May 27, 2009 | General

Facility Upgrade Yields Higher Quality Compost

BioCycle May 2009, Vol. 50, No. 5, p. 21
Northwestern company upgrades its composting operation enabling it to make higher quality compost and soil blends, and to diversify its business.
Molly Farrell Tucker and Rhodes Yepsen

Lenz Enterprises of Stanwood, Washington had been recycling organics for decades, but is now operating a state of the art, automated aerated static pile (ASP) composting system. The facility composts several types of materials including food waste, yard trimmings, wood, manure and paper fiber.
Lenz Enterprises is an offshoot of Schenk Packing Company, a beef packing company started in the early 1900s and purchased by John Lenz in 1966. In 1985, John’s son Tom started Lenz Enterprises to sell sand and gravel to wholesale customers, and truck cattle from around the Pacific Northwest to the family’s beef packing plant. The trucks brought back manure from the plant’s cow pens, as well as paunch manure (the hay and feed from the slaughtered cows’ stomachs) to the Stanwood site for composting. “That is the only part of the cow that the beef packing company has no market for,” notes Jason Lenz, Tom’s son and Vice President of the company.
The company combines the paunch manure with chicken manure that it collects from Draper Valley Farms, a network of broiler chicken farms in North Snohomish and Skagit Counties, Washington. Lenz Enterprises had been using a simple process to compost this chicken litter and paunch manure – windrows were formed and turned using a bucket loader – which worked but wasn’t as efficient as the present system. “There was no temperature tracking and control, which created a lot of anaerobic conditions,” says Lenz. “Because the compost wasn’t fully monitored, we only sold it in a topsoil mix, blended with soils from excavation sites, sand and sawdust.”
However, Lenz wanted to make higher quality compost and soil blends. The company continued to diversify by operating a recycling site for dirt, asphalt, concrete, brush and stumps. “We felt that our other business activities were closely related with composting,” says Jeff Gage, Compost Facility Manager at Lenz Enterprises. “So we decided that upgrading our composting operation would help meet public demand for green waste recycling and provide us with an additional business model for diversification.”

It took five years to complete all of the necessary permits and approvals from state and local regulatory agencies for the new composting facility. Lenz hired Harold Ruppert of O2 Compost as a consultant to help with the regulatory process. In 2003, Lenz Enterprises submitted an operating plan to the Snohomish Health District, the primary regulator for solid waste. “It got bounced back between O2 Compost and the district until mid-2005,” says Lenz. “From there, we needed to get approval from the Washington State Department of Ecology and Puget Sound Clean Air, and that took roughly six to eight months. Finally, we applied for building permits with Snohomish County Planning and Development Services, and were essentially grandfathered in with preexisting, nonconforming status, because we had been processing organics before the laws were established.” With the help of Trond Hagen, an engineer, construction began in late 2007.
The new facility started operating on July 1, 2008, and is permitted to compost up to 30,000 tons/year of Type I, II and III feedstocks. In Washington State, Type I is preconsumer food waste and green waste, Type II is agricultural manures from herbivore animals and Type III is postconsumer food waste and raw meats.

Sited on 5 of the company’s 140 acres, Lenz Enterprises currently accepts yard trimmings, wood waste, agricultural manure, pre and postconsumer food waste, food-soiled paper, paper fiber, land clearing debris and clean three-dimensional lumber. Woody materials are processed in a 12-foot GET tub grinder, purchased used in 2002.
Lenz says most of the generators have both financial and environmental motivations to compost their organics at his facility. “Our posted rate is $40/ton for all materials except food waste, which is $50/ton. We also have special contract pricing for large volume, commercial and bulk services.” The facility is located close to two county transfer stations, which have rates starting at around $80/ton.
Carbon sources are currently at a premium in the area, says Lenz, due to a few cogeneration plants that started up in the last couple of years. The facility therefore occasionally purchases sawdust and wood chips from local grinding operations for additional carbon, to supplement the woody feedstocks tipped at the facility (land clearing debris, three-dimensional lumber, etc.).
Lenz Enterprises collects all of its feedstocks, except curbside collected yard trimmings and self-hauled loads, with a variety of trucks and trailers, including IMCO live-floor trailers, and Sidump’r side-dump trailers. Schenk Packing Company and Draper Valley Farms are the facility’s largest customers. “However, we are now ready to expand and work with local haulers to target industrial, institutional and curbside food waste and paper wastes,” says Gage, who works with participating food waste generators and haulers to ensure clean loads.
Gage instructs haulers to check food waste loads when collected, and to provide direct feedback to the customer. “In addition, we have cameras at our unloading area, and staff are on hand to discuss the load quality with the delivery person,” says Gage. “If the hauler cannot resolve the contamination problem, we work directly with the source and provide more training.” He notes that some customers have switched completely to compostable plastics, which makes it especially important to look at each load carefully, as they initially appear to be contaminants.

