HIGH RATE CLARIFICATION TREATMENT FOR WET WEATHER FLOWS: A SIDE-BY-SIDE COMPARISON

High rate clarification technologies are increasingly being considered for treatment of wet weather flows because they provide effective treatment at hydraulic loading rates that are significantly greater than a conventional settling tank. The City of Columbus, OH, is one municipality that is considering the application of these ballasted flocculation technologies. The City of Columbus has been working on developing wet weather control strategies for managing and treating combined sewer overflows and separate sewer overflows. Most of the alternatives developed to control the wet weather flows recommend some form of high rate physical/chemical wastewater treatment in addition to sewer system improvements. The overall goal of the pilot study was to evaluate the treatment performance and operational issues for full-scale implementation of the HRT technologies. A side-by-side pilot test of the ACTIFLO® and the DensaDeg® processes was performed during the spring and summer of 2004 to assess the two technologies. A key objective of the testing was to evaluate the performance of different coagulant chemicals for both dry weather and wet weather wastewater flows for removal of suspended solids and organic materials. Secondary objectives included obtaining information on other operation issues that need to be considered for full-scale application.The pilot testing demonstrated that both technologies provided effective wastewater treatment with some differences in overall performance. Each technology has its own particular set of advantages which will be factored into the decision on how the technologies may be used for treating wet weather flows.