Biomedical Engineering Reference
In-Depth Information
Table 4. Flocculation activity of cross-linked
γ
-PGA (CL-
γ
-PGA) on various suspensions
pretreated with different concentrations of polyacrylamide (PAC)
Flocculation activity (l/OD)
a
PAC (
μ
g/mL)
Suspension
CL-
γ
-
PGA
(
μ
g/mL)
0
0.1
(0.01)
b
0.25
(0.025)
b
0.5
(0.05)
b
1
(0.1)
b
2
(0.25)
b
4
(0.5)
b
Kaolin
10
−
−
−
14.54
39.94
41.56
−
Bentonite
5
0.6
-5.2
2.9
33.4
0.0
−
−
Diatomaceous
earth
10
-0.2
−
23.3
30.0
29.6
33.4
−
Escherichia
coli
10
2.4
-7.2
16.0
25.9
8.5
1.1
−
Mycrocystis
aeruginosa
5
-0.3
6.6
9.5
29.3
41.0
71.7
88.2
Crystal violet
5
60.7
50.4
38.1
18.4
8.1
2.2
0.6
Mandai pond
20
10.8
7.4
7.9
6.1
12.6
23.0
−
Yamato river
20
28.2
25.1
28.7
26.6
26.7
26.1
−
Source
: Taniguchi et al. 2005.
a
incubation at 30°C and pH 5 for 30 min;
b
PAC dose for
Mycrocystis aeruginosa.
3.7. Mechanism of Flocculation
Among various factors, the metal cations played a prominent role in affecting the
flocculation activity of γ-PGA. In accordance with Schulze Hardy's law [59], although both
suspended particles (like kaolin) and the γ-PGA-based-bioflocculants are anionic, their
interaction to facilitate flocculation is possible only through charge neutralization and
bridging by added metal cations. Based on this phenomenon, two flocculation mechanisms
were suggested [31] as follows:
I.
The metal cations may decrease the negative charge on suspended particles, which
in turn result in a charge reversal from negative to positive. Finally, the negatively
charged carboxyl group (COO
-
) of γ-PGA may react with the positively charged
site of the suspended cation-kaolin particles (Figure 7a).
II.
The metal cations may neutralize and stabilize the residual negative charges of the
γ-PGA first, followed by bridge formation with the negatively charged kaolin
particles (Figure 7b).
Thus, metals cations could facilitate charge neutralization and bridging between γ-PGA
and suspended particles, resulting in an increase in floc density, floc size and floc resistance
to shear. This explains why both the trivalent and bivalent cations possess stronger synergistic
effect than monovalent ions.
