My previous column noted that composting and anaerobic digestion (AD) facilities which operate in harmony with neighboring communities provide an incentive for approval of new facilities and expansion of existing ones. Now I will explore some causes of odors at organics recycling facilities and tools that are available to prevent and control odors. Although the following discussion will focus on composting facilities, most of the information can be applied to AD facilities as well.
Unfortunately most feedstocks for composting, such as food waste, yard waste and biosolids, contain odorous compounds and more are formed during decomposition. As a result, some release of odorous compounds is inevitable during the composting process. The good news is that odors can be managed when they are generated onsite so that offsite transport is minimized.
Although anaerobic composting is more odorous than aerobic composting, aerobic composting does produce odors. Since process conditions influence the level of odor that will be generated, maintaining optimal process conditions during aerobic composting minimizes odor generation.
It is important to recognize that, at every stage of the overall composting operation, there is the potential for odors, which must be controlled. These stages include receiving and staging of feedstock materials, pre-processing (e.g., grinding, mixing, etc.), preparing windrows or piles depending on system design, curing and finishing/screening the product for market. In addition, housekeeping procedures and maintenance of the site surface should be considered as ponding of water and buildup of residual organics can also generate odors. Although a single odor source may or may not generate enough odor to be detected in the surrounding community, it is the sum total from all odor-producing activities at a facility that can result in detectable odor levels and subsequent complaints.
A preferred step in controlling odors is to develop an odor management plan (OMP) as an integral part of the facility development process. This involves site layout, system selection and design and managing operations to mitigate odor generation at each step of the process. If an OMP is not developed in the planning stage, subsequent odor problems and complaints may result in the development of an OMP as part of remediation efforts for odor control.
In many states, even though an OMP may be a regulatory requirement, successful odor control is often an ongoing process.
Although the desire to maintain the biological integrity of the composting process is crucial, it is important to recognize that practical aspects of facility operations may warrant revision as needed in order to prevent off-site emissions and odor complaints. In a study on Odor Control during the Composting of Grass and Other Yard Waste, it was shown that even within the limitations of an open air turned windrow system, a level of control over process conditions through the manipulation of specific factors can be achieved which is compatible with maintenance of low odor levels (Buckner, 1995, 2002).
The high odor potential of grass and other feedstocks, however, makes it necessary to consider both the biological needs for process management and the practical aspects of windrow management. For example, while periodic turning early in the process may be prescribed, delaying turning or limiting it to specific rows may be warranted during periods of adverse meteorological conditions.
When attempting to control odors at a given site, it is essential to consider their concentration and persistence at each phase of the process where odors may be released. This enables the site manager to plan operations that are compatible with existing and forecast meteorological conditions.
In future columns, we will explore additional tools for odor prevention and mitigation. Some of these include dispersion modeling; induced turbulence by structures or natural objects; odor neutralizers and counteractants; bio-filters and other treatment technologies. We will also discuss the importance of quantitative evaluation of odor concentration, surface odor emission rate (SOER), and how this information can be used to mitigate off-site odor emissions.
Stuart Buckner, Ph.D., is president of Buckner Environmental Associates LLC, a consulting firm specializing in organics management.