Types of plants, activated sludge plants
Table 4.5 shows that the volumetric loading, Bv.soo. must be 0.2-0.6 kg BOD/(m 3 · d)
in dry weather to obtain a 90-95 per cent BOD treatment. In wet weather the volumetric loading can be 0.6-1.5.
In other words, design must in this case be made on the basis of the dry-weather situation. It is estimated that Bv.soo = 0.4 kg BOD/(m 3 · d).
From Expression (4.20) is found:
V2 =a, · C,IBv.soo = (1,200 kg BOD/d)/0.4 kg BOD/(m 3 · d) = 3,000 m 3
On the basis of the figures in Table 4.6 the population equivalent represented by the
wastewater can be calculated:
PEwater = a,/0.2 = (5,000 m 3 /d)/(0.2 m 3 /(PE · d))= 25,000 PE
PEsoo = a, · C,/0.06 =
(1,200 kg BOD/d)/(0.06 kg BOD/(PE · d)) = 20,000 PE
The two calculations of the population equivalent will usually always deviate somewhat
from each other. The deviation can reveal industrial influence, infiltration, exfiltration,
etc.
4.3.7 Design by means of sludge loading
or sludge age
A somewhat more advanced design can be carried out by using sludge loading or
sludge age. Sludge loading can be used for ordinary biological removals whereas
the sludge age should be used in connection with nitrification processes and other
processes utilizing slowly growing bacteria for the removal of special pollutants in
wastewaters, such as phenol and cyanide. When designing on the basis of the
BOD-sludge loading
Bx,Boo= Q1 · Cooo,J!(Xz · Vz)
the volume, V2, of the aeration tank can be found from the expression:
Vz = Q1· CBoo,J!(Xz · Bx,ood
(4.21)
Typical treatment degrees as a function of the sludge loading are stated in Table 4.5.
For many years, sludge loading has been preferred as the design parameter for
biological treatment plants. With the introduction of processes such as biological
phosphorus removal, simultaneous precipitation, nitrification and denitrification it
will in many cases be dangerous, difficult or quite impossible to use the sludge
loading as the design basis.
If the sludge age is used as the design basis, the aerobic sludge age will in most cases
be used as the design basis. Expression (4.14) can be transformed
ex= Mx/Fsp= Vz · Xz/Fsp
Vz = 9x · Fsp/Xz
(4.22)
136
Table 4.5 shows that the volumetric loading, Bv.soo. must be 0.2-0.6 kg BOD/(m 3 · d)
in dry weather to obtain a 90-95 per cent BOD treatment. In wet weather the volumetric loading can be 0.6-1.5.
In other words, design must in this case be made on the basis of the dry-weather situation. It is estimated that Bv.soo = 0.4 kg BOD/(m 3 · d).
From Expression (4.20) is found:
V2 =a, · C,IBv.soo = (1,200 kg BOD/d)/0.4 kg BOD/(m 3 · d) = 3,000 m 3
On the basis of the figures in Table 4.6 the population equivalent represented by the
wastewater can be calculated:
PEwater = a,/0.2 = (5,000 m 3 /d)/(0.2 m 3 /(PE · d))= 25,000 PE
PEsoo = a, · C,/0.06 =
(1,200 kg BOD/d)/(0.06 kg BOD/(PE · d)) = 20,000 PE
The two calculations of the population equivalent will usually always deviate somewhat
from each other. The deviation can reveal industrial influence, infiltration, exfiltration,
etc.
4.3.7 Design by means of sludge loading
or sludge age
A somewhat more advanced design can be carried out by using sludge loading or
sludge age. Sludge loading can be used for ordinary biological removals whereas
the sludge age should be used in connection with nitrification processes and other
processes utilizing slowly growing bacteria for the removal of special pollutants in
wastewaters, such as phenol and cyanide. When designing on the basis of the
BOD-sludge loading
Bx,Boo= Q1 · Cooo,J!(Xz · Vz)
the volume, V2, of the aeration tank can be found from the expression:
Vz = Q1· CBoo,J!(Xz · Bx,ood
(4.21)
Typical treatment degrees as a function of the sludge loading are stated in Table 4.5.
For many years, sludge loading has been preferred as the design parameter for
biological treatment plants. With the introduction of processes such as biological
phosphorus removal, simultaneous precipitation, nitrification and denitrification it
will in many cases be dangerous, difficult or quite impossible to use the sludge
loading as the design basis.
If the sludge age is used as the design basis, the aerobic sludge age will in most cases
be used as the design basis. Expression (4.14) can be transformed
ex= Mx/Fsp= Vz · Xz/Fsp
Vz = 9x · Fsp/Xz
(4.22)
136