BioCycle October 2007, Vol. 48, No. 10, p. 19
The workhorses of open-air windrow composting are becoming more efficient to enhance compost process control.
Craig Coker

WINDROW turners, along with front-end loaders, screens, conveyors, blowers and grinders, are the workhorses of the composting industry, but for windrow composting, the turner is leader of the pack. Unlike their hardworking brethren adapted from other industries, turners were developed in the 1970s specifically for composting. The pioneers in windrow turning equipment were SCARAB (1972), Wildcat (1973) and Resource Recovery Systems International (1975). All had origins in agriculture. Following them were Brown Bear (1977) and Double T Equipment (1978), the latter originating in the mushroom composting industry. Other manufacturers with agricultural roots are: Doppstadt, Frontier, HCL, and Komptech. ALLU and Vermeer (formerly Scat) got their start in biosolids composting. Midwest Bio-Systems and Backhus evolved from composting operations looking to increase turning efficiencies.
Turning windrows accomplishes several objectives. It provides fresh air to the oxygen-needy materials in the center of the windrow. It agitates and mixes materials, which distributes pathogen-killing heat throughout the mass. It releases excess heat, water vapor, biogenic carbon dioxide and other gases into the atmosphere. It breaks up clumps of material and individual particles which can result in higher screening efficiencies downstream. The overall effect of turning is to invigorate the composting process – in the short term with a supply of oxygen, and in the long term by homogenizing the composting materials.
This article of BioCycle’s “What’s New?” series looks at new developments in windrow turners, as reported by 14 manufacturers responding to a survey sent out by BioCycle editors (information for those who did not respond was culled from their websites). The comparisons that follow are presented for general information only and are based entirely on information supplied by each manufacturer. Claims and information presented have not been independently verified.
The defining characteristic of windrow turners that distinguishes them from each other is the mechanical action of the turner. They can be categorized as: auger-type, elevating face, rotating drum with a housing that covers the windrow, straddle-type and trapezoidal. Auger-type turners use a slanted auger or auger-type paddles to turn the windrow and move it to one side (picture how a snow blower works). An elevating face turner has a wide backward-sloping conveyor with cleats or teeth that lifts the compost up and over itself, where it either falls down in the same place or onto a conveyor that moves it to one side. Many on-farm operations use a drum-type turner pulled behind a tractor that has a horizontal spinning shaft with paddles, roughly one to three feet in diameter, in a metal windrow-shaped housing. They can be operated to turn either one-half of a windrow in a pass, or the entire windrow in one pass, depending on size. Straddle-type turners are basically drum-type turners but with self-propelling capability. They turn an entire windrow in one pass. These tend to be used more for larger windrows, although small straddle-type turners are available. Trapezoidal turners slice a layer off the side of a large compost pile, lifting it from the windrow and conveying it to the side across the aisle, where it is added to the side of a new windrow.
NEW TURN OF EVENTS
The trend among windrow turner manufacturers is to expand the breadth of their product lines, making turners that can handle larger windrows (reflecting the growing importance of maximizing processing throughput), equipping them with mobility options (tracks, four-wheel drive, trailering capabilities, etc.) and ensuring they can be used to irrigate windrows with a spray system, which is becoming important as a component of storm water Best Management Practices at a composting facility.
ALLU plans to introduce two smaller model windrow turners and new engine options to increase efficiencies. Backhus improvements have focused on computer controls; in 2007, it introduced speed control (tied to material bulk density) and a management system to optimize hydraulic system power. Later this year, the company will add on-board remote diagnostics. Farmer Automatic recently upgraded its CompostCat turner to make it wider, and with a larger diameter auger, eliminating the flow-through belt formerly used to transport compost behind the machine. Frontier is expanding beyond the world of turners to offer a small low-cost compost tea brewer. “This is part of our innovation to educate customers about the principles of biological farming,” said Brad Glaze, President of Frontier. “We believe that an educated consumer will demand nutritious and chemical free foods and thereby drive our industry.” HCL now offers its turners with built-in spray systems and has modified the center teeth on the drum to produce a higher peaked windrow.
