Batstone D J, Pind P F, Angelidaki I
Department of Biotechnology, Lund University, Lund, Sweden.
Biotechnol Bioeng. 2003 Oct 20;84(2):195-204. doi: 10.1002/bit.10753.
The degradation kinetics of normal and branched chain butyrate and valerate are important in protein-fed anaerobic systems, as a number of amino acids degrade to these organic acids. Including activated and primary wastewater sludge digesters, the majority of full-scale systems digest feeds with a significant or major fraction of COD as protein. This study assesses the validity of using a common kinetic parameter set and biological catalyst to represent butyrate, n-valerate, and i-valerate degradation in dynamic models. The i-valerate degradation stoichiometry in a continuous, mixed population system is also addressed, extending previous pure-culture and batch studies. A previously published mathematical model was modified to allow competitive uptake of i-valerate, and used to model a thermophilic manure digester operated over 180 days. The digester was periodically pulsed with straight and branched chain butyrate and valerate. Parameters were separately optimized to describe butyrate, i-valerate, and n-valerate degradation, as well as a lumped set optimized for all three substrates, and nonlinear, correlated parameter spaces estimated using an F distribution in the objective function (J). Each parameter set occupied mutually exclusive parameter spaces, indicating that all were statistically different from each other. However, qualitatively, the influence on model outputs was similar, and the lumped set would be reasonable for mixed acid digestion. The main characteristic not represented by Monod kinetics was a delay in i-valerate uptake, and was compensated for by a decreased maximum uptake rate (k(m)). Therefore, the kinetics need modification if fed predominantly i-valerate. Butyrate (i- and n-) and n-valerate could be modeled using stoichiometry consistent with beta-oxidation degradation pathways. However, i-valerate produced acetate only, supporting the stoichiometry of a reaction determined by other researchers in pure culture. Therefore, lumping i-valerate stoichiometry with that of n-valerate will not allow good system representation, especially when the feed consists of proteins high in leucine (which produces i-valerate), and the modified model structure and stoichiometry as proposed here should be used. This requires no additional kinetic parameters and one additional dynamic concentration state variable (i-valerate) in addition to the variables in the base model.
在以蛋白质为食的厌氧系统中，正丁酸和戊酸以及支链丁酸和戊酸的降解动力学非常重要，因为许多氨基酸会降解为这些有机酸。包括活性污泥和初级废水污泥消化池在内，大多数全规模系统处理的进料中，化学需氧量（COD）的很大一部分或主要部分是蛋白质。本研究评估了在动态模型中使用一组通用动力学参数和生物催化剂来表示丁酸、正戊酸和异戊酸降解的有效性。还探讨了连续混合菌群系统中异戊酸的降解化学计量，扩展了先前的纯培养和批次研究。对先前发表的数学模型进行了修改，以允许对异戊酸进行竞争性摄取，并用于对运行180天的嗜热粪便消化池进行建模。该消化池定期脉冲注入直链和支链丁酸和戊酸。分别优化参数以描述丁酸、异戊酸和正戊酸的降解，以及针对所有三种底物优化的一组总参数，并使用目标函数（J）中的F分布估计非线性相关参数空间。每个参数集占据相互排斥的参数空间，表明它们在统计上彼此不同。然而，从定性角度来看，对模型输出的影响是相似的，并且该总参数集对于混合酸消化是合理的。莫诺德动力学未体现的主要特征是异戊酸摄取存在延迟，并通过降低最大摄取速率（k(m)）来补偿。因此，如果主要投喂异戊酸，则动力学需要修改。丁酸（异丁酸和正丁酸）和正戊酸可以使用与β-氧化降解途径一致的化学计量进行建模。然而，异戊酸仅产生乙酸，这支持了其他研究人员在纯培养中确定的反应化学计量。因此，将异戊酸化学计量与正戊酸化学计量合并将无法很好地表示系统，特别是当进料中含有高亮氨酸（产生异戊酸）的蛋白质时，应使用此处提出的修改后的模型结构和化学计量。这除了基础模型中的变量外，不需要额外的动力学参数和一个额外的动态浓度状态变量（异戊酸）。
