Finding the right wastewater solution for the City of South Beloit

South Beloit and Integrated Fixed-Film Activated Sludge Treatment (IFAS)

To prepare for nitrogen and phosphorus removal requirements, the City of South Beloit, Illinois, turned to Fehr Graham to plan and design its Wastewater Treatment Plant to remove unwanted nutrients. The improvements, designed by Fehr Graham in 2018, are under construction. The plant was originally an activated sludge package plant providing biochemical oxygen demand and ammonia-nitrogen removal.

Finding the right wastewater solution for the City of South Beloit

The City chose BNR to avoid annual chemical costs associated with coagulant addition. One of our design challenges was working within the footprint of the old plant because nearby homes and a railroad restricted growth. The improvements were designed in three phases to increase capacity - start-up, intermediate and ultimate - to better accommodate the growing City. With these restrictions in mind, IFAS treatment became an option with many advantages.


The City chose IFAS with BNR treatment. Like a traditional BNR plant, this design included tanks in series, where each tank uses a controlled environment to promote different biomasses capable of taking up nutrients and removing them from wastewater. The recommended design takes sequenced bio reactors and adds IFAS media to the aerobic/aerated tank.

The term fixed-film in IFAS comes from the biofilm that grows on the plastic media. This media is specially designed to provide a large surface area in which these populations of microorganisms can develop. These little disks are suspended within the liquid with the help of diffusers and mixers, and special screened discharge piping ensures all media stays within the aerobic tank.

One of the biggest benefits of IFAS treatment, and why it was selected for the South Beloit project, is how well-suited it is for retrofit projects. The efficiency of organic and nutrient removal can be increased simply by adding media. Since the South Beloit facility was landlocked, building additional tanks for increased capacity was not a suitable solution. Also, this design needed to be flexible to prepare the City for all three phases of buildout, where each phase would increase the flows and loads to the plant. This IFAS design allows the City to increase treatment capacity by adding media – not tanks - making this a great solution for South Beloit and communities like it. By working with South Beloit through the planning and design phases, Fehr Graham was able to understand the community’s unique needs and recommend the best-suited design. The team at Fehr Graham brings this same care and attention to all of its projects.


Katie Badskey circleKatie McKirahan develops Facility Plan Reports and designs
wastewater treatment plants, water mains and gravity sewers, and
force main extensions. She is involved in all phases of a project from
preliminary concepts to design to construction.