What kinds of waste does the ISS dispose of? To mind come:
* - why not compost those and use for plants?
** - resulting from what?
What kinds of waste does the ISS dispose of? To mind come:
- human waste
Excrement is not recycled. The ISS does not have a composting station. Urine is mostly recycled. However, the concentrated brine that results becomes trash that either is returned to the Earth's atmosphere to burn up or is vented (although might not be a good idea).
Water used for washing is similarly mostly recycled. The gray water from urine and washing becomes new wash water (and sometimes new drinking water). Water in the form of excess humidity in the air is recycled as drinking water.
- household items like torn clothes or a broken toilet brush
Clothing typically doesn't get worn out on the ISS. It gets thrown out well before that. The ISS does not have a laundry. Astronauts toss their underwear after three or four uses. For cosmonauts, it's a bit longer.
- poisonous chemicals (resulting from what?)
Some potentially hazardous materials are brought up to the ISS as, for example, experiments on crystal growth. These are supposed to be well isolated. Equipment and materials outgas. The environmental control and life support systems either collects those or vents the gases into space.
The most common poisonous chemical, carbon dioxide, is created by humans. There has been an experiment to use water and CO2 to create methane and oxygen, but it didn't work well. The CO2 scrubbed from the breathing atmosphere is mostly vented.
- food wraps.
That's a sizable fraction of the trash sent to be incinerated by reentry into the Earth's atmosphere.
In addition to the above, there are
Given the huge added expense of sending stuff back to the Earth's surface and reused, it's oftentimes cheaper to treat it as trash.
David Hammen's answer gives a great overview of common ISS trash categories.
One category that is large by volume that was omitted is packing material. Supplies and equipment launched to the ISS are packed in protective material against the forces of launch. This material tends to be quite bulky (e.g. foam) and takes up a lot of volume in the ISS.
The linked presentation says that 30% of cargo volume is used for packing material.
Much of this packing material is not needed once on orbit [and] becomes a substantial component of the waste stream
Source: Alternative Packaging Study (emphasis mine)
See also Cargo ship inner organisation
In places where there is routine garbage pickup, there is usually restrictions against particularly large or toxic/dangerous items.
Those require special handling.
From the (currently unanswered) question How many kilograms of nickel particles will be dispersed in Earth's atmosphere by dumping old ISS batteries overboard?
Weighing 2.9 tons... this heap of old batteries is now the heaviest single piece of garbage to be jettisoned from the International Space Station.
begins Gizmodo's ISS Ditches 2.9-Ton Pallet of Batteries, Creating Its Most Massive Piece of Space Trash
Digital Trends' What was inside the space station pallet jettisoned into space on Thursday says:
On Thursday, March 11, mission controllers in Houston commanded the space station’s Canadarm2 robotic arm to jettison an external pallet containing old nickel-hydrogen batteries into Earth orbit.
The nickel-hydrogen batteries were once used for the ISS’s power system but have since been replaced with newer lithium-ion batteries featuring improved power capacity, smaller size, and lighter mass.
Fortunately, the pallet and the batteries inside it won’t remain as space junk indefinitely (there’s enough of that already orbiting our planet), as the whole lot will burn up when it enters Earth’s atmosphere in several years’ time.
Further reading:
and I'll inject my own uninformed opinion from this answer to Do space industry companies want their defunct satellites back?
