Paper is usually biodegradable, and can usually be disposed of over the side in large paper bags that are designed to sink. The exception to this is classified materials, which have a different disposal method.
Metal and glass are processed through a crushing machine, and can usually be disposed of over the side. The crushing prevents/minimizes air being trapped within, and causing flotation when discarded.
Plastics are (on Porter and most newer ships, I believe) processed by a nifty machine that heats it up to melting point, then pours the melted plastic into a mold, resulting in a 1-foot diameter plastic disc – usually 1 to 3 inches thick. The plastic discs are sealed in plastic bags and held until the next port visit for disposal.
General garbage (uneaten food) is usually disposed of over the side, as it’s biodegradable. However, I’m not certain how humane it is to be feeding Flipper some of the stuff that humans wouldn’t eat (just kidding).
HAZMAT is also kept aboard for disposal in port – things like oily/greasy rags, dead batteries, paint and so on.
Continued in Part 5 - Conclusion
