Courtesy : www.mswmanagement.com
Composting innovation
point of view. For the waste industry, it’s ideal to create compost that can be used (sold) rather than disposed of. With governmental imperatives to reduce landfill levels and with landfill capacities continually shrinking, finding better ways to make quality compost and finding more markets make perfect sense.
It wasn’t that many years ago when many jumped into composting, fueled by visions of compost empires. Dire predictions of shrinking landfill capacity, visions of flow control, and $100-plus per-ton tipping fees made composting look like the new promise land. “Man, we want a piece of this,” people said, according to Sharon Barnes, owner of Barnes Nursery in Huron, OH, and the president of the United States Composting Council (USCC) in 2000. “Perhaps 15 to 20 $30 million plants, involving high-tech composting systems, were built and then closed,” she adds. “Many monstrous plants, based on a big projected flow control, didn’t pan out. And if there was MSW in the big plants, it was impossible to sell the finished product because the quality was so poor with garbage, glass-everything in it. Yet they counted on the back end money flow of selling the finished product.”
For many, the big compost dream melted like today’s tech stocks. For others, holding to the steady course-the turtle rather than the hare-continues to bring important improvements and innovative approaches, which help transform the basic good sense of compost into a good, growing business.
Matt Cotton, president of Integrated Waste Management Consulting in Nevada City, CA (and a board member of USCC), explains, “Basically there are three levels of composting technologies: (1) open windrows-you turn the materials, (2)aerated static piles-forcing air in via ducts, and (3) in-vessel-a totally contained system in big drums. There are hybrids of all these.” One issue facing composting is odor control. Cotton, who permits and develops sites, says material can be processed so that odors don’t bother people. “It involves siting, operations, and a good basic composting knowledge.” He adds that people have two choices: “Either you can increase the process control [which increases costs] or you can find a new site.”
Most people interviewed for this article believe it is not possible to achieve total control of odor. According to Jack Hoeck, president of Rexius Forest By-Products Inc. in Eugene, OR, “There’s always going to be a certain amount of odor, even with incoming materials, what they are, and the time of year. Plus there are climatic conditions [such as wind flow] and how sensitive and close neighbors are.”
Says Oley Sheremeta, president of Sheremeta Environmental Consultants LLC in Bellingham, WA, “As an industry, the technology of odor control has risen. There’s less generated, and what is generated is better controlled. The market is more sensitized to odor-how to control odors on the first hand and how to deal with residual odor. We learned how to manage it much better over the last 10 years.” Dave Hardy of California Biomass, an independent compost facility near San Bernardino, CA, points out, “Technically you can reduce odors. The conflict arises if these measures are not enough to satisfy the local residents. Once they are [angry] and organized, your days are numbered.”
Jan Allen, senior technologist at CH2M Hill in Seattle, WA, states, “You can’t compost without odors, but you can minimize odors to levels that are acceptable. We can get down below a problem level, that’s for sure.” Allen knows that firsthand. The Cedar Grove composting site received 3,224 complaints in 1997. In 1998, that number dropped to 232. In 1999, 178 people complained. As of February 20, 2001, the site received only 48 complaints. Three things happened at Cedar Grove to reduce odor issues. Allen says, “They expanded the biofilters; they applied an Environmental Management System, which is structured to comply with ISO14000; and they had a much tighter control over the feedstock preparation by controlling the percentage of grass.” Feedstock at Cedar Grove includes landscape materials (e.g., grass), foodwaste (primarily vegetable), woodwaste, wax-coated cardboard, and land-clearing vegetation. For these feedstocks, Cedar Grove uses aerated static piles and biofilters. It has also undertaken a residential postconsumer program, including meats and fats, in an enclosed process.
Allen says he’s spending most of his time converting windrow facilities to alternative technologies because of the odor problems with windrows. The original concept of windrow composting “made sense in an arid environment as a means to drive off moisture as the materials composted. They definitely do not make sense for wet or cold climates or for urban areas. So the technology has been applied in places where it probably shouldn’t have.”
Rexius Forest By-Products, a 45-year-old company, started out recycling woodwaste. As restrictions on burning took hold, the company began making soil amendments and in the early 1990s began composting yard debris. “That was the first time we had to take materials on a daily basis,” Hoeck recalls. “So we set up a windrow system, turning the material with a front-end loader. It was a low-tech system.” Allen came up with a low-cost aboveground airflow technology that allows Hoeck tremendous flexibility at a quarter of the cost of an engineered site. He says, “Paving and buried pipes were too expensive considering our tipping fees. So we adopted that technology to an aboveground system where we don’t need paving or trenching. An ocean container holds the motor, fans, controls, et cetera. It’s lockable but not a concrete building. The piping is aboveground, and it slides together with a series of manifolds, and the pipes go under the piles. We can push air through or run negative air, pulling air back through and exhausting it.” Odor control can be improved because pile surface area, agitation frequency, and surface emissions have all been minimized. One pilot study at a windrow facility measured odor reduction at 98% while reducing the footprint of the facility by nearly 70%.
