BioCycle July 2011, Vol. 52, No. 7, p. 34
Compost operators and equipment manufacturers discuss innovations and insights.
TWO years ago, as part of BioCycle’s 50th Anniversary celebration, a series of articles traced the history of the major categories of equipment used for composting, organics recycling and anaerobic digestion. “Evolution Of The Compost Windrow Turner” (July 2009) described a “mechanical stirrer” (circa 1960) built by an Oregon farmer to “replace the slower method of stirring by hand.” The machine was constructed from old automobile parts and scrap materials, and powered by a 1938 Ford V-8 engine. “The stirring machine is moved forward in the pile with a … tractor for a pusher,” described an article in Compost Science (BioCycle’s original name) from the early 1960s. “The revolving drum shreds and kicks the material onto a revolving chain conveyor which deposits the material to the side, rebuilding the pile to the same depth.”
Windrow turning equipment has come a long way since that time. For example, ALLU’s Model AS 38H, powered by a 450-HP turbo diesel, is capable of turning windrows that are 10-feet high and 26-feet wide. Komptech’s TOPTURN X has a hydrostatic drive combined with a solid telescopic frame that enables it to operate on any terrain. On the other end of the spectrum, Resource Recovery Systems International (RRSI) has developed a 4-wheel drive KW windrow turner to reduce wheel pathways to under 0.75 meter. “This particular customized KW 716 is being delivered to a palm oil mill for composting the empty fruit bunches,” says Les Kuhlman of RRSI.
CONTINUOUS AERATED WINDROW
Transform Compost Systems, in response to increased interest in food waste composting and the associated environmental factors regarding odor, air and water quality, has been developing a new continuous aerated windrow composting process since 2009. The technology takes advantage of a combination of forced aeration in the floor and windrow turning. This system, says John Paul of Transform, combines an agitated bed process where the raw material enters at one end and leaves at the other end, with an aerated windrow process. “It can be enclosed in a cost-effective, corrosion-resistant building structure,” notes Paul. “It was also designed to take advantage of capturing heat energy from the composting process.”
The remotely controlled compost turner is designed to turn a windrow that is 26 feet wide and 10 feet high, and move it backwards 25 to 40 feet. “Moving the product backwards along the windrow has three advantages,” he explains. “The turner operates in 30-foot wide buildings that do not require walls for containment. Operating costs are reduced because there is no need to prepare and remove windrows, and use of space is optimized because the turner compensates for product shrinkage during composting resulting in the windrow size remaining at 26 feet wide and 10 feet high throughout the entire composting process.” Transform is working on an agreement with a turner manufacturer to produce a prototype of the new turner in the next 12 months.
BIGGER AND BELT-DRIVEN
Since SCARAB Manufacturing introduced its belt-driven drum turner two years ago, sales have overtaken its hydraulic-driven drum turners, says Mike Winter of SCARAB. “The fuel economy and production of the belt-driven machine makes it a logical choice for our customers,” he notes. “With the belt drive, there is a direct transfer of energy from the engine shaft to the drum, so it is operating at 98 percent fuel efficiency. With the hydraulic-driven drum, you get about 64 percent efficiency from the hydraulic pump and motor. That’s a tremendous difference in fuel economy and man-hours dedicated to turning.”
Customers also are ordering larger machines, providing them the ability to build much smaller pads, adds Winter. “Our most popular size turner used to be our 18-foot, but now our machines ranging in height from 20 to 27 feet are more in demand. Our clients may spend $300,000 more for the machine, but they are saving millions in concrete and windrow cover costs.” This summer, SCARAB is on tour with its 20-foot model, stopping at composting sites around the country. “At the first three sites we visited, the machine turned over 14,000 cubic yards/ hour,” he says.
TURNER AS INTEGRATED PEST MANAGEMENT TOOL
Flies, beetles, and rodents are serious problems in manure management on farms operating under strict environmental regulations, leading to use of Integrated Pest Management (IPM) programs. Research done by the Penn State Poultry Science Department showed benefits of mechanical composting as part of an IPM plan. “During experiments with poultry manure conducted in chicken houses, manure was mechanically turned using the CompostCat designed and patented by Farmer Automatic of America,” recalls David Leavell of Farmer Automatic. “Turning every two to three days killed flies in the pupae stage, thus decreasing fly populations and reducing the amount of pesticides required.”
