2

Mechanical Methods

Shredders and Compactors

Mechanical methods for waste management under consideration in this section are concerned with paper, metal, glass, and plastic, as regulated under Annex V in Special Areas. Mechanical methods are valuable in that they can reduce the volume of waste and convert it to a form that is more easily packaged, stored, and transported. The domestic trash compactor is becoming increasingly familiar and does not differ in concept from the compactors discussed in this section. For ease of handling, it is usually more convenient to have the material present in small pieces. This is accomplished by means of a shredder that crushes glass, tears metal cans apart, and shreds paper and plastic. The size-reduced material can be placed in bags or cans or baled for storage or transport. This material is also easily fed into a compactor.

Shredders and compactors can deal with mixed waste or with individual waste types separately. If it is desired to keep aluminum separate for recycling, this component can be shredded, compacted, and packaged and stored apart from other waste. If ocean discharge outside Special Areas is planned, it will be necessary to separately process and store the plastic component.

A shredder is a chamber containing robust counter-rotating shafts to which many cutters are attached. The machine will process paper, metal, glass, plastic, and other materials, rendering the waste into small, more or less uniform, pieces. Because of the power for destruction built into the machine, the design has interlocks that isolate the chamber during operation.

A compactor is usually a piston or ram that is hydraulically driven. Most industrial compactors function in two stages (i.e., with two perpendicular rams operated sequentially) for greater volume reduction. Some compactors offer sanitizing; deodorizing; packaging in plastic, paper bags, or boxes; baling; and other options. For “dry” (i.e., not food-contaminated) Annex V waste, odor and sanitation problems do not normally occur.

One commercial shredder-compactor combination machine can process and store the Annex V waste generated by a complement of 250 personnel over a 30-day mission. Processing and storage are accomplished in a 10 ft × 10 ft room. The processor itself has a footprint of 2 ft × 6 ft. One person can handle a 1-day accumulation in about 1 hour. One station of this kind could service the needs of frigates and other smaller vessels, and two stations could accommodate destroyers, cruisers, and other ships with complements of fewer than 500. The Navy has fewer than 100 ships that are larger than this. Larger ships could be served with more stations.

A special kind of compactor, called a plastics processor, has been developed (both Navy and commercial). In this machine, the compression chamber is heated to melt the plastic, which is compressed and then cooled under pressure. This not only achieves the minimum attainable volume, but the resulting block or disc forms a plastic skin that encapsulates food contamination. The Navy is proceeding with a plan to install its plastics processor fleetwide. The plan involves storing the discs in odorproof bags for disposal ashore.

The amount of volume reduction or compaction can be defined as the volume of unprocessed waste divided by the volume of processed waste. These numbers, particularly the volume of unprocessed waste, are elusive, since they depend on an unknown state of packing. The Navy reports (U.S. Navy, 1993) that unprocessed paper has a density of 6 lb/ft3. A loosely filled waste basket has a density of about 4 lb/ft3, consistent with the Navy number, and a book has a density of about 45 lb/ft3, very dense indeed. Waste paper might be compacted to about 20 lb/ft 3 or 0.055 ft3/person/day assuming a compaction ratio of



