The myriad systems for processing municipal recyclable materials all work toward a common goal, but the process is not as simple as it sounds.
Two major subgroups of processing systems include those that require source separation and separate recyclables collection and those that focus on recovering recyclables from mixed solid waste.
In most cases, source separation has become the preferred approach for maximizing the recyclables quality and recovery rates.
Initially, the burden of sorting source-separated recyclables rested either with the generator (such as households) or the collector (through curb-sorting). But when these practices added new categories of recyclables, residents and businesses often found multiple separations inconvenient. Since only a limited amount of materials can be cost-effectively sorted on a collection route, MRFs were developed to solve the problems.
In the three cases that follow, the facilities have been designed to process separately collected recyclables into one or more fiber streams and a mixed container stream.
King Of Prussia, Pa. Browning-Ferris Industries' (BFI) King of Prussia Recyclery, King of Prussia, Pa., illustrates the two-line MRF process design. The facility has a 250 tons-per-day, two-shift processing capacity and accepts residential paper (primarily ONP with kraft bags), mixed residential containers (glass, aluminum, steel, PET and HDPE) and mixed commercial recyclables (corrugated or mixed office paper, aluminum cans).
All materials are received and in-spected on an 18,000-square-foot tipping floor, which provides sufficient space to stockpile each stream and still allow enough space for normal materials-handling traffic. The Recyclery uses a Bollegraaf elevated paper sorting line for residential paper and mixed commercial recyclables.
The paper and container streams are processed on separate lines. Manual sorting on either processing line relies on a combination of positive sorting (where materials are pulled from the sorting line) and negative sorting (where materials are left on the primary sorting conveyor).
Residential paper is processed by positively sorting kraft bags, other paper grades (such as magazines) and trash while the ONP is negatively sorted into a live bottom storage conveyor. Mixed commercial recyclables are processed on the same line by positively sorting old corrugated containers (OCC), high-grade papers and rejects.
All positively sorted materials are deposited into drive-through bunkers beneath the paper sorting platform, then pushed by a front-end loader onto a conveyor feeding a Harris 1041 baler. The ONP is conveyed from its storage conveyor to the same baler in-feed line.
The mixed container processing line is a modified McMRF processing system manufactured by Count Recycling Systems. Mixed containers are deposited into a below-surface pit with an infeed conveyor leading to an elevated sorting platform. The containers pass over a screening system that removes broken glass and fines. Ferrous containers are then magnetically removed prior to an air separation of light containers (aluminum, plastics) from glass containers for sorting on separate lines.
Glass containers pass by an inspection station for manual reject removal. Amber and green glass containers are then positively sorted on the glass line. PET and HDPE containers are positively sorted on the light container line. The negatively sorted aluminum is densified while other container grades (except glass) are baled. All color-sorted glass is stored in outdoor concrete bunkers for marketing to a local processor.
Cape May County, N.J. An enhanced two-line MRF processing system, the Cape May Coun-ty, N.J., Intermediate Processing Fa-cility (IPF), was designed, con- structed and is operated by Re-source Recycling Technologies Inc. (RRT). The facility began commercial operation in May 1990 with a two-line paper and mixed container processing system similar to the BFI Recyclery.
Recyclables are separately collected by municipal crews in Cape May County from residential and commercial stops. The county originally assumed that most of the commercial OCC would be diverted through existing scrap paper recycling systems, so the paper processing line was designed to manually sort materials from a predominantly ONP paper stream.
However, the amount of OCC in the paper stream far exceeded expectations. In some cases, it comprised more than 40 percent of the total. This large quantity significantly exceeded the line's manual sorting capacity.
In 1992, RRT installed a system to separate OCC from other paper grades automatically. Paper deposited on the tipping floor is now conveyed to a special screening device designed by RRT that automatically separates OCC from newspaper and other mixed paper grades and sends it to a separate sorting line.
Non-corrugated paper grades and rejects are then positively sorted from the OCC on one line, while on the ONP and mixed paper line, only small amounts of corrugated material and rejects are positively sorted. The recovered paper grades are then marketed to end users.
RRT also has upgraded its commingled container processing lines by installing automated trash handling conveyors on the commingled lines, enhanced glass crushers and mixed glass screens and primary and secondary eddy current separator (ECS) units to automate the recovery of aluminum cans and miscellaneous non-ferrous scrap.
The current capacity of the upgraded Cape May IPF went from 225 to 375 tons per day (two shifts), which is equivalent to 15 tons per hour for the paper processing system and 10 tons per hour for the commingled container system.
