AIR EMISSIONS PERMITTING FOR THE TWIN CITIES' NEW FLUID BED INCINERATION PROCESS

The Metropolitan Council Environmental Services (MCES) owns and operates the Metropolitan Wastewater Treatment Plant (MWWTP), which serves the greater Minneapolis/St. Paul area. The plant has been incinerating sewage sludge for six decades, using multiple hearth incineration technology developed over a century ago. The MWWTP treats approximately 225 million gallons on an average day (mgd) and processes approximately 200 tons of dry solids. Most equipment components of the existing solids processing system, which includes thermal conditioning, dewatering and multiple hearth incineration, are 20 years old. Because of the age of the equipment, MCES is faced with increasing maintenance costs.Construction of a new solids processing facility began in October 2001. The new facility will include fluid bed incineration as the primary solids stabilization technology and will begin operation in 2004. The facility will provide significant improvements in air emissions compared to the existing multiple hearth incineration process. Before construction was allowed to begin, however, a permit amendment was required from the Minnesota Pollution Control Agency (MPCA). Preparations for this amendment application began in 1998 with the completion of a Permit Engineering Technical Memorandum that developed the conceptual design of the fluid bed incineration process. The application was submitted in January 1999 with the permit amendment issued in August 2001.This paper will identify the steps taken to obtain the air permit amendment for the new facility. There are some 120 publicly owned treatment works (POTWs) in the US that operate multiple hearth incinerators, many of which will require replacement over the next two decades. The permitting process described in this paper will be of interest to POTWs who find themselves in similar positions.