There are numerous potential sources of odor at composting facilities, including feedstock delivery, the composting process and materials handling operations. While the active composting phase is typically the primary source of odor, poor management practices can significantly increase odor levels produced from other sources.
Although a single source may generate enough odor to be detected in the surrounding community, it is often the sum total from all activities at a facility that can result in detectable odor levels and subsequent complaints. There are a number of strategies that can be used to control these odors. Some strategies are applicable to multiple aspects of site operations and stages of the composting process while other strategies are relevant to specific ones.
Process stages include pre-processing of feedstock materials (e.g., grinding, mixing), composting, curing, screening and storage of finished product. Site operations associated with these process stages include feedstock delivery and placement, and all materials handling operations, including material transport, forming piles and stockpiles, and cleanup of residual organics. This article will focus on preventive measures and management practices that apply to a variety of site operations and composting process stages.
Good drainage is crucial to effective odor control at composting facilities. Proper design for drainage requires that all areas of the site be graded and sloped so that runoff and leachate drain away from piles, windrows, and structures. This is to avoid ponding of water and runoff which can be laden with organic material and quickly become anaerobic making it a significant source of odor.
The ability to maintain the integrity of the site surface for proper drainage depends to a large degree on the composition of the site surface. Site surfacing materials can vary from impermeable, such as asphalt or concrete, to those with varying degrees of permeability, including compacted blends of stone and/or aggregate.
The choice may be determined by local or state regulations on surfacing materials. Specific feedstocks, such as food residuals, may require impermeable or near impermeable surfaces in specific areas, e.g., receiving pad, pre-processing, mixing, etc. Other regulations may require that there be no discharge of runoff or leachate from the piles which will affect site surfacing materials, retention pond capacity and reuse of collected water. Regardless of the materials chosen, routine maintenance is required to repair and regrade the site surface.
Inadequate housekeeping is often a contributing factor to odor emissions. One ASP facility I visited had such a large buildup of organic residuals on site surface
s that odorous emissions could be detected as heavy equipment traversed the areas. Another facility had so much organic material accumulated between the windrows that there was little room for runoff or leachate to move away from the piles.
Routine housekeeping includes cleaning up residual organics from all site surface areas, i.e., spillage in the receiving area from incoming vehicles and onsite from material transport and handling operations as well as removal of residual organics between windrows after turning, or around aerated static piles after they are formed. Good housekeeping involves maintaining the site surface in optimal condition by replacing surfacing materials, filling ruts, and regrading as needed to maintain good drainage and eliminate areas of ponding. Proper drainage also requires the maintenance of sedimentation ponds and retention ponds to handle runoff and leachate.
Understanding local meteorological conditions and how they affect the potential for odor transport off-site is important for effective odor management. For example, inversions that inhibit vertical dispersion of air will promote ground level transport of odors. Compost facilities often monitor wind direction with flags or wind socks or install a weather station to monitor current weather conditions. Often more important is awareness of forecasted weather conditions.
By knowing current and forecasted weather conditions, particularly wind direction and speed, the site manager is given some latitude when deciding on which site operations to perform. For example, after turning new windrows with highly putrescible organics, odor emissions will be elevated and persist for some period of time, but if weather conditions are such that emissions will be transported off-site and possibly detected, a decision can be made to turn aging windrows with less odor potential instead, or postpone turning and other odorous operations altogether.
An experienced site operator will learn what combination of site operations can be performed under various meteorological conditions to prevent odor detection downwind of the facility and subsequent complaints. Computerized weather forecasting services can be installed at compost sites, and some weather apps available for cell phones are adequate for planning site operations. As we know, however, weather forecasting services can be wrong some of the time so a contingency response plan needs to be in place to resolve a situation quickly.
Stuart Buckner, Ph.D., is president of Buckner Environmental Associates LLC, a consulting firm specializing in organics management.