Pontiac Wastewater Treatment Plant Improvements

The City of Pontiac hired Farnsworth Group to develop a Phosphorous Removal Feasibility Study and Optimization Plan. The plan was undertaken to meet the requirements set forth in the wastewater treatment plant's NPDES permit. The city’s plant has not had a major upgrade since the 1980’s and most of the equipment is from that time period. Therefore, in conjunction with the improvements necessary for nutrient removal, additional plant upgrades were also incorporated.

The existing plant has screening, aerated grit, primary clarification, trickling filters, activated sludge, secondary clarification, liquid chlorine disinfection, and anaerobic sludge digestion. The city collected influent samples for a variety of sample criteria. The results were used as inputs into a GPS-x process model. The model evaluated many alternatives to determine how to best achieve nutrient removal biologically. The selected plant improvements related to nutrients include the:

• Elimination of trickling filters
• Reconfiguration of existing aeration basins
• Addition of a secondary clarifier
• Addition of tertiary filters to existing unused basins
• Re-purposing of existing tanks for a two-stage fermenter
• Addition of a small clarifier for chemical treatment of the dewatering underdrain flow

Furthermore, there are additional plant enhancements that pertain more to the age of equipment rather than nutrient-related aspects, including:

• Replacement of all sewage pumps and most sludge pumps
• Replacement of aeration blowers with high efficiency units
• Digester improvements
• Conversion to vortex grit removal
• Bar screen replacement
• CSO storage improvements
• New storage building
• Addition of mechanical thickening
• Replacement of the dewatering equipment
• Assorted electrical and SCADA improvements

Where possible the existing infrastructure was reused. The aeration basin improvements include the reconfiguring of the basins with four anaerobic/anoxic selector zones, two full size aeration basins, and two half-size aeration basins. All of the basins include supplemental mixing, in addition to aeration. The aeration system is controlled via ammonia/nitrate probes for low DO operation. After submitting the plan, the city moved forward with designing the proposed improvements. After the loan financing was available, the project was bid, and construction was started.

Lift Station Improvements

Additionally, our team designed several sanitary sewer system improvements and upgrades to provide increased capacity, capability, and to prevent possible backups during storm events, Improvements include:

• Illini Lift Station 
  • Added an additional wet well and a third pump to increase the lift station capacity from 1,120 GPM to 2,240 GPM. Upgraded the electrical and controls, including the addition of a flow meter and backup generator.
• Lions Park Lift Station 
  • New lift station to pump wet weather flow to a gravity sanitary sewer interceptor instead of discharging this flow to a CSO outfall. Added electrical, controls, and flow monitoring for CSO 004 into the control panel.
• New West Lift Station and Force Main
  • New lift station and force main to serve current and future development with a capacity of 500 GPM.
• New Rec-Plex Lift Station
  • New lift station to service the recreational complex on the south side of the City with a capacity of 350 GPM.
• New 14" Shared Force Main Piping 
  • New force main piping to service the Illini and Lions Park lift stations, as well as a future East Lift Station.
• Controls and Telemetry 
  • Added controls for monitoring at the WWTP from the lift stations.

From an operations standpoint, it was determined that the Illini Lift Station was the most critical, so the new force main was designed and sized around these existing pumps.

We performed several hydraulic calculations for various scenarios to verify the pumps will perform with any combination of the three lift stations operational at any given time.