November 19, 2007 | General

What’s New? Contaminant Removal

BioCycle November 2007, Vol. 48, No. 11, p. 41
Specialized equipment can improve materials processing and compost product quality.
Craig Coker

THE road between incoming raw compostables and market-ready finished product is often littered with glass, metal, plastic film, soda and water bottles, rock, gravel, large chunks of wood and small plastic items, often leaving composters to take a deep breath and reach for a trash can to begin the tedious process of manual sorting and separation. As the boundaries between single-stream recyclables processing, construction and demolition debris materials handling and multifeedstock composting become less distinct, equipment developed in those parallel industries for sorting, separating and cleaning waste streams is available for use in composting operations.
This article in BioCycle’s 2007 What’s New? series looks at developments in contaminant removal equipment, as reported by several 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 or available from their websites. Claims and information presented have not been independently verified.
The types of equipment used to remove contaminants are basically machines that take advantage of differences in physical properties (weight, density, particle size, etc.) between that which is wanted and that which is unwanted, and often separate those components with some sort of physical movement (rotation, vibration, etc.). Equipment types include debaggers and destoners, gravity and ballistic separators (by throwing the material up and forward by a paddle, a ballistic separator sorts materials according to their ballistic properties), density separators and air classifiers, and screens of all types and configurations (finger, deck, disk, vibrating, trommel and star, to name a few).
Screening is the most common contaminant removal mechanism used in composting. Screening technologies have been discussed in previous BioCycle articles (see “What’s New? Screens,” March 2007; “Compost Facilities Take On Film Plastic,” September 2006; and “Screening Strategies To Optimize Product Quality,” June 2006). Some yard trimmings and MSW composters are using bag opening equipment to start the separation process, although only a few commercially viable technologies are available. Clearly, it makes more sense (from both an economic and product quality perspective) to take in only clean, source separated organic materials, but the trend towards single-stream recycling, maximum convenience for small-scale waste generators, and the importance of dealing with the growing food discards problem mean composters may have to make investments in separation equipment to preserve both process and product quality.
The companies profiled in this article are all well-represented in the industries of mechanical-biological treatment of MSW, materials recovery facilities and construction and demolition (C&D) debris processing.
Aggregates Equipment, Inc. (AEI) designs and manufactures material processing equipment and systems for the aggregate, mining, scrap, composting, power generation and waste industries. It makes the bivi-TEC® screen system, which operates by dynamically tensioning and relaxing flexible screen mats using a dual-vibration principle. Enhanced by resonance, one drive can produce two vibration movements. The screen box is accelerated approximately twice the nominal acceleration due to gravity on Earth at sea level, defined as 32.174 ft/s2 (also known as 2g’s) while the screen mats can receive up to 50g’s. The bivi-TEC® screens are designed for screen cuts of 35 mesh to 2 inches. It is available in sizes ranging from 3 feet by 10 feet to 8 feet by 27 feet. Available options include single or double deck, a rigid scalping deck and either portable or stationary units.
Bulk Handling Systems handles bagged materials, like yard waste or MSW, which are gravity fed into the BHS Bag Breaker via a conveyor to achieve an evenly metered flow rate. Large, counter-rotating drums stretch the incoming bags to an extreme, causing the plastic film to break and release the contents. The empty bags and recyclables are discharged from the bottom of the machine. The bag breaker was designed to process recyclables without damaging the commodities, but is also in use at some composting facilities (e.g., Mariposa County, California). Each empty bag is typically released in one to three large, elongated strips to reduce plastic contamination and facilitate removal. A conveyor is required to collect and transport the processed material out from under the bag breaker. Models are available for processing up to 35 tons/hour, while exceeding a 90 percent efficiency rating.
Construction Equipment Company (CEC) provides portable rock crushing and screening equipment for the aggregate, recycling, compost and wood waste industries. Much of its equipment line is oriented to aggregates processing (i.e. crushing, screening, washing, etc.). CEC offers several different types and sizes of portable deck screens, both wheeled and tracked-mounted. It also offers stacked deck screens, like its ScreenIt 6×16 – 3 Deck, which has three separate screen sizes in the three decks, with three discharge conveyors. CEC also markets a wet separation system for contaminant removal in wood processing and C&D applications.