Komptech has recently introduced the Model X67 Windrow Turner, the largest machine in its product line. Midwest Bio-Systems has added a 14-foot wide straddle-type turner to its product line. Resource Recovery Systems International plans to offer a track system in lieu of front wheels on its models. SCARAB plans to introduce a new temperature control system, along with a “down time” monitor in 2008, and is interested in exploring the use of Global Positioning Satellite (GPS) technology for its turners. Vermeer will be adding a straddle-type elevating face turner to its product line, driven by a 200 HP engine and with a 10-foot wide by 10-foot tall face. Wildcat plans to offer a stainless steel turner tunnel (essentially the steel housing over the drum that encloses the windrow as it’s being turned) to resist the corrosive effects of biosolids windrow composting.
When we asked manufacturers the question, “What are your customers asking for in turning equipment these days?” the answers were as varied as the size and nature of the composting facilities that use their machines. High capacities and good mixing results, said one. Inexpensive water trailers, said another. Other responses were: efficiency, low operation costs, quality, convenience, more horsepower, self-propulsion, rear side discharge conveyor, help in selling their old turners, fuel savings and space savings. “We’re seeing more and more customers asking for help in using our turners for bioremediation of contaminated soils,” says Grey Williams, Midwest Bio-Systems Sales and Marketing Manager. “Of course, using a turner to recondition heavy materials like soils requires that the machine be beefed up significantly.”
TURNING TO THE DETAILS
While the following details were provided by the manufacturers who responded to the BioCycle survey, many of these turner sources have extensive product information on their websites (see Directory for website addresses). Table 1 summarizes some of the data provided.
ALLU offers the AS 38H straddle-type track-driven turner that uses a combination auger and rotating drum turning system. It can handle windrows up to 10 feet tall and 26 feet wide. The outer edges of the drum are a reverse auger that moves material toward the center, where the paddles on the rotating drum mix and agitate the windrow; the drum has 80 inches of ground clearance adjustment. The unit is powered by a Mercedes Benz 450 HP diesel engine and can handle heavy soil materials (as in bioremediation) with densities up to 1.8 tons/cubic yards (cy). It has a turning capacity of 8,000 cy/hour. Options available include a watering system and a negative air cabin system for operator protection, if used in a waste remediation project where exposure to toxic contaminants is a concern. The unit comes with an automatic overload protection system that slows the driving speed if the drum rotation speed slows due to overload. The turner can be transported in a low bed trailer and therefore does not require special transportation to move the unit from jobsite to jobsite.
Backhus makes nine straddle-type turners for windrows, a trapezoidal turner for static piles and ten models of lane and bridge turners for use in enclosed aerated static pile tunnel systems. Its straddle turners can handle windrows up to 10.8 feet high by 24.6 feet wide, which is the largest straddle-type turner on the market today. Processing capacities vary from 523 cy/hr to 8,500 cy/hr and windrows can be laid out “toe-to-toe,” thus maximizing throughput on a given pad area. All Backhus turners use Cummins diesel engines; all are certified for Tier III emissions, can run on biodiesel, and have power varying from 31 HP to 625 HP. All turners meet ISO 9001 manufacturing requirements. Options available with Backhus turners include: elevating cab, side transposing conveyor, windrow fleece wind-up systems, windrow irrigation systems, hose reels, particulate reduction system (dust suppression), landfill undercarriage and armored drum tools (welded to enhance abrasion resistance).
Brown Bear makes 12 different models of aerators for use as attachments to loaders, or for use with their own tool carrier tractors. These aerators – essentially pitched augers, hydraulically driven by either the loader or by the tool carrier – are used for turning windrows, mixing soil blends, dewatering sludges and bioremediation of contaminated soils. As the windrow is turned, the auger pitch moves the compost to one side of the unit. One advantage to the use of turner “attachments” to a loader is that, unlike straddle-type turners, the loader can drop the turner attachment and reinstall the bucket (or another attachment, such as a snow blower, a sweeping broom or pallet forks) and go on to perform other tasks. Brown Bear’s own tool carrier tractors are equipped with 130 HP to 350 HP Caterpillar or Cummins diesel engines. “Our Models 400 and 500 are already Tier 3 compliant, while the Models 200 and 300 are Tier 1 compliant but will be upgraded soon,” says Stan Brown, President of Brown Bear. “Both CAT and Cummins have told us their engines will run on B20 biodiesel.” On the Brown Bear 200B, 300B, 400C and 500C they now offer an electronic load control that varies the ground drive of the carrier to maintain the engine speed at the best combination of torque and HP.
CBT Wear Parts, Inc. is an after market parts supplier to the compost industry. CBT makes the replacement flails for compost turners such as SCARAB and KW (made by Resource Recovery Systems International).
