[Table of contents | Executive Summary | Sections 1 · 2 · 3 · 4 · 5 · Glossary | Tables | References ]
Because, as reported in the literature, plastic pellets are frequently mistaken for food by a variety of aquatic animals (Section 3.0), attention must be given to the sources of the pellets in the environment. One of the objectives of this study is to identify the sources of pellet release into the environment within the plastic industry. To this end, the Society of the Plastics Industry, Inc. (SPI), arranged for each sector of the industry pellet producers, transporters/contract packagers, and processors to be visited by the study team. The site visits were arranged with the understanding by all parties that the names of the visited companies would remain confidential. Each company was assigned a letter in the order in which it was visited (i.e., the first company was assigned the letter A, the second company was assigned the letter B, and so on).
The degree to which the observations reflect the overall conditions and practices of the plastics industry was not determined. Only at Company C did officials state that no inordinate maintenance or housekeeping activities were performed prior to the visit and that operations were conducted as usual during the visit.
In this section, the equipment and operations of each sector are described generally, and each general description is followed by a description of the sector's site visits. Sources of pellet release into the environment from each respective sector are also presented.
4.1 Organization of the Plastics Industry
For the purposes of this study, the plastics industry consists of three major sectors: pellet producers, transporters/contract packagers, and processors. Figure 6 shows the organization of the industry and, specifically, the flow of plastic pellets within each sector and among the sectors. The sectors are defined as
Estimates were not available of the numbers of companies from each sector in the U.S. plastics industry. SPI has approximately 2200 member companies, which are estimated to represent 75% of the total dollar volume of the plastics industry. SPI estimates that their membership represents 98% of the pellet producers, but only 10% of the total number of companies within the industry (Ms. Maureen Healey, SPI, personal communication, April 1992).
Figure 6. Pellet Flow through Plastics Industry Sectors
A) Pellet Producers/Extruders
B) Pellet Transporters/Packagers
C) Pellet Processors
4.2 Pellet Producers
The pellet producers create the polymers and extrude the pellets. The Environmental Protection Agency (EPA) (1990a) reported that a total of 477 resin-producing facilities were operating in the United States, based on U.S. Bureau of the Census (1988) estimates. Most of the 55,000 workers employed by the producers reside in Texas, New Jersey, West Virginia, Pennsylvania, Louisiana, Ohio, Michigan, and California. A diagram showing the flow of pellets through a pellet producer is presented in Figure 6(a) above.
4.2.1 Producer Equipment and Operations
Polymerization
The production of plastic pellets begins with polymerization. Polymerization is the chemical reaction(s) through which low-molecular-weight organic molecules (monomers) are linked to form long monomer chains, or polymers. Polymers are produced through either of two methods: bulk polymerization or solution/suspension polymerization.
The powders may be subsequently melted and formed into either pellets or end-products. Polymers produced through this process include high-density polyethylene (HDPE), polypropylene (PP), PS, and PVC. The ultimate use of polymers typically involves one or more stages in which the polymer is in pellet form.
Pelletizers
High-volume pelletizing systems have been developed that can process over 5000 lb of pellets per hour (2268 kg/h) (Hunt, 1978), or approximately 110,000,000 pellets per hour. The most common types of pelletizing equipment include dicers, strand pelletizers, die-face pelletizers, and centrifugal pelletizers.
The type of pelletizer used determines the size and shape of the pellets produced. Most modern pelletizers are large, enclosed, fully automated systems, where the pellet flow is controlled within the pelletizer.
Conveying Systems
Conveying systems are used to move pellets between plant operations, such as between the pelletizers, drying systems, and the storage silos, between the storage silos and the packaging or shipping containers, and between the silos or packaging and molding machines. The potential for pellet spillage is present during each conveyance. The rate of pellet entry into the conveying system cannot exceed the rate of pellet delivery from the conveying system, otherwise pellet spills will occur.
Pellet conveying systems can be either pneumatic or mechanical. Pneumatic systems may use either dilute-phase or dense-phase systems. Dilute-phase systems are low-pressure systems that use high-velocity air and a high air-to-pellet ratio to move the pellets into receiving vessels (e.g., storage silos, rail hopper cars). A vacuum can also be used to pull the air and pellets into the receiving vessel. Dense-phase systems are high-pressure, low-velocity systems with a low air-to-pellet ratio. In dense-phase systems, the conveyor is filled with pellets and pressurized; the flow of pressurized air carries the pellets through the conveying line.
Figure 7 (below) shows a pneumatic conveying system in a pellet-blending operation (e.g., where pelletized colorants are mixed with pure HDPE pellets). Each of these operations also requires properly sequenced procedures to avoid spills.
Mechanical conveyors also are used for in-plant pellet movement. These conveyors generally are used to transport pellets across short distances, as well as in operations that cannot be completed by using a pneumatic system (e.g., operations that require a continuously high pellet-delivery rate). Most mechanical conveyors use a rigid driven screw to move the pellets through a conduit. Because the screw shaft is flexible, these conveyors are suitable only where straight conduit runs can be installed.
Mechanical conveying systems may be used to transport pellets from transporting vessels (e.g., rail hopper cars and bulk trucks) either to storage areas or directly to other packaging or processing operations. Generally, the transporter empties the pellets into a hopper that, in turn, feeds a mechanical conveyor. These mechanical conveyors may also be used to transfer pellets from bag- or box-emptying stations to, for example, a blending silo or a bagging machine. In addition, mechanical conveyors may be used also to volumetrically feed pellets to a blending operation.
Figure 7. Example of a Pneumatic Conveying System in a Pellet Blending Operation (Adapted from Anon., 1990)
4.2.2 Site Visit Observations
Two pellet producers, Company F and Company G, were visited during this study. Both companies were visited on February 5, 1991.
Company F
Company F is a large manufacturer of HDPE polymers in pelletized form. Company F also produces PE powders and other nonpellet polymer products; most of the powders are subsequently pelletized.
