School of Environmental and Safety Engineering, Changzhou University, Changzhou 213000, PR China.
School of Environmental and Safety Engineering, Changzhou University, Changzhou 213000, PR China; Key Laboratory of Environmental and Applied Microbiology, Environmental Microbiology Key Laboratory of Sichuan Province; Chengdu Institute of Biology, Chinese Academy of Sciences. Chengdu, 610041, PR China; University of Chinese Academy of Sciences, Beijing 100864, PR China.
Waste Manag. 2021 Jun 1;128:25-35. doi: 10.1016/j.wasman.2021.04.015. Epub 2021 May 3.
Ammonium accumulation is inevitable during the fermentation of food waste (FW), challenging the application of chain elongation process upgrading FW into the high-value biochemical n-caproate, which is a medium chain carboxylate. This study is the first to investigate ammonium inhibition of lactate-driven chain elongation process. The short-term exposure of a Clostridium IV-dominated chain elongating reactor microbiome at an ammonium concentration of 1-4 g L linearly decreased n-caproate production by 25-80%. High levels of ammonium (≥5 g L) could cause failure of chain elongation, shifting the product from n-caproate to propionate. The involved mechanisms revealed that ammonium reshaped the microbial community from Clostridium IV domination to Clostridium IV and Propionibacterium co-domination (based on 16S rRNA sequencing) and reduced the activities of key enzymes involved in the reversed β-oxidization pathway. We propose an effective strategy from our study, which is the first one to do in our knowledge, to upgrade raw FW without dilution to n-caproate: lowering the ammonium accumulation to 1.0 g L at the setup phase for adaptation and prolonging the hydraulic retention time (10 days) during the operation phase for the colonization of chain-elongation bacteria. These findings lay a foundation for the implementation of the LCE process on FW, providing an alternative way to alleviate the global FW crisis.
在食品废物（FW）发酵过程中，氨的积累是不可避免的，这给将链式延伸工艺升级 FW 为高价值的生化正己酸（一种中链羧酸）的应用带来了挑战。本研究首次考察了氨对乳酸驱动的链式延伸过程的抑制作用。在 1-4 g/L 的氨浓度下，短期暴露于以梭菌 IV 为主导的链式延伸反应器微生物组，正己酸的产量线性下降了 25-80%。高浓度的氨（≥5 g/L）可能导致链式延伸失败，产物从正己酸转变为丙酸。所涉及的机制表明，氨重塑了微生物群落，从梭菌 IV 主导转变为梭菌 IV 和丙酸杆菌共同主导（基于 16S rRNA 测序），并降低了参与反向β-氧化途径的关键酶的活性。我们提出了一种有效的策略，这是我们所知的第一个从升级原始 FW 而无需稀释到正己酸的策略：在启动阶段将氨积累降低到 1.0 g/L 以适应环境，并在操作阶段延长水力停留时间（10 天）以使链式延伸细菌定植。这些发现为在 FW 上实施 LCE 工艺奠定了基础，为缓解全球 FW 危机提供了一种替代方法。
