plants out of necessity. There are new treatment facilities, particularly package
plants, designed and built as contact stabilization plants. The limit of the process
application, for some reason, is not properly recognized by many engineers. The
process should not be applied for the treatment of wastewaters whose organics occur
mostly in the dissolved form. For municipal wastewater or even for domestic
wastewater, laboratory tests should be performed to determine (1) the removable
fraction of the organic matters and (2) the contact time and sludge concentration
required to affect specified treatment efficiency.
Rich [35] assumes that adsorption removal per unit concentration of activated
sludge is related to the concentration of the removable portion of the organics:
À
dS a
dX
¼ k a S a
ð3:21aÞ
or
S a
S ao
¼ ÀK a X
ð3:21bÞ
in which S a ¼ concentration of remaining organics that can be removed by adsorption, mass per volume; S ao ¼ initial concentration of organics that can be removed by
adsorption; X ¼ initial concentration of activated sludge; and K a ¼ adsorption
removal constant, which is equal to 0.434 k a in Eq. (3.21a).
The following procedure can be followed for a laboratory development of design
criteria using Eq. (3.21b):
1. Use four or more batch reactors, each with a different amount of acclimated
activated sludge.
2. Allow a contact period of 20 min with the wastewater in each reactor.
3. Analyze the initial solid concentration and the initial and final BODs of the
wastewaters in each reactor.
4. Plot figures similar to Fig. 3.11a, b to establish the removable fraction and
removal constant at various solid concentrations.
The procedure may be repeated with different contact periods (30 min, 40 min,
etc.) to see whether a larger fraction of organics could be removed and whether such
operation is economically justifiable.
From Fig. 3.11, suppose a certain sludge concentration X is selected for operation
of the adsorption process with a (S a /S ao ) value of 0.1; then the total BOD removal of
the process is 90% – (90%)(10%) ¼ 81%. If a total removal of 90% is desirable, it
can be seen that 100% of the organics removable by adsorption is required, which is
highly unlikely for any wastewater. The limitation of the process application is
therefore self-evident.
3 Biological Processes
103
plants, designed and built as contact stabilization plants. The limit of the process
application, for some reason, is not properly recognized by many engineers. The
process should not be applied for the treatment of wastewaters whose organics occur
mostly in the dissolved form. For municipal wastewater or even for domestic
wastewater, laboratory tests should be performed to determine (1) the removable
fraction of the organic matters and (2) the contact time and sludge concentration
required to affect specified treatment efficiency.
Rich [35] assumes that adsorption removal per unit concentration of activated
sludge is related to the concentration of the removable portion of the organics:
À
dS a
dX
¼ k a S a
ð3:21aÞ
or
S a
S ao
¼ ÀK a X
ð3:21bÞ
in which S a ¼ concentration of remaining organics that can be removed by adsorption, mass per volume; S ao ¼ initial concentration of organics that can be removed by
adsorption; X ¼ initial concentration of activated sludge; and K a ¼ adsorption
removal constant, which is equal to 0.434 k a in Eq. (3.21a).
The following procedure can be followed for a laboratory development of design
criteria using Eq. (3.21b):
1. Use four or more batch reactors, each with a different amount of acclimated
activated sludge.
2. Allow a contact period of 20 min with the wastewater in each reactor.
3. Analyze the initial solid concentration and the initial and final BODs of the
wastewaters in each reactor.
4. Plot figures similar to Fig. 3.11a, b to establish the removable fraction and
removal constant at various solid concentrations.
The procedure may be repeated with different contact periods (30 min, 40 min,
etc.) to see whether a larger fraction of organics could be removed and whether such
operation is economically justifiable.
From Fig. 3.11, suppose a certain sludge concentration X is selected for operation
of the adsorption process with a (S a /S ao ) value of 0.1; then the total BOD removal of
the process is 90% – (90%)(10%) ¼ 81%. If a total removal of 90% is desirable, it
can be seen that 100% of the organics removable by adsorption is required, which is
highly unlikely for any wastewater. The limitation of the process application is
therefore self-evident.
3 Biological Processes
103