A fines challenge: the C&D recycling industry looks for solutions to the problem of H2S generation in ADC made from C&D fines.
C&D fines are the small fraction of mixed construction and demolition debris that are screened during the recycling process. C&D fines range in size, but are typically 3 inches or smaller. The fines are accepted at landfills and used as ADC.
As mentioned previously; C&D fines are an important component in the mix of end products produced by C&D recyclers. Manufacturing and marketing C&D fines is often mischaracterized as the goal of most C&D recyclers. However, C&D fines are really just a necessity given that C&D materials from a mixed material stream are fractured, broken and size-reduced during typical handling procedures prior to being accepted by the processors. Thus, the fines are already there and the processors are now handed a product that they have to manage. The goal of the C&D processor then is to manage the fines product in a cost-effective manner and produce as high a value product as possible with the other portions of the C&D stream (wood, metals, aggregates, etc.).
Given that C&D fines are as much as 30 percent or more of the total mixed C&D material stream by weight, the successful marketing of this material is essential for the overall economics of C&D processing. If the fines product cannot be cost-effectively managed, then the mixed C&D stream may not be viably processed to remove the other higher value products (wood, metals, aggregates, etc.). A lack of markets for C&D fines will restrict the development of higher value products being manufactured by mixed C&D processors.
BEST MANAGEMENT PRACTICES
ADC made from C&D fines is a useful product for landfills because it saves resources and landfill space by replacing virgin soil. However, due to the generation of H2S by gypsum-containing ADC, many individual landfills have stopped taking the product from C&D processors. Additionally; some local and state regulatory entities have greatly restricted or completely prohibited the use of C&D fines as ADC. Seeing the potential damage to the existing and future C&D recycling infrastructure, the CMRA hired Green Seal Environmental Inc. (GSE) to develop a Best Management Practices (BMPs) document for the production and use of C&D fines as ADC.
The BMPs document has been created in draft form and is currently being revised based on the comments from industry representatives. The BMP document focuses on the following points:
* Background information on how and why H2S is generated
* Other sources of H2S
* Gypsum removal
* Mixing C&D fines with other APC or virgin cover materials
* Chemical additives
* Biological additives
* Proper handling procedures at the landfill
* Gas collection and treatment methods
* Issues with leachate re-circulation.
The BMPs document makes several main points, which are discussed below.
The manufacturing methods of C&D fines and thus the make-up of the product varies depending on the facility producing it and the specific state or local regulations enacting or enforcing the specifications. In some cases, the C&D fines product mainly consists of the smaller (typically less than 1-inch) screened "dirt" portion of mixed C&D debris. In other cases, the C&D fines product consists of a combination of larger ground C&D debris materials (typically less than 3-inches) and smaller "dirt" fines (less than 1-inch). The variances in production methods and the resulting product may create variances in the methods for managing H2S generation.
C&D fines are used for different purposes in a landfill environment. In some cases, fines are used as ADC. In other cases, fines are used as shaping and grading material and/or capping material. The varying uses and environments within the landfill that the products are subject to may create variances in the methods for managing H2S generation.
The removal of gypsum prior to processing will provide a reduction in the amount of gypsum available for H2S production. However, markets for gypsum are largely in their infancy, and markets for gypsum from demolition debris (versus virgin construction scrap) are limited currently due to the potential for contamination from paints or treatments to gypsum wallboard.
The removal of additional organic materials (wood, paper) from C&D fines products will provide a reduction in the amount of organics available for H2S production. However, it appears that the paper backing of gypsum drywall alone may be an adequate source of the organics required to create the condition where H2S is produced. Thus the removal of additional sources of organics will not by itself eliminate H2S production.
Mixing C&D fines with other materials such as coal ash, wood ash, contaminated soils, virgin soils, processed concrete, etc., will provide a reduction in the total amount of gypsum available for H2S production. However, if other materials are substituted for C&D fines, the total market for C&D fines will be reduced by that same amount given that there is a set quantity of cover materials that can be used in landfill environments.
The introduction of chemical and biological treatments to C&D fines products is a promising element of the solutions to managing H2S production. Several studies have been conducted in simulated landfill environments and more studies in actual landfills are needed to prove this method's viability.
Landfill BMPs include, but are not limited to: quality assurance measures for incoming materials, proper temporary storage of C&D fines prior to placement, implementing blending procedures, implementing protocols that properly manage the extent of exposed waste areas and the time between covering, proper stormwater management, proper leachate management and gas collection and treatment systems operations and maintenance.
The recent development of more bioreactor-type landfills with the practice of recirculating leachate may increase the likelihood of the presence of conditions required for H2S production, given that moisture is a condition for H2S production. More research is needed to determine the compatibility with C&D fines products in bioreactor-type landfills.
Landfill gas collection and treatment systems are needed for H2S gas in landfills using C&D fines products. While most systems are adequately collecting and treating methane gases, these systems may not be as successful in collecting and treating H2S gas.
Given the results of the preliminary research performed and the significant collaborative input from industry representatives and other interested parties, the CMRA now has a clear understanding of the voids that need to be filled prior to creating a standard set of BMPs.
Several steps need to be taken to make this possible. First, obtain additional success stories from facilities that historically accepted C&D fines products. Research their methodologies and analyze the basis for their success compared to facilities where problems occurred. Then obtain data from industry representatives based on current research and field studies being conducted (see section below on the industry response in the northeast). Finally, revise and refine the current BMPs document and distribute it to the public for assistance in state and local policy decisions, processing facility operations standards and landfill operations.
The effects of the current issues with H2S are undoubtedly nationwide. However, in the northeastern United States, the issue is being pushed to the forefront by several contributing factors including:
* The large number of C&D facilities in operation that rely on landfills as an outlet,
* The number of facilities having issues with H2S,
* The Northeast states' recent limitations on the uses of C&D fines in landfills,
* The relatively small number of landfills in existence due to difficulties of developing new landfills in urban areas, and
* The Massachusetts Department of Environmental Protection ban on disposal of C&D components (wood, ADC and metal), which was adopted Oct. 7, 2005, and goes into effect July 1, 2006.
As a result, the C&D industry in the northeast has come together to develop a resolution to the problem. The resolution includes working with state regulatory agencies to develop a standard by which the industry will operate and develop a set of policies that the regulatory agencies can agree with to prevent further problems with H2S. The efforts include:
* Implementation of gypsum removal plans Gypsum content sampling & standardization of sampling methods
* Landfill demonstration projects with Different mixtures (fines, ash, soils, etc.) and different treatments (sulfur-eating bacteria, chemical treatments, etc.)
* Documentation of success stories
* Regional and national information dissemination to assist both the industry and regulatory agencies.
The C&D industry remains confident that the H2S issue can be resolved. However, the industry recognizes that many different procedures and technologies will need to be applied, versus one single quick fix. The CMRA will continue to champion these efforts.
Facilities that are successfully applying the methods and technologies discussed above, and that have successes to share with the CMRA are encouraged to contact either GSE or CMRA for possible inclusion in the final BMPs document.
John S. Blaisdell is a partner in Green Seal Environmental Inc. (GSE), Sandwich Mass. and Merrimack, N.H. and can be contacted at email@example.com.
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|Title Annotation:||GYPSUM UPDATE|
|Author:||Blaisdell, John S.|
|Publication:||Construction & Demolition Recycling|
|Date:||Mar 1, 2006|
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