BioCycle Magazine

Compost Site Comes Back From the Brink


Courtesy of Courtesy of BioCycle Magazine

The largest composter in the state of Washington, Cedar Grove Compost Company in Seattle, had its hands full of challenges in 1997 — confronted with a half million dollar fine, a lawsuit, and angry neighbors. With the adoption of an Environmental Management System (EMS), the compost facility has turned its precarious situation around and stayed in business, while dramatically cutting odor problems. With a generally satisfactory full year under its belt, the composter is looking forward to even better results in 1999.

Cedar Grove processes all of King and Snohomish counties’ yard trimmings. Originally sited in a fairly rural area, Cedar Grove is now surrounded by development. The facility modified its operations and made a number of site improvements as both the area and its own volumes grew (see “Overcoming The Challenges of Expanding Operations,” March, 1996). Cedar Grove was using aerated static piles when forces combined to create a major crisis in the spring of 1997.

That year, 192,000 tons of yard trimmings and preconsumer vegetative residuals were processed at the site, about 30 percent more than in 1996. A wet, warm Northwest spring yielded higher than normal volumes of grass clippings. In turn, this overloading reduced the effectiveness of the facility’s biofilter; a new wet scrubber was ineffective as well. Nearby homeowners registered hundreds of complaints with the Puget Sound Air Pollution Control Authority (PSAPCA) and the Seattle-King County Health Department.

With the facility operating at over 20,000 tons/month (an all time high), and with management still learning the capabilities of its new system, odors dramatically increased, according to PSAPCA’s complaint log. Tensions rose and subsequently Cedar Grove was hit with a class action lawsuit filed on behalf of the people living within a mile and a half radius of the site (that suit was recently settled). The uproar spawned a proposed state bill written by the legislative representative for the area that was highly prescriptive and costly if odor problems were present. While the bill didn’t pass, it reflected the high degree of emotion around the odor issue.

PSAPCA wrote up a $490,000 fine for Cedar Grove in August, 1997. At the same time, however, the air pollution agency held out a carrot: If an Environmental Management System or EMS (see accompanying article) could be implemented at the facility to mitigate the serious problems it was experiencing, the authority would consider reducing the fine.


The rationale behind this carrot was to address management issues at the core of the problem. Earlier in 1997 and prior to the grass season, Cedar Grove had processed significant volumes of yard trimmings without controversy during months of stellar performance using negative aeration technology. Indeed, neighbors took no notice from January through April. PSAPCA concluded that the technology and equipment at Cedar Grove had the potential to perform well. The implementation of an EMS offered the possibility of bringing the company’s process control skills to the same level of sophistication as its equipment.

After several months of negotiation, Cedar Grove received a Nonconforming Solid Waste Handling Permit for 1998 from the King County Health Department. The new permit imposed monthly limits on the amount of material to be accepted, ultimately allowing 165,000 tons for 1998 (which included 8,000 tons/year of preconsumer food residuals from area grocery stores), a significant reduction in the volume of allowable materials. The permit also stipulated a variety of conditions to be met. It did not preclude the facility from gaining experience with an approach and management technique like EMS. Rather, the company had the opportunity to improve its performance, which could ultimately allow for innovation without increasing its risk of unreliable environmental performance.

PSAPCA’s enforcement action required Cedar Grove to develop an EMS and Operations Plan, whereby the company would comply with over 20 measures designed to control odor complaints. A plan was prepared and implemented between August and December 1997. While this was not as flexible or innovative as the “pure” EMS originally proposed by Cedar Grove, it did allow the company to begin demonstrating the efficacy of this approach while meeting the agreed upon conditions. Over the next 14 months, Cedar Grove successfully used its new management method to control odors generated during delivery, mixing and processing of green waste. The process also positively affected product quality control. Compost from Cedar Grove was more aerated and had greater consistency as a result. Satisfied with the tremendous improvements as a result of using an EMS, PSAPCA settled the fine by reducing the original amount to just $50,000.


Communication was a key component of Cedar Grove’s management plan. Staff met early on with local, regional, and state officials to review grasscycling policies, stressing that this approach could be an important odor control policy by minimizing volumes going to the curb. During the fall leaf season as well as a late summer wet period that was expected to bring more grass to the curb, Cedar Grove also mailed a newsletter to the surrounding community of 1,400, outlining the steps the facility was taking to control odors.

In another effort to meet problems head on, the composter maintained a 24 hour odor hotline. Using an answering service allowed for a quicker response time if one were needed and gave callers more confidence than an answering machine might have. The hotline was publicized in newsletters, the local paper, and in agency notices that went out to the neighborhood in systematic mailings. Fewer than ten calls came in via the hotline in 1998.

Cedar Grove also communicated developments to its larger customer base of product users, landscaping organizations and garden clubs. This proved to be important in terms of building support for the operation with elected officials.