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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V 2 Mechanical Methods Shredders and Compactors Mechanical methods for waste management under consideration in this section are concerned with paper, metal, glass, and plastic, as regulated under Annex V in Special Areas. Mechanical methods are valuable in that they can reduce the volume of waste and convert it to a form that is more easily packaged, stored, and transported. The domestic trash compactor is becoming increasingly familiar and does not differ in concept from the compactors discussed in this section. For ease of handling, it is usually more convenient to have the material present in small pieces. This is accomplished by means of a shredder that crushes glass, tears metal cans apart, and shreds paper and plastic. The size-reduced material can be placed in bags or cans or baled for storage or transport. This material is also easily fed into a compactor. Shredders and compactors can deal with mixed waste or with individual waste types separately. If it is desired to keep aluminum separate for recycling, this component can be shredded, compacted, and packaged and stored apart from other waste. If ocean discharge outside Special Areas is planned, it will be necessary to separately process and store the plastic component. A shredder is a chamber containing robust counter-rotating shafts to which many cutters are attached. The machine will process paper, metal, glass, plastic, and other materials, rendering the waste into small, more or less uniform, pieces. Because of the power for destruction built into the machine, the design has interlocks that isolate the chamber during operation. A compactor is usually a piston or ram that is hydraulically driven. Most industrial compactors function in two stages (i.e., with two perpendicular rams operated sequentially) for greater volume reduction. Some compactors offer sanitizing; deodorizing; packaging in plastic, paper bags, or boxes; baling; and other options. For “dry” (i.e., not food-contaminated) Annex V waste, odor and sanitation problems do not normally occur. One commercial shredder-compactor combination machine can process and store the Annex V waste generated by a complement of 250 personnel over a 30-day mission. Processing and storage are accomplished in a 10 ft × 10 ft room. The processor itself has a footprint of 2 ft × 6 ft. One person can handle a 1-day accumulation in about 1 hour. One station of this kind could service the needs of frigates and other smaller vessels, and two stations could accommodate destroyers, cruisers, and other ships with complements of fewer than 500. The Navy has fewer than 100 ships that are larger than this. Larger ships could be served with more stations. A special kind of compactor, called a plastics processor, has been developed (both Navy and commercial). In this machine, the compression chamber is heated to melt the plastic, which is compressed and then cooled under pressure. This not only achieves the minimum attainable volume, but the resulting block or disc forms a plastic skin that encapsulates food contamination. The Navy is proceeding with a plan to install its plastics processor fleetwide. The plan involves storing the discs in odorproof bags for disposal ashore. The amount of volume reduction or compaction can be defined as the volume of unprocessed waste divided by the volume of processed waste. These numbers, particularly the volume of unprocessed waste, are elusive, since they depend on an unknown state of packing. The Navy reports (U.S. Navy, 1993) that unprocessed paper has a density of 6 lb/ft3. A loosely filled waste basket has a density of about 4 lb/ft3, consistent with the Navy number, and a book has a density of about 45 lb/ft3, very dense indeed. Waste paper might be compacted to about 20 lb/ft 3 or 0.055 ft3/person/day assuming a compaction ratio of

