Use of Dissolved Gas Flotation for Clarification of Biological Solids from a Petroleum Refinery Activated Sludge System

Dissolved gas flotation (DGF) is a feasible secondary clarification technology preceding a NPDES Permitted outfall. In 2009, a DGF was installed to separate mixed liquor suspended solids (MLSS) from wastewater originating from a petroleum refinery. Operational data indicates the technology can remove over 99% of influent suspended solids on a sustained basis. DGF clarification advantages, disadvantages, design considerations, and operational performance information are provided in this case study. Notable benefits of the technology are: low effluent suspended solids concentrations, concentrated recycle/waste activated sludge (RAS/WAS) solids, no sludge bulking concerns, compact footprint, and skid construction. The primary disadvantages are higher operating cost and more operator attention. Both conventional gravity (CGC) and DGF clarifiers should be considered viable technologies for separation of MLSS from biologically treated wastewater.