Doppstadt’s Model DU 320 Grizzly is a trapezoidal turner, with two 220 RPM cutting discs that slice a layer off the side of a windrow (or static pile) and a 4-foot wide transverse conveyor to move material into a new adjacent windrow. The unit is propelled by a 320 HP tractor that is integral to the turner. It can build a new windrow up to 11.5 feet tall, if equipped with an optional discharge drum. Other available options include protected aeration for the operator cab and a trailer for transporting the unit between sites.
Double-T Equipment (DTE) makes three models of straddle-type self-propelled turners, Models 10D, 13D and 16D. All DTE models are diesel hydraulic drives. The machine is designed to make a tall, narrow windrow, which they claim facilitates gas exchange through convection. Engine horsepower varies from 140 HP to 400 HP. Windrow capacities range from 6 feet high by 10 feet wide for the Model 10D to 7 feet high by 13 feet wide for the Model 13D, to 7 feet high by 16 feet wide for the Model 16D. Optional features available include hose reels (mounted on the side of the turner), water spray bars, cab heating and air conditioning.
Farmer Automatic offers two models of their CompostCat, a 6- to 9-foot wide self-propelled auger-type turner that moves 4-foot high windrowed material in towards the center of the turner. It is powered by a 57 HP Duetz diesel engine with a turbocharger. One model is equipped with a discharge conveyor belt to move the windrow to the rear of the unit, while the other uses a larger diameter auger in lieu of the Flo-Thru belt. The company plans to upgrade the engine as needed to meet more stringent air emission requirements; current models are not set up to run on biodiesel. Changes have been made recently in the drive and hydraulic systems to enhance both turner performance and longevity.
Frontier offers 13 different models of turners, ranging from the pull-behind MightyMike (available in either self-propelled or pull-behind versions) that turns windrows 3.5 feet high by 6.7 feet wide, to the self-propelled F-22, which uses a 525 HP engine to turn windrows up to 8.5 feet high by 22 feet wide. All Frontier turners are equipped with its patented Drum and Paddle system, which uses right, left and center paddles to lift and entrain air inside the windrow material as the material is mixed. All Frontier models are belt-driven and use a microprocessor-controlled “Smart Clutch,” which is self-adjusting and will disconnect if any disc slippage occurs under unusual loads or operator abuse. Options available on the straddle turners include a fifth wheel trailering package, four-wheel drive and watering systems (four different types of watering systems including a 200 gpm hose reel system with up to 1,200 feet of watering hose are also offered). Options available for the pull-behind models include electronic over hydraulic controls and a hydraulic wet-kit, in addition to self-trailering and watering system add-ons.
HCL Machine Works offers two models of tow-behind, power take-off (PTO) driven, straddle-type turners. They are capable of turning windrows 5 feet high by 10 feet wide, or 6 feet high by 12 feet wide. These units are well suited to both agricultural and municipal applications. The 10-foot model requires only an 80 hp tractor, and the 12-foot model requires only a 110 hp tractor; either size tractor would need to be equipped with either a hydro-static or creeper gear that would allow them to go only 10 to 12 feet per minute on the first few passes. The drum-roller-tooth configuration is designed to have an auger-like movement on both sides of the pile that moves the entire pile to the center and then throws the pile over the top of the drum. The pile is then reformed in the same space that it started. This drum-roller-tooth type of auger allows the replacement of a single tooth if the turner hits something hard in the pile. The manufacturer has made their rear tow hitch and double water bar standard for water or inoculant injections during the turning process. These turners are capable of being rotated upward from a work position to a transport position, making movement around the site easy for both models, and transport to different sites easy for the 10-foot model (the 12-foot model must be disassembled for public highway transport).
Komptech offers its Topturn line of self-propelled straddle-type turners, which are more oriented to larger windrow processing. Its three models vary in windrow size capacity from 7 feet, 10 inches high by 16 feet, 5 inches wide to 9 feet, 8 inches high by 21 feet wide. Turning capacities vary from 4,300 cy/hr to 5,900 cy/hr. All Komptech turners are run by Caterpillar’s ACERT engines, developed in 2004. ACERT technology is a new system that reduces air emissions at the point of combustion. These engines can run on biodiesel. Options available include a watering system, a lateral displacement conveyor to move the windrow completely over to either side, protective ventilation in the operator cab, a scraper bar (for picking up material at the bottom of a windrow), a choice of wheels or tracks, two types of drum configurations (a standard spiral screw and an optional mixing roller with two spiral screws), hydraulically-driven intake screws for moving material in towards the center of the turning drum tunnel, automatic lubrication, service ladders and a fast drive for wheels.
