Effects of exposing slimes on rotating disks
413
DISCUSSION
The results presented have demonstrated that direct exposure of slimes enriched with
oxygen accelerated the rate of removal of carbonaceous matter from wastewater
measured either in terms of B.O.D. 5 , COD. or T.O.C.
The reactions are concentration dependent (Fig. 1) within the ranges encountered and
follow first order kinetics. For this reason the organic concentrations can be converted to
percentage removals in order to facilitate quantifying the relative rates of removal with
and without oxygen enrichment of the atmospheres.
Specifically, the measured B.O.D.5 reduction across stage 1 was found to be 34%
during the base period, whereas when operating with an oxygen enrichment over stage 1,
the comparable value was 65%. Since the number of disks on stage 1, in the first period,
was 48 and in the second period 60, appropriate allowance for such increased surface
should first be made. On the basis that the removal of organics is essentially proportional
to the surface area for the same contact period, the corrected value for the second period
would be 52%. The rate of B.O.D.5. removal, attributable to oxygen enrichment, was
therefore increased from 34% to 52%. The ratio of the rates was therefore 1.53.
The C.O.D. reduction rates across stage 1, based on the data presented in Fig. 2, were
27% during the base period and 50% during the latter period when stage 1 was enriched
with oxygen. Making allowance for increased surface, the latter rate was 40% and the
ratio of rates was 1.48.
Similar calculations relative to the rates of removal of T.O.C. (see Fig. 3) indicate that
during the first period the measured removal was 33% whereas in the latter period the
actual rate of reduction was 51%. Making allowance for the increased surface, the
adjusted rate for the latter period was 41%. The relative rate of the latter period with
respect to that of the first period would have thus been 1.24.
The relative rates of S.O.C. reduction, after making appropriate allowance for
increased surface was 1,1. Therefore the S.O.C. rate did not increase as rapidly as did the
T.O.C. rate, which indicated that the acceleration must have been due mainly to the
increased rate of removal of dissolved organic matter (D.T.O.C.). Calculations involving
the actual dissolved organic removal rates indicate a ratio of rates for the latter period
with respect to the first period of 1.68. Operating with oxygen enrichments in the range
of 50% to 70%, the oxygen conceivably diffused deeper into the slime thus increasing the
active biological mass by a calculated 68%.
Microscopic examination of the slimes that developed on the disks of stage 1 with
oxygen enrichment revealed that in addition to zoogleal masses, the animal population,
which formerly did not appear until stage 4, had moved upstream. Sphaerotilus, which
was present in the first period, was found to have completely disappeared.
For the purpose of comparing the above described performances with conventional
processes, as to time of contact, reference should be made to Fig. 1. Based on the raw
wastewater strength of 160 mg/1, 90% of that B.O.D.5 was removed by 6 stages (36
minutes) of treatment during the base period (constant flow) and 3 stages (constant flow)
were able to accomplish the same rate of removal in 18 minutes when stage 1 was
operated with oxygen.
When three stage operation was practiced, stages 1 and 3 were enriched with oxygen.
Stage 2 received dissolved oxygen from upstream and served to restore the pH of the
influent to stage 1 by raising the pH from 7.0 to 7.3. The decrease in pH was the result of
containing the C0 2 from the respiration of the slimes in stage 1. The data obtained
413
DISCUSSION
The results presented have demonstrated that direct exposure of slimes enriched with
oxygen accelerated the rate of removal of carbonaceous matter from wastewater
measured either in terms of B.O.D. 5 , COD. or T.O.C.
The reactions are concentration dependent (Fig. 1) within the ranges encountered and
follow first order kinetics. For this reason the organic concentrations can be converted to
percentage removals in order to facilitate quantifying the relative rates of removal with
and without oxygen enrichment of the atmospheres.
Specifically, the measured B.O.D.5 reduction across stage 1 was found to be 34%
during the base period, whereas when operating with an oxygen enrichment over stage 1,
the comparable value was 65%. Since the number of disks on stage 1, in the first period,
was 48 and in the second period 60, appropriate allowance for such increased surface
should first be made. On the basis that the removal of organics is essentially proportional
to the surface area for the same contact period, the corrected value for the second period
would be 52%. The rate of B.O.D.5. removal, attributable to oxygen enrichment, was
therefore increased from 34% to 52%. The ratio of the rates was therefore 1.53.
The C.O.D. reduction rates across stage 1, based on the data presented in Fig. 2, were
27% during the base period and 50% during the latter period when stage 1 was enriched
with oxygen. Making allowance for increased surface, the latter rate was 40% and the
ratio of rates was 1.48.
Similar calculations relative to the rates of removal of T.O.C. (see Fig. 3) indicate that
during the first period the measured removal was 33% whereas in the latter period the
actual rate of reduction was 51%. Making allowance for the increased surface, the
adjusted rate for the latter period was 41%. The relative rate of the latter period with
respect to that of the first period would have thus been 1.24.
The relative rates of S.O.C. reduction, after making appropriate allowance for
increased surface was 1,1. Therefore the S.O.C. rate did not increase as rapidly as did the
T.O.C. rate, which indicated that the acceleration must have been due mainly to the
increased rate of removal of dissolved organic matter (D.T.O.C.). Calculations involving
the actual dissolved organic removal rates indicate a ratio of rates for the latter period
with respect to the first period of 1.68. Operating with oxygen enrichments in the range
of 50% to 70%, the oxygen conceivably diffused deeper into the slime thus increasing the
active biological mass by a calculated 68%.
Microscopic examination of the slimes that developed on the disks of stage 1 with
oxygen enrichment revealed that in addition to zoogleal masses, the animal population,
which formerly did not appear until stage 4, had moved upstream. Sphaerotilus, which
was present in the first period, was found to have completely disappeared.
For the purpose of comparing the above described performances with conventional
processes, as to time of contact, reference should be made to Fig. 1. Based on the raw
wastewater strength of 160 mg/1, 90% of that B.O.D.5 was removed by 6 stages (36
minutes) of treatment during the base period (constant flow) and 3 stages (constant flow)
were able to accomplish the same rate of removal in 18 minutes when stage 1 was
operated with oxygen.
When three stage operation was practiced, stages 1 and 3 were enriched with oxygen.
Stage 2 received dissolved oxygen from upstream and served to restore the pH of the
influent to stage 1 by raising the pH from 7.0 to 7.3. The decrease in pH was the result of
containing the C0 2 from the respiration of the slimes in stage 1. The data obtained