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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V about 3. This corresponds to the compacted volume given in Table ES.1, 0.056 ft3/person/day, estimated by a different method. The agreement for metal and glass is less satisfactory, but the volume contribution of these materials is so small that the discrepancy is unimportant. The agreement for plastics is very good, 0.005 ft3/person/day for the molded discs of the Navy plastics processor, and 0.010 ft3/person/day for compacted plastic. The total volume accumulated is about 0.07 ft3/person/day. These numbers should scale linearly with the size of the ship's complement and the length of the mission (between off-loading). The compacted volume of Annex V wastes for various classes of warship that will accumulate over a mission, i.e., the minimum volume of storage space that must be provided for compliance with Annex V, is given in Table 2.1. Table 2.1 Minimum Volume of Storage Space for Compliance with Annex V Requirements CLASS COMPLEMENT MISSION (DAYS ) STORAGE VOLUME IMPLIED (FT 3) ROOM SIZE (FT ) 1 Frigate 230 30 480 8 × 8 Destroyer 300 30 630 9 × 9 Cruiser 400 30 840 10 × 10 Auxiliary (AD 41) 2,100 30 4,400 24 × 24 Carrier 6,000 60 25,000 56 × 56 1   Room height of 8 ft is assumed. Eight feet by eight feet seems quite modest, and 56 ft × 56 ft seems very large. Only the Navy can decide how much space can be made available for Annex V compliance, but the numbers are encouraging and the committee believes that shredding, compaction, and storage of all Annex V wastes might enable the Navy to comply with the prohibition of discharge in Special Areas for many and possibly all Navy ships by the year 2000. Fire prevention measures are a necessary feature of this strategy. Pulpers In its 1993 plan, the Navy proposed to process food, paper, and cardboard waste by “pulping.” With this technology, the waste material is reduced in size and entrained in water as a slurry that can be conveniently pumped from one place to another and discharged into the sea. In separate operations, water content can be reduced substantially (dewatered) to facilitate storage in regions where discharge is not allowed (i.e., within the 3-mile limit). This technology was not discussed above because food waste is not part of the committee's Annex V assignment and admixture of paper renders discharge a violation of Annex V in Special Areas. Nevertheless, this process is very attractive. It is not clear whether admixture of paper and cardboard in the discharge is or is not environmentally sound. The concept of the pulper is simple: cellulose products and/or food wastes are pulped into small pieces (less than one-fourth inch in the Navy implementation) and pumped overboard in a stream of seawater in the following manner (Drake et al., 1994). First, pulpable waste is saturated by seawater in a slurry chamber and pulped by blade action (the final product is about 2 percent solids). A junkbox catches nonpulpable items. Plastics inadvertently loaded into the pulper are retained in the pulping chamber until the machine is cleaned. Finally, the slurry is discharged into the ship's wake. The discharge rate from an aircraft carrier is about 200 gallons/minute (Swanson et al., 1995). The Navy has satisfactory experience with a prototype pulper on the carrier USS George Washington. It is expected that pulped waste will be mixed rapidly in the surface layer of the ocean above the seasonal pycnocline and persist there for periods of hours to days (Swanson et al., 1995). Some fraction

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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V will slowly sink to the seafloor or be accumulated by marine organisms. Some fraction will remain in suspension and in principle can be transported over long distances. The critical information needed to assess the impact of the discharge of shredded cellulose (i.e., paper and cardboard) into ocean waters involves effects on the biota. The persistence of cellulose in the sediments, especially under conditions of rather slow degradation, could bring about undesirable impacts on the biota. The concerns involve the effects of the shredded materials on organisms both in the water column and in the benthos. Little research has addressed this problem. A rather modest activity ($220,000 for the current year) is being supported by the Navy, but results are preliminary and the investigations will continue. Clearly, to have a convincing set of data as to the biological effects of discharged pulp wastes, much more extensive experimentation will be necessary. The committee endorses support of an experimental program (of viable size) designed to elucidate the biological impact of pulp waste. Even if environmental aspects of pulper operation can be resolved, operational characteristics of the equipment must be considered in assessing possible advantages offered by pulping. The apparatus should allow for the waste to be pulped and then stored before discharge, using water conservation technology, while the ship is within the 3-mile limit. Tanks for storage of the dewatered waste material need only be of modest size. It should also be noted that paper waste stored in pulped (and dewatered) form does not present a fire hazard. This stored pulped material can be incinerated as an option. Pulper technology offers promise of an inexpensive and effective way of husbanding cellulose and food waste from Navy vessels with only modest demands on space. Use of pulpers (commercially available or Navy-developed) that allow for onboard storage (and thus controlled discharge or incineration) is worthy of further study. Demonstration of effective dilution, decomposition, and minimal impact on the ecosystem is essential. Food Contamination Contamination of Annex V waste streams with food waste can complicate the use of mechanical methods of waste management considerably. Waste that is contaminated with food can be processed in shredder-compactors, but storage of the compacted waste must be arranged to avoid odors, pathogens, and vermin. Paper storage bags are unsuitable in this connection. Plastic packaging may be adequate but it must have high integrity. Even a single opening could be disagreeable and dangerous. Sealed metal cans are probably satisfactory but should be tested for the integrity of the seal. Refrigerated storage, if available, could solve the problem. The committee does not have good information concerning whether Annex V waste streams are food contaminated. Glass jars and metal cans can presumably be washed before shredding. Fragmentary evidence indicates that plastic is the most urgent problem in this connection. The Navy has reported (Evans, 1994) that one-half of shipboard plastic waste is food contaminated. Plastic is often difficult to clean, as in the case of sheet and film form, for example. No information on contamination with food of paper has been found. It is probably desirable to process dry and food-contaminated waste in separate machines, and the product of the two shredder-compactors would be handled and stored differently. For this reason, special plastics processors have been developed that heat the charge, forming a plastic skin that encapsulates the food contamination. Even so, the Navy plans to place the blocks or discs in odorproof bags for storage. The blocks are said to be dry to the touch and easy to handle. Mechanical Processing Equipment Information on commercial and Navy-developed mechanical processing equipment is given in Table 2.2, Table 2.3, and Table 2.4.

