Concepts and definitions
The weight of material added per unit volume per unit time, 01 · C 1, is calculated at
a position prior to a possible recycle. The volumetric loading rate cannot be increased by an internal recycle in the plant.
Biofilm surface area has two meanings, the area of the filter tank in a horizontal
section and the surface area of the carrier. The latter area is normally calculated from
Expression (5.55)
Az·=ro· Vz
(5.55)
where ro is the specific surface of the carrier (for example m 2 /m~.
The surface area in a horizontal section, Az, is used for the calculation of the
hydraulic surface loading rate.
Organic surface loading rate is an expression of the load of the surface of the carrier
in the filter:
(5.56)
This is the figure which comes closest to the kinetic conditions in the filter.
Hydraulic surface loading rate (or nominal filter rate) is defined by the symbols in
Fig5.13 as
(5.57)
This parameter is a simple expression of the flow passing the biofilm and hence is
an expression of the hydraulic erosion which is considered to be crucial for the
control of the thickness of the biofilm. (In German literature 01 is set at the flow
during the daytime, for example calculated as the diurnal flow distributed over 18
hours for large plants, see Fig 1.6).
Sludge production, Fsp, is the mass of sludge leaving the plant per unit time.
According to Fig 5.13 it is
Fsp = Qs · Xs + 04 · X4
(5.58)
For further details concerning sludge production, see Chapter 4, Section 4.2. The
comments made in that chapter also apply to biofilter plants. Hence the sludge
production can be calculated from Expression (4.13). Note that yield constants for
biofilters deviate from yield constants for activated sludge plants.
Surplus sludge production is the part of the sludge production to be further treated
in the plant, that is, Os · Xs, see Fig 5.13.
166
The weight of material added per unit volume per unit time, 01 · C 1, is calculated at
a position prior to a possible recycle. The volumetric loading rate cannot be increased by an internal recycle in the plant.
Biofilm surface area has two meanings, the area of the filter tank in a horizontal
section and the surface area of the carrier. The latter area is normally calculated from
Expression (5.55)
Az·=ro· Vz
(5.55)
where ro is the specific surface of the carrier (for example m 2 /m~.
The surface area in a horizontal section, Az, is used for the calculation of the
hydraulic surface loading rate.
Organic surface loading rate is an expression of the load of the surface of the carrier
in the filter:
(5.56)
This is the figure which comes closest to the kinetic conditions in the filter.
Hydraulic surface loading rate (or nominal filter rate) is defined by the symbols in
Fig5.13 as
(5.57)
This parameter is a simple expression of the flow passing the biofilm and hence is
an expression of the hydraulic erosion which is considered to be crucial for the
control of the thickness of the biofilm. (In German literature 01 is set at the flow
during the daytime, for example calculated as the diurnal flow distributed over 18
hours for large plants, see Fig 1.6).
Sludge production, Fsp, is the mass of sludge leaving the plant per unit time.
According to Fig 5.13 it is
Fsp = Qs · Xs + 04 · X4
(5.58)
For further details concerning sludge production, see Chapter 4, Section 4.2. The
comments made in that chapter also apply to biofilter plants. Hence the sludge
production can be calculated from Expression (4.13). Note that yield constants for
biofilters deviate from yield constants for activated sludge plants.
Surplus sludge production is the part of the sludge production to be further treated
in the plant, that is, Os · Xs, see Fig 5.13.
166