This presentation will discuss the Aerobic Granular Sludge (AGS) treatment process with particular focus on selection of AGS for the new Grassland Sewage Treatment Plant (STP) in Franklin, TN, which will be Tennessee’s first application of AGS.

The AGS process was first developed in the early 1990s, piloted in 2005 and constructed in full scale in Garmerwolde, Netherlands in 2009.  The process uses sludge granules for simultaneous nitrification, denitrification, and phosphorus removal in the granules’ aerobic, anoxic, and anaerobic zones. The enhanced settleability of granules also allows for shorter settling phases and higher MLSS concentrations. GMC, along with Riviera Utilities in Foley, AL, and Aqua-Aerobics, assisted in facilitating the first full-scale AGS installation in the U.S., which began operation in early 2020.

This presentation centers on the Grassland STP, which is owned by Limestone Water Utility Operating Company (the TN utility of Central States Water Resources) and located within the Grassland community in Franklin, TN. Due to aging and undersized infrastructure, the STP required replacement to adequately serve its customer base. The primary challenge with upgrading and upsizing the biological process was the stringent total nitrogen (TN) limit of the receiving stream, the Harpeth River. After an evaluation of multiple treatment technologies, the Granite AGS™ Aerobic Granular Sludge process by Parkson Corporation was chosen as the basis of design due to lower O&M cost relative to other technologies, familiarity of operators with SBR-style biological process, and economical cost of equipment.

The proposed Grassland STP began design in May 2024 and is projected to begin construction in the fall of 2025.