Vancouver, Wash. While the two-line process design is typical for MRFs, it also is possible to operate a single-line MRF for multiple incoming streams of source separated recyclables. Since January 1993, the West Van Materials Recovery Center (WVMRC), located in Vancouver, Wash., and operated by Columbia Resource Co. (CRC), has received all the recyclables collected curbside within Clark County. The facility was co-designed and built by Ross Corp., Eugene, Ore.
WVMRC receives source-separated residential paper (primarily newspapers or mixed paper consisting of OCC, magazines, junk mail and chipboard), commercial mixed paper and OCC and mixed residential containers (aluminum, steel, HDPE, PET, glass and aseptic packaging).
All three streams are processed on the same Ross sorting line at different times on the first shift. Commercial OCC is typically floor-sorted. All other recyclables on the tipping floor are pushed by a front-end loader onto an in-feed conveyor leading to a raised sorting platform.
Broken glass and fines are first removed using a Rader TracSorter. Unprocessed recyclables are deposited onto steel bars that alternatively rise and fall in a circular motion, which causes the targeted, undersized materials to fall through the bars into a stationary roll-off container. At the same time, oversized materials are moved forward to the Ross sorting conveyor.
The sorting strategy used on the line depends on the mix being processed. Positive sorted recyclables are deposited manually into open bunkers or 20 cubic-yard roll-off containers under the sorting platform. Ferrous and non-ferrous recyclables are exceptions: at the end of the sorting line, after a reduction of the line burden depth has been achieved, an overhead magnet removes the ferrous containers and any scrap. If aluminum cans are still remaining on the line at that point, they are then removed with an ECS. All recyclables are then baled in a Ross two-ram baler.
CRC has provided sufficient space in the building layout to add a second line when incoming tonnages and market conditions warrant an expansion.
Phoenix, Ariz. It's a paradox: While many communities consider separate recyclables collection to be the most appropriate method, they often want to eliminate dedicated recycling collection vehicles.
In 1978, Phoenix, Ariz., adopted a fully automated solid waste collection system. The city began planning its recycling system in 1987 with the intention of preserving this capital investment and avoiding the cost of buying new collection equipment.
Since Maricopa County requires that Phoenix provide collection twice per week, one day was designated for collecting recyclables and another for solid waste. In 1989, Phoenix began looking for a system that could accept all recyclables collected as part of a single stream by the same automated collection vehicle. CrInc was selected in 1992 to de-sign, build, own and operate the city's MRF, which went into commercial operation in March 1993.
The 280-tons-per-day facility was designed to process 90,000 tons per year of source-separated recyclables on a two-shift, six-day basis. The MRF currently receives approximately 30,000 tons from one-third of the city's residents.
Recyclables are delivered into a 27,000-square-foot tipping hall, pushed into an infeed pit by a front-end loader and conveyed to a pre-sort platform where oversized materials such as OCC are removed. The mixed recyclables then proceed over a vibrating screen that removes fines, grit and dirt.
The next processing stage involves a Bezner inclined sorting machine. This machine consists of an inclined conveyor with a rough surface texture that vibrates slightly. Here, the fiber content of the mixed recyclables is separated from container products.
According to CrInc, the fiber/container separation efficiency is around 90 percent. Larger paper items like ONP bundles usually fall onto the first of two parallel paper conveyors, while ledger, envelopes and other similar paper items fall onto the second.
Mixed containers pass under an overhead magnet for removing ferrous cans and scrap, then pass through a second inclined sorting machine for the separation of light materials such as plastics and aluminum from container glass. A rotating chain curtain facilitates the separation of the light and heavy materials.
Glass containers roll forward through the chain curtain onto a glass sorting line, where the chain curtain diverts light materials onto another sorting line.
Aluminum cans and other non-ferrous products are recovered from the light material line by an ECS. The remaining PET and HDPE containers are then manually sorted. Only HDPE containers are color-sorted.
On the glass line, green and amber containers are positively sorted on a three-channel conveyor. The sorted glass remains on this conveyor where it is crushed and then diverted to the appropriate storage bunker prior to outloading.
Paper also passes under magnets to remove any stray ferrous materials such as flattened steel cans prior to the sorting. The paper then enters a Bezner multi-deck vibrating system to screen large from small paper items.