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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V Table 2.2 Commercial Mechanical Processing Equipment TYPE VENDOR CAPACITY (LB/H ) DIMENSIONS WEIGHT (LB ) PRICE ($) Shredder Shredding Systems, Inc. 1 2,000 12 ft × 3.5 ft × 4.5 ft 190 ft3 1,280 86,000 Compactor International Compactor, Inc. 1 3 ft3/15 sec 2 ft × 2 ft × 6 ft 25 ft3 550 8,000 Pulper SOMAT 1 1,000 wet 700 dry 4.3 ft × 2.2 ft × 4.7 ft 25 ft3 530 17,680 Shredder-compactor Strachan & Henshaw 440 6.5 ft × 2.5 ft × 6.5 ft 106 ft3 5,500 200,000 Plastics processor Strachan & Henshaw Cooling limited 6.5 ft × 2.5 ft × 6.5 ft 106 ft3 5,500 210,000 1   For each of these machines, larger models are available. Table 2.3 Navy-developed Mechanical Processing Equipment TYPE CAPACITY (LB/H ) DIMENSIONS, FT2 INCL. OPER. ENVEL. WEIGHT (LB ) PRICE ($) Shredder 600 30 1,500 – Pulper 1,000 wet (a small pulper has been developed) 500 dry 100 5,600 105,000 Plastics processor 30 96 5,000 65,000

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SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V Table 2.4 Partial List of Equipment Vendors VENDOR NAME ADDRESS TYPE OF EQUIPMENT SHIP INSTALLATION SOMAT 855 Fox Chase Coatsville, PA 19320 Tel. (610) 384-7000 Pulpers, hydro dryers 150 to 160 pulpers installed in cruise ships Shredding Systems, Inc. 9760 S.W. Freeman Dr. Wilsonville, OR 97070 Tel. (503) 682-3633 Shredders At least seven shipboard installations for cruise liners Cumberland 100 Roddy Ave. S. Attleboro, MA 02703-7951 Tel. (508) 399-6400 Shredders No Marathon 901 Industrial Park Rd. Dearfield, PA 16830 Tel. (800) 922-7062 Compactors No Strachan & Henshaw Ashton House, P.O. Box 103 Ashton Vale Road Bristol, BS99 7TJ England Tel. (0117) 966-4677 Waste-processing machine Shredder and two-stage compactor Yes International Compactor, Inc. P.O. Box 5918 Hilton Head Island, SC 29938 Tel. (803) 686-5503 Compactors No Jacobson Companies 2445 Nevada Avenue North Minneapolis, MN 55427 Tel. (612) 544-8781 Crushers Hammermills Shredders No Franklin Miller 60 Okner Parkway Livingston, NJ 07039 Tel. (201) 535-9200 Crushers Shredders No Norsk Hydro P.O. Box 44 N-3671 Notodden, Norway Tel. 47 35 01 71 00 Complete shipboard waste management systems Pulpers Dewatering equipment Incinerators Yes Deerberg Systems Moltkestrasse 6a D-26122 Oldenburg Germany Tel. 49-441-77 60 62 Complete shipboard waste management systems Yes