November 18, 2011 | General

Under Cover Composting

BioCycle November 2011, Vol. 52, No. 11, p. 33
Composting facilities are going “under cover” to improve process control and emissions management, and start receiving more putrescible feedstocks.
Nora Goldstein

FOR a variety of reasons – most related to process control, regulatory compliance and neighbor acceptance – an increasing number of composting operations are going “under cover.” Covered composting, defined for this article as outdoor piles covered with a fabric, is not new. Companies such as Midwest Bio-Systems, GORE Cover Systems and CV Compost have been selling pile covers with and without aeration systems for many years. What is new, however, is increased scrutiny of air emissions from composting operations, primarily volatile organic compounds that can contribute to ozone formation. Air quality districts in California have issued or have proposed significant restrictions on emission of VOCs at composting sites.
For smaller composting operations wanting more process control due to weather conditions, or those expanding to take more putrescible and odorous feedstocks such as food waste, compost covers can be a viable, and in some cases, less capital cost option. Insights into how several facilities are applying different systems are described below.

The Sechelt First Nation on the West Coast of British Columbia has jurisdiction over its lands and resources, and intends to increase its use of practices that enhance sustainability of the Nation. “Our goal as part of a tribal nation is to become more accountable for our own resource management by utilizing existing waste streams to produce a high-grade premium fish soil to grow food rather than burning or burying it in a landfill, which has been done for years,” says Aaron Joe CEO of Salish Soils, a composting and soil production operation. “Our plan is to integrate our economy with the surrounding communities, including remediating quarry mine lands with compost-enhanced soils.” The Sechelt First Nation is located on the Sunshine Coast, a 60-mile strip of land along the coast of British Columbia that is accessible only by ferry. There is very little fertile land and as a consequence, more than 99 percent of all food is trucked in from Vancouver.
A number of fish farms are within its traditional territory, and Salish Soil, a majority owned First Nations business, is partnering with the farms to receive their fish waste, which it is blending with ground yard and garden trimmings and forest and land clearing debris. In October 2010, Salish Soils initiated a pilot project to test the GORE Cover system to compost the fish waste and amendment. “Our objective was to test the technology and make sure it worked for our purposes,” says Joe. “We wanted to be sure we could produce a Class A fish compost that we could use to produce premium soils to help develop a local farming industry. We also needed to test the system for odor and vector control as the site is immediately adjacent to our regional hospital and a residential subdivision.”
To prepare the feedstocks, Salish contracted Coastland Wood Industries, which owns a Diamond Z tub grinder, to grind the yard debris with the huge stumps and forest waste. For the pilot, fish waste was unloaded directly onto a bed of the ground wood chips on an outside paved pad, then mixed with a front-end loader to build two 82-foot long windrows. The piles were covered with the GORE material and aerated with two 6-inch perforated pipes. Leachate was controlled with a berm of wood chips on the downward side of the windrow. “It was quite a process to handle the material like that, but once we got the hang of it the whole process it took less than five hours to prepare and build a new pile and once covered, the odors were negligible,” recalls Joe. “For the full-scale operation, the fish waste will be unloaded in a tipping building and the windrows will be housed within a 96-foot by 220-foot building equipped with a biofilter.”
Materials are composted for eight weeks in three phases — four weeks under cover, then uncovered and turned with the loader. The windrows are recovered for an additional two weeks of composting, and then left to mature without a cover for an additional two to three weeks before it is screened. “In the pilot phase, we were only processing 30 tons/month of fish waste,” he adds. “For the full-scale operation, we expect to be composting 150 to 200 tons/month.”
The next phase of the composting system trials will also include an in-floor system for recovery of heat for use in an adjoining greenhouse operation. The pilot greenhouse should be up and running by Spring of 2012.
In the summer of 2010, Mass Natural Fertilizer Co. (Mass Natural) in Westminster, Massachusetts was approached by INTEGRITY Ag Systems (IAS) in Chambersburg, Pennsylvania to see if they would evaluate IAS’s breathable fabric as an environmental barrier for composting. IAS had been working with Mass Natural on a dairy manure composting project in Vermont, and knew that its Massachusetts facility was permitted to process a wide range of organic feedstocks and could test the fabric. Mass Natural’s owner, William S. Page, Sr., was in his 24th year of operating an outdoor windrow composting facility for paper fiber, manure and industrial food waste, and had been testing a range of in-vessel composting technologies for commercial food waste.
“We had been receiving many requests for processing commercial food waste from supermarkets and restaurants, something I had resisted due to the inevitable glass and plastic contamination, and the odor potential,” says Page. “My facility had some odor issues in its early years, but for more than a decade we have not had any problems and I wanted to make sure it stayed that way. We had tested two different types of rotary drums with food waste, and I was able to purchase a used BW Organics Model 840, but I still needed to process the 3- or 4-day old food waste on my outdoor concrete pads after it left the rotary drum. I agreed to test IAS’ Vortron fabric on a 45 cubic yard static pile of chicken mortalities, manure and wood chips — a real odor challenge!”
