Aeration, a vital step in the wastewater treatment process, can also be an expensive one. Aeration blowers are typically the main consumer of electricity at a wastewater treatment plant, and since many aeration systems are oversized and outdated, they create inefficiencies that greatly influence overall treatment costs. Making upgrades to an outdated aeration system can significantly improve performance and save energy. Moreover, the energy saved coupled with funding opportunities can directly offset the costs of the upgrades.
Improving performance and saving energy
Identifying energy-saving upgrades to an aeration system starts with conducting a detailed analysis of the entire treatment system including identifying actual aeration needs. In the City of Nashua, NH, this analysis indicated that the City’s 20-year old blowers were too large for the facility’s needs. As a result, the blowers were running at a lower speed, reducing their efficiency. Woodard & Curran concluded that three new high efficiency blowers totaling one-half the existing horsepower of the existing system would be sufficient to meet the treatment process needs.
The new high-efficiency blowers are being sized to actual aeration demands based on biological modeling and statistical analysis of historic air flow rates. Modern instrumentation and controls are also being included in the design to precisely monitor dissolved oxygen and maximize efficiency. Nashua’s new aeration system is estimated to use 50% less energy than the previous system, which will reduce the plant’s overall electricity use by approximately 14% saving over $100,000 per year.
Funding and payback
Finding the capital to make improvements can be very difficult. Fortunately, given the efficiency improvements from aeration upgrades, the savings often cover the expense. For example, the Freeport Sewer District (FSD) in Freeport, ME implemented significant process upgrades, including an aeration system overhaul that resulted in enough energy savings to pay for itself within eight years. The updates save an average of 70,000 kWh per month or about $80,000 per year representing about a 50% saving in electricity costs. The savings allowed FSD to pay for additional capital projects without raising rates.
Many state and local agencies also offer funding for projects that save energy. Energy efficiency programs, grants, and loan and rebate programs are all viable funding options. Woodard & Curran helped FSD secure grant funding from Efficiency Maine, an independent trust that promotes energy efficiency. The grant funding covered about 25% of the total project cost. The district borrowed the remainder through the Clean Water State Revolving Fund (SRF).
Because aeration systems are the most energy-intensive process at a wastewater treatment plant, it is a smart approach to invest in upgrades. A well-designed upgrade can save money and increase efficiencies, significantly reducing overall costs.