Onsite pilot testing was recently completed to confirm performance and design criteria for the 380-ML/d (100-mgd) excess flow high-rate treatment facilities that are being designed for the City of Springfield's wastewater treatment plant. The performance of the compressible media filter pilot demonstrated consistent compliance with all regulatory requirements for CSO treatment and produced average effluent TSS concentrations below 30 mg/L while treating wetweather flows. Furthermore, dose response testing demonstrated that the effluent from the compressible media filter was consistently amenable to hypochlorite disinfection, requiring doses and contact times equivalent to those typically used for conventional secondary effluents. The new high-rate treatment facilities will consist of new structures and equipment for influent excess flow interception, screening, compressible media filtration, hypochlorite disinfection, bisulfite dechlorination and effluent pumping. Construction of these upgrades is scheduled to be completed in 2014.
Like many communities across the United States, Johnson County, Kansas and the City of St. Joseph, Missouri, are considering means to control collection system overflows from their publicly owned treatment works while maintaining or improving water quality. Planning studies for both communities evaluated several wet-weather treatment alternatives and included benchscale and pilot trials of the following processes during actual wet-weather peak flow conditions:(1) chemically enhanced sedimentation, (2) ballasted flocculation, (3) cloth media filtration, (4) dynamic tangential disc filtration and (5) compressible media filtration. These studies indicated that high-rate filtration processes, particularly compressible media filtration, produced effluent of a quality similar to that produced by high-rate clarification without the need for chemical coagulation and flocculation, and appear to be viable alternatives for certain wet-weather treatment applications.
Some wastewater utilities in the United States have implemented or are evaluating ballasted flocculation treatment as part of their solution to prevent combined sewer overflow (CSO) or sanitary sewer overflow (SSO) from wet weather events. Unfortunately, some such installations, both pilot-scale and full-scale, have experienced effluent foaming that appears to be caused by pass-through of surfactants. This paper presents the findings from a study conducted to assess the potential for effluent foaming from ballasted flocculation systems installed to control CSO/SSO. The study involved the following steps:• Sampling of wastewater treatment plant (WWTP) influent during wet weather conditions at seven publicly owned treatment works (POTWs) across the United States from spring 2004 through spring 2005. • Analyzing each influent sample for total, anionic and nonionic surfactants.• Subjecting each sample to bench-scale, ballasted flocculation treatment.• Agitating the treated effluent and observing its foaming characteristics.Results of the study indicate that the effluent from most ballasted flocculation facilities installed for CSO/SSO control should be expected to have a significant potential to foam. The extent and magnitude of the foaming will be site specific, but the potential for foaming appears to be closely related to the influent total surfactant concentration.Although not specifically addressed in this study, such effluent foaming may be expected from other physicochemical wastewater treatment technologies besides ballasted flocculation. Furthermore, it is anticipated that such foaming may be readily mitigated either through the addition of defoaming chemicals or through submerged outfall configurations.
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