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Y. Argaman et al.
The advantages of the proposed system, compared to the conventional and
existing advanced treatment processes, are as follows:
1. Nitrogen can be completely removed.
2. There is no need for electron donor supply to the denitrification process by
mixed liquor recycling or external BOD.
3. Nitrification by the entrapped biomass is less sensitive to the undesirable
conditions, such as presence of the inhibitors, changes in pH, temperature, etc.
4. Bacteria entrapment significantly increases the reliability of the process even
though nitrifYing bacteria are affected. Temporary activity reduction could be
recovered while suspended biomass is irreversibly washed out.
5. The overall system volume is much lower than that of the regular activated
sludge process.
6. A separate and relatively small nitrification reactor is easier to control.
7. If nitrogen requirement is not permanent (e.g., due to effluent reuse for
agricultural irrigation), the process might be readily adjusted for such an operation
mode.
All the advantages listed above make the reactor especially valuable for
retrofitting existing plants designed for BOD removal only. Energy requirement
should be comparable with conventional AS treatment or lower due to the
following facts:
• Significantly less energy is required for aeration of a small nitrification reactor.
• No need for the ML VSS recirculation.
• More organics is removed at denitrification than in the conventional process.
Notwithstanding the advantages above, the following weaknesses and expenses
should be considered for the specific applications:
• Inhibition of nitrification may occur when industrial toxic wastewater is
discharged to the wastewater treatment plant. For the proposed immobilized
system, toxic compounds should be removed upstream. Conventional AS
treatment would be advantageous due to the nature of CSTR, where the toxic
compound being removed would not affect the nitrification.
• Heterotrophic biomass can be accumulated on the gel surface, thus affecting
ammonia removal. This phenomenon should be prevented at the particular
system design.
• Specific cost of the immobilized biomass preparation decreases with the increase
of the entrapped biomass lifetime. According to Wijffels et al. (1993) 3 month
process durability justifies its cost effectiveness. Jekel et al. (1998) demonstrated
that nitrification using immobilized biomass could last as long as 2 years, which
significantly reduces the expense for the entrapped biomass preparation.
It should be noted that biosolids production and sludge characteristics related to
the wastewater composition and heterotrophic biomass SRT (solids retention time)
are not related to the proposed configuration and should be estimated/controlled
due to specific design.
Y. Argaman et al.
The advantages of the proposed system, compared to the conventional and
existing advanced treatment processes, are as follows:
1. Nitrogen can be completely removed.
2. There is no need for electron donor supply to the denitrification process by
mixed liquor recycling or external BOD.
3. Nitrification by the entrapped biomass is less sensitive to the undesirable
conditions, such as presence of the inhibitors, changes in pH, temperature, etc.
4. Bacteria entrapment significantly increases the reliability of the process even
though nitrifYing bacteria are affected. Temporary activity reduction could be
recovered while suspended biomass is irreversibly washed out.
5. The overall system volume is much lower than that of the regular activated
sludge process.
6. A separate and relatively small nitrification reactor is easier to control.
7. If nitrogen requirement is not permanent (e.g., due to effluent reuse for
agricultural irrigation), the process might be readily adjusted for such an operation
mode.
All the advantages listed above make the reactor especially valuable for
retrofitting existing plants designed for BOD removal only. Energy requirement
should be comparable with conventional AS treatment or lower due to the
following facts:
• Significantly less energy is required for aeration of a small nitrification reactor.
• No need for the ML VSS recirculation.
• More organics is removed at denitrification than in the conventional process.
Notwithstanding the advantages above, the following weaknesses and expenses
should be considered for the specific applications:
• Inhibition of nitrification may occur when industrial toxic wastewater is
discharged to the wastewater treatment plant. For the proposed immobilized
system, toxic compounds should be removed upstream. Conventional AS
treatment would be advantageous due to the nature of CSTR, where the toxic
compound being removed would not affect the nitrification.
• Heterotrophic biomass can be accumulated on the gel surface, thus affecting
ammonia removal. This phenomenon should be prevented at the particular
system design.
• Specific cost of the immobilized biomass preparation decreases with the increase
of the entrapped biomass lifetime. According to Wijffels et al. (1993) 3 month
process durability justifies its cost effectiveness. Jekel et al. (1998) demonstrated
that nitrification using immobilized biomass could last as long as 2 years, which
significantly reduces the expense for the entrapped biomass preparation.
It should be noted that biosolids production and sludge characteristics related to
the wastewater composition and heterotrophic biomass SRT (solids retention time)
are not related to the proposed configuration and should be estimated/controlled
due to specific design.