Are you familiar with the Wastewater Treatment Plant (WWTP) of Ann Arbor City in Michigan?
The Wastewater treatment plant was originally built in 1936 and thus had older parts of the infrastructure that lie beneath the center of the city that needed to be demolished. The plant currently services about 130,000 residents of Ann Arbor City and the nearby areas of Pittsfield and Scio Townships, processing almost 19 million gallons of wastewater per day.
Wastewater Treatment System
There are two plants in the existing Ann Arbor WWTP – the East and West Plants, which provide primary and secondary treatment to the wastewater in the system. Preliminary treatment is done using catenary bar screens, a climbing rake bar screen, and grit chambers. From this process, the flow is diverted to the East or West plants for primary treatment which consists of the gravitational settling of the bio-solids through ten rectangular clarifiers in the West plant, and four circular clarifiers in the East plant.
Secondary treatment follows which consists of the biological removal of dissolved solids through the activated sludge process. The processed solids will then settle in secondary clarifiers. Secondary treatment requires two aeration tanks and five circular clarifiers in the West plant and four aeration tanks and four circular clarifiers in the East plant.
Tertiary Treatment And Disinfection Process
Twelve sand filters are used for tertiary treatment while disinfection is done by chlorination and de-chlorination using sulfur dioxide. The treated water is then returned to the Huron River.
Approval To Overhaul Wastewater Treatment Plant
In February 2012, the Ann Arbor City Council granted approval for a massive project that will overhaul the city’s aged and ailing wastewater treatment plant located near Dixboro Road and Geddes Road in Ann Arbor Township of US-23. The Wastewater Treatment Services obtained a $92.9 million state loan to fund the massive rehabilitation project.
Scope Of Rehabilitation Works
The rehabilitation project identified the various structures and systems of the wastewater treatment plant that needed improvement which included:
- Rehabilitation of existing structures
- Upgrade of primary and secondary wastewater treatment processes
- Replacement of aging facilities with new ones
Meeting Future Demands
With these renovations, the rehabilitated wastewater treatment plant will be able to meet the future flow and loading demands of Ann Arbor City as well as regulatory requirements. The design capacity of the current plan is for 29.5 million gallons per day from two facilities: the West Plant which was constructed in the 1930s and the East Plant which was constructed in the late 1970s.
Phase I: Demolition Work
Phase I of the rehabilitation project included the demolition of the old storage building and the reaeration tank; relocation of utilities before actual demolition; electrical work to isolate the East Plant from the Solids Handling Building, and the installation of waste activated sludge line that would transport sludge to the Solids Handling Building.
Demolition of the storage building and the reaeration tank provided additional staging area and traffic patterns for the completed Residuals Handling Improvements Project. And as live utilities run through the storage building, relocation prior to demolition was effected.
Phase II: Survey, Design, And Construction
Phase II of the rehabilitation project involved a majority of the design and construction work including:
- The field investigation phase included a pre-demolition survey for hazardous and waste materials, concrete repair survey, access bridge survey, secondary clarifier equipment evaluation, East Plant bio-solids sedimentation survey, administration building evaluation, evaluation of plant isolation gate, geotechnical surveys and analysis, online verification, PICs field-wiring survey
- Design of the East Plant Modifications, West Plant Demolition and Reconstruction, electrical and site work
East Plant Rehabilitation Works
For the East Plant, the aeration system will be rehabilitated including the installation of new blowers with vibration spring isolators, new air piping, a new diffused aeration system, new mixers, and tank flow patterns reconfiguration. The East Electrical/Blower Building will also undergo renovation work which would include removing the standby generators and electrical gear, installing a new wastewater sampler room within the building, and replacing the return activated sludge pumps of the East Plant.
Rehabilitation work will also include miscellaneous repairs to the secondary clarifiers as well as electrical improvements to the Primary Building. The existing Dechlorination Building will be renovated and converted to the Tertiary Filter Blower Building. A new Ferric Building will be constructed in addition to some minor work on gates and concrete repair throughout the East Plant.
West Plant Demolition Works
On the other hand, demolition work at the West Plant includes six digester tanks, aeration tanks, primary and secondary clarifiers, Administration Building, Chlorine Building, Machinery Building, West Plant Blower Building, flow splitting structures, a portion of the old Chlorine Contact Tank, fabrication shop, and the old flocculation basins. The demolished structures will be replaced with new or reconstructed structures. The target completion date of the rehabilitation project is September 2017.
Do you know other old and aging wastewater treatment plants in your state?