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Per capita water supply to discharge
(litres/head/day)
Estimated daily per-head water consumption. The value is
commonly 200 litres a day.
Supplied oxygen factor (kgO
2
/kgBOD
5
)
Oxygen intake needed to eliminate one kg of BOD
5
Number of equivalent inhabitants
For residential applications, this coincides with the number of
residents.
Maximum flow per hour
(l/h)
This is twice the average flow per hour.
Average flow per hour
(l/h)
This is the daily discharge volume divided by 16 hours,
supposing that water users are only used for two-thirds of the
day.
Treatment efficiency
(%)
This indicates by how much the BOD
5
value is reduced during
the treatment.
SS
(mg/l)
Indicates the total quantity of suspended solids. It is the sum of
settled and non-settled suspended solids.
Primary settlement time
(hours)
Minimum interval of time required for the completion of the
settlement process. It can be calculated by dividing the primary
settlement volume by the average flow per hour.
Secondary settlement time (hours)
Minimum interval of time required for the completion of the
settlement process. It can be calculated by dividing the
secondary settlement volume by the average flow per hour.
Settlement rising speed
(m/h)
Maximum speed of liquid flowing through the settlement
compartments or tanks in order to avoid the entrainment of
sludge to the next compartment or tank. It is normally
calculated by dividing the average flow per hour by the area of
the settlement compartment or tank.
Sludge digestion volume
(litres)
Volume of that part of the system where coarse solid particles
are mineralised under conditions of inadequate air supply
(anaerobic process)
Oxidation/nitrification/de-nitrification volume
(litres)
Volume of that part of the system where the liquor is oxidised
and nitrified under conditions of abundant air supply (pump
running), and denitrified the air supply is scarce (pump off).
Daily discharge volume
(m
3
)
The number of equivalent inhabitants multiplied by the per
capita water supply to discharge.
Primary settlement volume
(litres)
Volume of that part of the system where the coarse solid
particles are separated from the liquid and precipitate to the
bottom.
Secondary settlement volume
(litres)
Volume of that part of the system where the activated sludge is
separated from the liquid and precipitates to the bottom.
Total useful volume
(litres)
This is the sum of the primary settlement, sludge digestion and
oxidation/nitrification/denitrification volumes.