The advantages of the air system are: (1) You can control the amount of air; you don’t have to rely on turning the material. (2) You can filter the air. (3) Moving air through helps with heavy winter rains, so in the spring the material is softer and easier to screen. “We still move the material about every three weeks,” Hoeck adds. “First we pull out the pipes, then we remove material and move it down one section. The technology is nothing really new; it was developed for biosolids by the Department of Agriculture [USDA] in the 1970s in Beltsville, Maryland. They had a series of fans with pipes there, a pile of wood chips with pipes, then biosolids, then 8 to 10 inches of sawdust for an insulation blanket. Airflow in the bottom of the pile and an insulation blanket on top made all the biosolids go up into temperature. Those systems only blew out air. There wasn’t an option for negative or positive air, nor were there any removable pipes.”
Hoeck’s flexible, basic, dual-air Express Composting System with a biofilter costs about $140,000. The system will process about 3,200 yd. at any one time. “That can be expanded,” he points out. “With yardwaste, it can handle 6,000 yards. We can expand the system up to 9,000 yards with our material.” With biosolids and chicken manure, fewer yards can be processed as a result of the need for a higher airflow. Hoeck says he’s just started marketing this simple and efficient system, which can be assembled and started up in less than two weeks. Because it’s appropriate for feedstocks with moisture levels between 50% and 60%, it’s an ideal system for mixtures of foodwaste and biosolids as well as greenwaste and woodwaste.
Another new millennium approach comes from Jim McNelly, president of NaturTech in St. Cloud, MN. In February 2001, McNelly began his Renewable Carbon Management (RCM) composting venture. RCM will use patented modified Intermodal shipping containers with a 110-yd.3-capacity, twice the size of the modified trash rolloff containers. Instead of selling equipment, as NaturTech does, McNelly says, “We’ll enter into strategic partnerships. I’ll be part of the operations to keep the business focused, plus it puts me back into operations. I’m the first person to operate a commercial composting facility that picked up grass clippings and other yardwaste from the curbside in Northglenn, Colorado, in 1976.”
RCM will go after larger facilities, starting at 120 tpd. “Our optimum size is 300 tons per day, where we’re the most economical. We call it our “˜sweet spot.’ We’ve got five different venture partners currently negotiating with us. We’re looking at projects in China and Belgium and with three different firms in America.” RCM will be a facility-developing company for other clients. The feedstocks it’ll use will be mostly raw wastewater treatment solids. “One of our NaturTech facilities proved we can handle most wastewater treatment plant biosolids to make Class B solids. We’ll take primary sludge only a few days old and thicken and treat it by going directly to composting.”
McNelly knows he can do this after what happened in Coldspring, MN, working with Mississippi Topsoils, who took raw chicken blood and fat from a slaughterhouse that axes 200,000 chickens daily. “For the last 15 months they’ve proven they can go from raw sludge to compost,” he states. RCM will be the marketing agent for NaturTech. Intermodal will not be for sale; McNelly will only work through strategic partnerships. Where NaturTech can handle 60-100 tpd maximum, RCM can work with 120-300 tpd.
Concerning odors, McNelly says, “One of the things we learned at Mississippi Topsoil was how to turn the compost curing system into the biofilter. In the past, NaturTech sold separate biofilters [also rolloffs]. Now they no longer have the extra expense of biofilters. We’ve cut the cost of composting in half over what NaturTech used to do. NaturTech used to be $35 per ton for capital and operating expenses. The RCM system costs less than $20 per ton and some operations are as low as $9 per ton. We’re very, very affordable. This isn’t for the faint of heart to go after 300-tons-per-day capacity, and all of our numbers are based on seven days a week, 365 days a year.”
The feedstocks that RCM will go after include (1) wastewater sludge, (2) dewatered pig manure, and (3) mixed solid waste in developing countries. McNelly remarks, “I don’t like mixed solid waste because there’s so much contamination with glass, batteries, and so on. But we’ll do both source-separated [clean] compost and mixed waste [dirty] compost at the same facility.