A Low Cost Open Tank Pure Oxygen System
391
In batch tests using 100 gallons of 0.8% return activated sludge in a 5 foot deep tank,
diffuser efficiencies of greater than 95% were obtained with pure oxygen.
Further testing with the high efficiency diffuser in parallel air and pure oxygen
systems resulted approximately equivalent mass reductions. While the air system required
thirteen times more gas volume to accomplish equivalent aerobic digestion, compressed
air oxygen transfer efficiencies defined as:
0 2 efficiency =
Pounds 0 2 utilized
Pounds 0 2 supplied
reached 72%. This transfer rate, which is approximately six times more efficient than any
other known oxygenation method, opens up new horizons for low cost waste water
treatment. Present research efforts include verification of the batch test results in a 5
GPM flow through pilot plant.
The high gas transfer efficiencies realized in these batch tests led to an investigation of
the possibility of increasing the sludge stabilization rate by substituting ozone for part of
the oxygen in the gas stream. Preliminary tests have shown that the % volatile solids in
the return activated sludge can be reduced in six hours from 75 to 50% using very small
quantities of ozone. Similarly, ozonation of the final effluent (COD=60 mg/1) for a
similar time period resulted in a 50% reduction in COD.
The major problem at Metro Denver since operations began in 1966 has been to
dispose of the large quantities of solids generated. In an attempt to alleviate this problem,
four of the twelve aeration basins (8 MG) were converted to "aerobic digesters", with an
eight day detention time. This modification has resulted in mass reductions averaging 35%
at an operating cost of approximately $20/ton. It was then postulated that even greater
economies could be achieved if the aerobic digestion facility was to be further modified
to utilize the more concentrated waste activated sludge, thickened to 4.5% solids by air
flotation.
Batch tests with the 4.5% material have fully substantiated this hypothesis.
Table 1 summarizes results of a typical ten day test aerobically digesting 4.5% waste
activated sludge using the high efficiency oxygen diffuser. Dissolved oxygen levels were
maintained at 10 ± 5 mg/1 and temperatures at 25 ± 5°C throughout the test run.
391
In batch tests using 100 gallons of 0.8% return activated sludge in a 5 foot deep tank,
diffuser efficiencies of greater than 95% were obtained with pure oxygen.
Further testing with the high efficiency diffuser in parallel air and pure oxygen
systems resulted approximately equivalent mass reductions. While the air system required
thirteen times more gas volume to accomplish equivalent aerobic digestion, compressed
air oxygen transfer efficiencies defined as:
0 2 efficiency =
Pounds 0 2 utilized
Pounds 0 2 supplied
reached 72%. This transfer rate, which is approximately six times more efficient than any
other known oxygenation method, opens up new horizons for low cost waste water
treatment. Present research efforts include verification of the batch test results in a 5
GPM flow through pilot plant.
The high gas transfer efficiencies realized in these batch tests led to an investigation of
the possibility of increasing the sludge stabilization rate by substituting ozone for part of
the oxygen in the gas stream. Preliminary tests have shown that the % volatile solids in
the return activated sludge can be reduced in six hours from 75 to 50% using very small
quantities of ozone. Similarly, ozonation of the final effluent (COD=60 mg/1) for a
similar time period resulted in a 50% reduction in COD.
The major problem at Metro Denver since operations began in 1966 has been to
dispose of the large quantities of solids generated. In an attempt to alleviate this problem,
four of the twelve aeration basins (8 MG) were converted to "aerobic digesters", with an
eight day detention time. This modification has resulted in mass reductions averaging 35%
at an operating cost of approximately $20/ton. It was then postulated that even greater
economies could be achieved if the aerobic digestion facility was to be further modified
to utilize the more concentrated waste activated sludge, thickened to 4.5% solids by air
flotation.
Batch tests with the 4.5% material have fully substantiated this hypothesis.
Table 1 summarizes results of a typical ten day test aerobically digesting 4.5% waste
activated sludge using the high efficiency oxygen diffuser. Dissolved oxygen levels were
maintained at 10 ± 5 mg/1 and temperatures at 25 ± 5°C throughout the test run.