Biological Nitrogen Removal Using Immobilized Bacteria
399
3
Research Goal
Two significant concerns are obvious when the immobilized nitrifiers are used in
the first stage of the process: nitrification inhibition by compounds that are usually
removed in conventional system, which has denitrification in the first stage;
development of the heterotrophic biofilm on the surface of the gel that limits mass
transfer into the nitrifYing layer. Libman et al. (2000) demonstrated that these two
problems might be avoided when treating domestic wastewater or municipal
wastewater not containing toxic compounds. Since current research did not
consider specific industrial wastewater toxic to the nitrifiers, these two problems
were included in the research objectives. A major difficulty in the proposed
system implementation is selection of the polymer appropriate for nitrifYing
bacteria immobilization. Akin (1987) and Leenen et al. (1996) defined that the gel
lattice for cell immobilization ideally should meet the following criteria: toxicity,
mechanical stability and strength, permeability, chemical and thermal stability,
elasticity, availability and cost, to be environmentally safe. Thus, the main goal of
this work was to develop a process for complete nitrogen removal. The following
specific objectives were considered: selection of the appropriate gel and
immobilization procedure, and determination of optimal operation parameters and
system stability and efficiency.
4 Methodology
The following scope was defined in this work to reach the goal above: (1) a
literature review of the available polymers used for bacteria entrapment and
verification of feasibility of these gels for immobilization of nitrifiers; selection of
the most appropriate gel and adjustment of the immobilization procedure to the
wastewater treatment conditions; (2) selecting the suitable configuration of the
nitrification reactor; (3) identification and estimation of the process-related and
cost-determining parameters; (4) feasibility study of prolonged nitrification
interruption enabling seasonal ammonium removal due to agricultural needs.
4.1 Selection of the Appropriate Gel Material
Selection of the appropriate immobilization method included a thorough literature
review of the available and applied gel materials and laboratory testing of these
polymers. Gel toxicity and physical stability/strength were considered as most
important properties for comparison, since they provide a minimum required for
the bacteria immobilization. Toxicity of the biomass was examined using kinetic
tests for ammonium removal. Autotrophic biomass was cultivated in lOOL-volume
continuous flow chemostate with dilution rate of 0.2 d- J • The chemostate was fed
with a synthetic substrate containing ammonium chloride and potassium
dihydrogen phosphate with concentrations of 500 mg NH/-N L- J and 100
399
3
Research Goal
Two significant concerns are obvious when the immobilized nitrifiers are used in
the first stage of the process: nitrification inhibition by compounds that are usually
removed in conventional system, which has denitrification in the first stage;
development of the heterotrophic biofilm on the surface of the gel that limits mass
transfer into the nitrifYing layer. Libman et al. (2000) demonstrated that these two
problems might be avoided when treating domestic wastewater or municipal
wastewater not containing toxic compounds. Since current research did not
consider specific industrial wastewater toxic to the nitrifiers, these two problems
were included in the research objectives. A major difficulty in the proposed
system implementation is selection of the polymer appropriate for nitrifYing
bacteria immobilization. Akin (1987) and Leenen et al. (1996) defined that the gel
lattice for cell immobilization ideally should meet the following criteria: toxicity,
mechanical stability and strength, permeability, chemical and thermal stability,
elasticity, availability and cost, to be environmentally safe. Thus, the main goal of
this work was to develop a process for complete nitrogen removal. The following
specific objectives were considered: selection of the appropriate gel and
immobilization procedure, and determination of optimal operation parameters and
system stability and efficiency.
4 Methodology
The following scope was defined in this work to reach the goal above: (1) a
literature review of the available polymers used for bacteria entrapment and
verification of feasibility of these gels for immobilization of nitrifiers; selection of
the most appropriate gel and adjustment of the immobilization procedure to the
wastewater treatment conditions; (2) selecting the suitable configuration of the
nitrification reactor; (3) identification and estimation of the process-related and
cost-determining parameters; (4) feasibility study of prolonged nitrification
interruption enabling seasonal ammonium removal due to agricultural needs.
4.1 Selection of the Appropriate Gel Material
Selection of the appropriate immobilization method included a thorough literature
review of the available and applied gel materials and laboratory testing of these
polymers. Gel toxicity and physical stability/strength were considered as most
important properties for comparison, since they provide a minimum required for
the bacteria immobilization. Toxicity of the biomass was examined using kinetic
tests for ammonium removal. Autotrophic biomass was cultivated in lOOL-volume
continuous flow chemostate with dilution rate of 0.2 d- J • The chemostate was fed
with a synthetic substrate containing ammonium chloride and potassium
dihydrogen phosphate with concentrations of 500 mg NH/-N L- J and 100