Almost all waste-to-energy ash produced in the US is landfilled, according to the EPA. But there are benefits to recycling WTE ash — such as metals recovery and reuse in road construction projects — according to a report by the Solid Waste Association of North America’s Applied Research Foundation.
The report highlights two innovative WTE ash recycling projects in the US: Pennsylvania’s Lancaster County Solid Waste Management Authority’s partnership with Inashco to recover metals from WTE ash and a project in Pasco County, Florida, to reuse ash as construction aggregates.
Of the nearly 30 million tons of municipal solid waste processed by WTE facilities in the US each year, about 7 million tons is left as bottom ash, non-combustible materials, and solids from the air pollution control systems (fly ash). That material is collective referred to as WTE ash.
Conventional metal recovery systems are often limited to processing of feedstock materials and large (greater than 12 millimeters) fragments in bottom ash. However, new systems being introduced in Europe have begun targeting the smaller fragments with a greater emphasis on bottom ash.
The report examines one such approach in Lancaster County, where the county’s solid waste management authority signed a 10-year contract with Inashco to use an advanced dry recovery system to supplement existing in-line metal recovery systems. The system is expected to increase the waste management authority’s metals recovery from ash by 46 percent, including greater recovery of ferrous, non-ferrous, and precious metals. This is also expected to provide additional revenues to the waste management authority over the 10-year period.
The study also suggests the European model of managing bottom and fly ash separately could lead to greater recovery. Most US WTE plants mix the two streams to manage them as a combined ash. This is because fly ash, managed individually, is considered a hazardous waste.
In Pasco County, waste management officials changed its ash management approach to mix only enough bottom ash with fly ash — at a ratio of 25 precent bottom ash to 75 percent fly ash — to render the mixture non-hazardous. This new approach frees up 83 percent of the bottom ash to be reused as construction aggregates.
Following a successful pilot test program, the Pasco County Solid Waste Recovery Facility received the first permit ever issued by a state government authorizing the use of WTE bottom ash as an aggregate in road construction. The use of bottom ash in road construction would increase local diversion to almost 94 percent of the waste processed through Pasco County’s WTE facility from landfill disposal into recovery as energy or reusable materials and metals, the report says.
In other efforts to recycle WTE ash, in June Republic Services opened an ash metal recovery facility at Roosevelt Regional Landfill in Washington. The facility will process new ash delivered to the Roosevelt Landfill as well as all of the existing ash currently in the landfill. Once recovered, the metals are recycled, shipped to manufacturers and repurposed to make new metal products.