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Handling and Disposal of Sludges From Combined Sewer Overflow Treatment, Phase I – Characterization (EPA/600/2-77/053a) May 1977

This report summarizes the results of a characterization and treatment test program undertaken to develop optimum means of handling and disposal of residual sludges from combined sewer overflow (CSO) treatment systems. Desk top engineering reviews were also conducted to gather, analyze and evaluate pertinent information relating to pump/bleedback of the treatment residuals to the dryweather sludge handling/treatment and disposal facilities.

The results indicate that the volumes and characteristics of the residuals produced from CSO treatment vary widely. For the residuals evaluated in this study, the volumes ranged from less than 1% to 6% of the raw volume treated and contained 0.12% to 11% suspended solids. The volatile content of these sludges varied between 25% and 63% with biological treatment residuals showing the highest volatile content and fuel values. The heavy metal and pesticide concentrations of the various sludges were observed to be significant and are presented.

It was concluded that the pump/bleedback of CSO treatment residuals may not be practical for an entire city because of the possibility of hydraulic and/or solids overloading of the dryweather treatment facilities and other adverse effects. However, controlled pump/bleedback on a selective basis may be feasible. For low solids content residuals (storage, screen backwash, waste activated sludge, etc.), gravity or flotation thickening were concluded to be the optimum steps for the removal of the major water portion while centrifugation and vacuum filtration were concluded to be the optimum dewatering techniques for the high solids content residuals (settled storage treatment sludge, flotation scum and other thickened sludges) prior to their ultimate disposal by incineration or landfill. As a result of the findings and conclusions of this initial study, the EPA conducted a followup study (see reference No. 181) to:

  1. Evaluate on a pilot scale basis the process treatment systems of thickening followed by centrifugation or vacuum filtration for handling and disposing of CSO treatment sludges, as well as stabilization methods such as anaerobic digestion.
  2. Develop capital and operating costs for the above mentioned treatment systems.
  3. Evaluate alternative methods for ultimate disposal of storm generated residuals and assess the potential impacts of such handling and disposal.

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