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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.
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.