Environmental Engineering Reference
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2-methylnaphthalene [72], and reusable more than 50 times at various pH and tem-
peratures [73]. The PVA entrapment process only slightly affects the cell viability
based on the viable plate count and a fluorescence based assay [28].
7.3.1.4 Cellulose Triacetate Entrapped Cell Bioaugmentation
There have been less numbers of applications of CTA entrapped cells for wastewater
treatment compared to CA and PVA. This could be because the CTA entrapped
cell preparation procedure involves the use of toxic chemicals as mentioned above.
The chemicals may severely damage the contaminant-degrading cultures and pose
health risk to the personnel involved. In addition, hazardous wastes are generated
from the procedure. Advantages of the CTA matrix include very high mechanical
and chemical strengths. The entrapped cells can be used for longer than eight years
without the breakage of the matrix. Even though the entrapment procedure could
be very harmful to microorganisms, high contaminant removal efficiencies by CTA
entrapped cells have been reported [6, 12-14, 34, 59].
Cellulose triacetate entrapped cell bioaugmentation is utilized in a novel wastew-
ater process called immobilized cell augmented activated sludge (ICAAS), which
was developed to improve the ability of activated sludge process to degrade con-
taminants (Fig. 7.11). The ICAAS system is an activated sludge system with an
off-line enricher reactor growing CTA entrapped cells, which are induced to have
specific activities such as toxic contaminant degradation, nitrification, and denitri-
fication [6, 34]. The enriched entrapped cells are used for bioaugmentation in the
aeration tank. Once they are less active due to unfavorable conditions in the aeration
tank such as the absence of the target contaminants and/or competition with indige-
nous microorganisms, they are returned for reactivation in the enricher reactor and
in the mean time replaced by the active cells from the enricher reactor.
Jittawattanarat et al. [6] investigated pentachlorophenol (PCP) removal by com-
pletely mixed activated sludge (CMAS) and ICAAS processes (Fig. 7.12). Synthetic
wastewater containing PCP at 40 mg/L was used. The ICAAS systems with and
without powder activated carbon (PAC) entrapped along with the cells removed
PCP more than the CMAS system (no bioaugmentation) as shown in Fig. 7.12.
Fig. 7.11 A diagram of immobilized cell augmented activated sludge system [6], Reprinted by
permission of the publisher
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