School of Chemical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
J Biotechnol. 2012 May 31;159(1-2):38-43. doi: 10.1016/j.jbiotec.2012.02.001. Epub 2012 Feb 14.
Fermentation of waste activated sludge produces volatile fatty acids (VFAs), which can be used as the carbon sources for numerous biological processes. However, product inhibition can limit extent of fermentation to VFAs. In this study, product inhibition during fermentation of waste activated sludge pre-treated by a thermal hydrolysis process (THP-WAS) was investigated. Product inhibition was confirmed as spiking reactors with high levels of a mix of VFAs prevented fermentation taking place. Various inhibition models were trialled and it was found that a threshold model (based on thermodynamics) provided the best fit between model and data. This is the first time that threshold type inhibition has been shown for a mixed substrate, mixed population system. Batch fermentations carried out with THP-WAS of different dilutions were used to evaluate the impact of different organic loadings. The threshold VFA concentration for the systems studied was determined to be 17±1gCOD(VFA)L(-1). Inhibition was shown to be due to the presence of a combination of VFAs containing 2-6 carbon atoms each. When evaluated individually, by spiking individual VFAs, all VFAs except for acetate had the same impact at this threshold; acetate being approximately 50% as inhibitory as the other organic acids (COD basis). Based on this, a weighted model could be proposed to better represent the data. Strategies to improve overall yield could be increased production of acetate, or dilution to below the inhibitory level.
发酵废活性污泥产生挥发性脂肪酸 (VFAs)，可作为多种生物过程的碳源。然而，产物抑制可能会限制发酵到 VFAs 的程度。本研究考察了经热水解预处理的废活性污泥 (THP-WAS) 发酵过程中的产物抑制。向反应器中投加高浓度的混合 VFAs 会阻止发酵进行，从而证实了产物抑制。尝试了各种抑制模型，发现基于热力学的阈值模型最能拟合模型和数据。这是首次在混合底物、混合种群系统中显示出阈值类型抑制。用不同稀释度的 THP-WAS 进行分批发酵，评估不同有机负荷的影响。确定所研究系统的阈值 VFA 浓度为 17±1gCOD(VFA)L(-1)。抑制是由于含有 2-6 个碳原子的各种 VFA 的组合存在所致。当单独评估时，通过投加单个 VFA，在这个阈值下，除了乙酸盐之外的所有 VFA 都具有相同的影响；乙酸盐的抑制作用约为其他有机酸的 50%（以 COD 为基础）。基于此，可以提出加权模型来更好地表示数据。提高整体产率的策略可以是增加乙酸盐的产量，或者稀释到低于抑制水平。