The oversized pa-pers that exit this stage are primarily newspaper, with added corrugated and some magazines. Newspaper is negatively sorted. Any mixed paper found on these two paper lines is sorted and sent via transfer conveyors to the mixed paper sorting lines. A cross conveyor is used at the end of both paper lines for final quality control. All newspaper is currently being marketed as a number eight grade.
Undersized paper (ledger, junk mail, chipboard, etc.) from the paper screening system goes onto a cross conveyor leading to the mixed paper sorting line. On this line, the objective is to create a high-value mixed paper through positive reject sorting. Other sorts may be performed as required by marketing conditions. All sorted material is dropped into live bottom bunkers under the sorting platform that reverse for accessing either of the facility's two Bolle-graaf balers.
Interest in the other processing subgroup, waste processing and recovery facilities (WPRFs), has been steadily growing for the last few years for several reasons:
* A desire to avoid the cost of separate recyclables collection;
* The apparent success of these projects to recover and market multiple grades of recyclables; and
* The belief that having control over the entire waste stream provides greater cost control and better operating economies of scale.
Huachuca City, Ariz. Since 1972, the town of Huachuca City, Ariz., has operated a regional landfill for a population of approximately 50,000. In 1989, the town realized that the landfill had only a five-year capacity left. To prepare for closure, the tipping fees would have to rise from $9.62 per ton to about $35 per ton. At $35 per ton, many disposal alternatives became viable that could help keep their landfill open.
The town issued a request for proposals in 1989 and 1991 that called for a technology to achieve 70 percent volume reduction. It was also important to the town not to spend any additional money for recycling.
The town decided to select a solid waste material recovery and win-drow composting system designed, built and operated by Universal En-tech. The facility went into operation in June 1993 and currently processes an average of 80 tons per day on a single-shift basis and is capable of handling 150 tons per day on a two-shift basis.
All types of non-hazardous municipal solid wastes are accepted, with the exception of liquids, tires and batteries. Waste is dumped on the tipping floor and non-processible materials such as large stumps, metal scrap and other similar items are extracted from the mix. Clean wood waste is shredded to be used as a bulking agent for composting. Household hazardous wastes also are removed if detected on the tipping floor.
The mixed wastes are sent onto a single, 42-inch wide sorting conveyor equipped with eight sorting stations. MSW is processed at about eight or nine tons per hour using four sorters where ONP, OCC, high-grade papers, aluminum cans and natural HDPE are recovered.
The positively sorted recyclables are dropped by the sorter down into bunkers under the sorting platform, where a front-loader pushes the materials onto a parallel conveyor leading to a horizontal, high-density baler. The same sorting line is used for processing source-separated materials that have been delivered to the facility through a bag-based co-collection system developed by local haulers.
After the MSW is tipped, the bags are pulled out, set aside and then processed later. An overhead magnet removes ferrous cans and scrap. Huachuca City is currently experimenting with a similar co-collection system for source-separated recyclables.
With the new facility and a re-designed landfill, the town's landfill capacity has been extended 12 to 15 years. The town originally thought that material recovery would reduce the processible waste stream by 10 to 11 percent. Currently, approximately 14 to 18 percent of the total MSW is recovered. About 150 to 160 tons per month of recyclables are marketed, primarily ONP (50 to 60 tons per month), OCC (80 to 100 tons per month), CPO and white ledgers.
One significant source of OCC, high-grade paper and aluminum cans comes from the nearby Fort Huachuca Army base. The dry desert climate results in a low-moisture waste infeed that makes positive recyclables sorting easier.
Medina County, Ohio Medina is a semi-rural county with a population of about 130,000, located 35 miles southwest of Cleveland. The county's solid waste management plan selected centralized waste processing to recover municipal recyclables. This decision was based both on the county's assessment that current WPRF technology would effectively recover municipal recyclables and the desire not to increase collection costs by adding a separate collection system.
The county selected Norton En-vironmental to design, build and operate a central processing facility (CPF). Norton Environmental, in turn, selected Lindemann Recycling Equipment as its principal equipment supplier.
Through flow control, Medina County directs all non-hazardous waste to the CPF. Incoming MSW ranges from 250 to 400 tons per day. Approximately 15 percent of the delivered MSW is considered non-processible and is transferred immediately for disposal.
Floor workers pull oversized bulky waste, including wood, tires, mattresses, drums, furniture and white goods and place them into roll-off containers. They also prevent hazardous waste from intruding into the facility and perform general housekeeping functions. The remaining MSW is pushed by front-end loader onto a single infeed conveyor.
