Environmental Engineering Reference
In-Depth Information
increased product yield and stability, increased reaction selectivity, and versatility
in the selection of the reactor. Several studies reported that entrapped cells pro-
vided better waste treatment performances and/or are more durable than free cells
[7, 20, 62-64]. For example, in a previous study, PPVA entrapped cells were used for
removing total organic carbon compared to free cells. The results indicated that the
PPVA entrapped cells had substantially higher specific growth and substrate utiliza-
tion rates [20]. The main drawbacks of entrapped cells are metabolic changes, cell
morphology changes, substrate and chemical growth factor diffusion limitations,
and inconsistent growth pattern [61, 64].
7.3 Applications of Entrapped Cell Bioaugmentation
In the past two decades, bioaugmentation and cell entrapment processes have
been separately applied in the environmental field. Examples of bioaugmentation
applications include removal of 2,4-dichlorophenoxyacetic acid, 3-chlorobenzoate,
3-chloroaniline, diesel (oil spills) [2, 3, 64] whereas the cell entrapment has been
applied for removing phenol, dyes, and cyanide [1, 28-32]. Although both processes
alleviate several problems associated with traditional contaminant removal schemes,
the roles of the two processes are different. Bioaugmentation provides a number
of specific or acclimated contaminant-degrading cultures whereas cell entrapment
maintains the cultures in the system and protects them from stresses.
Combining bioaugmentation and cell entrapment results in a novel process,
called entrapped cell bioaugmentation, which inherits the benefits of both processes.
Entrapped cell bioaugementation has been studied for environmental applications
only in recent years. The applications involved the degradation of collective and
specific pollutants in wastewater treatment plants and contaminated sites. Although
entrapped cell bioaugmentation has not been applied at field scales since it is rela-
tively new, the bench-scale results thus far are very promising. The technique can
retain effective contaminant-degrading cultures within the target systems and the
matrices can protect the cells from environmental stresses. Table 7.2 presents a
summary of previous studies on entrapped cell bioaugmentation for environmental
applications. Since the technology has been studied mainly for wastewater treatment
and site remediation, only these two categories of applications are reviewed below
for each cell entrapment matrix separately. For matrices that have not been used for
entrapped cell bioaugmentation, their technological outlook is provided.
7.3.1 Wastewater Treatment
7.3.1.1 Calcium Alginate Entrapped Cell Bioaugmentation
Calcium alginate is the most common matrix studied in the applications of entrapped
cell bioaugmentation for wastewater treatment. There were several successful appli-
cations of the CA entrapped cell bioaugmentation for removing toxic compounds
in domestic and industrial wastewater such as oil, phenol, and cresol, as listed in
Table 7.2. The bioaugmented cultures were pure or enriched mixed cultures.
