Environmental Engineering Reference
In-Depth Information
to form spherical beads. Note that in the method by Chen and Lin [21], the cell-
PVA mixture is dropped into a stirred boric acid solution for 10-120 min. Then, the
formed hydrogel beads are then soaked in a 1.0 M sodium phosphate solution at pH
7 for 60 min for hardening. The final PVA concentration is 10% (w/v).
The de-entrapment procedure of the PPVA involves adding the PPVA entrapped
cells into DI and heating to about 60
◦
C. As mentioned above, the de-entrapment
process is normally performed for measuring cell number and/or growth inside
the matrix. This thermal de-entrapment may damage the cell viability making
plate counting of the de-entrapment product an unsuitable method for quantify-
ing the cells in the PPVA matrix. Measuring the cell mass (represented by volatile
suspended solids) after the de-entrapment is an alternative to this limitation [20].
7.2.2.4 Cellulose Triacetate
Cellulose Triacetate Chemistry and Gelation
Cellulose is a natural polymer extracted from plants. Its structure is a chain of
organic compounds containing glucose molecules of which the number and loca-
tion in the chain vary based on the sources [43]. Natural cellulose itself is not
appropriate for cell entrapment; however, modified cellulose compounds via chem-
ical processes, such as esterification and etherification, can form fiber networks.
Examples of the modified cellulose compounds are cellulose azide, diazo cellulose,
and CTA. Cellulose triacetate has been applied as a cell entrapment matrix since
1980s. The CTA entrapped cells were first developed for food technology appli-
cations. The CTA cell entrapment matrix is rubber-like, which is different from
the other entrapment media described earlier. The CTA entrapped cells have very
high mechanical strength. It was reported that the CTA entrapped cells can be used
continuously for more than 8 years [13, 14].
Procedure of Cellulose Triacetate Cell Entrapment
The CTA entrapped cells are prepared by the plated gelation. A procedure to prepare
CTA entrapped cells was introduced by Kolarik et al. [58]. Later, Yang and See
[59] modified it to ease the preparation. The modified procedure has been used in
several studies [6, 12-14, 34]. Cellulose triacetate powder is dissolved in methylene
chloride at a concentration of 10% (w/v). Concentrated microbial cells are uniformly
mixed with the CTA solution. Then, the mixture is plated into toluene for hardening.
The hardened CTA sheet is cut to small cubes and washed with water to rinse the
residual chemicals. Currently, there is no procedure for CTA de-entrapment.
7.2.3 Advantages and Drawbacks of Entrapped Cells
There are several advantages of entrapped cells over suspended cells [60, 61].
Basically, cell entrapment leads to the enhancement of both biological and mechan-
ical stabilities. The entrapment matrix can alleviate physicochemical challenges,
such as temperature, pH, solvents, shear, and heavy metals. Other advantages of
entrapped cells include high biomass concentration, no need for cell separation,
