The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
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 AnnexV Requirements
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.
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