56    BIOLOGICAL TREATMENT OF A SIMULATED INDUSTRIAL
WASTEWATER USING CHITOSAN-IMMOBILIZED
ACTIVATED SLUDGE
John N. Veenstra, Professor
School of Civil and Environmental Engineering
Oklahoma State University
Stillwater, Oklahoma 74078
Suresh Subramanian, Environmental Engineer
Brown and Caldwell Consultants
Irvine, California 92714
INTRODUCTION
An emerging technology in the field of environmental engineering is the use of microorganisms
immobilized in a matrix to biologically degrade hazardous and toxic wastes. The technique of using
immobilized cells is not new; it has been used for many years by the pharmaceutical and cosmetic
industries to transform organic compounds into desired end products. However, the application of
this biological method to the breakdown of recalcitrant chlorinated organic compounds is new. Work
done to date, using immobilized microorganisms, has shown this technique to hold promise as a
method for treating toxic wastes.1,2
Immobilization is a biotechnique which keeps catalytically active enzymes or cells within a reactor
system and prevents their entry into the mobile (liquid) phase which carries the substrate and products. Wastewater treatment reactors using immobilized microbial cells can have significant advantages
over conventional free cell reactors. Immobilized cells have a much higher cell density than free cells,
potentially resulting in high rates of biodegradation per unit volume of reactor. In addition, an
immobilized cell reactor facilitates separation, thus preventing washout of biomass and providing
greater operational flexibility to the system. Finally, immobilized microbial cells have been shown to
be more resistant to high concentrations of toxic or hazardous chemicals because the cells are
entrapped in polymer gels.1
This study was undertaken to explore the feasibility of applying chitosan-immobilized cells in the
treatment of complex, synthetic chemical, plastics, petrochemical and petroleum industrial wastewater by comparing the treatment efficiency of this system with that of a bench-scale internal recycle
activated sludge reactor operated under similar conditions. The base mix was used for evaluating the
biodegradability of the target compound 2,4 diaminotoluene (2,4 DAT), a toxic organic compound
that can occur in such complex wastewaters.
LITERATURE REVIEW
Immobilized cells may be defined as cells that are physically confined or localized in a certain region
with retention of their catalytic activities, and which can be used repeatedly and continuously.3 Cell
immobilization may be achieved by the four following methods;4 covalent coupling (including
crosslinking), adsorption, entrapment in three dimensional polymer network, and physical entrapment in porous materials.
Entrapment of whole cells in the course of carrier preparation is by far the most common approach
in cell immobilization4 by a process known as ionotropic gelation. Generally, in this process, a
precultured cell suspension is mixed homogeneously with a linear polyelectrolyte, usually a long-chain
polymer. This mixture is then dropped into a solution of multivalent counterions. Ionotropic gelation
takes place resulting in a microporous network that holds the cells within. Also, as a result of the
porous network, transport processes for substrates and products are sufficiently fast to obtain a high
efficiency of catalytic activity.5 Several synthetic and natural polymers have been used as immobiliz-
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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