The company operates several pelletizers during routine operations. In the extruder observed during the visit, PE powder is melted, the liquid polymer is extruded through a die, and the resulting polymer bead is cut into pellets. The pellets are first water-cooled, then air-dried, and are pneumatically conveyed to storage silos. Pressure sensors throughout the pneumatic system monitor the pellet transfer, enabling the operators to detect potential blockages and thereby prevent spills. During routine operations, pellets may be removed for quality control inspection after they have been cooled. In addition, the system may be opened for maintenance or corrective action (i.e., purging during system shutdowns); all waste pellets removed from the extruders during maintenance or corrective action are placed in specially labeled waste bins and recycled; no PE is disposed into landfills.
Pellets are stored in large silos until transferred into either rail hopper cars or bulk trucks; over 90% of the pellets produced by Company F are directly loaded into these bulk-transport vessels. Less than 10% is loaded into gaylords or paper bags (bagged pellets are primarily for overseas shipment). Spills in the bagging areas are cleaned up immediately and the spilled pellets are recycled.
All rail hopper cars and bulk trucks are thoroughly cleaned inside and outside before loading, and outside after loading. Before loading, the inside of the car must be cleaned to remove all residual trapped and clinging pellets as well as other contaminants (e.g., dust) that may be present. Pellets are removed first by suctioning; residual pellets are then washed out with water. The water rinse is performed in an enclosed area where residual pellets are washed into the facility drainage and containment system (discussed in detail below). Several pounds of residual pellets may be washed out of a rail hopper car.
Pellets are pneumatically transferred into rail hopper cars or bulk trucks through a closed loading system where the spreader is connected directly onto the loading spout so that the loading spout does not have to be reconnected at each loading port. After loading, the outside of each rail hopper car or bulk truck is rinsed, and the rinse water is directed into the facility drainage system. The pellets are shipped either directly to a processor or to a contract packager for repackaging (e.g., bulk shipments bags or gaylords). The processor or packager returns the empty rail hopper cars or bulk trucks to Company F.
The Company F property is graded so that storm-water and wastewater drain from all areas of the plant into a facility containment system for recapturing plastic pellets and powders (see Figure 8 below). The containment system consists of a series of dams, skimmers, and surface booms arrayed within a weir that runs along two sides of the facility grounds.
A major focus of the site visit was to observe this pellet-recovery system that the company has been refining for several years. The first stages of the recovery system were installed in late 1980. The current recovery system consists of two fixed skimmers and two floating skimmers within a weir. By the end of 1991, it is expected that additional modifications to the system will more effectively control the flow of pellets under the dams.
Figure 8. Basic Design of the Company F Pellet Containment System (Side View)
A: Pellets entrained in water enter drainage system; B: Paddle skimmers remove pellets retained by the dam skimmers; C: Fixed surface boom retains pellets that escaped the dam skimmers; D: Pellets retained behind the underflow skimmer; E: Pellets retained behind the portable surface boom are siphoned off the water surface; F: Water passes through water-quality monitoring station and into the environment. 1: Effluent of facility drainage system; 2,4: Paddle skimmers; 3,5: Dam skimmers; 6: Fixed surface boom; 7: Underflow skimmer between retention ponds 8: Portable surface boom; 9: Water quality monitoring station and facility outfall
The storm water and wastewater drain into the weir system; PE pellets and powder are carried by the water into this system. A water spray (see Figure 9 below) is directed at the surface of the water to prevent the pellets from moving back into the storm-water drainage system and concentrates the pellets and moves them toward the first fixed skimmer.
The first fixed skimmer is a motor-driven paddle skimmer comprising several rectangular paddles and a drive system that is attached to the weir walls. It is designed to operate under normal weather and operating conditions (se Figure 10 below). The paddles skim the pellets and powder from water surface and push them up a trough to street level. As the pellets are skimmed from the surface, the water passes under the retaining wall immediately downstream of the paddles. At street level, the paddles push the pellets off the end of the trough into a containment area. The contaminated (unclean) pellets are collected from this containment area and are shipped loose via truck to a recycler or to be sold as scrap. According to Company F officials, this first fixed skimmer generates a very large (but unknown) volume of recyclable material; during the site visit, approximately 100 cubic feet of waste pellets was observed in the containment area of the first fixed skimmer (see Figure 11 below).
Figure 9, Facility Drainage System Outfall into Company F Containment System
Figure 10. Upstream View of the First Fixed Skimmer in the Company F Containment System.
Figure 11. Pellets in the First Fixed Skimmer Containment Area at Company F.
During normal conditions, the first fixed skimmer is nearly 100% effective in removing powders and pellets. However, during and after periods of heavy precipitation, the fixed-skimmer system is breached by high water levels, and the paddles become partially or totally submerged and do not skim the pellets from the surface; according to company officials, this was the condition just prior to and during the site visit. By contrast, during periods of drought or abnormally light precipitation, the water level can drop so low that the paddles are completely out of the water. In either of these two situations, the first fixed-skimmer system cannot operate properly, allowing the pellets to bypass the skimmer and proceed downstream to the second fixed-skimmer system.
The second fixed skimmer is located several hundred yards downstream of the first fixed skimmer. The second fixed skimmer and its pellet containment area are configured identically to the first fixed skimmer and its containment area. A white mass of accumulated pellets and powders was observed between the two fixed skimmers. The mass resulted from either a breach of the first fixed-skimmer system or entry into the weir system in the storm-water runoff from areas downstream of the first fixed skimmer. The water level had not yet receded, and the paddles were completely submerged in the water and could not skim pellets from the surface. Pellets and powder were also accumulating on the downstream side of the second fixed skimmer and in front of a fixed surface boom located downstream of the second skimmer; this accumulation was likely the result of a breach of the second fixed-skimmer system.
A short distance downstream of the surface boom are two retention ponds. The first pond holds the wastewater before it is pH-adjusted. The water flows from the first pond through the pH-adjusting station and into the second retention pond. No pellets could be seen at the upstream side of the pH-adjusting station.
In the second retention pond, a portable surface boom is positioned in front of waste-water culverts that lead to the facility outfall. Pellets and powders collected at this point are removed by using a vacuum (see Figure 12 below). From this basin, the water passes into the environment through the culverts, through a water quality monitoring station and the outfall, and through a small stream into a nearby river.
Three times each week, one 24-h sample is collected at the outfall water-quality monitoring station. Total suspended solids (TSS), along with all other National Pollutant Discharge Elimination System (NPDES) analytes, are measured for each sample. Company F officials stated that the water sampler may not collect pellets, but it does collect powder. Only one pellet could be seen along the banks of the stream immediately below the outfall, despite the heavy rainfall and extremely large numbers of pellets in the weir.
