Operations-Friendly Facilities Address Current and Future Wastewater Challenges

Stanley Consultants was hired by Iowa City, Iowa, to address current and future wastewater treatment challenges.

Necessitated by new ammonia regulations, the $26.5 million expansion at Iowa City's south wastewater treatment plant doubled its capacity from 5 MGD to 10 MGD.  Iowa City used the opportunity to configure the system to serve long-term city growth and allow phase out of the older, downtown north wastewater treatment plant.

The design of the wastewater facilities was a collaborative effort between City staff and Stanley Consultants.  The result was an innovative, operations-friendly facility that has the flexibility to address current and future wastewater treatment challenges.

The project included flow equalization and pumping modifications; conversion to vortex grit removal to minimize foaming; additional clarifier, RAS pumping, and disinfection capacity; conversion of the carbonaceous activated sludge system to a single sludge nitrifying system; a new anaerobic digester complex with high strength flow equalization; administration building with laboratory; and a vehicle building.

The heart of the project included a novel biological process that used a combination of anoxic and aerobic zones along with mixed liquor return, fine bubble diffused aeration, and robust computer process control to reduce the plant's energy use by an estimated 25 percent while meeting ammonia discharge limits.  The process also reduced the amount of discharged total nitrogen.

Other features included clarifiers that minimized hydraulic short circuiting using baffles and an inset effluent launder; corrosion resistant materials including galvanized steel clarifier equipment and stainless steel digester covers; and rotary drum sludge thickeners.  It featured temperature phased digestion which used a 135° F digester followed by traditional mesophilic digesters to convert biosolids to methane gas fuel and destroy pathogenic bacteria.  The digested biosolids, high in organic matter and nutrients, are applied to agricultural land as fertilizer.