TE supplementing Grass silage Anaerobic Digestion (TE-GAD)

Wall et al. (2014) attempted to determine the optimal mix of silage/slurry in biomethane based AD. Trials showed that although BioMethane Potential (BMP) was highest in 100% silage tests, generation of biomethane was more stable with a 20% inclusion of dairy slurry (by VS%). At higher loading rates BM output in 100% silage (R-G) and 80%silage:20% slurry (R-SG) reached parity, possibly an effect of incomplete degradation of solids within the retention time, but may also be imformed by the microbial community created by increased rate of feedstock addition.Another trend documented both in the original study and more broadly is the decline in reactor stability with increased organic loading rate (OLR), as measured by the FOSTAC ratio (effectively the reactor's buffering capability and frequently an indicator for process stability). Increases in OLR from 2.5 to 3 kgVS/m3/d led to rapid accumulation of VFAs (AcO, PrO) in R-G, while no issue was observed over the course of R-SG operation. Due to the constant turnover of organic material and active biology of the reactor community, issues with reactor operation are frequently linked to limiting concentrations of trace elements such as Fe, Co, Ni, etc.. However it is not externally apparent which portions of the community are restricted by the lack of trace elements (TE) - this study aims to characterise the communities stressed by Wall et al., 2014, and determine which populations relate to bottlenecking of (TE).The two reactors characterised in this study (R-G,R- SG) were sampled over 68 and 65 weeks respectively after being seeded from the same sludge inoculum, fed 100% silage and 80:20% silage:slurry, and operated along the same design principles. R-G was sampled at week 1, 20, 37, 40, 43, 49, 54, 64, 65, 68. R-GS was sampled at week 01, 20, 37 and 65 to act as a positive control for R-G.

Wall等人（2014）旨在确定基于生物甲烷的厌氧消化（Anaerobic Digestion, AD）中青贮料与粪浆的最优配比。试验结果显示，尽管100%青贮料组的生物甲烷潜能（Biomethane Potential, BMP）最高，但当以挥发性固体百分比（Volatile Solids percentage, VS%）计添加20%乳牛粪浆时，生物甲烷的生成稳定性更佳。在更高负荷速率下，100%青贮料组（R-G）与80%青贮料:20%粪浆组（R-SG）的生物甲烷产量趋于持平，这一现象可能源于停留时间内固体未完全降解，亦可能受原料添加速率提升所形成的微生物群落影响。
在原始研究及更广泛的研究中均观测到另一趋势：以FOSTAC比值（可反映反应器缓冲能力，常作为工艺稳定性的表征指标）衡量时，反应器稳定性随有机负荷率（Organic Loading Rate, OLR）升高而下降。当OLR从2.5提升至3 kgVS/m³/d时，R-G组内的挥发性脂肪酸（Volatile Fatty Acids, VFAs，包括乙酸AcO与丙酸PrO）快速积累，而R-SG组运行全程未出现此类问题。
由于反应器内有机物质持续更新且微生物群落活性旺盛，反应器运行故障常与铁、钴、镍等微量元素的浓度限制相关。但目前尚无法明确微生物群落中哪些类群受微量元素缺乏的限制——本研究旨在表征Wall等人（2014）研究中受胁迫的微生物群落，并明确哪些类群与微量元素限制瓶颈相关。
本研究表征的两座反应器（R-G、R-SG）均源自同一污泥接种物，分别以100%青贮料和80:20的青贮料:粪浆为进料，且遵循相同的设计原则运行，采样周期分别为68周和65周。R-G组的采样时间为第1、20、37、40、43、49、54、64、65、68周；R-SG组的采样时间为第1、20、37和65周，作为R-G组的阳性对照。