At the 2004 Washington Organics Recycling Council’s annual conference, Lenz met Steve Diddy, Project Development Manager for Engineered Compost Systems (ECS). “I had been researching composting systems, and was considering some more labor intensive methods,” recalls Lenz. “But after meeting Steve, I saw the benefits of having an automated system of aerated static piles (ASP) with controls. Data tracking was probably the biggest factor in my decision to choose ECS, because the automation saves a full-time employee’s work. Otherwise somebody would have to walk around and collect measurements every day.”
ECS designed the system specifically for Lenz Enterprises’ feedstock input and facility layout. Highly putrescible feedstocks are tipped inside a building equipped with a biofilter. All feedstocks are then run through a stationary mixer, provided by ECS, which sizes and blends the feedstocks. “Located inside the tipping building, the Luck/Now is a twin screw, vertical auger mixer that is powered by a 200 HP electric motor, connected to three-phase power,” says Lenz.
The mixer discharges material via conveyor outside, where bucket loaders move it to concrete-walled ASP bays. The Lenz facility has a series of eight bays, each 70 feet deep, 33 feet wide and 10 feet tall. Each bay can hold up to 900 cy of material. “The bay wall design reduces the facility’s footprint, which minimizes surface water collection and retention,” says Tim O’Neill of ECS. After material is loaded into a bay, it is covered with a 6-inch blanket of finished compost, which serves as a biofilter when the pile is positively aerated.
The aeration control and monitoring system provides reversing aeration, which switches from negative to positive based on the temperature profile of the biomass. Two biofilters scrub the process air exhaust while the system is in negative aeration mode. The in-floor aeration channels collect leachate and condensate from the pile, which are directed to a sump located before the fans, then flow into a collection tank and finally an aerated holding tank. From the holding tank, the leachate is reused in new compost piles.
The Lenz ASP process is monitored by ECS’s Comptroller, an automated system that controls the air volume and timing of reversing the aeration, based on temperature readings from the piles. Two temperature probes are inserted in each pile, with two sensors on each probe, one at the tip and the other three feet up the shaft, to obtain temperatures in different depths of the pile. “The system is designed to modulate the total volume of air through average temperatures,” explains O’Neill. “For example, when the bottom of the pile is hotter than the top, air is set in positive mode to cool it; while the bottom is cooling, the top is getting hotter and vica versa. The Comptroller monitors and adjusts each bay individually.”
The aeration to each bay is separately controlled with two motorized dampers that connect the aeration floor to either the supply or exhaust plenums. The plenums are in turn connected to a supply fan (pressure) and an exhaust fan (suction). “The fans are connected, so that the exhaust blower discharges into the inlet of the supply blower as well as into the biofilter plenum,” says Gage. An automatically controlled damper on the exhaust plenum brings in fresh air to control the air temperature in the supply plenum. The supply plenum temperatures can be set higher for low energy piles or cold weather, or lower for high energy piles. “This feature helps conserve moisture and control temperature in the system, which reduces drying or overcooling,” he adds.
Feedstocks are composted for 14 days in one ASP bay, and then remixed (via front-end loader) and moved to a different ASP bay for another 14 to 21 days for secondary composting. “This process homogenizes the material and breaks up any channeling that may have occurred from settling over the aeration floor,” says O’Neill. After secondary composting, the pile is removed from ASP bays and is passively cured for an additional 14 to 21 days in a large static windrow. This windrow is approximately 33 feet wide and 10 feet tall, with lengths varying from 70 to 200 feet.

Finished compost is screened with one of two deck screens: a Powerscreen on tracks, or towable CEC screen. “We screen our compost as fine as 7/16 inch, and as coarse as 1-inch,” says Lenz. “Mulches are screened up to size of 6-inch minus.” The product is sampled and tested through the Seal of Testing Assurance (STA) program by the USCC, with results provided to customers.
Lenz Enterprises is processing about 1,000 tons of feedstocks per month, resulting in 1,000 cy/month of finished compost, sold both bulk and retail. “We are targeting wholesale to landscapers and the Department of Transportation, and retail sales to homeowners,” he adds. Lenz estimates that the compost facility will process close to 20,000 tons of feedstocks in 2009.
Two separate composts are produced. The first is marketed as a horticultural mix, made from yard trimmings and food waste. “This product changes with the seasons, but the postconsumer and preconsumer food waste provides more nutrients in the fall and winter months,” says Gage. “During the grass season from April through June, this is a potent mixture with initial C:N ratios of around 17:1.”
The second is an agricultural compost mix, a higher nutrient blend of manure composts: paunch manure, cow manure and bedding, broiler chicken litter, sawdust, paper fiber and wood chips or yard trimmings. “The initial C:N ratio is targeted at 25:1,” says Gage. “The feedstocks do not change with the season as much and give us a dependable mixture and product.”
Lenz Enterprises’ future goals include increasing the size of the composting facility, with additional aerated bays, and adding more food waste to the compost recipes. “We are open to the idea of expanding into a variety of different feedstocks, so long as they meet with environmental regulations, are financially feasible and will not negatively affect the quality of our finished compost,” says Lenz.

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