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10.12.3 Bacterial filter
Model
Operating parameters
DBF10 DBF10
Type of premises
Residential
Number of equivalent inhabitants
up to
10 20
Total useful volume
litres
1150 1380
Volume of plastic elements (denitrification)
litres
380 460
Volume of filter
litres
90 90
Settling volume
litres
680 830
Combinations with Depurbox
BASE and MAXI
DUO
10.12.4 Process Description (Depurbox)
Chamber
Process Stage
Description
1 Imhoff
tank
Primary settlement
Suspended solids settle and accumulate on the bottom (sludge
digestion)
Anaerobic
sludge
digestion
Sludge accumulates on the bottom and undergoes a slow
anaerobic mineralisation process
2 Biological
reactor
Biological treatment, oxidation and
nitrification
The sewage oxidation and nitrification processes takes place
simultaneously with the entry of atmospheric air via a Venturi
system combined with the electric pump: the pump recirculates
the sewage in the tank, sucking in air from the outside and
putting it into contact with the liquid to be treated. As a result,
no mechanical parts need to be installed on the outside of the
product.
Biological
treatment,
denitrification
During the stages when the electric pump is off, anoxia
conditions are induced in order to enable the denitrification
process
3 Settler
Secondary settlement and
activated sludge recirculation
The activated sludge produced in the biological reactor settles:
the funnel-shaped chamber forces the sludge to concentrate on
the bottom: from there the sludge is returned to the oxidation
tank by gravity and thanks to the suction effect of the pump.
Main chemical reactions
1.
Oxidation of the organic and non-organic substances (measured in COD);
2.
Oxidation of the organic carbon fraction (measured in BOD5);
3.
Nitrification: oxidation of ammonia nitrogen molecules into nitrites and nitrates (measured in NH4);
4.
Denitrification: reduction of nitrites and nitrates to molecular nitrogen in the absence of oxygen (measured in NO2 and NO3).
The reactions take place under conditions of fluid aeration (1, 2 and 3) and under conditions of anoxia (4), as regulated by the daily
adjustable programmer.
10.12.5 Glossary
Explanations of the most commonly used wastewater treatment terms mentioned in this manual are given below.
Term
Definition
Equivalent inhabitant
(g BOD
5
/head day)
Amount of biodegradable organic substances that are
discharged in one day, resulting from the normal activities of a
person, such as the use of bathroom and kitchen. It is measured
indirectly based on the quantity of oxygen needed to enable the
bacteria to modify the biodegradable organic substances
contained in the wastewater and render them harmless within a
time span of five days (Biological Oxygen Demand 5 = BOD
5
).
On average, the reference value is 60 grams of oxygen per day.
Daily organic load (kgBOD
5
/day)
This represents the kilograms of BOD
5
that reach the system
daily. It is obtained by multiplying the 60 grams of oxygen per
day by the number of equivalent inhabitants.
Volumetric organic load
(kgBOD
5
/m
3
day)
This represents the ratio between the daily organic load and the
oxidation volume.
Inlet BOD
5
concentration (mg/litre O
2
)
This is the ratio between the daily organic load and the daily
discharge volume. To obtain the mg/litre value, the result of the
division must be multiplied by 1000.
Outlet BOD
5
concentration (mg/litre O
2
)
This represents the residual quantity in the discharged effluent.
Inlet COD concentration (mg/litre O
2
)
Amount of organic and inorganic substances that are
discharged in one day, resulting from the normal activities of a
person, such as use of bathroom and kitchen. It is measured
indirectly based on the quantity of oxygen needed to oxidise the
organic and inorganic substances found in the wastewater and
render them harmless (Chemical Oxygen Demand = COD).
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