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Our previousestudies demonstrated that mercury-resistant strain
Pseudomonas aeruginosa PU21 (Rip64) is capable of effectively
adsorbing a variety of heavy metals including Hg, Pb, Cu, and
Cd. At pH 5, saturation biosorption capacity of biomass of P.
aeruginosa PU21 (Rip64) for Pb, Cu, and Cd was 520, 632, and 327
mmol/g dry cell, respectively. In order to evaluate the
feasibility of utilizing the biomass as a practical heavy-metal
biosorbent, it is of importance to further reveal the
biosorption behavior of the biomass under the multi-metal-
component environment, as often occurred in the industrial
effluents. This study started from batch-mode operations to
investigate the competitive biosorption and ion exchange
behaviors when two or three of Pb, Cu, and Cd ions were
simultaneously present. The research then switched to the
design of continuous biosorption processes, which applied
hollow-fiber membrane reactors for the regeneration of the
biomass, as well as for the recovery of the trapped metal ions.
The batch biosorption results showed that metal adsorption
capacity of the biomass decreased in the order of Cu > Pb > Cd.
Evidence also showed that the adsorption sites of Pb and Cd were
probably included in Cu biding sites, whereas Pb and Cd
adsorption sites may be partially overlapped. When Pb, Cu, and
Cd co-existed, the biomass exhibited the highest affinity to Pb,
while adsorption of Cd was the least favorable. The ability to
replace adsorbed metal ions from the cell surface was in the
order of Pb > Cu > Cd. It is thus not surprising to observe the
highest initial adsorption rate for Pb, followed by Cu, and then
Cd. The results obtained from continuous hollow fiber systems
showed that the removal efficiency was clearly Pb > Cu > Cd,
which appeared to be consistent with batch biosorption results.
In the hollow-fiber processes, the efficiency of Cu and Cd
removal can be appreciably enhanced with a multi-column
operation, and different adsorbed metal ions may be recovered
individually with appropriate operation strategies. This study
also made an attempt to modify traditional Langmuir isotherm to
describe the experimental data resulted from multi-component
adsorption. It is found that Model II and Model III exhibited
better description of the experimental results than the original
Langmuir model did. The dynamic adsorption models (Model A and
B) were also developed for continuous hollow-fiber biosorption
processes. Model A showed excellent predictions for the results
of single-metal processes. However, the derivation of Model A
may become extremely complex, and required tedious numerical
manipulations, when it was arranged to describe multi-component
systems. In contrast, Model B introduced the concept of mass
transfer to simplify the trouble-causing dq/dt term in Model A,
and thus can be easily utilized to predict the results from
continuous multi-metal biosorption processes.
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