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For users that are in sensitive
areas where there is need for limitations also in the concentrations
of nitrogen and phosphorus in the drainages as indicated in Lgs D.
04/03/2006, the Musilli Spa proposes biological systems of active
sludge using the “nitro-denitro process”. Rather than regarding the
traditional outline, it involves an additional treatment for the
removal of nitrogenous compounds originally present in drainage
waters.
The denitrification process is aimed partially at the removal of the
nitrogenized substances, present in the watery phase in the form of
NO3 and NO2, and works by using optional heterotropic denitrifying
bacteria that are able to transform NO3 almost entirely into gaseous
N2 that frees itself therefore into the atmosphere. The removal of
NO3-N and NO2-N from the sewage waters is performed both to avoid
eutrophication, and to protect the potable water uses from the risks
connected to the presence of nitrates that reduce into nitrites that
can cause infantile cyanosis.
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The denitrification is verified in thick enough
biological film even in the presence of free oxygen in the
liquid mass, because while a thin layer of the film stays
aerobic, the nitrates can diffuse in depth, through such layer,
in an oxygen-free zone where the denitrification develops. So it
naturally happens only if the organic substrate concentration in
the sewage water is sufficient to allow for the penetration to
be beyond the aerobic layer. These are two non-contemporaneous
biological reactions of oxide-reduction: the substrate donor of
common electrons to both the reactions (soluble organic
substrate Dred) and the substrate acceptors of electrons (dissolved
oxygen A1, ox and the nitric nitrogen A2, ox). Therefore to
prepare for a classic biological treatment of active sludge that
proposes an efficient removal of total nitrogen of the order of
10-40% due to the bioflocculation phenomena and bacterial
synthesis, the proposed typology is the nitro-denitro process,
in which the denitrification is coupled to the nitrification,
and is capable of an efficiency of removal of total nitrogen of
90% and beyond. |
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The nitro-denitro outline is diversified from
the traditional outline in that a denitrification basin is
included between the Imhoff system and the biological oxidation
basin. The basin consists of one reservoir equipped with a
submerged mixer. At the same time, the biological oxidation
basin comes installed with a submerged pump connected to a
recirculation pipe to the denitrification basin where it also
leads back to the recirculation pipe of the air lift of the
basin of secondary sedimentation. |
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