Doppstadt offers the Wind Sifter WS 720 Taifun, used for removal of lightweight contamination in composting or the preparation of rubbish and mixed construction waste. Mounted on a hook lift frame, the WS 720 is suitable for both stationary and mobile applications. The feeding hopper is designed as a vibrating conveyor, which separates the material. A longitudinal compressed air blower lifts the lightweight material to be sifted on top of the heavy components, where it is most accessible for the subsequent separation process. The machine can be adapted to suit different feed materials through adjustment of the air flow. For materials with high moisture content, separation can be improved with the adjustable vibration rollers. The lightweight material is collected by the perpendicular air flow and discharged through the sifting chamber into a collection container situated at the side of the machine.
Forsbergs’s primary equipment is vacuum gravity separators. It also markets pressure type gravity separators, vacuum and pressure destoners, screeners, pneumatic aspirators, hullers, conveyors and fans. Forsberg manufactures two types of destoners: a pressure-type with an open deck and a fan placed inside the box (creating a positive air pressure up through the vibrating deck with screen), and a vacuum-type that is completely enclosed with a fan mounted away from the machine (creating a “suction” of air through the vibrating deck with screen). The destoner operates on the basic principle of flowing dry granular material over a vibrating screen-covered deck that is inclined. Steady air flow holds the material in stratified flotation. The lighter material stays in the upper strata as it flows down the inclined vibrating deck with screen. The heavier material, such as stones, coarse sand, glass, metal, etc., travels up the inclined vibrating deck and out. New for 2007 is the G-Series Pressure Destoners. The 7-G Model and the 5-G Model are a heavier duty all-steel construction with a high efficiency fan utilizing less horsepower.
General Kinematics Corporation was established to market, design and custom fabricate innovative vibratory materials handling and processing equipment. It offers finger, star and trommel screens, as well as the De-Stoner Air Classifier. This classifier combines vibratory action and high velocity, low-pressure air streams to stratify commingled materials according to differences in terminal particle velocity. Many of the De-Stoner systems are designed with “air curtains” to provide further separation after the initial cut of “heavies.” The device removes heavy materials such as stones, metals and glass from lightweight materials such as aluminum, paper, plastics and wood.
Hawker Corporation was developed by a pair of veteran Oregon composters and offers three models of its Airlift Separator (the hydraulic Model AL200-H, the electric Model AL200-E and the diesel Model AL200-D). Over 50 units are now in service in the composting and wood waste recycling industries. This vacuum-based air classifier attaches to the discharge conveyor of a screening system and is capable of removing 65 to 95 percent of plastic contamination (depending on processing speed, compost moisture content and plastic bulk density). The plastic removed can be blown into a drop box when large volumes of material are processed. For smaller amounts, a tube sock is attached to the fan assembly and catches the plastic as it is blown off. The AL200-H runs off the hydraulic power of the screening system and needs 15 to 20 gallons per minute (gpm) at 2,000 pounds per square inch (psi). The AL200-E requires 460 volt 3-phase electric power. The AL200-D is powered by a 46 HP Duetz diesel engine. The device is constructed of heavy steel and weighs 1,025 lbs. Safety features include extra long inlet and discharge assemblies to keep hands away from the fan, remote mount emergency stop switch and electrical lockout key switch.
Karl W. Schmidt & Associates (KWS) manufactures equipment used mostly in materials reclamation facilities (sorting, shredding, baling, etc.) and support equipment like conveyors. It makes an air classifier vacuum separator assembly, designed to separate MSW into various fractions. The air classifier automatically separates the products into three different fractions: Heavies (whole and broken glass), lights (aluminum and plastics) and paper, film and dust. The heavy fraction continues on the main transfer conveyor for further separation downstream; the light fraction is deposited onto the cross-belt take-away conveyor for further separation downstream; and the paper and film fraction is blown through the vacuum fan to a bin or container for disposal.