The infeed conveyor turns right onto the first elevated, enclosed sorting platform with 10 sorting stations for up to 20 sorters. Here, sorters remove large bulky wastes such as fabric and carpeting, OCC, wood, metal scrap and ONP.
Material then passes through a 40-foot long, 10-foot diameter, three-stage trommel, which opens bagged waste and separates some of it into -2-inch and -6-inch streams. The -2-inch material (grit, fines, dirt and some organics) is conveyed to a roll-off container on the tipping floor. The -6-inch stream goes through an automated metal recovery sub-system.
The MSW stream then proceeds through a second enclosed sorting area with 12 stations that can ac-commodate up to 24 sorters. At this stage, ONP, OCC, mixed paper and color-mixed HDPE and PET containers are positively sorted. Material is dropped into bunkers under both sorting platforms where the baleable recyclables are pushed by a front-end loader onto two baler conveyors that converge on an American horizontal auto-tie baler.
The remaining MSW then exits through an intermediate wall and is conveyed to a slow-speed, high-torque shredder for size reduction into -6-inch particles. The shredded waste is loaded into open-top transfer trailers for shipment to the Akron waste-to-energy facility. The material recovery rate averages 15 percent of the total MSW flow, which is equal to the recovery rate that the operator is contractually required to meet at the end of the first operating year.
Norton Environmental is seeking a permit from the Ohio EPA to use the recovered -2-inch fines as a bulking agent in a windrow composting system to be operated on the same site.
San Diego County, Calif. The North County Recycling and Waste Reduction Facility is owned by Thermo Electron Energy Systems, constructed by Babcock & Wil-cox/National Ecology and operated by North County Operations Associ-ates (NCOA) under a 24-year contract with San Diego County. The facility operates five days per week and accepts more than 2,100 tons per day from the northern third of San Diego County, which has a population of approximately 600,000. Dedicated loads of green wastes, tires or C&D debris are not accepted for processing. The present system has been in commercial operation since February 1994.
MSW is delivered onto a tipping floor of approximately 67,000 square feet. Oversized bulky wastes, hazardous wastes and large recyclables are removed on the tipping floor.
The MSW is then pushed onto one of three steel apron conveyors feeding five trommels (with room to build a sixth trommel). The peak design capacity is 40 tons per hour. These trommels are approximately 60 feet long and 10.5 feet in diameter with bag-breaking blades inside. They have five stages using holes ranging from two to 10 inches.
When materials fall through the four to 10-foot trommel holes, they hit an angled conveyor. The bounce-adherence system, developed by the French company Novergie, is the first North American application of the technology.
Heavy materials bounce off this conveyor onto one of two main conveyors leading to sorting areas for heavy recyclables. Light materials, primarily paper and film plastic, adhere to the conveyor, which transfers it to another conveyor that directs it to the facility's main sorting area.
Three rooms in the main sorting area are equipped with stations where newspapers, corrugated and mixed paper are positively sorted.
Newspaper is being marketed as a number six grade, but NCOA hopes that they will eventually market it as a number eight grade. Mixed paper consisting of magazines, junk mail, chipboard, white ledgers and phone books are sorted to a super-mixed paper grade. Materials dropped down the sorting station chutes land on cross-conveyors leading to horizontal balers that are dedicated to newspaper, corrugated and mixed paper.
The grit, dirt, fines and broken glass fall onto their own conveyor for landfilling. Heavy materials separated by the trommels are directed into a plastics sort room for recovery of PET and HDPE. This material then passes under two overhead magnets that pull off approximately 60,000 pounds per day of ferrous scrap. In the next stage, all colors of container glass are positively sorted.
The final processing step is the re-covery of non-ferrous recyclables. The material stream is directed to two ECSs that pull off aluminum cans and non-ferrous onto their own two conveyors. The last processing step involves positively sorting mixed non-ferrous scrap and trash from aluminum cans. The aluminum cans, HDPE and PET containers are baled in dedicated balers.
All unrecovered wastes are processed through two 1,250-horsepower horizontal shredders for size re-duction into -4-inch particles for disposal at the county landfill. NCOA states that 87 percent of the targeted recyclables in the total waste are recovered by this system. Total disposal reduction of the process stream is about 15 percent. The facility operates in concert with a county source separation curbside collection system.
Despite their differences, many of these processing systems were created to recover recyclable materials while minimizing collection costs. But each facility's development occurs in response to specific collection and market conditions, area demographics and geographic factors and regional solid waste management practices.