Improving Air Quality in Buncombe County

The city of Asheville, North Carolina, located in the heart of Buncombe County, prides itself in having a clear focus on sustain­abil­ity and the development of a green economy. By balancing the values of envi­ron­men­tal stewardship, social respon­si­bil­ity and economic vitality, Asheville works to meet its residents’ current needs while upholding its respon­si­bil­ity to future generations. 

When the Envi­ron­men­tal Protection Agency (EPA) set forth new emissions control system require­ments for its Maximum Available Control Technology (MACT) provisions of the Clean Air Act, the facility owner was tasked with reha­bil­i­tat­ing its existing sanitary sewage sludge incinerator to comply with stringent mercury emissions limits. With CDM Smith’s help, Buncombe County’s Metro­pol­i­tan Sewerage District (MSD) began imple­ment­ing unique advanced technology upgrades to its French Broad River Water Reclamation Facility's Sewage Sludge Incinerator (SSI). The MSD and CDM Smith employed several cutting-edge air pollution control tech­nolo­gies to deliver a cost-effective and regulatory-compliant instal­la­tion by the EPA’s strict March 21, 2016 deadline.  

MSD's SSI improve­ments are a shining example of how embracing advances in technology can provide safe and cost-effective solutions that protect air quality and the environment. 

• Incor­po­ra­tion of a multi-venturi scrubber in lieu of a single tube venturi scrubber and tray scrubber: This scrubber system reduced capital cost by requiring less equipment and piping systems to achieve emissions compliance within a more energy- and space-efficient instal­la­tion.

• Use of sorbent polymer composite (SPC) filters in lieu of carbon adsorption for mercury removal: The innovative SPC technology to remove mercury in sewage sludge incin­er­a­tors was pilot-tested during the design phase and proved to meet the new EPA emissions limits. This technology eliminated the need to modify the fluidizing air blowers or use caustic chemical feed system for sulfur dioxide control and a secondary heat exchanger system, shortening fabrication lead time and delivery in the process. This revo­lu­tion­ary approach —one of the first municipal instal­la­tions in the nation—reduces future operation and maintenance expenses by decreasing the volume of cont­a­m­i­nated waste that requires disposal. Currently, the SPC system removes mercury at an average of 71%. 
  
  
• Creative procurement approach: Following a pause in the design phase to allow for the pilot testing of the SPC system, MSD and CDM Smith were forced to initiate a creative approach in order to obtain the long-lead-time equipment necessary to success­fully complete instal­la­tion and compliance testing by the EPA deadline. The team used competitive bid solic­i­ta­tion to pre-purchase a primary heat exchanger and pre-negotiated both price and scope of the multi-venturi scrubber to expedite shop drawing preparation and equipment fabrication. These two approaches shaved four months off the project schedule.

The entire project team—including owner, engineer, contractors and vendors—collab­o­rated to deliver complete startup and compliance testing on time and well below the original MSD capital budget. Construc­tion teams worked tirelessly to execute the improve­ments within limited working space inside the existing incinerator building, working within a stringent 40-calendar day incinerator shutdown period required to minimize the cost and risk of alternate disposal of biosolids. 

“This approach saved us over $4 million in construc­tion costs and will continue to reduce future operation and maintenance expenses,” says Thomas E. Hartye, PE, general manager for the Metro­pol­i­tan Sewerage District of Buncombe County. “These improve­ments will help us better serve our customers in Buncombe and northern Henderson counties, as well as protect the western North Carolina environment and air quality that so many inside and outside North Carolina cherish.”