The lower speed appears to be adequate for mixing. Calculations indicated that 13,000 cfm would be sufficient. This would minimize the demand charges imposed by the electric utility. Previously at the Metro WWTP, a fine bubble aeration project was implemented. This is an excellent example of how energy consumption can be reduced because the air supplied to the treatment process is provided in small bubbles that transfer oxygen more efficiently to the wastewater.
Microbes use the oxygen to process organics in the wastewater.
The energy management audit determined that heat recovery from incineration at the Metro WWTP is an option for generating electricity. High-pressure steam is generated from the incineration process, which could be used to drive a turbine for power generation. At another plant, digester gas is used to fuel an internal combustion engine-driven blower for the aeration basins. In addition to having a free fuel supply, the engine-driven blower also is used for peak shaving. Unlike electricity, natural gas is a deregulated commodity.