Environmental Engineering Reference
In-Depth Information
as K
+
,NH
4
+
,Ca
2+
,Cu
2+
,Mg
2+
,Fe
3+
, and amines [38, 43, 47]. Additionally, the
strength of
-CN gel can be improved by adding polymers such as galactoman-
nans, locust bean gum, and taragum [38, 43]. Normally,
κ
-CN entrapped cells have
relatively high biological activities and in turn broad utilizations. However, the
applications at high temperatures are not suitable because
κ
κ
-CN gel dissolves [48].
Procedures of
κ
-Carrageenan Cell Entrapment and De-Entrapment
The
-CN cell entrapment can be accomplished by both droplet and plated gela-
tions. The droplet method is suitable for a laboratory scale since the setup is simple.
However, the droplet method would be time-consuming for preparing a large vol-
ume of entrapped cells; the plated method is more appropriate for it. The following
procedure is a general droplet method implemented in several studies [20, 47, 49].
Kappa-CN powder is dissolved in stirred DI at a temperature of 50
◦
C and the solu-
tion is allowed to cool down to 35
◦
C. Then, concentrated microorganisms are mixed
with the
κ
κ
-CN solution. The mixture is dropped into 0.3 M potassium chloride and
0.18 M calcium chloride solutions for gel formation and gel hardening, respectively.
The final
κ
-CN concentration is about 2-5% (w/v). The de-entrapment procedure
for the
-CN entrapped cells involves continuous shaking in a 1% sodium citrate
solution at 37
◦
C [20, 27].
κ
7.2.2.3 Polyvinyl Alcohol
Polyvinyl Alcohol Chemistry and Gelation
PVA is a polymer that can be prepared in the forms of film and hydrogel with
high mechanical strength and durability [4, 21, 50]. Similar to CA and CN, PVA
is non-toxic even though it is a synthetic polymer. Therefore, it does not nega-
tively affect both microorganisms and environment. Raw PVA appears in a white
and free-flowing granule. The chemical structure of PVA is shown in Fig. 7.5. The
properties of PVA are based on the polymer chain length (molecular weight) and
degree of hydrolysis. Polyvinyl alcohol with high molecular weights and degrees of
hydrolysis has high mechanical stability and low water solubility [51].
Several gelation techniques are available for producing PVA gels for cell entrap-
ment including boric acid-PVA (BPVA), freezing and thawing of PVA (FPVA), and
phosphorylated-PVA (PPVA) methods. The BPVA technique is the simplest and
most economical. The technique is a one-step droplet gelation method [52]. The
BPVA gelation process is a cross-linking of boron and PVA as shown in Fig. 7.6. The
BPVA hydrogel beads present high mechanical strength and durability. However,
Fig. 7.5
Chemical structure
of PVA
