THE CHALLENGES OF A SKIMMINGS-ONLY INCINERATION SYSTEM

“Skimmings” is the term commonly used to identify floating material (e.g., scum, grease, plastics, etc.) that are skimmed from the top of the wastewater in primary settling tanks, final settling tanks, and gravity thickening tanks.Due to the nature of this material, its disposal has always been an issue of concern for publicly owned treatment works (POTWs). Some POTWs directly send their skimmings to landfill, others mix their skimmings with biosolids and incinerate the mixture in biosolids incinerators, while others mix their skimmings with biosolids, and/or grit and screenings and send the resulting mixture to landfill.In 1975, the Northeast Ohio Regional Sewer District (hereinafter “District”) placed-into-service an innovative skimmings incineration system at its Easterly Wastewater Treatment Plant (WWTP). The system uses a 13-foot diameter fluidized bed incinerator (FBI) to thermally oxidize the skimmings.While FBIs are often used to incinerate biosolids, the District's Easterly WWTP contains a highly successful pioneering application of fluidized bed technology for the incineration of skimmings.Several of the challenges faced/overcome by the Easterly incinerator operators include: operating within incinerator design parameters and regulatory requirements, responding to unusual maintenance problems, being cost-effective, and last but not least -- preparing and handling the skimmings for incineration. These challenges are mainly due to the fact that the skimmings’ quantity and quality vary from time to time and from treatment plant to treatment plant.This paper contains detailed information concerning the initial design and operations of Easterly's FBI and its ancillary equipment, problems encountered during the mid 1980s along with subsequent upgrades, current operations, and initiatives taken to reduce operating costs.