Despite torrential rainfall the previous night, the Company F containment system was extremely effective in preventing the discharge of pellets. Company F developed this relatively simple but effective system, in part, to comply with NPDES permit regulations that limit TSS discharges. Prior to developing this system, Company F exceeded the NPDES permitted levels for TSS owing to the presence of polymer powder and pellets. However, the company recognizes the environmental hazards that pellets pose and is making a commitment to minimize its contribution to the problem. The company also recognizes the economic advantages to recovering and recycling waste pellets.
Company F officials believe that the successful operation of their pellet containment system is accomplished through a combination of physical plant systems and employee commitment. As a result, all new employees are trained in pellet spill prevention and cleanup. In addition, Company F has made a video of its pellet containment measures; this video is required viewing by all new operators.
Currently, company officials estimate that the recovery system is nearly 100% efficient under normal operating conditions, as evidenced by the absence of pellets at and beyond the outfall. However, during periods of heavy rainfall, the efficiency of the system decreases allowing plastic powder and, to a lesser degree, pellets to be discharged into the environment. On the day of the site visit, the heavy rainfall had stopped before the visit began, and the recovery system was returning to normal conditions. Company F anticipates that future system modifications (scheduled to be completed by the end of 1991) will control powder and pellet discharges during abnormal conditions (i.e., heavy rainfall).
Company G
The second pellet producer visited under this study was Company G. Company G manufactures approximately 600 million pounds of pellets each year, the bulk of which are shipped by rail hopper car. Pellet manufacturing is only one of several operations at this facility. Pellets are also bagged or boxed onsite, and a portion of the pellets are shipped by using bulk trucks.
Drainage ditches are located along the roads throughout the Company G facility. All storm-water and wastewater runoff are directed into the facility drainage system for treatment and are discharged into the river adjacent to the property. Disposable surface booms were located at several junctions in the drainage ditch system. The surface booms prevent floating material, such as plastic pellets, from backflowing into nonpellet-related areas of the facility.
The first area observed was the rail hopper car loading area. The rail hopper car loading area is paved and has drainage gutters or troughs between each pair of rails. Pellets spilled during loading are washed into the gutters and carried into the facility drainage system. Pellets could be seen throughout the rail hopper car loading area, on the ground, and in the gutters. Pellets, including those that had been flattened underneath rail hopper cars, were also visible throughout the area.
At the point where the gutters discharge into the facility drainage system, Company G had installed a simple containment system. After flowing from the gutters, the pellets are collected by using concrete barriers that act as fixed skimmers in a reservoir separated from the facility drainage system. (The water in the reservoir is deeper than the water in the drainage system.) Pellets enter the reservoir from beneath the fixed skimmers and float to the surface of the reservoir. An electrically-powered surface skimmer pumps floating pellets and water from the surface of the reservoir into a box-shaped basket made of small-mesh (smaller than the diameter of the pellets) screens. This system continuously skims the pellets and collects them in the screened baskets where they remain until they are removed by Company G employees. The screened baskets are checked twice each workshift and pellets are removed.
Water flows through the screened baskets into the reservoir and into the facility drainage system under a second fixed skimmer. The second fixed skimmer prohibits the flow of pellets into the drainage system, even during periods of heavy precipitation. (Both fixed skimmers extend well above the normal water level in the reservoir.) Additional small, portable floating skimmers are used at strategic locations to capture any pellets that enter the containment system from other areas of the facility.
The rail hopper car cleaning area was also visited; this area was located some distance from the loading facility. Before loading, the interiors of the rail hopper cars are completely cleaned to remove residual pellets. These pellets are rinsed onto the ground and are directed by using a water spray into troughs alongside the rails. The troughs transport the pellet-laden wastewater to a collection reservoir where it passes through a small-mesh screen capturing the pellets.
During the site visit, piles of pellets were visible on the ground throughout the rail hopper car cleaning area and the area's containment system had overflowed; in some areas, pellets were piled as high as 1 ft. The containment system in the rail hopper car cleaning area, configured similar to the system in the rail hopper car loading area, was completely clogged with pellets, and several employees were shoveling the pellets into barrels for disposal (the barrels were then emptied into dumpsters). An employee said that this pellet-overflow condition was typical during periods of heavy rainfall and during unusually busy periods. It was unclear whether the containment system at the rail hopper car cleaning area was linked to the facility drainage system. It was also unclear whether the runoff in the rail hopper car cleaning area and surrounding areas (where pellets covered the ground) was directed into the drainage system or elsewhere.
Scattered pellets and small patches of accumulated pellets were observed on walkways and in the parking areas of the rail hopper car loading area and the rail hopper car cleaning area. Loose pellets from the rail hopper car cleaning area apparently were tracked to areas outside the rail hopper car cleaning area. The fate of these pellets was not identified during this site visit.
Pellets collected by using the containment systems described above are recycled. Company G officials estimated that between 25,000 and 60,000 lb of recyclable pellets are recovered each month from the rail hopper car cleaning area alone. No estimates were available for the total volume of pellets recycled by the facility each month. In addition, Company G officials stated that rail hopper car valves are often found open when the empty rail hopper car returns to the rail hopper car cleaning area; a source of pellet release to the environment.
No pellets were visible at the facility outfall that discharges into the nearby river. However, the area of the outfall was not closely scrutinized owing to time limitations and resumption of rainfall. Considering the extremely large numbers of pellets that were seen in the rail hopper car cleaning area and the lack of visible pellet accumulations at the outfall, the containment system at Company G appears to be effective in controlling the release of pellets into the environment.
Because of the lack of time, the resin powder production area and the pellet extruding areas could not observed during the site visit. In addition, maintenance activities in these areas and employee awareness of the environmental hazards posed by plastic pellets were not discussed during the visit.
4.2.3 Sources of Pellet Releases from Producers
Officials of Company F and Company G were able to provide insight into several sources of pellet releases, including sources that the companies were attempting to control. Through the site visit observations, discussions with industry officials, and a review of existing literature, several sources of pellet release were identified at pellet production facilities. I
Observations at the two exemplary facilities visited during this study indicate that effective pellet containment measures can be developed and implemented at pellet production facilities. The number of pellet production facilities in the U.S. that have installed such containment measures is not known.