Midwest Bio-Systems (MBS) offers three rotating drum tractor/loader-pulled models (for 10-foot wide, 11-foot wide and 14-foot wide windrows) and one self-propelled straddle-type turner (also 14-foot width). MBS machines can turn a windrow of height equal to half the windrow’s width. Its PT-170 and SP-170 (pull-type and self-propelled models, each capable of turning 14-foot wide windrows) have a vertical lift system for pulling the rotating drum up out of the windrow. Options available include a watering spray system based on a spray bar inside the windrow tunnel, watering tanks that are pulled behind the turner, a windrow fabric cover system, microbial inoculants to retain nutrients and reduce odors, and other aspects of the MBS Advanced Composting System (ACS) program. MBS is outsourcing the drive engine on the new SP-170, but indicated its supplier will meet any required air emissions limits and that they will follow the engine manufacturer’s recommendations on the use of biodiesel fuels.
Resource Recovery Systems International (RRSI) offers seven self-propelled models with tunnel sizes ranging from 4 feet high by 8 feet wide to 8 feet high by 18 feet wide. With many available options, the equipment is designed and manufactured to meet each customer’s specific needs. A KW 614 will turn a windrow 6 feet high and 14 feet wide. Because all KW turners can be raised in increments up to one foot, a 7-foot windrow can be turned if it stands on a 14-foot base. “Turning capacity is related primarily to engine horsepower and not tunnel size,” says Les Kuhlman, President of RRSI. “Turning capacities over the entire range of KW turners is 1,000 to 6,000 cy/hr. However, capacities are best stated in tons per hour because of the high variability of bulk densities of wastes. Expressed in tons per hour, turning capacities range from 700 to 3,000 tons/hour.” Engines used are Caterpillar, Cummins and John Deere, ranging in horsepower from 225 to 550; all are Tier III compliant. Options available from RRSI include nonstandard tunnel sizes; various brands of engines; various front and rear tire sizes; full tracks; 4-wheel drive; watering systems; reversing fans; choice of belt driven, clutch engaged drums or hydraulic driven drums; choice of drum style; and option of low profile (to lower overall height of machine). Improvements for durability and safety have included upgrading wheel hubs, hard surfacing flails for longer wear and installing a steel plate under the operator cab and the fuel and hydraulic tanks.
SCARAB custom builds each straddle-type turner to a customer’s specification by matching up the frame, engine and drive system components. Frame options vary from 8 to 20 feet wide (in 2 foot increments); frame width is equal to windrow width. Engines are by Cummins, Caterpillar or Detroit Diesel and vary in power from 185 HP to 600 HP. Available drive systems are rubber tire, full track, four-wheel drive and four-track drive. Options available include a spray system for irrigating windrows, an anti-vandalism package, a noise suppression system and an automatic fire suppression system. The main thing that SCARAB has been developing for the future has to do with the ‘interface’ with the new Tier III engines. The ability to monitor temperature, RPMs and fuel load, as well as many other characteristics, have helped to improve the fuel efficiency and maintenance costs of the SCARAB turner.
Vermeer purchased Scat Engineering’s product line in 2006 and now offers the Model CT670, an elevating face turner pulled by a tractor or loader, capable of turning a windrow up to 12 feet wide and 6 feet tall in two passes. Vermeer has made several safety and durability improvements, including a mechanism that stops the elevating face if the machine stops for more than a few seconds. Vermeer’s engine manufacturers all agree that B5 biodiesel (5% biodiesel, 95% petroleum diesel) is an acceptable fuel, and some will allow B20 biodiesel. All of Vermeer’s equipment will be compliant with Tier III emissions limitations. The CT670 can be operated by a remote control from the towing vehicle.
