸引力，但有关基于SCG的沼气反应器的运行环境的信息仍然不足。本研究调查了SCG和牛粪厌氧消化过程中的最佳I：S比。在中温条件下进行了生化甲烷潜力测试，并在0.5：1至4：1的宽范围的I：S比率（基于挥发性固体（VS）的基础上）评估了I：S比对甲烷产生和消化稳定性的影响。 。甲烷的产率从I：S的0.5：1逐渐增加到3：1，并且在I：S的3：1时达到了最高的甲烷产率（225 mlCH4 gVS-1）。在3.5：1和4：1的比例下，甲烷的产率相对较低。在最低的I：S比（0.5：1）下建立了不稳定的AD条件，这导致挥发性脂肪酸（VFA）积累。结果强调，厌氧消化SCG和牛粪肥是一种有前途的方法，而I：S比应保持良好，因为这些原料快速和/或过量VFA的生产具有很高的潜在风险。在最低的I：S比（0.5：1）下建立了不稳定的AD条件，这导致挥发性脂肪酸（VFA）积累。结果强调，厌氧消化SCG和牛粪肥是一种有前途的方法，而I：S比应保持良好，因为这些原料快速和/或过量VFA的生产具有很高的潜在风险。在最低的I：S比（0.5：1）下建立了不稳定的AD条件，这导致挥发性脂肪酸（VFA）积累。结果强调，厌氧消化SCG和牛粪肥是一种有前途的方法，而I：S比应保持良好，因为这些原料快速和/或过量VFA的生产具有很高的潜在风险。