61    IMMOBILIZED MIXED MICROBIAL CELLS
FOR WASTEWATER TREATMENT
P. Y. Yang,Professor
Tiande Cai, Graduate Research Assistant
Ming-Li Wang, Graduate Research Assistant
Agricultural Engineering Department
University of Hawaii at Manoa
Honolulu, Hawaii 96822
INTRODUCTION
Immobilized enzymes for synthetic chemical reactions have been used for years. Immobilized
enzymes work as the solid-phase catalysts to carry out chemical reactions. Immobilized microbial cell
systems may be considered as an alternative either to the immobilized enzymes or fix the free suspended cells. Compared to the immobilized enzymes, the immobilized microbial cell eliminates the
often tedious, time consuming and expensive steps involved in isolating and purifying the enzymes. It
also provides to improve the operational stability of the enzyme by retaining it in its natural surroundings. According to Chibata et al.,1 the advantages of immobilized microbial cells are summarized as
follows:
• The process for extraction or purification, or both, of enzymes are not necessary
• The yield of enzyme activity on immobilization is high
• The operational stability is generally high
• The cost of the enzyme is low
• Application for a multi-step enzyme reaction may be possible.
Obviously, the immobilized microbial cells, instead of immobilized enzyme system, offers the
possibility of continuous operation and higher stability. Also, it offers the advantages of higher
volumetric productivity over the conventional fermentation system. This system has been increasingly
used in industry for the conversions of ammonium fumarate to L-aspartic acid, sodium fumarate to L-
malic acid, penicillin to 6-APA, glucose to high fructose corn syrups and hydrolysis of lactose and
sucrose, etc.
Wastewater treatment process requires mixed population of microorganisms. The activated sludge
and its modification and the trickling filter processes have been used for years in treating organic
wastewater. Traditionally, biological treatment processes, such as trickling filter, anaerobic fixed bed
and fluidized bed systems, can be considered as one type of immobilized microbial cell system.
However, there are still some difficulties or handicaps associated, such as transport of gaseous
reactants and products through the support material and a poor understanding of the intrinsic kinetics
of growth and product formation. Studies of entrapped microbial cells for wastewater treatment
processes are necessary for overcoming these difficulties and to provide an effective removal or
degradation of organic-toxic materials, such as pesticides from water supply and wastewater systems
and upgrade traditional biological treatment processes.
The purpose of this report is to select the proper carrier of entrapping mixed microbial cells for
removal of organics from wastewater, to determine optimal loading rate for maximum organic
removal and to evaluate long term operational stability.
MATERIALS AND METHODS
Cell Immobilization
As indicated by Chibata et a/.,' no ideal and general method has been developed for the immobilization of all types of microbial cells. Therefore, it is necessary to select suitable methods and conditions applicable for the immobilization of each type of microbial cell.
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