4.3 Pellet Transporters / Contract Packagers
The pellet transporters and contract packagers are the mechanisms by which plastic pellets move from the producer to the processor. The pellet transporters carry bulk shipments (in rail hopper cars or bulk trucks) of pellets from the producer to the contract packagers and processors, and carry repackaged shipments (in bags or gaylords) from the contract packagers to the processors. The major methods of transporting pellets include cargo and containerized ships, rail hopper cars, and bulk or freight trucks. Cargo ships are being replaced increasingly by containerized ships as the preferred vessels for overseas pellet shipments.
The contract packagers, or, simply, packagers, receive from producers bulk shipments of pellets in rail hopper cars and bulk trucks, and break down these bulk shipments into smaller containers such as bags and gaylords. These smaller containers are subsequently carried by transporters to other contract packagers or processors. In the following discussion, the term packagers refers to those facilities that only repackage or store pellets (i.e., contract packagers), and does not refer to packaging operations of pellet producers.
Each time pellets are moved, whether within a facility or between separate facilities, the potential exists for a pellet spill and subsequent release into the environment. The type of packaging may also affect the potential for a pellet spill. Pellet transport and packaging methods are discussed in the following sections. A flow diagram is again presented in Figure 6(b). [figures were not available at access time]
The numbers of transporters and contract packagers operating in the U.S. are not known.
4.3.1 Equipment and Operations
Equipment and operations at pellet transporters and packagers involve moving and repackaging large volumes of pellets, such as in rail hopper cars, and small volumes, such as in bags and gaylords. Some producers ship pellets by rail hopper car or bulk truck directly to the processors that use large volumes of pellets. However, pellets are often repackaged into smaller containers for shipment to processors that use small volumes of pellets.
Packaging
Pellet producers may ship pellets either in bulk shipments (i.e., rail hopper cars or bulk trucks) or in smaller packages. Frequently, bulk shipments are sent to contract packagers, where pellets are packaged into smaller containers, such as bags, gaylords, or cardboard drums, for storage and shipment by freight truck. The capacities of bags and gaylords (i.e., 50 and 1000 lb, respectively) are limited, and mechanical conveyors (i.e., forklifts) are needed at the offloading point. The extra handling involved in filling, handling, and emptying these smaller containers makes this method of shipping prone to accidental spills at the plants and in transit.
Several different types of bags are used for shipping pellets, and each bag type has advantages and disadvantages (Table 9). The most commonly used bag material is paper, which has the advantage that it can be broken easily for quick emptying by the processor, but has the disadvantage that it can be easily broken or torn during shipment and storage. Bags are also made of PE or woven PP. Bag openings are either open-mouthed or equipped with a valve that is incorporated into the bag. Valved bags are filled by placing the valve over filling tubes and releasing the pellets into the bags directly from the storage silos, a process that is very quick and inexpensive. These bags are designed to be self-sealing; once a bag is filled full, the mass of pellets inside the bag presses the bag valve shut. The advantage of valved, self-sealing bags is that filling and sealing are completed at one machine, eliminating the need for additional equipment to seal the bag; however, the disadvantage to valved bags is that the valves often leak. Sew-close bags and heat-sealed bags require additional handling and equipment to seal the opening.
Bags typically are stacked onto a wooden pallet covered with a cardboard tray to catch pellets that leak from valves or punctured bags. When all of the bags have been stacked on the pallet, the entire pallet and the bags are wrapped in plastic to prevent the bags from shifting during shipment and to retain any pellets that leak from valves or bag punctures. The wrapped pallets are moved by using a forklift to storage areas or onto freight trucks.
Cardboard gaylords are lined with a large plastic bag to contain the pellets. Gaylords usually are set on a wooden pallet to be moved via forklift. The gaylords typically are filled by conveyor and sealed.
Bags and gaylords are moved to storage areas and to shipping vehicles (i.e., freight trucks) by using forklifts or other similar equipment. Depending on the spill maintenance protocols at a facility, punctured bags or gaylords may be repaired or the pellets may be repackaged into a new container. Spilled pellets may be recovered and recycled, or unusable pellets may be disposed into the municipal waste system.
Shipping
For nearly 20 years, rail hopper cars have been available for bulk pellet transport. Rail hopper cars have a 100-ton capacity, or approximately 4.4 billion pellets per hopper car. A rail hopper car can have either a single tank or be compartmented into two or more tanks. On top of the cars are ports that couple with a conveyor system for pellet loading, and on the bottom are ports that couple with conveyors for rapid flow of pellets during unloading to bulk storage facilities. Each port has a rotatable tube valve that controls the pellet flow rate by increasing or decreasing the opening of the discharge slot. Each top and bottom port is equipped with a cap that must be secured over the port whenever the rail hopper car is not being loaded or unloaded. If these caps are not secured or if there is vandalism of the caps, spillage can result (see Figure 13 below).
There are two kinds of trucks used to transport pellets: bulk trucks and freight trucks. Bulk trucks are used to transport large volumes of pellets where rail service is unavailable. The design and operating features of bulk trucks are similar to those of rail hopper cars, and all are loaded and unloaded similarly. Bulk trucks have a 50-ton capacity or approximately 2 billion pellets (22,000 pellets per pound) per truck.
Freight trucks and cargo/containerized ships transport bag- and gaylord-packaged pellets. Pellets may also be transported aboard ship in bulk shipments. Pruter (1987) has reported that pellets have been used as ball bearings on the decks of ships to ease the movement of cargo, and pellets would likely enter waterways as a result of this practice. Because they completely enclose bulk and packaged pellet shipments, contain pellet spills, and prevent leakage to the environment, sea containers are increasingly becoming the preferred method of shipping pellets.
The costs of shipping by ocean-going vessels are relatively low as compared to air freight costs, thereby making the former method attractive for shipping pellets overseas. According to EPA (1990a), the world fleet of containerized ships had grown from 508 fully containerized ships and 597 partially containerized ships in 1976 (<5% of the world fleet), to 1097 and 1720 ships, respectively, in 1988 (12% of the world fleet). Therefore, with the use of containerized ships increasing, pellets are more likely to be transported by using these vessels than by using cargo ships filled with bulk shipments of pellets.
