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CASE STUDY

Aeration Systems in Wastewater Treatment Plants PG&E, Northern CA

Situation

A major city in Northern California provides treatment services to approximately 98% of its total population of over 109,000 inhabitants. The Water Reclamation Facility (WRF), a tertiary treatment facility, has a capacity of 14 MGD and includes primary clarification, equalization basins, an activated sludge process designed for biological nitrogen nutrient removal, secondary clarification, tertiary filtration, and chlorination. This facility has a minimum requirement of 5 MGD estuary discharge, and produces recycled water for turf and landscape irrigation.

Solution

Lincus engineers developed a benchmark analysis to identify potential energy savings for the facility which has an annual electric consumption of 8.0 million kWh. A study by the California Energy Commission found that an urban wastewater treatment plant uses between 1,000 to 3,500 kWh/MG processed depending on the type of treatment. For comparison, the city’s treatment plant consumed an average of 2,357 kWh/MG processed. Lincus’ benchmark showed that potential energy savings could be gained in the secondary aeration blower, mixers in anoxic zones, and the Gridbee mixers in oxic zones.

Lincus’ engineers proposed multiple solutions to yield energy savings of 1,270,272 kWh/year.

Replace Secondary Aeration Blower: The existing secondary aeration blower process included three single stage centrifugal Roots blowers that were 500hp each. Lincus determined that one blower should be replaced with a 300hp high-speed blower to improve the wire-to-air efficiency from 39.8% to 70%.

Pulse Air Mixers in anoxic Zones: The facility’s anoxic zone included two tanks that both had two 15hp submersible pumps, one 4.4hp Wilo submersible mixer, and two 2.7hp Wilso submersible mixers. Lincus advised that the existing mixers be replaced with a pulsair mixer system, which consists of stainless steel bubble forming plates and a 15hp air compressor.

Grdibee Mixers in oxic Zones: The wastewater treatment plant had four aeration basins with 12 zones. Zones 1-9 are aerated with one 500hp blower, while the air headers for zones 10-12 are closed for the anoxic zone. Lincus recommended to install additional Gridbee mixers to shut down the air headers for zones 7-9 to increase the anoxic zone volume and decrease blower air being supplied with fewer diffusers.

Results

  • Replacement of the Secondary Aeration Blower resulted in a 34% annual energy savings which provided an $80,571 reduction in annual utility costs (with a simple payback period of 4.9 years).
  • By improving the Pulse Air Mixers in anoxic zones, the facility was able to reduce their energy usage by 71% and save $37,257 on their utility bills (with a quick payback period of 0.2 years).
  • And, with installation of additional Gridbee mixers, savings resulted in a 14% annual energy reduction and a lowered annual utility bill by $28,561 (with a simple 0.3 year payback).

Water Infrastructure and System Efficiency (WISE™) Program: The Lincus WISE™ program is a comprehensive turnkey solution for municipalities which offers no-cost engineering services, project support, and cash incentives. Lincus uses a holistic approach, combining existing pump tests, energy audits, and hydraulic modeling to evaluate how a water reclamation facility can optimize its performance. In this project, Lincus completed its review of the system and an overall analysis in a single phase. Lincus engineers conducted an onsite assessment to understand system operations, and then developed a savings analysis to show the payback based on improving blowers and mixers within the system.

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