Process Separates, Recovers MSW Incineration Ash

Peggy Tyler

An ash management program for the SEMASS Resource Recovery Facility in Rochester, Mass., processes bottom incineration ash into marketable materials and isolates and stabilizes fly ash for safe disposal.

The technology, from Albany-based Energy Answers Corp. (EAC) differs from the standard practice of combining the two types of ash and then diluting the heavy metals in the fly ash throughout the bottom ash to pass landfill testing standards.

At the SEMASS facility, 17 percent by weight of the incoming waste is left as ash - 10 percent bottom ash and 7 percent fly ash.

The facility serves Cape Cod and most of coastal southeastern Mas-sachusetts, turning 2,700 tons per day of waste into enough electricity to supply 75,000 homes.

The bottom ash collected from the boiler grates is a dry, granular material that can be recycled. The facility recovers three products from the material:

* Ferrous metals - iron-bearing materials removed with a magnet and sold for recycling;

* Non-ferrous metals, such as aluminum, tin, brass, copper, silver and gold, which are mechanically separated from the ash (including jewelry, machine parts, silverware, keys and almost $1,000 a day in discarded coins); and

* Boiler Aggregate, a granular material which can replace gravel and crushed stone in some construction applications. The facility uses Boiler Aggregate in concrete blocks, drainage structures, floors, asphalt and as road base and fill. New York State regulators are reviewing permits for commercial sale of the material. Currently the facility stockpiles the material in landfill cells and plans to mine it upon regulatory approval.

According to EAC, approximately 40,000 tons of metal and 80,000 tons of Boiler Aggregate are recovered each year.

During incineration, combustion and air pollution control result in the concentration of heavy metals in the fly ash. The heavy metals and other polluting elements then are collected and removed.

The fly ash is mixed with other ingredients to form a non-toxic, non-hazardous mortar, which includes kiln dust (a waste product from cement manufacture) and collected landfill leachate. The mortar stabilizes the kiln dust, leachate and fly ash, which then can be disposed in a lined landfill, where it hardens permanently.

The Syracuse School of Environ-mental Science and Forestry and independent laboratories hired by EAC found that the heavy metals are binded and cannot leach out, even when they tested the mortar with acids. Potential uses for stabilized fly ash, such as landfill cover, also are being studied.

The ash management program recently received a 1993 excellence in environmental engineering a-ward from the American Academy of Environmental Engineers.