Blending and Storage Blending is the mixing of polymer pellets (or powders) with additives by using either a continuous-blending process or blending in batches. Continuous-blending processes require the coordinated, steady input of each ingredient into the blender. The pellet feed streams may be either volumetrically or gravimetrically metered from a feed hopper. Controlled feeders generally deliver the pellets by free fall into a blending unit.
Storage silos are used primarily by the large, high-volume producers, packagers, or processors. Pellets are conveyed from the silos to packaging or processing areas through permanent instrument-monitored conveying lines.
Warehouses are used typically by the low-volume processors to store smaller containers. Packages are mechanically transported (a pallet load on a forklift) to the molding area. Pellet deliveries may be in bags or cardboard drums anchored on a pallet, in large boxes, or in large bulk bags. These units are likely to be offloaded from trucks and handled with a forklift.
4.3.2 Site Visit Observations
Two pellet transporters/contract packagers, Company B and Company C, were visited during this study. Both companies were visited on February 4, 1991.
Company B
Company B ships and packages many different commodity, transitional, and engineering resins in pelletized form. Photographs were not permitted to be taken during this site visit.
Company B receives on the average approximately 300 rail hopper cars (or 54 million pounds) of pellets annually. Officials stated that approximately 99.75% of the pellets (179,500 lb out of each 180,000-lb shipment) received by Company B are repackaged and shipped to processors, and 0.25% of the pellets are lost or recycled. The facility has 500,000 ft2 of available storage space.
Plastic pellets are received from rail hopper cars in a graveled area adjacent to the rear of the facility. The pellets are transferred by pneumatic conveyor directly from the rail hopper cars to the packaging areas. Before offloading the pellets, a portable screen is placed beneath the valve outlet of the rail hopper car. This screen is used to capture pellets that escape during coupling and uncoupling of the rail hopper car's valve; loose pellets fall from the valve and from the conveyer system hose. The screen consists of windowscreen-sized mesh mounted on a 1- 3-ft rectangular frame made of 2- 4-in. lumber. The screen can easily be handled and moved by one person. Pellets captured by the screen are temporarily placed in a specially designated bin and are eventually sent to a recycler.
Despite the use of the screened boxes, a large number of loose pellets were seen along the siding (a short track connecting a railroad directly with the premises of a business concern) where the rail hopper cars are unloaded; the presence of these pellets could indicate improper use of the screened boxes. These pellets had become interspersed with the large stones that formed the bed of the siding. Only large pellet spills had been cleaned up in this area; stray pellets were not recovered. Drainage routes for the rail hopper car siding areas were not observed and, therefore, the release of pellets from this area could not be assessed.
Two packaging operations were observed at Company B. The first packaging operation was the filling of valved paper bags. Paper bags are manually placed over a spout and the pellets are pneumatically transferred into the bags. After filling, some of the bags pass through a quality control checkpoint, where the weight of the bags is checked; bags that fail the quality control check are retained. The filled bags are then passed along the conveyer belt to a wooden pallet. Once the pallet is loaded, the pallet and the load are wrapped with plastic and moved via forklift to the storage area. In some cases, the bags are palletized for temporary storage before being individually stacked in large shipping containers or truck trailers.
Pellets were seen to be leaking from the bagging machine valve before bags were placed over the valve and after bags had been removed. Pellets were also seen to be leaking from incompletely sealed bag valves while the bags were being moved by the conveyer. As a result, pellets were scattered on the floor beneath the entire bagging system. Employees were observed sweeping the pellets and collecting them for recycling. The pellets were not removed from areas immediately underneath the bagging machine, presumably because of safety considerations during machine operation. However, areas around the machine were swept nearly clean.
The second packaging operation was the filling of 1000-lb-capacity gaylords. As in the bagging process, pellets were pneumatically transferred into the gaylords through a spout. The plastic bags lining the gaylords, as well as the gaylord themselves, were sealed shut. Some pellets were scattered on the floor in this area, but no one was observed sweeping. Each gaylord contains a significantly larger volume of pellets than does each paper bag. Because residual pellets fall from the spouts at both bagging and boxing operations, pellets may be lost more frequently from the bagging machine spouts than from the gaylord machine spouts. This is probably a function of the number of gaylord/paper bag changes that are made in a given period.
Wood-framed screens were installed along the edge of the shipping docks; these screens are of the same mesh size as those used beneath the rail hopper cars, but frames at the docks are larger that the portable frames. The screens are designed to catch any pellets that might leak from broken packages or that could be tracked onto the dock from other areas of the facility. At the time of the visit, screens were installed only at those docks that have a concrete overhang, and the screens were installed below the overhang. Company B was in the process of developing a method for installing screens beneath docks lacking an overhang. Although most of the pellets appeared to be recovered before they could enter the environment, pellets were seen in rainwater flowing from the shipping docks into facility storm drains.
Company B stated that they occasionally receive information from processors regarding package damage and pellet loss during transit. Most of the information relates to exported shipments, and less information is received in regard to domestic shipments. Approximately 99% of all international shipments are in paper valve bags, which are inspected for damage by independent inspectors during cargo vessel onloading. In some cases, the inspectors photograph damaged shipments and notify Company B of pellet loss. Company B is not notified of pellet spillage or loss during offloading at the receiving port. However, most large shipments are sealed in containerized cargo vessels where pellet spillage during shipment would be minimal.
Pellets that escape onto the parking lot and into the storm-water drain are removed by another set of screens, one coarse and one fine, installed just inside the storm drains. The fine screen is the same as that in the screens used under the loading docks and rail hopper car outlets. A small number of pellets were seen on the screens over the observed storm drains. Other storm drains were submerged owing to the heavy rains and flooding and, consequently, only a few drains were seen during the visit. The frequency with which these storm-drain screens were cleaned was not noted during the visit.
Throughout the visit, employees were observed sweeping and collecting spilled pellets, particularly in the packaging area. In addition to hand-sweeping, large street-type cleaners routinely sweep the aisles and receiving areas. To monitor the effectiveness of routine maintenance procedures at the facility, Company B developed an environmental inspection check list (see Figure 14 below). The frequency of these inspections was not noted during the site visit.
