Treabnent Plants for Denitrification
composition of the sludge is developed which may have another decay constant than
for a plant into which raw wastewater, or primary settled wastewater is discharged. The
decay constant also includes phenomena such as grazing (predation) which will also
be influenced by the sludge conditions in the plant.
Note the interaction between decay and maximum growth rate. In some cases we will
get about the same result from the computer simulation, whether the decay is increased, or the maximum growth rate is reduced.
- The somewhat lower value for the saturation constant is due to the
very easily degradable substrate which is included in the process and
in the model. It has been found from experience that the more easily degradable a substrate is, the lower saturation constant should be used.
- The saturation constant for oxygen by denitrification (and removal by oxygen) is
found to be 0.5 g/m 3 which is higher than the normal standard value in the model
used. The difference between the value determined by the batch experiment and in
the pilot plant itself is assumed
to be due to the small floes which are found in the batch experiment.
The smaller the floes, the smaller saturation constant for oxygen, see
the biofilm kinetics.
By using the procedure outlined above, we can in this case obtain results from
computer-simulation as the one shown in Fig 7.24. The major part of the work is to
characterize the influent water. Normally it is only necessary to change very few of
the process constants as it is also seen in this case. Once the constants have been
found for a given plant, experiences seem to indicate that they are rather constant
with time. One of the reasons is that in spite of the fact that the wastewater changes
its concentration in the course of weeks and months, the percentage distribution of
the individual substance fractions is assumed to be rather constant. For the process
constants it applies that some of them are influenced by the design of the plant and
its operation (for example floc sizes and sludge composition).
7.3.8 Design of biofilters for denitrification
The design is carried out on the same principle as for nitrifying filters, Chapter 6,
Section 6.3.3.
The design is carried out by means of a mass balance by finding the necessary
surface area of the carrier, Az•.
Based on the concentrations of organic matter and nitrate through the filter (it may
be ideally mixed, but normally it looks more like plug flow), it is determined (by
using Expression (7.6a) or (7.6b)) which component is limiting.
Next the reaction kinetics are determined by using Expression (5.13), and finally the
reaction rate expression is determined by Expression (7.7a), (7.7b), (7.7c), or (7.7d).
From Expression (7.5), the necessary area of the carrier, Az•, is found.
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composition of the sludge is developed which may have another decay constant than
for a plant into which raw wastewater, or primary settled wastewater is discharged. The
decay constant also includes phenomena such as grazing (predation) which will also
be influenced by the sludge conditions in the plant.
Note the interaction between decay and maximum growth rate. In some cases we will
get about the same result from the computer simulation, whether the decay is increased, or the maximum growth rate is reduced.
- The somewhat lower value for the saturation constant is due to the
very easily degradable substrate which is included in the process and
in the model. It has been found from experience that the more easily degradable a substrate is, the lower saturation constant should be used.
- The saturation constant for oxygen by denitrification (and removal by oxygen) is
found to be 0.5 g/m 3 which is higher than the normal standard value in the model
used. The difference between the value determined by the batch experiment and in
the pilot plant itself is assumed
to be due to the small floes which are found in the batch experiment.
The smaller the floes, the smaller saturation constant for oxygen, see
the biofilm kinetics.
By using the procedure outlined above, we can in this case obtain results from
computer-simulation as the one shown in Fig 7.24. The major part of the work is to
characterize the influent water. Normally it is only necessary to change very few of
the process constants as it is also seen in this case. Once the constants have been
found for a given plant, experiences seem to indicate that they are rather constant
with time. One of the reasons is that in spite of the fact that the wastewater changes
its concentration in the course of weeks and months, the percentage distribution of
the individual substance fractions is assumed to be rather constant. For the process
constants it applies that some of them are influenced by the design of the plant and
its operation (for example floc sizes and sludge composition).
7.3.8 Design of biofilters for denitrification
The design is carried out on the same principle as for nitrifying filters, Chapter 6,
Section 6.3.3.
The design is carried out by means of a mass balance by finding the necessary
surface area of the carrier, Az•.
Based on the concentrations of organic matter and nitrate through the filter (it may
be ideally mixed, but normally it looks more like plug flow), it is determined (by
using Expression (7.6a) or (7.6b)) which component is limiting.
Next the reaction kinetics are determined by using Expression (5.13), and finally the
reaction rate expression is determined by Expression (7.7a), (7.7b), (7.7c), or (7.7d).
From Expression (7.5), the necessary area of the carrier, Az•, is found.
265