7

Waste Handling on Submarines

The U.S. submarine force is composed largely of attack submarines (SSNs) and ballistic missile submarines (SSBNs), along with a few research submarines. The current fleet is described in Table 7.1. Many of the 637s will be decommissioned in the next 13 years. The Seawolf class is apparently complete, and no firm date has been established for commissioning the new class (NSSN).

All U.S. submarines are nuclear-powered and have the ability to stay submerged for entire missions lasting up to several months. Control of the ship's atmosphere is very important. Unlike surface ships, submarines are almost never resupplied at sea. They begin their patrol with a full load of foodstuffs and other supplies adequate for the crew. The limited available space in a submarine means that all unnecessary packaging material must be eliminated. Cardboard boxes are unpacked, and the cardboard is left at the dock. Many of the foodstuffs come in metal cans. Syrups are usually used for mixing soft drinks. Many spare parts are partially unpacked before being stored aboard.

Waste that is discharged overboard must either be pumped out against the ambient sea pressure or blown out using pressurized air. Waste materials are collected and periodically discharged. The potential impact on ship safety associated with opening valves to the sea and on ship detectability by running pumps or blowing tanks to the sea makes waste disposal operations a significant event. Mission considerations may force waste disposal operations to be suspended for some period of time.

Dry waste is consolidated using a trash compactor and then placed in special cans. These cans are fabricated on board from prepunched galvanized, perforated steel sheets, using a roller tool. The resulting cans are 28.5 inches long and 9 inches in diameter. They have metal tops and bottom caps. Metal weights are added to ensure that the cans will go to the bottom. The cans are ejected from the submarine using a trash disposal unit (TDU), which is a long cylindrical, vertical tube connected to the ocean through a ball valve. Several cans are placed atop one another in the TDU, the top of the TDU is sealed by closing a pressure cap, the ball valve is opened, and the cans ejected through a combination of gravity and air pressure.

Table 7.1 Major U.S. Submarine Classes

CLASS

NAME

COMPLEMENT

NUMBER 1

SSBN 726

Ohio

155

18

SSN 21

Seawolf

130

2

SSN 688

Los Angeles

133

59

SSN 637

Sturgeon

107

24

1   Number of submarines in each class currently in active commission or under construction.



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OCR for page 41
SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V 7 Waste Handling on Submarines The U.S. submarine force is composed largely of attack submarines (SSNs) and ballistic missile submarines (SSBNs), along with a few research submarines. The current fleet is described in Table 7.1. Many of the 637s will be decommissioned in the next 13 years. The Seawolf class is apparently complete, and no firm date has been established for commissioning the new class (NSSN). All U.S. submarines are nuclear-powered and have the ability to stay submerged for entire missions lasting up to several months. Control of the ship's atmosphere is very important. Unlike surface ships, submarines are almost never resupplied at sea. They begin their patrol with a full load of foodstuffs and other supplies adequate for the crew. The limited available space in a submarine means that all unnecessary packaging material must be eliminated. Cardboard boxes are unpacked, and the cardboard is left at the dock. Many of the foodstuffs come in metal cans. Syrups are usually used for mixing soft drinks. Many spare parts are partially unpacked before being stored aboard. Waste that is discharged overboard must either be pumped out against the ambient sea pressure or blown out using pressurized air. Waste materials are collected and periodically discharged. The potential impact on ship safety associated with opening valves to the sea and on ship detectability by running pumps or blowing tanks to the sea makes waste disposal operations a significant event. Mission considerations may force waste disposal operations to be suspended for some period of time. Dry waste is consolidated using a trash compactor and then placed in special cans. These cans are fabricated on board from prepunched galvanized, perforated steel sheets, using a roller tool. The resulting cans are 28.5 inches long and 9 inches in diameter. They have metal tops and bottom caps. Metal weights are added to ensure that the cans will go to the bottom. The cans are ejected from the submarine using a trash disposal unit (TDU), which is a long cylindrical, vertical tube connected to the ocean through a ball valve. Several cans are placed atop one another in the TDU, the top of the TDU is sealed by closing a pressure cap, the ball valve is opened, and the cans ejected through a combination of gravity and air pressure. Table 7.1 Major U.S. Submarine Classes CLASS NAME COMPLEMENT NUMBER 1 SSBN 726 Ohio 155 18 SSN 21 Seawolf 130 2 SSN 688 Los Angeles 133 59 SSN 637 Sturgeon 107 24 1   Number of submarines in each class currently in active commission or under construction.