Komptech supplies technology for the mechanical and biological treatment of solid wastes and biomass, consisting of more than 20 different pieces of equipment. For contaminant removal, through a partnership with Farwick, it offers the HURRIKAN Air Separator and both trommel and star screens equipped with plastics removal technology. It also offers the BRINI stationary ballistic separator. The electric-powered HURRIKAN has been in use in the U.S. since 2001 and is found in over 30 composting or wood recycling facilities. The separation system combines the use of vibration, blowing and suction to produce clean output. The 15 kW suction fan is also height adjustable by a winch to accommodate changing input. The separated light fraction is delivered to a container via a manifold. New in 2007 is the HURRIKAN S, designed to handle the higher throughputs of larger screens. The increase in performance has been achieved by installing a second suction fan in the series. Volume flow per fan remains unchanged. The throughput of the S version is up to 50 percent higher than that of the standard model (dependent on material). Options available include a 42 kW diesel generator, a stone trap (an inclined conveyor) and a magnet drum separator. Komptech’s MAXX trommel screen has a HURRIKAN unit built in.
SCARAB offers the Model 15 portable Bag Breaker, designed to release waste material from plastic bags by slicing the bags open, rather than grinding or shredding them into small pieces. The bags are sliced, but remain in one piece, eliminating the need to screen small plastic shards from the waste stream. The drum is covered, protecting the bags and material from the climate. The opener drum measures 3 feet wide and 6 feet in diameter, and has 104 replaceable “openers” that protrude 6 inches from the drum surface. The rotational speed of the drum is variable between 0 and 600 feet per minute. The drum can be adjusted from 1 inch to 8 inches above the feed belt to accommodate different sized bags. The unit is powered by a Tier III-compliant, 200 HP diesel engine. It is moved with a fifth-wheel tandem axle trailer with a load capacity of 60,000 lbs.
Triple S Dynamics serves the mining, food processing, recycling, bulk handling, agriculture, chemical processing and foundry industries, and makes the Overstrom High-Speed Vibrating Screen. The screens are made in both inclined circle-throw and horizontal straight line configurations. Vibrations are generated by unbalanced rotors, which are V-belt driven from an electric motor. In the inclined screen, a single rotor generates vibratory motion in the vertical plane, which may be either a circular or elliptical motion. The material being screened moves over the downward-sloping surface by gravity, assisted by the vibration. The horizontal screen moves material by the opposite rotations of two unbalanced rotors, which produce a straight line pitching motion.
Using these types of contaminant removal technologies adds to the cost of processing organics into compost. The economic justification for the investment should include careful consideration of source control (whether the waste source is able to remove contamination), the cost of alternative methods of removal (manual picking stations, used by some composters handling food discards), and setting of the operation (some processing equipment is not designed for open-air, all-weather operation). However, contaminant removal equipment can be a very favorable alternative to filling up yet another garbage bag with noncompostables.
Craig Coker is a Contributing Editor to BioCycle and a Principal in the firm of Coker Composting & Consulting ( in Roanoke, Virginia. He can be reached at (540) 904-2698 or by email at
Aggregates Equipment Inc.
9 Horseshoe Road, P.O. Box 39
Leola, PA 17540-0039
Bulk Handling Systems
1040 Arrowsmith
Eugene, OR 97402
Construction Equipment Company
P.O. Box 1271
Lake Grove, OR 97035
Doppstadt U.S.
1030 Jaycox Road
Avon, OH 44011
Forsbergs, Inc.
P.O. Box 510, 1210 Pennington Ave.
Thief River Falls, MN 56701
Hawker Corporation Airlift Separator
2111 Prairie Road
Eugene, OR 97402
General Kinematics
5050 Rickert Road
Crystal Lake, IL 60014
Karl W. Schmidt & Associates
3900 East 68th Ave.
Commerce City, CO 80022
Komptech USA, Inc.
1369 Forest Park Circle
Ste. 204
Lafayette, CO 80026
SCARAB Manufacturing & Leasing, Inc.
1475 County Road W
White Deer, TX 79097
Triple S Dynamics
PO Box 15102
71031 South Haskell Ave.
Dallas, TX 75223

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