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Suggested Citation:"Comminuters, Pulpers, and Shredders." National Research Council. 1995. Clean Ships, Clean Ports, Clean Oceans: Controlling Garbage and Plastic Wastes at Sea. Washington, DC: The National Academies Press. doi: 10.17226/4769.
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Page 148
Suggested Citation:"Comminuters, Pulpers, and Shredders." National Research Council. 1995. Clean Ships, Clean Ports, Clean Oceans: Controlling Garbage and Plastic Wastes at Sea. Washington, DC: The National Academies Press. doi: 10.17226/4769.
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Page 149

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INTEGRATING VESSEL AND SHORESIDE GARBAGE MANAGEMENT 148 bottles, containers, bulbs, plate glass) is best achieved with glass crushers, which shatter rather than compress the materials. A plastics processor, such as the one being developed by the Navy, is a hybrid of a shredder, a compactor, and a thermal treatment device. Plastic materials are shredded and then compressed and heated (not combusted) to form fused bricks of plastic. Developers claim the process produces sterile blocks that meet the federal quarantine standards for food-contaminated plastics. If such claims can be substantiated, then the device may be attractive to maritime operators struggling to satisfy both Annex V and Animal and Plant Health Inspection Service (APHIS) mandates. Compactors may reduce the cost of waste disposal by reducing the volume of materials to be handled. Wastes destined for quarantine may be suitable for compacting, but APHIS treatment standards are calibrated on normal-density, uncompacted wastes. Those standards fail to meet the complete needs of the Annex V regime. To support Annex V implementation and expanded use of compactors aboard ships on international voyages to the United States, APHIS could arrange a series of calibration tests to establish appropriate quarantine treatment of compacted wastes. (A range of calibrations might be needed to allow for differences in compaction among units.) Compactors are considered safe and efficient and are suitable for vessels that remain at sea for up to two or three days. These units effectively compact most shipboard garbage into paper or plastic containers, which can be sealed and stored safely on board for short periods until disposal ashore. Builders of small vessels could consider offering compactors as part of an integrated on- board garbage management system. Such technology could be incorporated readily into the design and construction of new vessels, and retrofitting may be a viable option on some existing vessels. Comminuters, Pulpers, and Shredders A comminuter is an oversized garbage disposal that reduces food scraps to a finely chopped residual, which is rinsed out of the unit with a steady stream of water. The effluent is a slurry of water and food bits. Commercial devices are made specifically for marine use. Annex V permits discharge via a comminuter, which is the single piece of shipboard equipment for which the Annex establishes a performance standard (see Appendix B, Annex V, Regulation 3). Therefore, disposal of food wastes is not a problem, because they can be ground up and discharged into the ocean3; the organic detritus can be assimilated into the envi- 3 A greater problem is disposal of food-contaminated cellulosic material, such as paper, waxed paper, paperboard, cartons, and cellophane. Cellulosic materials also can be ground up, but it is difficult to separate out plastic coatings and film to prevent their discharge.

INTEGRATING VESSEL AND SHORESIDE GARBAGE MANAGEMENT 149 ronment. Even so, food discharges are prohibited within 3 miles of the coast (12 miles in all special areas except the Wider Caribbean). A pulper is a powered device that reduces paper, cardboard, and other readily pulped materials into a mush that resembles papier-mâché. This pulp is rinsed out of the unit with a heavy, continuous stream of water, and the effluent is a slurry of pulp and water. A commercial unit has been manufactured for years. The Navy improved this device for its own shipboard use, developing both a small unit and a large unit designed for continuous heavy use. The small pulper can process up to 64 kilograms (kg) (140 pounds [lbs.]) per hour of mixed wastes, including paper, cardboard, and food wastes. The large pulper can process up to 308 kg (680 lbs.) of mixed wastes per hour. Both units capture plastics and metal and prevent their discharge. This equipment is designed to occupy the least amount of space possible and can be maintained in place; even so, the units resemble large industrial washing machines set on angled foundations. Use of pulpers can reduce the aesthetic problems caused by intact garbage and permit discharges closer to shore than otherwise would be allowed. Some Navy personnel even see pulpers as an acceptable means for discharging wastes other than food (or plastics) into special areas. They assert that the biodegradable, pulverized, cellulosic effluent poses no harm, even in highly sensitive environments. The Navy is conducting research on this issue. At present, however, Annex V and the Marine Plastics Pollution and Control Act (MPPRCA) prohibit discharge of nonfood wastes into special areas. As noted in Chapter 2, little is known about the behavior or effects of pulped garbage, paper, or cardboard in the marine environment. Larger, denser particles such as bone and seeds settle rapidly, while small particles could become widely dispersed in the surface water layers. Some fraction of pulped waste may float and eventually be found on beaches, while some accumulation of pulped waste could be expected on the sea floor of shallow special areas, such as the Persian Gulf and Baltic and North seas (Swanson et al., 1994). Another way to treat paper on board vessels is with shredders, machines with rotating blades that also can be designed to shred bones, metal, glass, and plastics. One cruise line employs four types of shredders: a bone shredder and crusher; a paper shredder used upstream of an incinerator to improve combustion; a glass shredder and crusher; and a plastics shredder used prior to storage of this material (Richard Wade, Princess Cruises, personal communication to Marine Board staff, August 29, 1994). The Navy's shredder originally was designed to process 272 kg (600 lbs.) of glass and metal per hour (Swanson et al., 1994). The pieces were to be placed in burlap bags and thrown overboard. This plan has been abandoned and the shredder technology is now part of the Navy's plastics processor. Once thrown overboard, bags of metal and glass tend to settle to the ocean floor. Swanson et al. (1994) estimated that, to ensure sinking, the ratio of metals to glass in a bag should be at least 1 to 2. Some bags may be recovered by

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Marine debris is a serious environmental problem. To do its part, the United States has agreed to abide by the international treaty for garbage control at sea, known as MARPOL 73/78 Annex V.

Clean Ships, Clean Ports, Clean Oceans explores the challenge of translating Annex V into workable laws and regulations for all kinds of ships and boats, from cruise ships to fishing crafts and recreational boats. The volume examines how existing resources can be leveraged into a comprehensive strategy for compliance, including integrated waste management systems and effective enforcement.

Clean Ships, Clean Ports, Clean Oceans describes both progress toward and obstacles to Annex V compliance. The book covers:

  • How shipborne garbage orignates and what happens to garbage discharged into the seas.
  • Effects of discharge on human health, wildlife safety, and aesthetics.
  • Differences in perspective among military, industrial, and recreational seafarers and shoreside facilities.

Clean Ships, Clean Ports, Clean Oceans will be important to marine policymakers, port administrators, ship operations officers, maritime engineers, and marine ecologists.

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