Increasing Oxygen Flux Density in the Aeration Basins

Situation

With the implementation of the previously described projects the utility was in a position to implement the next and greatest efficiency improving project; fine bubble diffuser implementation.

The existing jet-aeration system produced large bubbles of air which has a relatively poor surface area to volume ratio. The ability to transfer oxygen to the bacteria is more dependent upon the surface area of the air bubbles rather than the volume of air in each bubble. The efficiency of the transfer mechanism is dependent upon improving the surface area to volume ratio of the bubbles and hence the amount of energy required.

Problem

Both blowers were scheduled for replacement according to the 30 year asset management plan and blower technology had reached new heights. The opportunity to improve blower efficiency and to improve the oxygen flux density (increased surface area to volume ratio) was at hand.

Implication

The opportunity to improve blower efficiency was available but the opportunity for even larger efficiency improvements became obvious. The combination of the previous projects, the turbo-blower technology and the chance to implement a fine bubble diffuser system could not be ignored and the utility was in a position to take advantage of this opportunity.

Need Payoff

An oxygen flux density study was undertaken to evaluate the efficacy of continuing to utilize the jet aeration system that was originally installed. The study indicated, along with the other indicators mentioned above, that there would be substantial opportunity for efficiency improvement by addressing the aeration system change opportunity.

The state of fine bubble diffusing technology was evaluated and it was determined that this was the time to move. Plans were put in place, designs and bids were solicited and best value procedures were used to select both product and installation labor.

The Time Line

The figure below illustrates the time line of continuous improvement efforts and the results.
• The top arrow is the overall project time line.
• The second set of arrows show the running and eventual removal of the two jet aeration pumps.
• The third row arrow represents the time line for this project under consideration.
• The red blocks illustrate the reduction in power consumption from June of 2008 to present.
• The line of blue rounded rectangles represents the installed blower types during the five stages of energy reduction.
• The line of vertical arrows and text describe the equipment running & idle
• The line of vertical green arrows with text describe the major milestones.

What's may not be so Obvious

Had it not been for the previous efficiency improvements and hence the cost reduction, the capital dollars to implement the fine bubble diffuser system would not have been available. The Continuous Improvement process implemented during the previous years enabled the utility to take advantage of implementing the fine bubble diffuser system along with the turbo-blower technology.