Company B officials estimated that the annual pellet spillage is 10,000 to 30,000 lb during packaging and 2000 to 10,000 lb during shipping and warehousing. Spilled pellets are collected in specially labeled containers and are recycled. Company B officials were aware of the SPI efforts to educate the industry about the problems associated with pellet releases, and recommended that the SPI information be made available in bilingual form.
The company's quality assurance office is in the process of developing written protocols for routine maintenance and spill cleanup; these protocols will be written in English and Spanish. During training, the company plans to discuss economic and environmental reasons for strict adherence to quality control and maintenance protocols.
Company C
Company C receives and packages bulk shipments of many different pellet types. A few photographs taken during the visit are presented below.
Company C is located in one section of a large industrial park that includes at least one other pellet packager/transporter. The company receives and packages bulk shipments of many different pellet types. Company C officials stated that it packages and ships approximately 65 million pounds of pellets per month, and between a minimum of 5000 to 10,000 lb and a maximum of 20,000 lb of spilled pellets are recycled each month. The company also handles plastic powders that are shipped in supersacks (8 X 4 X 4 ft).
Company C receives bulk shipments of pellets in rail hopper cars that offload at a railroad siding behind the facility. This railroad siding is paved with large stones and a storm-water ditch and drain are located alongside the siding area. Pellets are transferred pneumatically from the rail hopper cars into storage silos located in the packaging areas of the facility. The rail hopper car valves are not resecured after the cars are emptied. No screens or other containment apparatuses are used during the coupling and uncoupling of the pneumatic hoses. Although company officials stated that attempts are made to recover large pellet spills in the siding area, many pellets were lodged between the stones throughout the siding area and in the stormwater ditch (see Figure 15 below). Pellets are carried by storm water through the drain and into a storm-water interceptor that retains storm water from Company C as well as from several other businesses in the industrial park.
Pellets are also pneumatically transferred from the silos to the bagging or packaging machines. At the bagging machine, the paper bag valve is manually placed over a spout, and the pellets are blown into the bag. The bag valve seals when the bag is removed from the spout and falls onto a conveyor, and the pellets inside the bag press against the valve end and seal the opening.
The filled bags are passed by conveyer belt onto a wooden pallet covered with a cardboard tray. The cardboard tray is used to capture pellets that may spill from leaking valves or bag punctures. Company C officials believe that the cardboard trays on pallets are only somewhat, but not entirely, effective. Once the pallet is loaded with bags, the pallet is wrapped with plastic and moved via forklift, to a storage area.
Pellets were seen on the floor beneath the bagging machine (see Figure 16 below). Residual pellets also were seen to be spilling from the spout before and after a bag was secured. After the filled bag was placed on the conveyer, pellets were seen to be leaking through incompletely sealed valves. Similar, but not as dense, were accumulations of pellets found beneath other parts of the machine and the conveyer. No spill cleanups were observed in this area.
After packaging, bags of pellets are moved by using a forklift into the warehouse where they are stored until shipment. Scattered pellets, pellet spills, and several punctured bags and gaylords were observed throughout the warehouse. Several spills were the result of leaky valves. Spills and/or breakages seemed to be a common occurrence throughout the warehouse and loose pellets were obvious in every aisle. Spills in storage areas are swept up and disposed in recycling bins.
Palleted bags of pellets are transferred via forklifts onto truck trailers at the loading dock. Pellets in torn or broken bags are repackaged at the dock before they are loaded on to the truck. Large numbers of pellets were observed in the loading dock area (see Figure 17 below). Because no pellet containment systems were installed at either the loading docks or over the parking lot storm drains, pellets spilled at or near the docks can fall onto the outside pavement. These pellets would be carried by storm water to storm drains located several feet away in the middle of the parking lot (see Figure 18 below).
The storm drains in the railroad siding area and in the facility parking lot empty into a storm-water interceptor adjacent to the industrial park where Company C is located (see Figures 19 and 20 below). Because several inches of rain had fallen (and continued to fall) on the day of the visit, the storm-water interceptor contained a very large number of pellets. In some areas of the storm-water interceptor, the pellets formed a mass across the surface and were scattered along the high water line among the debris (see Figures 21 and 22 below). Because Company C is not the only pellet-handling facility in the industrial park, it is highly unlikely that all of the pellets in the interceptor came from Company C. Once in the interceptor, the pellets would be transported downstream and into nearby waterways.
Broom-sweeping was observed throughout the facility. Company C officials stated that the entire facility is broom-swept and vacuumed at least once daily, and broom-swept throughout the day as needed. During training, managers are instructed to clean up all spills within a few hours; on a typical workday, this would involve broom-sweeping recyclable pellets two or three times. The parking lot and loading dock areas are swept once weekly and large spills are cleaned up as soon as possible. Pellets collected during routine maintenance and spill cleanups are recycled.
During the discussions after the site visit, Company C officials identified three pellet-release points. These areas were (1) the rail hopper cars, particularly when a load of pellets is quality-control inspected before offloading (valves are opened briefly to collect a subsample of the load); (2) the storm drain in the siding area where spilled pellets are washed into the municipal drainage system; and (3) the loading docks, where pellets are washed into the parking lot storm drains.
Company C officials believed that more pellets are lost from bag breakage than from accidental spills or leaking bag valves, although all bag valves tend to leak regardless of the bag material. Other than general housekeeping (e.g., sweeping), no special measures have been instituted at Company C to minimize pellet release into the environment. However, Company C is installing pellet containment systems at a new facility.
Company C officials felt that their employees are not well-informed in regard to environmental concerns associated with plastic pellets, although the SPI literature has been discussed at monthly Company C meetings. The officials recognized that employee awareness of the environmental impact of pellets is directly related to the investment that management is willing to make in employee education.
4.3.3 Sources of Pellet Releases from Transporters/Contract Packagers
Through the site visit observations, discussions with industry officials, and a review of existing literature, several sources of pellet release were identified at pellet transporters/packagers. These sources included
Observations at the two companies indicate that inexpensive control measures can be developed and quickly implemented at pellet transporter/contract packagers.