INTEGRITY Ag, formed in 2001 by Brad Whitsel and Tim Rensch, specializes in agricultural/industrial waste management and conveyance and includes pumps, agitators, separators, thickeners, land application systems and in-vessel composting. “Brad has expertise in the fabric industry and we saw a need for a fabric composting cover that was very strong but very light, as well as waterproof and breathable,” recalls Rensch. “We also didn’t want a product that required specialized equipment to handle. Our design parameters led to other features, including a fabric strip that is woven into the cover to dissipate static electricity so the fabric won’t cling or attach to itself. Panels can be zipped together, which makes it easier for assembly and disassembly, as well as adjust the length of the material. The trade name is Integrity Vortron Covered Aerated Static Pile.”
Mass Natural placed the fabric on top of the pile, which had a moisture content between 55 and 60 percent, and anchored it in place with tires. Temperature readings were taken at three locations in the pile: top, middle and bottom, and recorded over a 5-week period. Temperatures went as high as 137°F within the first week. The pile started to cool during the third week, indicating it needed to be remixed and covered again with the fabric. The temperatures climbed back up to 133°F. Page reports that there was a strong odor when the pile was constructed, but once the fabric was put on the pile, virtually no odor was detectable while standing next to it. When the fabric was lifted a strong odor was observed beneath it. There was one day of rain during the 5-week period, and the fabric shed the water, preventing the pile from becoming wet, or cooling off.
“Our assessment of the first trial with the Vortron fabric concluded that it allowed the compost pile to ‘breathe’ as air passed through the cover and into the pile, as evidenced by the increase in pile temperatures,” says Page. “It also contained the moisture that was already in the pile as it condensed on the underside of the fabric, and dripped back on to the pile. In addition, temperatures were maintained in the desired PFRP range.”
Based on the successful first trial, Mass Natural purchased at 30 foot by 60 foot piece of the fabric and in the summer of 2011 installed an aerated static pile system designed by IAS to test the system with food waste. “In June of this year I finally agreed to take commercial food waste from supermarkets and restaurants in central Massachusetts, but I wanted to make sure I had an aeration system and an enclosure such as the fabric,” says Page. “To really test its performance, I did not use the rotary drum as a preprocessing step, but mixed the fresh food waste, which had a considerable proportion of waxed corrugated cardboard in it, with paper fiber and a wall board by-product from a recycling plant in Boston.”
Over the span of two weeks, a 150 cubic yard pile was built on top of a 1-foot deep layer of wood chips covering three 60-foot long aeration pipes. The aeration pipes are connected to a header pipe that pushes air up through the pile from a 1 HP blower with a timer. “As we added more food waste to the pile, we added additional 20 foot sections of aeration pipe,” explains Page. “End caps on the pipes kept air from short-circuiting.” Additional sections of the fabric were unfolded to keep the composting material covered at all times.
After approximately 30 days of constant aeration, Page disconnected the aeration pipes from the header pipe, and pulled them out with a loader. He then opened up the pile and found the food waste mostly unrecognizable. Because of a relatively low amount of odor, he was comfortable moving the 30-day old material into an uncovered pile for additional curing. No additional moisture was required since it was still above 50 percent moisture content.
Waste Management launched two source separated organics composting facilities in Florida in 2011. The first, in Okeechobee (processing capacity of about 30,000 tons/year), began operating in June. The second site, at the Vista Landfill in Apopka (designed to process about 45,000 tons/year), was just starting up in October. Both facilities are utilizing the AC Composter™ covered composting technologies supplied by Engineered Compost Systems (ECS).
“The Okeechobee facility utilizes the AC Composter with the CompDog™ system,” says Eric Myers of Waste Management. “There is a 45 day under-cover retention time broken into three phases, with all process air treated through a biofilter.” The Apopka facility is using in-floor aeration and a bunker wall configuration for primary composting. During the primary phase the composting piles are covered using a layer of natural material (finished compost or wood chips). The secondary composting takes place outside of the bunkers and under covers. Biofilters are used for both processes at this site as well.
The two facilities compare and contrast two types of covered ASP systems. “Every system type has its pros and cons,” says Myers. “When designing these facilities, it was a balance of economic and process control factors. For example, the bunker system will process more throughput in the same footprint as the AC Composter; the CompDog costs less by using an inflatable form to create aeration vaults (instead of in-floor aeration). In general, composting with both approaches provides important VOC emission and odor control.”
Steven Wisbaum, owner of Champlain Valley Compost Co. in Charlotte, Vermont, has offered custom composting services to farms and other clients for over 15 years. Not long after he started, he was participating in a farm composting demonstration. “I was leasing a turner to this dairy farm, and they were using a fleece compost cover,” recalls Wisbaum. “It was extremely simple and effective in shedding rain when necessary.” He became a distributor for the ComposTex cover, a breathable, nonwoven fabric made of 100 percent UV-resistant polypropylene.
“Moisture control is a very important part of odor control,” he says. “Managing moisture conditions is more than half the battle for decomposition and reduced odors.” The cover can be held down with sandbags and truck tire sidewalls. He adds that one common misperception with pile covers is that they need to be used all the time. “I encourage my clients to only use them when necessary. That helps to preserve their life.”
Composting operations with tractor-pulled windrow turners can use that equipment to put on and pull off the covers. Otherwise, they can be pulled to the side to enable the piles to be turned. “Because they are macroporous, they are pretty light weight,” says Wisbaum.

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