Biomedical Engineering Reference
In-Depth Information
COO
-
in CL-γ-PGA. Among various added metal cations, the trivalent ions (Al
3+
and Fe
3+
)
demonstrated a marked effect on flocculation activity of CL-γ-PGA, whereas the divalent ions
(except Mn
2+
) and monovalent ions did not show any effect [57].
Under the optimum conditions of CL-γ-PGA and PAC, the flocculating rate expressed in
“decrease in turbidity” increased linearly with incubation time for bentonite suspension, while
it was rapid in the initial 5 min followed by a gradual decline for diatomaceous earth (Figure
6) [58]. This may be caused by the faster precipitating behavior of diatomaceous earth
compared to bentonite. On the other hand, for
E. coli
suspension, no flocculation was
observed until 5 min, but increased with time thereafter [58]. However, a sharp decline in
turbidity was noticed within 5 min for
M. aeruginosa
and then reached a plateau (Figure 6).
Table 3. Flocculation activity of
γ
-PGA in various inorganic and organic suspensions
a
Suspensions
Metal cations
Flocculation activity (l/OD)
Inorganic suspension
Kaolin
b
90 mM Ca
2+
8.5
8 mM Ca
2+
3.3
Active carbon
c
2 mM Mg
2+
2.9
0.05 mM Fe
2+
2.8
8 mM Ca
2+
1.1
Solid soil
c
8 mM Mg
2+
1.0
6 mM Fe
2+
1.9
6 mM Ca
2+
10.9
Acid clay
c
4 mM Mg
2+
14.0
0.1 mM Fe
2+
34.7
Ca(OH)
2
c
Nil
21.3
CaCO
3
c
Nil
2.0
[Ca(PO4)
2
]
3
⋅Ca(OH)
2
c
Nil
5.7
Mg(OH)
2
b
Nil
8.1
MgCO
3
c
Nil
9.3
Al
2
O
3
b
Nil
6.1
Organic suspension
b
Cellulose powder
90 mM Ca
2+
3.0
90 mM Ca
2+
Carboxymethylcellulose
2.6
90 mM Ca
2+
Saccharomyces cerevisiae
4.6
90 mM Ca
2+
2.8
a
suspension concentration: 5 g/L;
b
treated with γ-PGA from
B. licheniformis
(CCRC 12826) at 80 mg/L;
c
treated with γ-PGA from
B. subtilis
(IFO 3335) at 20, 10 and 10 mg/L for Ca
2+
, Mg
2+
and Fe
2+
,
respectively.
Source
: Yokoi et al. 1996; Shih et al. 2001.
Bacillus circulans
