Warsaw Wastewater Treatment Plant

With average flows approaching the plant’s design capacity of 3.9 MGD and a high potential for future industrial and residential growth, the City needed to increase capacity and to also meet a new discharge limit for phosphorus. The City elected to convert its fully aerobic facility to anaerobic digestion and biological nutrient removal to minimize energy usage and meet current and future nutrient limits.

Wessler evaluated options for expanding the WWTP to 6.0 MGD design average flow and 18 MGD design peak flow. The options included remaining fully aerobic with oxidation ditches and aerobic digesters versus converting to anaerobic processes by adding primary clarifiers and anaerobic digesters.

With a vision for the long-term and potential for ultimate expansion to a 12 MGD capacity on the current site, the City elected to convert to anaerobic processes in order to minimize energy consumption and reduce sludge production over the life of the facility.

The project included new grit removal, new circular primary clarifiers, a new 3-stage anaerobic selector tank, conversion of the Carrousel oxidation ditch to separate mixers and diffused aeration, a new secondary clarifier and replacement of existing clarifier equipment, new chemical feed building for back-up phosphorus removal, and expansion of the UV system. Solids handling improvements included conversion of the aerobic digesters to WAS, digested sludge, and septage holding tanks, new anaerobic digester complex, new volute dewatering press, new plantwide SCADA system, and new 5-bay parking garage.

The highlight of the new processes is the converted oxidation ditches to the BioLoop® process with separate aerobic and non-aerated anoxic zones for simultaneous nitrification/ denitrification (SND). A new turbo blower and control system based off both ammonia and dissolved oxygen levels will provide the minimal amount of air needed for aerobic treatment and to maintain anoxic zones which will provide additional energy savings.

Provisions were also made for a future co-generation system to add a gas conditioning system and engine-generators for utilizing digester gas to produce electricity.

The project, funded by the State Revolving Fund (SRF) Loan Program, was completed in 2021 with a construction cost of $27.8 million.