OCR for page 41
SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V Submarine waste streams differ in some respects from the waste generated by surface ships. Table 7.2 gives Navy data obtained from brief surveys taken on two submarines. Surface ship waste generation data are included for comparison. The differences in the numbers are impressive. One must suppose that there is submarine-to-submarine variation that is substantial, but the accuracy of the data is probably not high. The data do support the diligent job the submariners have done in reducing unnecessary packaging materials. It has been suggested that the cardboard portion (0.10 and 0.50, for the two submarines) is not discharged, but stored on board. With present practice, the weight of the metal TDU cans (including metal weights), which ranges from 0.26 to 0.61 lb/person/day, must be added to the submarine waste streams. These additional TDU metal weights are not included in Table 7.2, since they have no counterpart in the surface fleet and result solely from the current submarine discharge process. The data suggest that a storage volume as low as 0.01 ft3/person/day would be necessary to accommodate this waste if it is not discharged. This assumes a compaction ratio for the total waste stream of about 15, which is commercially obtainable. Another important result of the shipboard surveys is that a substantial portion of the paper and plastic (but not the cardboard, metal, and glass) is food contaminated (Table 7.3). The compacted volume of the food-contaminated paper and plastic is not very large, less than 0.01 ft3/person/day, or about 1 ft3/day for the entire ship. If this waste cannot be eliminated and has to be stored under Annex V, storage in the frozen food lockers appears to be the only solution. Precautions to avoid contamination of unused supplies will be necessary. Since submarines operate as closed systems leaving port with everything they will use aboard, an argument can be made that there is space to continue storing the Annex V waste rather than discharge it through the TDU. The waste-handling study (U.S. Navy, 1994) for the new design NSSN concluded that proper management of the solid waste stream could allow storage and eliminate any waste discharges. Again, food-contaminated waste materials would need special handling, probably storage in sealed cans held in the frozen food lockers. There appears to be a strong conservation ethic among submariners, and a number of crews have already voluntarily made significant reductions in the amount of solid waste discharged. The consensus of the committee is that there are no technological solutions to the submarine waste problem beyond installation of garbage disposals, better compactors, and sealed storage packages. Thermal destruction in the submarine environment is not appealing. Further, the committee sees no route to an integrated solution to the larger waste problem going beyond Annex V. Submarines generate food waste, gray water, and black water in proportion to the complement. Present storage and discharge strategies have not been improved upon by committee deliberation. The submariners have done an excellent job on their own. Table 7.2 Rate of Generation of Annex V Solid Waste (lb/person/day) ITEM DESCRIPTION USS K AMEHAMEHA USS C INCINNATI SURFACE Paper and cardboard 0.25 0.67 1.0 Plastics 0.09 0.19 0.2 Metal 0.22 0.31 0.5 Glass 0.0 0.13 0.1 TOTAL 0.56 1.30 1.8

OCR for page 41
SHIPBOARD POLLUTION CONTROL: U.S. Navy Compliance With MARPOL Annex V Table 7.3 Rate of Generation of Contaminated and Noncontaminated Paper and Plastic Waste (lb/person/day) ITEM DESCRIPTION USS K AMEHAMEHA USS C INCINNATI Paper (food contaminated) 0.13 0.12 Paper (clean) 0.02 0.05 Plastics (food contaminated) 0.08 0.12 Plastics (clean) 0.01 0.07