Analysis of Biofilm Formation and Detachment on Oyster Shells in Low Velocity Flow
Date Issued
2011
Date
2011
Author(s)
Wang, Hsing-Jui
Abstract
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.
Subjects
Oyster shell
Contacted bed
Biofilm formation
Biofilm detachment
Optical method
low velocity
Type
thesis
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