410
W. Torpey, H. Heukelekian, A.J. Kaplovsky, and R. Epstein
OPERATING RESULTS - USING THREE STAGES ONLY
Since enrichment of the atmosphere with oxygen over stage 1 had accelerated the
removal of organics, enrichment of an additional stage was tested to observe possible
further acceleration. Accordingly, an additional hood was placed over stage 7, and
equipped with 71 disks. The flow of wastewater was bypassed from the effluent of stage
2 to the influent of stage 7. Thus, stage 7 became stage 3 during the month of September,
1970. Using these three stages, oxygen was fed at .8 to 1.2 liter per minute, the oxygen
rose under the hood of stage 3 to 35% to 40%, whereas under stage 1 hood the range
remained 50% to 70%. The results are compared in Table 2 with the former operation of
three stages using a hood over stage 1 alone. The B.O.D. 5 at stage 3, with oxygen
enrichment on the first stage alone was 16 mg/1, as compared with 10 mg/1, when using
an oxygen enrichment over the first and third stages. The S.O.C. was markedly reduced to
1 mg/1 in the latter. No nitrification was evident in the effluent from stage 3 when the
oxygen enrichment was confined to stage 1. When the third stage was enriched with
oxygen, 7.6 mg/1 of nitrates were produced. Thus, about 18 minutes of contact with the
slimes was required to carry the oxidation process through the carbonaceous zone into
the nitrogenous zone.
OPERATING PROCEDURES AND GENERAL OBSERVATIONS
The accumulation of biological growths, without oxygen enrichment, was rather rapid
in the first three stages. By controlling the thickness of the slimes bridging was prevented
across the disks and anaerobic conditions in the lower layers of the slimes. Thickness was
controlled by removal of the growths from the first, second and third stages every three
to five days. The fourth stage was harvested on a weekly basis, the fifth stage after 10
days and the sixth stage every two weeks. The downstream nitrification stages did not
require thickness control. The slime thickness was maintained at less then 1.5 mm and
operated with a relatively high surface concentration without bridging. Cleaning was
accomplished, either by a water jet or reversing the direction of rotation of the disk
assembly for a few minutes.
After the disks were cleaned by water, the biological growths recovered in the first
stage after about 18 hours and the very thin slimes, so formed, were capable of restoring
the efficiency thereafter. The time required for the growths to recover remained
substantially the same downstream to stage 3. Beyond this stage, increased time was
required as the organic concentration was being reduced and slower-growing biological
forms colonized those stages.
When using the hood over stage 1, the frequency of removing the excess slimes was
reduced markedly. For stage 1 and 2, reversing the direction of rotation weekly prevented
bridging even though the spacing between disks was about .64 cm. Most of the organics
were removed by stages 1 and 2. Reversing direction of rotation of stages 3 to 6 no more
often than every 3 to 4 weeks controlled slime thickness effectively.
In the base period, sphaerotilus and zooglea constituted the predominant biological
species in the slimes on stages 1 - 3 . When these growths sloughed off, they had a
rope-like form, probably due to rotation, and settled rapidly, at 4.57 m/hr. Upon
microstraining the successive effluents from stage 1 through 10, showed a progressive
increase in filterability proceeding downstream. Coincident with that particular stage
W. Torpey, H. Heukelekian, A.J. Kaplovsky, and R. Epstein
OPERATING RESULTS - USING THREE STAGES ONLY
Since enrichment of the atmosphere with oxygen over stage 1 had accelerated the
removal of organics, enrichment of an additional stage was tested to observe possible
further acceleration. Accordingly, an additional hood was placed over stage 7, and
equipped with 71 disks. The flow of wastewater was bypassed from the effluent of stage
2 to the influent of stage 7. Thus, stage 7 became stage 3 during the month of September,
1970. Using these three stages, oxygen was fed at .8 to 1.2 liter per minute, the oxygen
rose under the hood of stage 3 to 35% to 40%, whereas under stage 1 hood the range
remained 50% to 70%. The results are compared in Table 2 with the former operation of
three stages using a hood over stage 1 alone. The B.O.D. 5 at stage 3, with oxygen
enrichment on the first stage alone was 16 mg/1, as compared with 10 mg/1, when using
an oxygen enrichment over the first and third stages. The S.O.C. was markedly reduced to
1 mg/1 in the latter. No nitrification was evident in the effluent from stage 3 when the
oxygen enrichment was confined to stage 1. When the third stage was enriched with
oxygen, 7.6 mg/1 of nitrates were produced. Thus, about 18 minutes of contact with the
slimes was required to carry the oxidation process through the carbonaceous zone into
the nitrogenous zone.
OPERATING PROCEDURES AND GENERAL OBSERVATIONS
The accumulation of biological growths, without oxygen enrichment, was rather rapid
in the first three stages. By controlling the thickness of the slimes bridging was prevented
across the disks and anaerobic conditions in the lower layers of the slimes. Thickness was
controlled by removal of the growths from the first, second and third stages every three
to five days. The fourth stage was harvested on a weekly basis, the fifth stage after 10
days and the sixth stage every two weeks. The downstream nitrification stages did not
require thickness control. The slime thickness was maintained at less then 1.5 mm and
operated with a relatively high surface concentration without bridging. Cleaning was
accomplished, either by a water jet or reversing the direction of rotation of the disk
assembly for a few minutes.
After the disks were cleaned by water, the biological growths recovered in the first
stage after about 18 hours and the very thin slimes, so formed, were capable of restoring
the efficiency thereafter. The time required for the growths to recover remained
substantially the same downstream to stage 3. Beyond this stage, increased time was
required as the organic concentration was being reduced and slower-growing biological
forms colonized those stages.
When using the hood over stage 1, the frequency of removing the excess slimes was
reduced markedly. For stage 1 and 2, reversing the direction of rotation weekly prevented
bridging even though the spacing between disks was about .64 cm. Most of the organics
were removed by stages 1 and 2. Reversing direction of rotation of stages 3 to 6 no more
often than every 3 to 4 weeks controlled slime thickness effectively.
In the base period, sphaerotilus and zooglea constituted the predominant biological
species in the slimes on stages 1 - 3 . When these growths sloughed off, they had a
rope-like form, probably due to rotation, and settled rapidly, at 4.57 m/hr. Upon
microstraining the successive effluents from stage 1 through 10, showed a progressive
increase in filterability proceeding downstream. Coincident with that particular stage