解析生物程序之氧化還原電位—以線性不可逆熱力學為基礎

Abstract

解析生物程序之氧化還原電位—以線性不可逆熱力學為基礎 研 究 生:鄭宏邦 指導教授: 林志高 博士

國立交通大學環境工程研究所 摘要 即時監測生物程序的氧化還原電位變化，能獲取與生化反應相關的訊息。而這些訊息的意義，常透過涅斯特方程式來加以解讀。然而此方程式的推導主要基於古典熱力學的平衡假設，因此只能被用來解釋生物程序的結果，卻難以有效解釋程序的動態過程。為有效解決這個問題，本研究以線性非平衡熱力學作為理論基礎，推導出符合生物程序狀態的氧化還原電位模式，此模式被命名為微生物氧化還原電位模式一號。除此之外，微生物氧化還原電位模式一號也被用來模擬許多已發表的文獻數據。根據許多統計方法的驗證後，結果顯示微生物氧化還原電位模式一號能有效模擬生物硝化與脫硝反應過程的氧化還原電位，且與修正後的涅斯特方程式相比，更能反映真實的生物程序狀態。 利用微生物氧化還原電位模式一號模擬生物脫硝反應後，產生許多的模式參數，其中電極反應與生物異化反應的耦合參數與反應過程中所傳遞的電子數有關。微生物氧化還原電位模式一號的參數較修正後的涅斯特方程式來的多，因此利用微生物氧化還原電位模式一號模擬氧化還原電位時，較容易得到良好的擬合結果，然而調整比較的基礎並透過統計的檢定分析後發現，微生物氧化還原電位模式一號的模擬效果仍優於修正後的涅斯特方程式。 除了發現微生物氧化還原電位模式一號可有效描述生物程式的氧化還原電位變化之外，透過演繹過程也預測出許多過去未被發現的微生物生化反應規律。第一個規律是”當某生化反應的基質為該反應的限制因素時，此基質的降解速率與氧化還原電位成正比”，雖然已有學者觀察到生物脫硝反應符合這樣的規律，然而該學者並不知道這樣的規律，理論上適用於所有的生物程序。此外，經由微生物氧化還原電位模式一號模式也可預測出在微生物的生化過程中，氧化還原電位不僅像涅斯特方程式所描述的只與反應物有對數關係，當反應物濃度持續消耗，直到該反應物成為生化反應的限制因子時，氧化還原電位與反應物濃度的關係，將呈現為線性化。 以微生物氧化還原電位模式一號的研究成果為基礎，可延伸出兩項新的技術突破，包括(1)在反應基質為生長限制因子的前提下，可利用氧化還原電位作為監測反應速率的工具。雖然目前已有許多的工具可即時且間接的監測微生物的基質代謝速率，然而這些工具都不如氧化還原監測儀來的普遍且容易使用。(2) 本研究發現氧化還原電位與微生物生長基質濃度變化具有兩階段不同的關聯性，而這兩階段分別為當生長基質濃度並非限制因子時與生長基質濃度成為限制因子時。因此當生長基質濃度變化在此兩階段進行轉換時，氧化還原電位曲線的變化斜率也隨改變，並且對應到許多文獻已發現的氧化還原曲線折點。已有許多文獻表示，在硝化與脫硝程序中，氧化還原電位曲線的折點變化對應到生物硝化與脫硝反應的終點，也因此氧化還原電位常被用來作為生物硝化與脫硝程序自動化控制的基礎。然而氧化還原電位曲線的折點常受到監測條件所影響，雖然目前已有許多文獻指出造成折點消失的情況，然而還未有明確的理論依據可統一解釋所有的情況。基於上述的理由，本研究的理論推導可作為解釋折點特性的理論依據，使得以氧化還原電位折點作為生物程序自動化基礎的技術能有所突破。

關鍵字: 涅斯特方程式、微生物氧化還原電位模式一號、氧化還原電位、生物硝化反應、生物脫硝反應。

Interpretation of redox potential variations during biological processes using linear non-equilibrium thermodynamic model

Student:Hong-Bang Cheng Advisor: Jih-Gaw Lin Institute of Environmental Engineering National Chiao Tung University

ABSTRACT Various forms of Nernst equation have been dceveloped using simplified assumptions and/or modifications to depict the process of reversible and irreversible thermodynamic reactions in terms of the oxidation reduction potential (ORP). However, these assumptions are sometimes inappropriate in the quantification of ORP for non-equilibrium systems. A linear non-equilibrium thermodynamic model, called MIRROR model No. 1 (MIcrobial Related Reduction and Oxidation Reaction Model No. 1), is proposed in this research for interpreting ORP of biological processes. In the proposed model, ORP is related to affinities of catabolism and anabolism, and the energy expenditure of catabolism and anabolism is directly proportional to overpotential (η), straight coefficient of electrode (LEE), and degree of coupling between catabolism and ORP electrode. In addition, modeling the ORP of the biological nitrification and denitrification processes is addressed using MIRROR model No. 1. Laboratory data based on temperature, dissolved oxygen, COD, amonium, nitrite, nitrate, pH and ORP, were excerpted from literature and used for calibrating the model to determine the optimal values of various stoichiometric, kinetic, and phenomenological model parameters. The calibrated model was used to simulate the ORP variation of a biological nitrification and denitrifcation processes. The simulation results are in good correlation with the experimental observations (R2>0.93). Additionally, the performance of MIRROR model No.1 was compared with a commonly used modified-Nernst equation for simulating the biological nitrification and denitrification processes. MIRROR model No.1 has superior efficiency based on statistical analyses on deviance (i.e. root mean square error and mean absolute error), residual analyses and model discrimination. Overall, MIRROR model No. 1 appears to be an effective alternative to several modified-Nernst equations for simulating the ORP of biological processes. The limitations of MIRROR Model No. 1 have also been discussed for expanding the applicability of this model. When the final ORP value of biological denitrification processes is between -80 to -160 mV, the deviance of simulation results using the model is within a narrow range. If the final ORP is lower than -160 mV, the deviance increases sharply. The occurrence of some other non-nitrogen biological processes such as biological sulfate reduction may affect the ORP measurement so that the deviance increases sharply when the final ORP decreases. There is a close relationship between the affinities of catabolism and the system ORP of the biological denitrification process, but the ORP variation per unit affinity of catabolism is not a constant but proportional to the molarity of electrons transferred catabolically. The linear relationship between redox potential and reaction rate that has been derived based on MIRROR model No.1 in this research is verified by using the experimental results reported in the literature. This linear relationship enables evaluation of the biological denitrification rate based on the real-time monitoring of the system ORP. In addition, MIRROR model No. 1 predicts a distinctive curvilinear dependence of redox potential on the utilization of a selected substrate in microbial processes. With the substrate is excess, the system ORP is a logarithmic function of the substrate concentration. When the substrate in question becomes limited, the system ORP is observed to be linearly proportional to the substrate concentration.

Keywords: Nernst equation, MIRROR model No. 1, redox potential, biologcial nitrification and biological denitrification.