Treatment Plants for Denitrification
Fig 7.16 Simultaneous denitrification plant with varying aerobic and anoxic conditions.
Another form of an alternating process is shown in Fig 7.16. The supply of oxygen
is designed in such a way that zones with oxygen and zones without oxygen occur
throughout the tank. The processes occur alternately when the sludge with the
water is carried from zone to zone through the plant. The system is for example used
on the large Vienna-Blumental treatment plant in Vienna, Austria. The organic
matter for the denitrification comes from the wastewater as well as from the
degradation of the sludge.
A treatment plant, as shown in Fig 7.16, requires a very precise control to function.
During changes in the loading or changes in the process rates, it may be difficult to
control the supply of oxygen so as to achieve an optimum distribution between
zones with nitrification and zones with denitrification.
The switching between nitrification and denitrification are so frequent in this type
of plant (1-2 minutes) that it more resembles a simultaneous nitrification-denitrification. In this type of plant as well as in other plants with combined sludge, a
denitrification will take place simultaneously with the nitrification. The reason is
that in the innermost part of the floes or the biofilm there will be oxygen-free zones
where nitrate is present which will result in denitrification. There may also be zones
in the nitrification tank where the aeration is not efficient. This will also facilitate
"simultaneous" denitrification.
7.2.3 Biofilters for denitrification
All biofilters for denitrification are submerged, which means they are water-filled.
Where rotating discs or packed filter media (plastics discs or loose carriers) are used,
the sludge production is removed from the treated water by settling as shown in Fig
7.17. For filters with backwash (gravel, Leca and the like) the plant design is shown
in Fig 7.18, whereas for fluidized filters the design is shown in Fig 7.19. Fluidized
filters can either use sand or plastics as carrier or function with spherical bacterial
Fig 7.17 Denitrifying filter (packed plastics filters or rotating discs) with continuous sludge
separation.
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Fig 7.16 Simultaneous denitrification plant with varying aerobic and anoxic conditions.
Another form of an alternating process is shown in Fig 7.16. The supply of oxygen
is designed in such a way that zones with oxygen and zones without oxygen occur
throughout the tank. The processes occur alternately when the sludge with the
water is carried from zone to zone through the plant. The system is for example used
on the large Vienna-Blumental treatment plant in Vienna, Austria. The organic
matter for the denitrification comes from the wastewater as well as from the
degradation of the sludge.
A treatment plant, as shown in Fig 7.16, requires a very precise control to function.
During changes in the loading or changes in the process rates, it may be difficult to
control the supply of oxygen so as to achieve an optimum distribution between
zones with nitrification and zones with denitrification.
The switching between nitrification and denitrification are so frequent in this type
of plant (1-2 minutes) that it more resembles a simultaneous nitrification-denitrification. In this type of plant as well as in other plants with combined sludge, a
denitrification will take place simultaneously with the nitrification. The reason is
that in the innermost part of the floes or the biofilm there will be oxygen-free zones
where nitrate is present which will result in denitrification. There may also be zones
in the nitrification tank where the aeration is not efficient. This will also facilitate
"simultaneous" denitrification.
7.2.3 Biofilters for denitrification
All biofilters for denitrification are submerged, which means they are water-filled.
Where rotating discs or packed filter media (plastics discs or loose carriers) are used,
the sludge production is removed from the treated water by settling as shown in Fig
7.17. For filters with backwash (gravel, Leca and the like) the plant design is shown
in Fig 7.18, whereas for fluidized filters the design is shown in Fig 7.19. Fluidized
filters can either use sand or plastics as carrier or function with spherical bacterial
Fig 7.17 Denitrifying filter (packed plastics filters or rotating discs) with continuous sludge
separation.
247