BALLASTED FLOCCULATION – SURFACTANTS AND EFFLUENT FOAMING POTENTIAL

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.