4.4 Pellet Processors
Pellet processors mold the pellets into fabricated user products. More than 12,000 pellet processors were operating in the United States in 1988, and employed a work force of approximately 580,000 workers Nationwide (U.S. Bureau of the Census, 1988; EPA, 1990a). According to SPI, this accounting is dependent upon the definition of processor used during the census (Mr. Ronald Bruner, SPI, personal communication, January 1992).
The terms converter and processor are used in this Section to refer to the production of plastic goods from pellets and granules. After conversion of the polymer pellets to commercial and industrial products, the potential for spills and entry into the environment is eliminated. However, ancillary handling of the pellets is required prior to molding.
4.4.1 Equipment and Operations
At the processors [see Figure 6(c)], pellets are fed into molding or conversion systems where the pellets are melted and formed into user products. Manual addition of pellets to a feed hopper on a molding unit frequently is performed at small conversion operations. However, as the size of the converter output (and the numbers of pellets used) increases, the use of automated pellet-handling systems increases. Pellets are manually, mechanically, or pneumatically conveyed from storage silos or bags and gaylords into the blender/converter hopper. Manual loading of pellets may be into a bag, drum, or box hopper, from which the pellets are mechanically or pneumatically conveyed to the next operation in the feed sequence (i.e., screening, blending, or drying).
Pellet spills may occur during any of the manual and mechanical transfers to downstream equipment. Spills are less likely in a pneumatic system where the feed transport is contained and the fill/flow rates are monitored and controlled. After the feed has entered a hopper on the conversion unit, there is little potential for a spill during normal operation. There is some possibility for a spill, however, when the product produced in the conversion unit is changed and the hopper is emptied manually.
Two primary processes are performed by conversion equipment. The initial process is to fuse and consolidate the feed pellets. The second process is to shape and cool the product. These process functions are performed by several different types of equipment, and the pellet-use rate may be controlled or demand-based. Most of the conversion equipment utilizes pellets fed from a hopper.
4.4.2 Site Visit Observations
Three pellet processors, Company A, Company D, and Company E, were visited during this study. Company A was visited on August 22, 1990, and Company D and Company E were visited on February 4, 1991.
Company A
For several years, Company A has produced food-grade plastic containers made from HDPE, LDPE, PP, and PS pellets, and pellets containing pigmentation [e.g., titanium oxide (TiO2)]. Company A granted permission to photograph all phases and areas of their facility.
At Company A, bulk pellet shipments are pneumatically transferred from bulk trucks to the facility's primary storage hoppers or silos (see Figure 23 below). Each hopper holds approximately 60,000 lb of plastic pellets or granules. Company A officials stated that the pellets commonly escape into the environment during connection and disconnection at the pneumatic transfer tube (see Figure 24 below), and pellets also occasionally escape from the hopper air vent when the hopper is accidentally overfilled. Pellets were seen beneath and in the vicinity of the hoppers (see Figure 25 below).
The pellets are then pneumatically transferred through the conveying system from the storage hoppers into a small room adjacent to the processing room. Connections to the various internal operations, including internal storage hoppers, are manually made in this small room. At the internal storage hoppers, pellets are removed manually through a slide valve on the bottom of the hoppers. Company A officials noted that pellet spillage has been observed during connection changes, and pellets were seen on the floor and accumulated in the fence guard surrounding the interior storage hoppers (see Figure 26 below).
Pellets are added to the molding machines either manually, pneumatically, or by a combination of these methods. Company A officials stated that there is little likelihood of pellet leak- age in the pneumatic delivery system once the pellets are inside the plant, except in the cases of equipment malfunctions. Plastic scrap produced during the injection molding process was observed on top of several molding machines (see Figure 27 below), and pellets also were observed on top of one manually loaded machine.
Accumulations of pellets were observed in several expansion joints in the concrete floor of the shipping area and in other areas of the plant (see Figure 28 below). Pellets also were seen in the expansion joints in the printing shop, even though no pellets are handled in this area. Company A officials explained that pellets cling to forklift tires, workers' clothing and shoes, etc., and are transported throughout all interior and exterior areas of the facility. The pellets are then swept up during routine maintenance and are disposed of in the facility's dumpster.
Because the facility parking lot slopes toward the building, water historically leaked into the shipping area during rainfall. To correct this problem, a catchment basin was installed near the overhead exterior doors of the shipping area to intercept the storm-water runoff from the parking lot before it can flow into the facility (see Figure 29 below). The catchment basins serve as collection points for pellets released in the transfer area and in other exterior areas of the facility. During the site visit, a number of pellets were found in this catchment basin. All runoff from the facility, including runoff from the parking lot, catchment basins, and roof, flows down the driveway and into the street (see Figure 30 below). Once in the street, the runoff flows along the curb to a storm-water interceptor, where it enters a municipal storm-sewer system.
Until recently, Company A officials were unaware of the hazards to aquatic life posed by plastic pellets floating on the surface of the ocean, and to their knowledge, employees were not aware of the hazards. These officials believed that employees would be generally apathetic toward the pellet issue. However, Company A officials also believed that the pellets used at their facility would not float in water. They tested this theory by placing handfuls of LDPE, HDPE, PS, and polyethylene-base TiO2 pellets into a small container of tap water. Only the LDPE and HDPE pellets floated, the PS pellets floated initially and sank after gentle agitation, and the TiO2 pellets sank immediately. Similar results were found subsequently when the same pellet types were added to saline water (at room temperature and 30-32 ppt salinity).
Because food-grade containers are produced at Company A, the cleanliness of the physical plant is closely monitored. Company A officials frequently stated that the facility is routinely swept clean of pellets, both inside and outside, and that the pellets are discarded into an onsite dumpster. The dumpster contents are collected by a commercial waste hauler and is subsequently disposed into the municipal waste stream.
Company D
For over 50 years, Company D has produced specially molded products for a diverse clientele. Most of the pellets used by Company D are engineering (or performance) resins that have a limited range of uses and narrowly defined applications; these pellets are the most expensive pellets available. Company D production runs are limited in size and small volumes of any one particular pellet type are used. The company has the capability to extrude small amounts of special blends of pellets. As much as possible, the company purchases precolored pellets, but may color pellets as needed.
