Springfield, MO: A Plant-Wide Challenge

The Springfield, MO Southwest Wastewater Treatment Plant (SWTP) is a 35 mgd facility that is composed of two separate plants: Plant 1 is a two-stage system that incorporates pure oxygen activated sludge in the first stage and biological nitrification in the second stage, while Plant 2 features a uniquely-configured biological phosphorus removal system. The influent waste stream is a challenge to treat for several reasons. Flow rates are highly variable due to excessive I/I problems, resulting in peak day: average flow ratios as high as 3.6:1. Peak flow events are also atypical in that they are often of multiple day duration. BOD and TSS loads to the plant are highly variable due to a significant industrial contribution; effluent BOD limits in the peak flow outfall are not consistently met due to an exorbitantly high soluble BOD fraction that is often observed during extreme wet weather flow events.The SWTP staff currently faces two additional challenges. The most pressing issue concerns a new effluent total phosphorus limit. Second, the Springfield population is steadily growing, requiring that the plant be expanded by about 50% within the next two decades. To address these challenges, several alternatives were examined to expand the plant and incorporate nutrient removal while staying within the bounds of a strict budget. The selected plan was to expand Plant 1 as a single stage biological nutrient removal (BNR) system with air activated sludge and increase Plant 2 capacity by adding primary and final clarifiers to the existing single stage BNR system. This combination resulted in the lowest total project cost; lowest O&M, manpower, and chemical requirements; and lowest sludge production while providing the most streamlined design. Instead of implementing this multi-million dollar capital improvement plan all at once, three phasing plans were developed to distribute the capital investment over the planning period. The selected long-term phased expansion plan allows for a reduction in current capital expenditure from about 70M to 30M by delaying construction on items that will not be needed for several years.