Cedar Grove management took several steps to better control the operation, including revising batch sizes to adjust for the density of grass clippings. In mid-1997, to create more workable conditions, the company diverted 9,000 tons to other facilities.
 This diversion was critical to the success of the EMS. If the process control measures revealed potential odor problems, the diversion plan took pressure off the facility. (In 1998, about 30,000 tons were diverted to other sites.)

Further, a framework of measured tolerances was specifically developed for the compost facility in the early planning stage of the EMS. Specified measurements included the C:N ratio, bulk density, pile dimensions, oxygen, aeration flow rates and moisture content. Similar tolerances for operation of the biofilters also were developed and implemented. In applying the measurements to feedstock and batch preparation, the essence of the EMS approach took hold at Cedar Grove. This also was the framework that allowed the facility to administer a meaningful system of checking and correcting the process on a continuous basis.

“We had paint and brushes,” recalls Jan Allen, former operations manager at Cedar Grove, “but we lacked technique.” The EMS provided that technique in batch recipes and careful attention to height, weight and porosity of the piles. “We wanted light and fluffy 2,000 ton piles since porosity is everything,” he adds. Each batch was carefully mixed to be uniform and within the specified tolerances. Additionally, grass content was strictly controlled. Working within this framework, operators improved moisture control of the primary composting system, which is composed of six large rectangular, loaf-like batches covering a three acre area.

After three weeks in aerated static piles, materials are conveyed to a secondary, five and a half acre processing area and shaped into wedges (forming a giant pizza). Activity is closely monitored. While the air flow through the piles is reversible, the facility operates under a negative aeration mode for nearly all conditions. Cedar Grove minimizes agitation of piles to prevent unnecessary movement and potential emissions. The captured airstream is then treated through a biofilter.


The composter agreed to five major capital investments as part of its odor control strategy, including enclosure of the receiving/tipping area with a permanent building, venting to a biofilter, and installation of four new systems (the first three experimental) — an air containment system for the reclaim (transfer) hopper and conveyor, a water cooled heat exchanger for the primary biofilter, a portable enclosure for use in one primary processing zone, and a system for loading bulking agents onto the infeed conveyor.

To control odors in the ponds (used to collect leachate and water from the site), Cedar Grove made multiple changes. The company installed a pure oxygen dosing system, increased discharge to the regional wastewater treatment, and emptied ponds for annual cleaning. In addition, management designed a condensate holding and treatment tank to prevent imbalances. Finally, a solids separator was installed to minimize solids loading to the pond system.

The composter also installed an exhaust biofilter on the secondary processing zone and discontinued use of an ineffective exhaust scrubber. The primary biofilter was expanded from 10,000 to 20,000 square feet. To decrease the inventory of oversize material and rejects and to reduce demand on its existing grinders, Cedar Grove purchased a third grinder that is used during critical periods of high volume. All of these investments were viewed as equipment/infrastructure adjustments, resulting in a technology with distinct and well-defined steps.


While the capital improvements and equipment changes were intended to focus on the greatest sources of odor, outside expertise was sought for a fresh, objective review of sources that those closest to the problem may have overlooked. Odor experts assessed how odors traveled, along with their intensity and duration. Management discovered that ammonia, for example, rapidly evaporates leaving a more prominent smell composed of volatile fatty acids, and that odors changed over distance and varied in duration. During this time, Cedar Grove also retained a chemist to evaluate biological pond odor and odor prevention, and outside compost facility experts to help evaluate the operation and suggest improvements.

Two employees were hired to focus on surface odor sources. Responsibilities included immediately treating or eliminating any trapped or puddling water. To curtail pile leachate, they applied crushed limestone, sand and various other materials to wet surfaces at the base of all the existing piles. Today, negative aeration has “dried” the piles out to such a degree that the facility no longer has a leachate issue to contend with.

Finally, management explored products to neutralize odor and applied a variety of them through an overhead misting system. A number of brands were tested, all based on plant-derived essential oils. For example, orange scented misting was used that smelled great on the immediate site but turned out to have little or no impact a mile away. Each product had to be submitted to PSAPCA for review prior to application; local regulations prohibited the use of masking agents like perfumes or fragrances.

The King County Health Department issued a 1999 permit renewal to Cedar Grove that kept the 1998 level (165,000 tons) of total material it can receive this year. The facility would like to see the level raised, but the agency has taken a wait-and-see approach, considering if or how another year’s weather conditions and yard trimmings volumes will affect operational improvements.

A year and a half later, management has found that some of the steps taken worked well, and those that didn’t were discontinued. Overall, Cedar Grove believes the EMS is a promising operational approach that minimized its odor problems and could be used for other environmental emissions. “It was well suited to our difficult situation and we recommend it for others as long as provisions are made for corrective course changes,” says Jerry Bartlett of Cedar Grove. “Revisions need to be made continuously to adjust the process based on measured performance. Even though it is based on a written, agreed upon plan, the EMS is a living document for a dynamic process with promising results.”

By A. Pandora Touart.

Customer comments

No comments were found for Compost Site Comes Back From the Brink. Be the first to comment!