低流速條件下牡蠣殼生物膜的生成與剝離研究

Abstract

礫間接觸是一種利用微生物代謝作用以進行現地的污水處理方法，具有低成本並高效率的優點。藉由提供微生物附著表面，使附著之微生物於介質表面進行污染物吸收與生物降解作用。前人研究指出，牡蠣殼可應用於礫間接觸處理基質，且具有高處理效率；而另一面，牡蠣殼也是沿海養殖漁業的廢棄物，因此不論就環境或經濟考量，皆有利用其材料的價值。本研究嘗試以牡蠣殼為介質，探討其上之生物膜生成與生長環境之流體動力條件之關係，以供進一步應用於牡蠣殼礫間接觸場的操作。 本研究的第一部份旨在探討牡蠣殼上生物膜在不同流體動力條件底下的生成特徵，包括初始附著階段、發展階段、生物膜剝離、生物膜崩落、和再生階段。因此我們進行了為期約三個月的長時間實驗，設定流速範圍為0 到0.13m/ s之間，並以平均生長厚度作為生物膜生長的指標進行分析。結果發現，合理的增加流速有助於生物膜臨界平均厚度的增加，但也因此導致了剝離機率的增加而需較長的發展期。在本研究中，牡蠣殼生物膜的最大臨界平均厚度約900μm，並且至少皆會維持89 到140μm的基礎平均厚度。至於崩落時間也隨流速條件有明顯差異。在無流速環境下，牡蠣殼生物膜在第23 天發生崩落，而在低流速條件下則是分別在第52 和55 天發生。 本研究的第二部份主要專注於牡蠣殼生物膜的剝離現象。我們利用所推導的一個較為簡單的模式分析牡蠣殼生物膜的面積剝離率，以及雷諾數對其的影響力。同時，我們也提出了一種光學方法作為測量生物膜平均密度的非破壞性方法，且利用其於連續培養的生物反應器的測量。 總結來說，我們發現在低流速條件下，環境流速對牡蠣殼生物膜的剝落(erosion)影響為正相關，對生物膜崩落(sloughing)成負相關，其中該生物膜主要由格蘭氏陽性菌所組成，包括芽孢桿菌屬(Bacillus sp.)、短芽孢桿菌屬(Brevibacillus sp.)、和微小桿菌屬(Exiguobacterium sp.)。研究並求得一些低流速環境下牡蠣殼生物膜的生成參數作為未來現地處理的設計與操作參考參數。

atment efficiency, in order to understand the relationships between fluid velocities and biofilm formation and detachment, and applicate them into the operation of oyster shells’ contacted beds. In the first part of this study, we observed biofilm formation in a long period (about 3 months), in order to discuss biofilm formation processes including initial cultivation, development, detachment, collapse, and re-growth durning different fluid dynamics. We set fluid velocities from 0 to 0.13 m/ s , and took biofilm mean thickness as the growth index in results analysis. Mainly, we found out that a reasonable increasing of fluid velocity is benefit to critical mean biofilm thickness but also lead to a longer development period because of higher detachment frequency. The maximum critical mean thickness of oyster shells’ biofilm is about 900 μm in our results, and there will remain a basic mean thickness from 89 to 140 μm . The sloughing time is also significantly different in free velocity environment and velocity environment. In a free velocity environment, oyster shells’ biofilm occurred sloughing at day 23, on the other hand, it occurred at day 52 and 55 in slow velocities environment. In the second part of this study we focused on the detachment process of oyster shells’ biofilm. We derived a relatively simple model to analyse the areal detachment rate of oyster shells’ biofilm and discussed the influence of Reynolds number on it. Moreover, we also proposed an optical method to measure biofilm mean density in a non-destructed way and utilized it in the measurement of a continuously cultivated biofilm reactor. Conclusively, we found that fluid velocities are possitive correlation to erosion but negative corelation to sloughing in low velocity flow ( < 0.13 m/ s ), and obtained some reference parameters of oyster shells’ biofilm which is mainly composed of gram-positive bacteria including Bacillus sp., Brevibacillus sp., and Exiguobacterium sp. in the flow condition in order to be a reference of in-situ operation and future design.