BioCycle June 2009, Vol. 50, No. 6, p. 28
At a renowned composting facility, a perfect storm of odor causing events necessitated the implementation of a series of odor mitigation steps.
HAVING been in the compost business for well over a decade, and working for a company that has been in the business for almost two decades, there have been a lot of challenges to creating a composted product in an environmentally friendly manner. Our company, Cedar Grove Composting, has processed over 4 million tons of feedstocks in that time, and has a set of values that we follow (see sidebar). However it has not been easy to achieve or to follow these principles.
Cedar Grove Composting is now on its seventh composting technology since it opened in 1989. With each technology change we were trying to deal with a particular issue, typically either increased volume or a change of feedstocks. While all seven technologies were very effective in producing marketable compost, they were more importantly addressing land use and neighborhood issues, including odor control, processing more feedstocks on the same acreage and producing better product in a shorter timeline.
With these parameters in mind, our latest technology – the GORE™ Cover composting system – was incorporated into our operation seven years ago. This type of technology was put through our screening process, not mechanical screening but applications and business screening. We have a very low tolerance for risk in the selection of a composting system; we are not inclined to experiment with new or unproven technology. Our neighbors do not like to be guinea pigs. So our basic criteria is that the system has to have three qualities before we even consider it: 1. Operating experience at multiple sites for at least 3 to 5 years; 2. Sites are composting exactly the same feedstocks; and 3.It is backed by a large enough company that will guarantee it works if we operate according to the manufacturer’s instructions. Believe it or not, these three simple principles tend to weed out many technologies, not because they are bad but because we do not want to find out they do not work the hard way.
SETTING THE SCENE
The point of this article is not to focus on the composting technology, but rather on all the other issues that together represent a big challenge when it comes to odor management. Our case in point is Cedar Grove’s Everett, Washington composting facility. By 2008, the facility had been operating for over four years and composted over 432,000 tons of material without one odor complaint. Then, last summer, we were in the hot seat. What happened? Essentially, it was a strange combination of events that typically occur one or two at a time at many facilities to generate malodors. But in our case, it was the culmination of many odor emission points simultaneously occurring in a kind of strange perfect storm of events that created this unusual circumstance.
First, remember it is June and July, late spring and ample rainfall of over 45 inches. (We in the compost business know what came next – large volumes of wet grass). Second, we are located next to a slough that has large areas of mud flats. Extremely low, negative tides occurred during the same period of time. Third, we find out after adding leachate to the material in the grinding area (which we have done for years) that our aeration system in the leachate tank was mostly plugged. Thus we were adding odorous water to the outdoor grinding area.
Fourth, we got notice that one of the transfer stations we receive material from had held feedstocks for well over three weeks. In fact, it might have been over five weeks old, and this is with every other week curbside collection of residential food waste and yard trimmings. Because this material was unloaded in our negatively aerated tipping building that vents to a biofilter, we were unaware of its ripeness until we brought it outdoors for grinding. Fifth, the Everett facility is designed so that the grinding area is downwind from the rest of the plant. If there are odor issues, we only know it after the odors reach off-site receptors, i.e., the downwind city.
Sixth, although there are many other odor sources in the area – two wastewater treatment plants, one pulp mill, two bark facilities, one topsoil stockpiler and one lumber plant – an anonymous person/company (who has yet to come forward and identify themselves) decided to send out a notice on an official looking mailer to area residents that said Cedar Grove was the only source of the odor and to call the air agency to complain.
ADDRESSING THE PROBLEM
The first step in odor management is to identify all the emission points. Figure 1 outlines potential emission points from most facilities. The composting source points in Figure 1 pretty much follow the GORE processing methodology. However many facilities employ a phased approach to composting so those items could be replaced with windrow turning or aerated static (ASP) pile technologies. The larger goal of this article is to look at all the other emission points, not the specific composting technology.
Discussions with the local community and regulating agency reviewed various strategies for identifying the cause of the odor on site as well as odor sources from offsite. A third party odor specialist was employed to evaluate emission sources on and offsite and make recommendations. The following outlines the odor mitigation recommendations that we implemented at the Everett facility:
1. Cleaned out and repaired the leachate tank with new procedure to monitor conditions.
2. Discussion with haulers and transfer station about keeping material fresh by more frequent collection and less time at the transfer station.
3. Hired receiving building monitor to review loads as they arrive.
4. Installed doors on the receiving building to keep odors contained when not unloading material. The oldest material is processed first to reduce the impact of material being stored in the building overnight.
5. Reevaluated receiving building aeration system and biofilter design. The changes in height and attention to moisture levels in the biofilter are small changes but important.
6. Planted over 5,000 trees as a wind buffer and absorptive potential for emissions.
7. Added misting to the grinding process, evaluating enclosing the grinding operation. Also considering a slow speed shredder to provide grinding/mixing and reduce emissions from this operation.
8. Shrouded the screening plant operations to keep down dust.
9. Shrouded the conveyor drop points.
10. Hired Odor Specialist to drive around areas downwind of the facility during most operational hours and report back odors observed, as well as document other odor sources (e.g., from the wastewater treatment plants, pulp mill).
11. Load finished compost behind the storage pile to provide a wind block and move material for the next day’s sales during more favorable climatic conditions, i.e., based on wind direction and speed.
12. Tried to cover the finished compost pile with felt but the felt had a higher odor potential than the compost. The felt had its own odor qualities and was not odorless.
13. Notified the neighborhood through a community letter outlining the changes we had made to the facility. Indicated the name and phone number of our Odor Specialist in case they needed to contact us.
In the end, no changes were made to the composting system itself but rather to the elements both before and after the active process. Odor crisis lesson learned: It’s not always about composting.
As for the future, my crystal ball predicts that anaerobic digestion will be used for the first phase, processing grass and food waste – the most putrescible feedstocks. Digestate coming out of the back of the digesters will be composted with yard trimmings and other clean wood sources in the existing system. The type of grinding or mixing will be changed so it can be located in a building. Materials will not be ground as aggressively, thus reducing the odor emission potential.
Jerry Bartlett is the Chief Environmental and Sustainability Officer at Cedar Grove Composting.
CORPORATE COMPOSTING PRINCIPLES
Cedar Grove Composting is committed to:
Practice environmentally sensitive manufacturing.
Develop products from recovered organic waste material with economically sustainable local markets.
Design operational units to minimize impact to the environment.
Apply the best available control technology to product manufacturing areas, and to continual improvement.
Find the highest and best use for the amount of material that has not been incorporated into a salable product.
Recognize impacts from the processing facility concerning the community and participate in open discussions with local citizens to work through issues.
Continuously strive to reduce air emissions to levels below the nuisance threshold.
Maintain a leadership role nationally in the development of innovative methods in the composting process, including odor management, and marketing of recycled products.
Design products that take life-cycle thinking into account and minimize environmental impacts in production, use and disposal.
June 19, 2009 | General
Getting To The Bottom Of An Odor Challenge
BioCycle June 2009, Vol. 50, No. 6, p. 28