The company purchases pellets in small quantities. These pellets typically are shipped by truck in bags or gaylords and are subsequently stored in the receiving area until used. The trucks are offloaded at the loading docks; no materials are handled outside the loading docks. A storm-water drain was located next to the building and at the bottom of dock incline; a few pellets were seen near the drain and along the dock wall. No pellet-containment devices were seen in the loading dock area.
Company D had recently expanded their shipping and receiving area to accommodate a growth in business. Pallets of bagged pellets and gaylords were stored in one area, and packaged products were stored in another area. Loose pellets could be seen beneath the pallets and, occasionally, scattered on the floor.
In general, pellets are manually loaded into the molding equipment, but Company D can load the pellets directly from gaylords, if necessary. Employees are encouraged to avoid spills, primarily because the pellets are expensive and spilled pellets are not recycled. Scattered pellets were observed on the floor beneath and around the molding equipment.
A few pellets were present in the cooling-water tanks adjacent to the molding machines; molded parts are placed in these tanks to be cooled before inspection and packaging. The cooling water is disposed of into the facility drains, which in turn feed into the municipal sewer system. Officials stated that pellets could enter this cooling water only through accidental spills during manual machine loading.
Maintenance protocols require that the work areas, including the areas around the molding machines, be cleaned at the end of each shift. The floors are swept, vacuumed, and mopped every other day. Spilled pellets typically are broom-swept and disposed into a refuse container. No effort is made to recycle or reclaim materials, and waste pellets are disposed of into the municipal waste stream. Routine maintenance and spill-cleanup protocols appear to be the primary methods for controlling pellet releases into the environment.
Company D officials stated that the employees are trained to minimize spills primarily for economic reasons (the pellets are expensive) as opposed to environmental reasons. The officials were aware of the SPI educational efforts, but the information was not disseminated or otherwise posted in the facility for the workers to read. Workers had not been briefed or otherwise trained with regard to pellet-related environmental concerns.
Company E
Company E is an injection molder that manufactures specialty parts for industrial applications; no consumer items are manufactured. These specialty parts are made of engineering resins, such as polycarbonate and nylon. The company has resin-handling approval from the Underwriters Laboratories (UL); this approval is used as a measure of quality assurance and is issued after successful spot inspections by UL.
Company E receives pellets by truck, and the pellets typically are packaged in either paper bags or gaylords. Company E officials stated that pellet packaging often arrives punctured or torn; the receiving clerk records the condition of the pellets, and Company E may ask for compensation from the shipper or packager if the damages are extensive. Scattered pellets were observed in and around the loading docks and in the facility parking lot. A storm drain was located at the bottom of the inclined driveway at the docks. Because rainfall was heavy during the visit, there was a heavy flow of water through the drain and into a storm-water ditch a few feet from the warehouse. Pellets could be seen in this storm-water ditch.
Small quantities of a wide variety of pellets are stored at the facility; however, there are no storage silos at the facility. All pellet packages are stored above floor level; the packages are stacked both manually and via forklift, depending on the size of the shipment and the storage location. Loose pellets were seen throughout the storage or warehousing areas, primarily in areas where routine sweeping would not reach them. Specifically, pellets were seen under loaded pallets and pallet racks, between storage racks, and between stacks of bags. Very few pellets were seen in the working areas of the warehouse, and an employee was seen broom-sweeping a small pellet spill.
The injection molding machines are loaded manually, and small numbers of pellets were found around and underneath the molders. Company E officials stated that all spilled material is disposed of in a dumpster and is not recycled because spilled pellets may be contaminated with a mixture of grease, oil, absorbent materials, dust, etc., as well as other pelletized resins. The equipment is completely cleaned and vacuumed between each production run to prevent crosscontamination between different products.
The facility generally was clean, and there were no accumulated plastic-scrap piles. A few pellets were visible in cracks in the concrete floor and in areas inaccessible to routine maintenance equipment. Company E officials believe that good housekeeping practices are the best way to control pellet loss.
No containment apparatuses, such as screening over drains or catchment devices under the loading docks, are in place at the facility. The company appears to follow effective routine maintenance protocols, as evidenced by the presence of very small numbers of pellets throughout the facility. The employee in charge of shipping and receiving seemed conscientious about sweeping up spilled pellets and taking every precaution to ensure that spilled pellets do not become a safety hazard.
Company E officials were aware of the problems that plastic pellets pose to the environment, and recognized that they may be contributing to the problems. Issues were not discussed regarding employee education about the environmental hazards of plastic pellets.
4.4.3 Sources of Pellet Releases from Processors
During routine operations at pellet processors, pellets are most likely to be released prior to the actual conversion (molding) process. Through the site visit observations, discussions with industry officials, and a review of the existing literature, several pellet release pathways were identified at pellet processing facilities. These sources included
Observations at the facilities visited during this study indicate that pellet control measures can be developed and implemented at pellet processing facilities. None of the visited facilities processed large volumes of pellets, and the facilities did not mass produce consumer products. Sources of pellet loss and general housekeeping and operation procedures may be different at larger-scale facilities than at these smaller-scaled processors. However, the pellet release points identified above should be applicable to all processors.
4.5 Summary of Identified Sources
The representativeness of the visited companies as indicators of pellet release and containment conditions industry-wide could not be determined. The possibility that the visited companies represented best-case conditions is suggested by the fact that the companies volunteered to participate in the study; companies with significant pellet containment problems would not volunteer access to a regulatory agency regardless of assurances of no regulatory assessment or action. The fact that the two visited producers, Companies F and G, recognized the uniqueness of their containment systems and developed materials highlighting the systems, supports this possibility. Despite the unknown representativeness, the study team was able to identify several pellet release points in each sector. No attempt was made to rank the release points in order of significance or quantities released. Basically, the release pathways may be categorized into eight general areas where deficiencies may exist. These areas are
The identified pellet release pathways can be eliminated by implementing a few simple control mechanisms. Several possible control mechanisms were identified based on the site visits conducted during this study, and recommendations to the plastics industry were developed. Recommendations for controlling pellet releases, including the legal framework for controlling the releases, are described in Section 5.0.
source: http://www.epa.gov/owow/OCPD/PLASTIC/sect4-.html 13apr03
February 11, 1997
[Table of contents | Executive Summary | Sections 1 · 2 · 3 · 4 · 5 · Glossary | Tables | References ]
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