Aeration and Energy Savings

A talk by Michael Kuss
General Manager, Michigan City Sanitary District

Proper and adequate aeration is the most important aspect of any activated sludge type wastewater treatment facility, and typically more energy is used to provide the necessary aeration than any other single aspect of treatment.

Making small changes in the aeration (oxygen) supply can provide big savings in energy costs. However, it’s not a simple straight forward process. A wastewater treatment operator cannot simply turn down the air flow to save energy and money. Without the proper amount of aeration, the overall objective of treating the wastewater will be compromised, violations of environmental rules will occur, and polluted water will be discharged to the receiving stream.

The theoretical amount of oxygen required to provide adequate treatment can be calculated using the flow, BOD loading, and Ammonia (NH3-N) loading. Ten State Standards, Section 92.331, contains the design criteria for activated sludge systems. By Converting the pounds of oxygen required to cubic feet per minute of air, the theoretical aeration requirements can be calculated.

To begin an energy savings analysis, the aeration and blower system must be evaluated. Because aeration also provides mixing, the next step is to determine the minimum amount of air needed to meet the mixing requirements. Then a comparison between the theoretical air/oxygen requirements and actual operating data must be performed. It is critical that such analysis also evaluate daily/hourly fluctuations. Average data is excellent for design, but as any good operator knows, the high flow and/or high loading periods of time must be accounted for when considering any design and/or operational changes.

New blowers can provide excellent energy savings with quick pay back. Combined with proper dissolved oxygen control, the energy savings, and ultimately the pollution prevention of these small changes, can provide big positive impacts.