Biofilters
to a reaction of first order. The whole biofilm will then behave as having a first order
reaction with reduced efficiency; see Section 5.1.
The transition between the zero and half order reaction can be directly determined.
The transition criterium is, according to the previous section:
kov= rokoA
k~J.zv = ro ,.J2 kovf D
The transition from half order to first order can be determined correspondingly
Example 5.6
k11.!V = ro ,.Jkovf D
klV = klVf · L ·£
A 4 m high submerged filter filled with plastics packing with a specific surface of 100
m 2 /m 3 has a nominal filter velocity of 1 mlh. The wastewater has a concentration of
500 g COD/m 3 . The same process constants as in Examples 5.3 and 5.5 are used.
Air is constantly bubbled into the filter resulting in an efficient aeration so that the whole water column on the whole depth is assumed to have an oxygen concentration of 2
g 0 2/m 3 . According to Example 5.5, the filter will be oxygen limited from the top to the
position in the filter where SoiScoo = 0.14 g 0 2/g COD, that is, when Scoo has been
reduced to 14 g COD/m 3 .
In the upper part of the filter, the removal is of a half order in the oxygen concentration
which, however, occurs in the filter itself as a zero order because the oxygen concentration is assumed to be constant.
kov
%
= ro · k%A.02 · So2
k%A,02 = ,J2 Do2 · kot,02
llmax
kot,02 = -YH X · VQ2,COD
6
1
3
kot.02 = 0.67 · 56 u = 295 g02/(m · d)
k%A.02 = 'V2 · 1.7 · 10- 4 · 295 · 10 3 = 10 (g 0 2)%m- 112 d- 1
kov
= 100 · 10 · -Y2 = 1400 g 02/(m 3 · d)= 2400 g COD/(m 3 · d)
which corresponds to a high-rate filter.
(5.48)
(Hence the result in Example 5.3 was not realistic because oxygen is limiting for the removal.)
163
to a reaction of first order. The whole biofilm will then behave as having a first order
reaction with reduced efficiency; see Section 5.1.
The transition between the zero and half order reaction can be directly determined.
The transition criterium is, according to the previous section:
kov= rokoA
k~J.zv = ro ,.J2 kovf D
The transition from half order to first order can be determined correspondingly
Example 5.6
k11.!V = ro ,.Jkovf D
klV = klVf · L ·£
A 4 m high submerged filter filled with plastics packing with a specific surface of 100
m 2 /m 3 has a nominal filter velocity of 1 mlh. The wastewater has a concentration of
500 g COD/m 3 . The same process constants as in Examples 5.3 and 5.5 are used.
Air is constantly bubbled into the filter resulting in an efficient aeration so that the whole water column on the whole depth is assumed to have an oxygen concentration of 2
g 0 2/m 3 . According to Example 5.5, the filter will be oxygen limited from the top to the
position in the filter where SoiScoo = 0.14 g 0 2/g COD, that is, when Scoo has been
reduced to 14 g COD/m 3 .
In the upper part of the filter, the removal is of a half order in the oxygen concentration
which, however, occurs in the filter itself as a zero order because the oxygen concentration is assumed to be constant.
kov
%
= ro · k%A.02 · So2
k%A,02 = ,J2 Do2 · kot,02
llmax
kot,02 = -YH X · VQ2,COD
6
1
3
kot.02 = 0.67 · 56 u = 295 g02/(m · d)
k%A.02 = 'V2 · 1.7 · 10- 4 · 295 · 10 3 = 10 (g 0 2)%m- 112 d- 1
kov
= 100 · 10 · -Y2 = 1400 g 02/(m 3 · d)= 2400 g COD/(m 3 · d)
which corresponds to a high-rate filter.
(5.48)
(Hence the result in Example 5.3 was not realistic because oxygen is limiting for the removal.)
163