In order for significant increases in the diversion of organics from landfills and incinerators to become a reality, increased composting capacity is required. As discussed in a previous column, it appears that a substantial shortage of composting capacity exists particularly for food residuals. Some of the barriers that prevent the expansion of composting capacity and infrastructure include regulations, which vary among states, and siting issues for new facilities. Among the issues associated with siting new facilities and expanding existing facilities is the potential for odor impacts in nearby communities. During the past decade, significant advances have been made in composting technologies and their ability to control odors.
Composting methods typically include windrows, aerated static piles and in-vessel systems. In general, in-vessel systems are used primarily for composting a variety of sludge materials and other highly putrescible organics. Aerated static piles have historically been used for composting wet substrates that do not require agitation, such as biosolids. The windrow method is used for composting a wide variety of materials, and it is the most prevalent system used for composting yard trimmings.
For the uninitiated, windrows are elongated piles of decomposing organic matter (feedstocks) that typically are turned on a routine basis to accelerate decomposition. Aeration and temperature control are primarily limited to pile structure, material composition and turning frequency. Since windrow systems offer no opportunity to collect and treat the off-gases from the process, good process management is required for odor control. Aerated static pile systems use aeration by blowers to control key process variables, such as oxygen and temperature. Use of negative aeration provides the opportunity to treat off-gases from the process. Additional control of odors can be obtained by enclosing the system. In-vessel systems use some type of enclosure to contain the composting material. Typical systems include containers, agitated beds, tunnels, and rotary drums. In these systems, key process variables and materials handling operations may be automated. In-vessel systems typically allow for the highest degree of process management and odor control possible.
In the U.S., a number of composting systems and technologies are available to fill the need for increased capacity and infrastructure. Selecting the best system for a particular application depends on a number of factors, including feedstocks, tonnages, site location and proximity to residential communities, local meteorology and many other factors. No matter how good the composting system design, however, knowledgeable and experienced site managers are essential to the implementation of operational efficiency, optimum management of the composting process and effective odor control. At a minimum, this position requires a good understanding of the biology of composting, the factors that govern the process, and practical application of the science to real world situations.
In addition, there are many site-specific factors that must be addressed to control and mitigate odor production and transport. Each composting system and technology requires management of key process variables as well as a skilled site manager with the ability to both understand the system needs and to implement system and operational controls in order to best manage odor while producing a high quality compost product.
The need for increased composting capacity is imminent for states, such as Vermont, which is phasing in mandatory composting of food scraps and other organics, and Massachusetts, which has proposed legislation to ban organics from landfills and incinerators. The sharing of success stories about well-run composting facilities will help to encourage states to streamline regulations and, in turn, encourage facility expansion and new infrastructure development to increase composting capacity. This will help states achieve higher recycling rates and increase diversion of organics from landfills and incinerators. Concurrently, this is in line with the U.S. Environmental Protection Agency’s “Solid Waste Management Hierarchy,” which promotes reuse and organics recycling and supports the agency’s recent focus on sustainable materials management.
Composting technologies and odor control are two of the many topics to be addressed at the 1st Annual Composting and Organics Recycling Program at WasteExpo in New Orleans, May 20-23. To learn more, visit www.wasteexpo.com and click on the link to the conference program.
Stuart Buckner, Ph.D., is president of Buckner Environmental Associates, LLC, a consulting firm specializing in organics management.
The author welcomes comments from readers. E-mail him at [email protected].