碩士 / 逢甲大學 / 化學工程研究所 / 85 / Mercury-resistant bacteria usually harbor mercury-resistant
genes called mer operon, which is often incorporated into
plasmids and transposons. The merB gene of mer operon encodes
for organomercurial lyase, which degrades organomercurial
compounds to form Hg2+. The merA product mercuric reductase
catalyzes the reduction of Hg2+ to Hgo, which is very volatile
and easily diffuses out of microbial cells. This research
utilized the mechanism of enzymatic mercury reduction to develop
batch, fed-batch, and continuous bioreactors able to detoxify
soluble mercuric ions from wastewater. The mercury-resistant
strain used in this study was Pseudomonas aeruginosa PU21, which
harbors a mer-operon-containing plasmid Rip64. The strain can
tolerate mercury concentrations up to 150 mg/L in LB broth, and
up to 20 mg/L in Pseudomonas minimal medium (PMM). Mercuric
ions readily interacted with components of LB to form complexes,
which were found to reduce the availability of mercury to the
microorganisms. As the mercury concentration was below 10 mg/L,
the complex formation between PMM and mercuric ions was
negligible. Therefore, this study used PMM as the microbial
growth medium for the mercury-detoxification experiments. An
increase in mercury concentration tended to extend the lag
periods of the cell growth, while addition of amino acid
complements not only enhanced specific growth rate and maximal
cell concentration, but also shortened the lag phase of cell
growth. In batch cultivation, the strain was able to rapidly
detoxify the mercury content (2-10 mg/L) in the medium within
less than 2 h. The optimal specific detoxification rate (RHg)
was 1.1 x 10-6 *g Hg/cell/h, which was achieved with the initial
mercury concentration of 8 mg/L. The RHg was significantly
affected by the growth phase of the cells with the order of lag
phase > exponential phase > stationary phase. In the fixed-
interval fed-batch (FIFB) operations, mercury solutions
containing 3 or 5 mg Hg/L were fed sequentially (every 1 or 1.5
h) into the cell culture. The results showed that the average
mercury detoxification efficiency was 2.9 and 3.3 mg/h/L for the
fixed-interval feeding of 3 and 5 mg Hg/L, respectively. In
continuously fixed-rate fed-batch (CFRFB) operations, optimal
feeding rate was found to be 140 ml/hr, which was utilized for
the fed-batch operation with initial culture volumn of 400 and
1200 ml. The results showed that the average mercury
detoxification efficiency was raised to 5.26 and 5.6 mg/h/L,
respectively, in contrast to about 2.9-3.3 mg/L/h for FIFB
operations. The CFRFB operation was repeatedly operated for 2-3
cycles (about 40hr), during which the mercury detoxification
efficiency was able to maintain at the original level. In
continuous chemostat operations, as the dilution rate (D) was
0.18 h-1, and the mercury concentration in the feeding stream
([Hg]f) was 1-6.15 mg/L, the cells appeared to efficiently
detoxify mercury from the culture, and the resulting effluent
mercury concentration ([Hg]e) was lower than 5 ppb (EPA*s
requirement). The mercury detoxification efficiency obtained
from the operation was about 0.64 mg/h/L. As D was raised to
0.325 h-1, the [Hg]e could satisfy EPA*s requirement only when
[Hg]f was less than 2 mg/L. However, [Hg]e became 0.18 mg/L when
[Hg]f was increased to 6.15 mg/L. This operation led to a
mercury detoxification efficiency of 1.94 mg/h/L. The mercury
recovery process connected to the gaseous effluent of the
bioreactor completely remove vapor mercury contentsresulted from
mercury detoxification processes. In the batch operation mode,
the acid-digestion columns can collect 80.6%, 82.2 %, 80.0 %,
and 88.3 % of total added mercury when initial mercury
concentrations were 2, 5, 8 and 10 mg/L, respectively. However,
the mercury concentration leaving down-stream activated-carbon
trap was negligible.
| Identifer | oai:union.ndltd.org:TW/085FCU00063001 |
| Date | January 1997 |
| Creators | Law, Weng-Shin, 羅文鑫 |
| Contributors | Chang Jo-Shu, 張嘉修 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 113 |
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