Fine-bubble diffusers provide additional oxygen to a Pennsylvania wastewater treatment system
In 1991, the village of Intercourse, located in Leacock Township, Pa., was in need of a new wastewater treatment system. Sequencing Batch Reactor (SBR) technology was emerging at the time as an efficient and economical alternative to conventional flow-through systems. Knowing this, the township’s engineer, Rettew Associates, began looking at the AquaSBR system for Leacock Township’s upgrade.
Following the evaluation of various treatment methods, Rettew and the local sales representative proposed the modern AquaSBR system to the township as the best solution for the upgrade. The new plant would consist of a dual-basin SBR system designed to treat an average flow of 0.30 million gal per day (mgd) and peak flow of 0.75 mgd. Each of the basins would include retrievable coarse-bubble diffusers, AquaDDM mixers and Aqua-Aerobic electric actuated decanters.
The AquaSBR system went online in September 1991 and consistently met the plant’s treatment objectives of BOD5, TSS, NH3-N and Total Phosphorus for nine years. After several years, the organic and ammonia loadings began to routinely exceed the nominal design values. The plant was originally designed to handle influent BOD5 of 250 mg/L but was receiving an average of 340 mg/L. Through proper management of the existing aeration capacity and careful solids management, the plant operator was able to maintain effective levels of treatment; however, the long-term solution to the excessive loadings was to provide additional oxygen.
Engineers at Aqua-Aerobic Systems Inc. , evaluated several possible solutions for the plant and presented recommendations to the township’s engineer. One option was to build a third SBR basin, but this would be costly. A second option was to increase the amount of oxygen in the reactors, which involved replacing existing, retrievable coarse-bubble diffusers with retrievable fine-bubble diffusers. The fine-bubble diffusers would increase the amount of oxygen transfer, thus promoting successful BOD reduction and nitrification.
To minimize cost, as well as maintain both SBR basins in operation during the aeration system upgrade, Aqua-Aerobic Systems  suggested the plant retrofit the existing track beams of the coarse-bubble diffusers racks with the new fine-bubble assemblies. In June 2000, the aeration expansion was completed in just one day, without dewatering the basins. Both reactors, each with two (10 tube) coarse-bubble diffuser racks were retrofitted with (20 tube) fine-bubble assemblies. In addition, the existing blowers were re-sheaved to operate at a higher capacity and the motors upgraded from 15 hp to 20 hp so there was no need to purchase new blowers.
According to Jerry Brackbill, plant operator, “The aeration expansion was easy to install by Leacock Township employees and changing of the air diffuser assemblies took less than one day, with no interruption to plant flow or performance.”
The aeration upgrade saved Leacock Township considerable expense compared to the construction of a third SBR reactor. The upgrade allowed the AquaSBR system to be re-rated by the Department of Environmental Protection to a higher organic and ammonia loading capacity, and extended the life of the facility well into the foreseeable future. The plant’s performance continues to be exceptional as indicated in the table below.
Average Operating Data (January 2010 to June 2012)
|Loading||Design Influent||Design Effluent||Average Influent||Average Effluent|
|Avg Flow (mgd)||0.3||-----||0.20||-----|
|Peak Flow (mgd)||0.75||-----||0.23||-----|
|Total P (mg/L)||10||2||7.4||0.41|
Brandon Thomas is senior application engineer, biological processes and membranes, for Aqua-Aerobic Systems. Thomas can be reached at firstname.lastname@example.org.