Environmental Engineering Reference
In-Depth Information
technique has been applied to remove several contaminants, such as 3-chloroaniline,
2,4-dichlorophenoxyacetic acid, and 3-chlorobenzoate, in wastewater and contami-
nated sites [2, 3].
The key attributes for the success of cell bioaugmentation are the viability and
retention of the bioaugmented cells in the target systems [2, 4, 7, 10]. In field
applications, the augmented cells might experience biotic and abiotic environmen-
tal stresses, such as predation and competition with indigenous species and presence
of inhibiting compounds [11]. Moreover, the augmented cells sometimes leave the
systems along with the effluent or groundwater flow for the cases of wastewater
treatment or site remediation, respectively.
Cell entrapment, a cell immobilization method by embedding microorganisms
in a porous polymeric matrix, can be used to alleviate the shortcomings associated
with the traditional planktonic (suspended or free) cell bioaugmentation scheme.
Some of the common natural and synthetic polymeric materials used as cell entrap-
ment matrices include calcium alginate (CA), carrageenan (CN), polyvinyl alcohol
(PVA), and cellulose triacetate (CTA). Cell entrapment has been studied and applied
mainly as stand-alone wastewater treatment processes for the removal of collective
pollutants, such as organic carbon [12-20] and nitrogen [21-27], as well as spe-
cific contaminants such as phenol [1], dyes [28-31], and cyanide [32]. Recently,
the technique was combined with cell bioaugmentation resulting in a new process,
known as entrapped cell bioaugmentation, for removing pollutants, such as nitrogen,
herbicide, and other hazardous compounds in wastewater and contaminated sites
[6, 7, 33, 34]. The entrapment matrix can protect the augmented cells against envi-
ronmental stresses and prevent their loss from the target systems making entrapped
cell bioaugmentation a more reliable technology compared to the traditional
planktonic cell bioaugmentation.
This article reviews the basics and applications of entrapped cell bioaugmenta-
tion for contaminant removal. The principles of cell entrapment, types and prepara-
tion procedures of selected cell entrapment matrices including CA, CN, PVA, and
CTA, and advantages and drawbacks of entrapped cells compared to suspended
or free cells are described. Previous studies on the applications of entrapped cell
bioaugmentation for wastewater treatment and site remediation including success,
concerns, and future perspectives of the technology are also discussed.
7.2 Cell Entrapment
Entrapment is one of the cell immobilization techniques in which microorganisms
are embedded within porous polymeric supporting materials (Fig. 7.1f) [35-37].
Some other common cell immobilization techniques include physical adsorption,
ionic binding, covalent binding, cross-linking, and encapsulation (Fig. 7.1a-e).
In entrapment and encapsulation, microorganisms are not directly bonded but
enclosed in supporting porous matrices. The cell entrapment technique confines
microbial cells within the pores and voids of immobilization matrix while the cell