Mechanical composting also reduces beetle and rodent populations by eliminating nesting possibilities. The CompostCat, a self-propelled machine, offers a 0-degree turn radius. New options include a 75 HP engine, 4B heavy duty track, chain conveyor and blower system.
The Region of Peel in Ontario, Canada has been composting source separated organics – food waste and yard trimmings – from the residential, commercial and institutional sectors for many years. The primary composting phase is done at one location that uses the Christiaens Composting system. After one week in the tunnels, material is delivered to a curing facility, where it stays under GORE covers for five to eight weeks. At this time the compost is ready for agricultural uses but needs to mature for at least another six months for landscaping uses.
Two years ago, the Region of Peel purchased an ALLU AS-38 turner, which has the “ability to turn windrows over a period of minutes rather than hours, reducing the amount of loader movements and exposure for odors,” says Al Pickens of the Region of Peel. “We are also able to mix water into the compost with an on-board watering system if an adjustment to the moisture content is required rather than trying to spray water with a hose.” Other key components of the compost curing facility – where odor and product quality control are paramount – include two weather stations, automatic weather alerts to site operators’ cell phones notifying them of critical weather conditions, and a screening system to classify the compost with the waste fraction automatically loaded into a transfer trailer and conveyors to move material to reduce loader movements.
CLEARING A PATH
The Virginia Peninsulas Public Service Authority (VPPSA), based in the colonial town of Williamsburg, was looking to replace its 20-year old compost turner several years ago. “We put out a bid, and awarded the procurement to Komptech, the lowest [responsible responsive] bidder,” says David Magnant, Director of Operations. “We purchased the Topturn X60.” The yard trimmings composting facility is on a 22-acre paved site. It receives about 25,000 tons/year of yard trimmings from three of the municipalities in the Authority’s service area. The site also accepts material from commercial landscapers and other private entities.
One of the benefits of the Topturn is that it doesn’t require space between the windrows in order to operate. “There are plows in front of the wheels that essentially clear a path for the turner while pushing the material back into the windrow,” explains Magnant. “This allows better use of the pad. We still like to have space in between the windrows so we can monitor the piles, taking temperatures and samples. And the engine is much more efficient from a fuel economy standpoint.”
As part of the service to the municipalities using the composting facility, the VPPSA agreed to accept yard trimmings from households in plastic bags. It evaluated various debagging options before deciding to modify its Komptech Mustang by putting knives in the drum to open the bags and keep them out of the fraction that is composted. “The material coming out of the trommel is very clean,” says Magnant. “We’d prefer that households used biodegradable bags but for now, we accept the material in plastic bags. One option we are going to present to one of the cities is to require its residents to only use bags that are biodegradable, and to have the city’s emblem on the bags so that those are the only ones collected.”
Earlier this year, the British company CompostManager began marketing its CMS2010 monitoring system to optimize the composting process. “It’s all about the bugs,” says Eric Crouch, who developed the system. “Work in sympathy with nature, rather than against it. Give them the best conditions to do their work, and things happen more efficiently. But disturb them unnecessarily and the process is delayed.” Crouch collaborated with some of the UK’s leading composting companies and over four years compiled more than 25,000 sets of data.
Some of the results were pretty surprising, he adds, and in some cases, counter-intuitive. For example, it is commonly expected that when turning a windrow, oxygen levels rise before slowly dropping off. Instead the opposite happens – levels of oxygen plummet to around 0 percent in the 2 to 3 hours immediately after turning, before gradually creeping back up over the next few days. By monitoring respiration levels in the windrow it becomes clear that turning is really about refreshing the feedstock for the bugs, not aerating, says Crouch.
The CMS2010 system incorporates a four-way probe to measure temperature, moisture, oxygen and carbon dioxide, as well as a software package that produces a simple instruction: “Turn,” “Irrigate” or, more often than not, “Leave Alone.” “Composters using the system found they were able to reduce not just the overall composting time – typically to nine or ten weeks – but also reduce very significantly the number of turns required, as few as four or five over the total cycle,” he notes.