Big Rapids improves plant with a $7.5 million SRF loan, and stays on-line throughout 3-year construction process.

The City’s existing wastewater  plant was aging. Several processes were at or near the end of their service life. Replacement parts were difficult to find, and maintenance issues were growing. The existing anaerobic digestion process used for solids handling was unreliable, making it difficult to meet permit limits. In addition, the motor control center and standby generator were located in a low-lying area that had previously flooded.

To qualify for State Revolving Loan (SRF) funding, Big Rapids retained Prein&Newhof to write a Project Plan — a comprehensive condition assessment of the existing system. 90% of this preliminary engineering work was funded by an S2 grant, part of a special economic stimulus package from the SRF fund.

Big Rapids chose to demolish and move electrical equipment and several buildings to higher ground. The City obtained approximately $7.5 million in SRF funding to construct the project.

The improvements included:

• Addition of a grease/grit removal facility with associated flow splitting.
• Addition of an equalization basin aeration system with dedicated air supply.
• Expansion of the aeration system, including the addition of a fourth aeration tank and air supply replacement.
• Construction of an aerobic digester.
• Conversion of the solids handling system to gravity thickening with aerobic digestion, including supporting air supply, pumping, and piping upgrades.
• Upgrades to the wastewater pumping system.
• An upgrade of electrical service with a permanent standby generator.
• Introduction of a Supervisory Control and Data Acquisition (SCADA) system.
• An addition to the maintenance facility and an expansion of the administration building.

The biggest challenge to this project was developing a construction sequence that would allow the existing plant to function until new portions of it were completed. Phased construction and demolition were required to ensure satisfactory operation and meet NPDES permit requirements.

In addition, system fluctuations caused by the Ferris State University schedule had to be factored into three phases. Demolition of obsolete components took place following successful transfer of treatment capabilities to new and retrofitted components.

The improved plant is far more efficient:

• Membrane diffusers are used in the aeration tanks and aerobic digesters to maximize transfer efficiency and save energy. The previous system provided more oxygen to the aeration tanks than needed.
• All three air supply systems (for the Equalization Basin, Aeration Tanks, and Aerobic Digesters) are equipped with variable frequency drives for operational flexibility and efficiency.
• The new Supervisory Control and Data Acquisition (SCADA) system allows operators improved monitoring and control of the system, freeing some of their time for pro-active maintenance and other tasks.