Wildcat Manufacturing’s models are all straddle-type turners and now include three towable models and four self-propelled. Improvements that Wildcat has made in terms of durability and safety features include OSHA-approved handrails on the work deck, a newly designed ladder with handrails, a drum braking system, improved sound dampening in the operator’s cab and a fold-down seat next to the operator for training purposes. Options available with Wildcat turners include hose reel hook-ups for windrow irrigation, and a misting system for delivering odor neutralizing chemicals or water for dust suppression water. Wildcat warranty programs start at a one-year, unlimited hours, parts and labor warranty (the engine has a 2-year, 2,000-hour warranty), and go up to five-year warranties. Wildcat is considering upgrading its turner engines to be compatible with Tier III emissions limitations and does not yet offer a biodiesel fuel capability in their turners.
THE FINAL RUN-THROUGH
Windrow turners are unique pieces of equipment as they only do a few materials handling functions well. Those functions, however, are absolutely critical to successful windrow composting operations, whether inside an animal barn or outside in the open. There are dozens of models available, suitable for everything from a small on-farm operation handling farm-generated agricultural and animal wastes to very large municipal yard trimmings and commercial composting establishments. They also are suitable in non-composting operations such as soil blending and soil remediation.
Turner manufacturers understand the trend in larger-scale operations to maximize compost processing throughput on fixed area composting pads. They also understand that reuse of storm water through windrow irrigation is a growing requirement (as well as good process management), and recognize that not all windrow turners operate on a flat, smooth concrete slab. Some think that windrow turner drum designs are moving away from the traditional paddle/flail configuration, with its necessary maintenance costs, towards more auger-shaped drums that lift and fluff the material as the turner passes through a windrow. Others disagree.
“In my opinion the flail type drums provide better particle reduction for wastes such as manures with straw bedding and green wastes which are often not finely shredded,” says Les Kuhlman, President of RRSI. “Auger type drums possibly do fluff to a greater degree. Composting facility operators must ask themselves where they can most effectively spend their money. Do they want finer shredding and to reduce the ‘overs’ from the screen by utilizing a turner with greater ability to reduce particle size? Perhaps the answer is that the manufacturer must find out what wastes are being composted and then make the drum most suited to the customer’s situation.”
Yet, for all their functionality, some turner manufacturers are adding features for operator comfort and safety, as well as structural designs and color schemes that cause composters’ heads – and not just the windrows – to turn.
Craig Coker is a Contributing Editor to BioCycle and a Principal in the firm of Coker Composting & Consulting (www.cokercompost.com) in Roanoke, Virginia. He can be reached at (540) 904-2698 or by email at craigcoker@cox.net.
WINDROW TURNER DIRECTORY
Allu Group
700 Huyler St.
Tetersboro, NJ 07608
800-939-2558
www.allu.net
Backhus/N40, Inc.
P.O. Box 1330
Rockwell, NC 28138
336-499-5881
www.backhus.us
Brown Bear Corp.
P.O. Box 29
Corning, IA 50841
641-322-4220
www.brownbearcorp.com
CBT Wear Parts, Inc.
13658 Hilltop Valley Rd.
Richland Center, WI 53581
608-538-3290
www.cbtwearparts.com
Doppstadt U.S.
1030 Jaycox Rd.
Avon, OH 44011
440-937-3225
www.doppstadtus.com
Double T Equipment Manufacturing, Ltd.
#2 East Lake Way
Airdrie, Alberta
T4A 2J3 Canada
403-948-5618
www.dte.ca
Farmer Automatic
Midwest Branch
5571 S. State Rd. 25
Rochester, IN 46975
574-857-3116
www.farmerautomatic.com
Frontier Industrial Corp.
P.O. Box 700
Lyons, OR 97358
503-859-3454
www.frontierindustrial.net
HCL Machine Works
15142 Merrill Ave.
Dos Palos, CA 93620
209-392-6103
www.hclmachineworks.com
Komptech USA, Inc.
1369 Forest Park Circle, Ste. 204
Lafayette, CO 80026
720-890-9090
www.komptechus.com
Midwest Bio-Systems
28933-35 E St.
Tampico, IL 61283
815-438-7200
www.aeromasterequipment.com
Resource Recovery Systems International, Inc.
511 Pawnee Dr.
Sterling, CO 80751
970-522-0663
www.rrskw.com
SCARAB Manufacturing & Leasing, Inc.
1475 County Road W
White Deer, TX 79097
806-883-7621
www.scarabmfg.com
Vermeer Manufacturing Co.
P.O. Box 200
Pella, IA 50219
641-628-3141
www.vermeer.com
Wildcat Manufacturing
P.O. Box 1100
Freeman, SD 57029
800-627-3954
www.wildcatmfg.com