Use
Secondary treatment of residential black water.
Total oxidation biological treatment plants are the right
equipment to achieve a high level of purification in wastewater
generated in restaurants, hotels, camping and houses without
sewer connections. Total oxidation biological treatment plants
can be installed directly downstream of the degreaser to allow
the drain of purified water directly into a watercourse, without the
risk of polluting the environment. An Imhoff or ST sedimentation
tank are installed downstream of the plant with a system (electric
pump or airlift) which recirculates the sludge within the FOT.
Operation
The active sludge biological process refers to a type of aerobic
treatment conducted by aeration of the wastewater in a biological
reactor in the presence of a microbial population (biomass). In
activated sludge plants, the bacterial populations, constituted
by numerous microorganisms, are produced continuously within
the reactor following the biochemical reactions of degradation of
organic carbon and nutrient utilization, resulting in the synthesis
of new cellular material. The activated sludge plants are equipped
with blowers that increase the presence of oxygen inside them
thereby increasing the capacity of the degradation of the organic
load by aerobic bacteria. In fact, these bacteria exploit the oxygen
to consume the biodegradable material, and the greater the
presence of oxygen, the greater is the ability to “consume” the
biodegradable organic material inside the tanks. Total oxidation
biological treatment plants are designed for volume not exceeding
0.25 (Cv < 0.25 BOD/m
3
) and daily organic volume not exceeding
60 g/P.E. The total oxidation biological treatment plant does
not include the inner decanter (sedimentation chamber) as
the high flow of oxygen permits the total oxidation of sludge,
but a sedimentation is necessary through Imhoff or ST tank
with appropriate system (electric pump or air lift) which will re-
circulate the sludge within the FOT.
Maintenance
For the correct management of the FOT plant and to achieve the
required purification results, please follow these guidelines:
•
Regularly inspect the FOT to check that there is no gross
material received accidentally to clog the pipes;
•
Regularly check that no anomalies have occurred to the
electrical panel if present;
•
Verify that the diaphragm blower works properly, that is,
movement must be observed in the volume of oxidation
coinciding with the operating time;
•
Every six months carry out the removal of excess sludge. Such
removal must be carried out by a specialized company;
•
As provided for by the Consolidated Act on Water (Legislative
Decree 152/06 as amended), and suggested by the normal
hygiene practice, periodically inspect and wash the inspection
well;
Specification Item
Totaloxidationbiologicaltreatmentplantsforthesecondarytreatment
of residential wastewater manufactured in rotational polyethylene,
in a single structure, free of joints and with reinforcement plate, and
equipped with inlet and outlet holes, a digestion tank and inspection
and sampling lids. Suitable for underground installation. The system
must be equipped with blower and micro-bubbles diffuser, according
to the plant specifications. The low-load activated sludge treatment
plant has been designed in compliance with the indications given by
experience, in particular, it has a retention time in the treatment stage
of approximately 22 hours and the indications summarised below:
RESIDENTIAL WASTEWATER
SECONDARY TREATMENT - DRAIN TO WATERCOURSES
PROJECT PARAMETERS
Water supply per P.E.
lt/d
200
Average flow (Q24) per P.E.
lt/h
8,3
Peak flow (Qp) per P.E.
lt/h
20
Specific organic load
gr BOD
5
/P.E.x d
42
Concentration of the biodegradable fraction
mg/l
240
COD/BOD
5
1,67-2,2
Total daily nitrogen load per P.E.
kg/P.E.x d
<0,012
Total surfactant concentration
mg/l
<15
Concentration of oils and fats
mg/l
<10
Retention time in the treatment stage
h
22 c.a
Air flow supplied to the process per P.E.
m
3
/h
0,45
Oxygen fed to the system per P.E.
m
3
/h
0,09
Figure 6
System composed of DG, IMHOFF, FOT models for domestic use, with drain into watercourses
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