See Service Details

The current status of Municipal Solid Waste (MSW) combustion ash technologies are areas that have great potential in the quest of improved waste management in the United States. Individuals and companies alike, continue exploring the best technologies to successfully approach and utilize ash management to achieve their financial and environmental goals.

In the U.S., about 450 million tons of MSW are generated annually. Approximately 130 million tons of MSW are recycled and 32 million tons are combusted – primarily for energy recovery. Combustion ash residuals comprise almost 8 million tons of material processed. Waste-to-Energy (WTE) is becoming a favorable option. Some of the benefits include diverting from the use of landfill waste and the environmental problems that can be associated with this practice, volume reduction and sterilization through this process and the opportunities seen not only with energy recovery or generation, but revenues generated through the sale of electrical power that in many cases is used to reduce the overall MSW processing costs.

With the practice of landfilling facing increasing opposition by both regulatory and public agencies, it only seems fitting that these types of technologies would see an increased interest generated. This can be seen in the reduced number of landfills currently n the United States. The numbers show that the original number of landfills in 1988 (8,000) decreased 1, 654 (74%) by 2004 and this number continues to decrease. While the initial combustion of MSW decreases the volume of waste 70 – 90%, the ash collected still remains a significant waste stream that needs to be effectively managed. We have also seen an increase in overall management and maintenance of landfills in recent years, further illustrating that the investigation of viable options for ash management will be increasing in need.

The ash portion itself can be divided into a bottom ash that accounts for 90% of the ash stream and the fly ash fraction that accounts for about 10% of the total ash generation. Because concerns still circulate about landfilling this ash stream, studies in treating and reusing the ash in a variety of beneficial ways have become an area of interest among many. Currently only about 1 million tons (5%) of the annually produced ash is being utilized in beneficial ways with the U.S. While the majority of uses for this material still lie in the construction and landfill cover areas, there are still studies and investigations of innovative uses being conducted.

Regulations

The EPA exempts WTE facilities that combust household and non-hazardous commercial and industrial waste from RCRA Subtitle C requirements for hazardous waste. However, the rule does not exempt the ash residuals from the subtitle C requirements for hazardous waste and, therefore, the ash is required to be tested for toxicity characteristics (TC) using either the Toxicity Characteristics Leaching Potential (TCLP), as described in 40 CFR sec. 261. 24, or by using knowledge of the combustion process to determine if the ash will exhibit TC. In general, the fly ash will have the higher possibility to fail the TC than the bottom ash fraction. Accordingly, most of the WTE facilities combine the fly ash and the bottom ash to dilute the fly ash portion and to avoid dealing with either portion as a hazardous waste. In general, ash reuse has not been subject to strict regulations by the EPA. However, almost half of the states have specific regulations for beneficial ash reuse.

Technologies

Many technologies are available and have been proven either locally of internationally, to be environmentally safe technologies for ash reuse. Nevertheless, some of the technologies for ash reuse need to be verified and permitted for beneficial reuse in accordance with local and state regulations.

Available Technologies

The following is a list for the major available technologies for ash reuse:

Landfill Cover (Combined Ash)
This is currently the main use for ash and has been an approved technological option by every state. The use of combined ash as landfill cover reduces the need and cost to obtain soil or other suitable materials, as well as providing a beneficial use for the ash.

Roadway Base and Sub-base (Ash or Combined Ash)
This technology has been proven to be environmentally safe and it has been applied on a small scale. Both bottom and combined ash exhibit structural properties for use in road construction material. The presence of an impervious top layer on roads in the form of asphalt, along with the road location designed above the water table, minimizes the potential for contact of the ash with groundwater.

Asphalt aggregate (Bottom Ash or Combined Ash)
This technology has been proven to be environmentally safe and it has been applied on small scale. There is a tradeoff which needs to be evaluated for this application, as the use of ash as an aggregate may increase the amount of this type of material required to meet the state or local roadway construction specifications. Use of ash in this application is often avoided in the top wearing or friction course of asphalt to avoid the issues associated with erosion and contact with storm water.

Concrete products aggregate (Bottom and Combined Ash)
This technology has been proven to be environmentally safe and it has been applied on small scale. The ash is used in construction products like concrete blocks and pavers. Ash is generally avoided in concrete products that contain reinforced steel due to the presence of chlorides and other elements that could lead to decreased performance of reinforced concrete.

Structural fill under lined landfills (Bottom and Combined Ash)
This technology has been proven to be environmentally and has been applied on a small scale.

Soil cement mixture (Combined Ash)
This technology has been proven to be environmentally safe and it has been applied on a small scale. Soil cement is sometimes used for road base or slope protection in areas located with high water tables.

Shore protection and erosion prevention (Bottom and Combined Ash)
This technology has been proven to be environmentally safe and it has been applied on a small scale in an application that included a long term risk assessment study performed to verify the effect of using fly ash cement blocks within a marine environment. The technology has proven to be environmentally safe with long term (5 years) test data.

While several technical advancements have evolved over the past decade that may help advance commercial development of ash recycling, there are several potential technologies that have not been fully proven currently, but may be developed in the upcoming years. From additional ash recycle processes for blending with recyclable aggregates for road construction use, to Waste to Energy options, there are several options that are being developed for future use and improved environmental performance.

About DNV
DNV is a global provider of services for managing risk, helping customers to safely and responsibly improve their business performance. As companies today are operating in an increasingly more complex and demanding risk environment, DNV's core competence is to identify, assess, and advise on how to manage risk. Its technology expertise and industry knowledge, combined with its risk management approach, have been used to manage the risks involved in numerous high-profile projects worldwide.

Call DNV to find out more and discuss your needs surrounding environmental impact and risk assessment.

1-800-486-4524
ContactUs@dnv.com

Download this paper as a PDF.

© 2009 Det Norske Veritas, All rights reserved. Any reproduction of this information in part or in whole is prohibited without written consent of the publisher, Det Norske Veritas (DNV).