對-甲苯對於以硫酸還原菌降解菲之影響

Abstract

菲（phenanthrene, PHE）為多環芳香烴物質（polycyclic aromatic hydrocarbons, PAHs）之化合物，為環境中具頑抗性及毒性之分難解物質。已知可利用硫酸還原菌（sulfate-reducing bacteria, SRB）做為優勢菌種降解菲；然而在我們的研究中發現到之前研究未曾測出的對-甲苯（p-cresol）為其代謝產物，並且當兩化合物同時存在時，對-甲苯對於菲的降解有著些許抑制性的影響。 本實驗的操作參數依照之前研究中所找出之最佳條件，改變菲及對-甲苯的濃度以不同比例混合進行批次式之實驗。實驗規劃分為兩部分，第一部分固定菲的濃度在18.5 mg/L，而對-甲苯的濃度由0增加到11.1 mg/L；第二部分依序降低菲的濃度從18.5至0 mg/L，而對-甲苯的濃度一樣由0增加到11.1 mg/L。藉由實驗結果探討對-甲苯對於菲之降解是否有其影響。 實驗結果顯示，在無對-甲苯的影響下菲的零階和一階動力反應k值分別為0.35 mg/L･d及0.03/d；隨著對-甲苯的濃度增加降至最低的0.1 mg/L･d及0.016/d，顯示會逐漸抑制菲的降解效率。而對-甲苯本身的降解情形並未明顯地受到菲的影響，初始濃度越高的對-甲苯其降解濃度值也越多。不論如何，對-甲苯相對於菲的分子量及毒性較低，在此次實驗中是較優先利於SRB分解之化合物。

Phenanthrene (PHE) is one of the persistent polycyclic aromatic hydrocarbons (PAHs), which could produce toxicity for the environment. It is well known that PHE could be degraded by sulfate-reducing bacteria (SRB). Nevertheless, it is reported that p-cresol is the metabolite of PHE. When these two compounds exist in the environment at the same time, i.e. PHE and p-cresol, p-cresol is likely to have inhibition in the biodegradation of PHE. The batch biodegradation experimental conditions were followed from the optical parameters by our previous study (Ref.). The experimental design was separated into two parts: in Part-1, the PHE concentration was kept constant at 18.5 mg/L whereas the p-cresol concentration was increased from 0 to 11.1 mg/L; in Part-2, the PHE concentration was decreased from 18.5 to 0 mg/L, and at the same time p-cresol concentration was increased from 0 to 11.1 mg/L. The experimental outcomes indicate that the k values of PHE degradation without p-cresol following the zero-order and first-order kinetics were 0.35 mg/L･d and 0.03/d. In the presence of p-cresol, the k-values were decreased to 0.1 mg/L･d and 0.016/d. These observations demonstrate that p-cresol addition has significant inhibition in the biodegradation of PHE. However, the p-cresol degradation is not significantly affected by PHE. The degradation of p-cresol was increased with the increase in the addition of p-cresol concentration. The molecular weight and toxicity of p-cresol are lower than PHE; thus, p-cresol is preferred over PHE by the SRB.